A Novel Approach for Miniaturization of Slot Antennas
基于超材料的高增益对拓Vivaldi天线设计
基于超材料的高增益对拓Vivaldi天线设计张月;井甜甜;杨君;徐娟;赵建平【摘要】随着无线通信技术对人类生活影响力的提高,无线通信在通信领域的地位越来越重要.无线通信系统依靠无线电波传递信号,而无线电波的接收和发射则离不开天线.Vivaldi天线是一种超宽带天线,是渐变缝隙天线的一种特殊情况,也是一类经典的行波天线.但是,Vivaldi天线一般存在后向辐射大、主辐射方向增益低的缺点.可以通过对Vivaldi天线加载零折射率超材料的方式,在保证阻抗带宽不变的情况下,显著提高天线在整个频带内的增益.【期刊名称】《通信技术》【年(卷),期】2018(051)012【总页数】5页(P2861-2865)【关键词】Vivaldi天线;零折射率;超材料;天线增益【作者】张月;井甜甜;杨君;徐娟;赵建平【作者单位】曲阜师范大学,山东曲阜 273165;曲阜师范大学,山东曲阜 273165;曲阜师范大学,山东曲阜 273165;曲阜师范大学,山东曲阜 273165;曲阜师范大学,山东曲阜 273165【正文语种】中文【中图分类】TN920 引言在过去的几十年里，无线通信成为发展最迅猛的领域之一。
天线是无线通信系统中极其重要的部分，通信系统中的信号的接收和发送都离不开天线[1]。
随着无线通信的不断发展，不但要求通信速率要高，而且通信质量的要求也较高。
但是，由于用户数量的增加，加上频谱资源比较匮乏，实现天线的宽带化和小型化的必要性日趋明显[2]。
Vivaldi天线是一种超宽带、小型化的天线，是渐变缝隙天线的一种特殊情况[3]。
Vivaldi天线呈指数状槽线，结构较为简单，可直接印刷在介质基板上。
Vivaldi天线的带宽很宽，但现实中会有很多因素限制其带宽，所以对拓Vivaldi天线应运而生。
比起普通的Vivaldi天线，它的结构更紧凑，带宽更宽，容易实现阻抗匹配，交叉极化水平更优[3]。
为了提高天线的增益，可以靠加载零折射率超材料来实现。
那神奇的纳米时代英语作文
那神奇的纳米时代英语作文The Miraculous Nanotech Era.As technology relentlessly advances, we stand on the cusp of a remarkable era: the Nanotech Era. This transformative field involves manipulating matter at the atomic and molecular scale, unlocking unprecedented possibilities for innovation and progress.The Essence of Nanotechnology.Nanotechnology operates on an incredibly small scale. A nanometer is one billionth of a meter, roughly the size of a few atoms. At this scale, matter exhibits unique properties and behaviors that differ significantly from its macroscopic counterparts. These unique characteristics stem from quantum effects, the laws that govern the subatomic world.Revolutionary Applications.Nanotechnology has far-reaching applications across diverse industries, paving the way for groundbreaking advancements in healthcare, energy, electronics, manufacturing, and more.In Medicine:Targeted Drug Delivery: Nanoparticles can be designed to deliver drugs directly to diseased cells, enhancing efficacy and minimizing side effects.Tissue Engineering: Nanomaterials can be used to grow and repair damaged tissues, offering hope for treating degenerative diseases.Diagnostics: Nanosensors can detect minute amounts of biomarkers, enabling early diagnosis and personalized treatment.In Energy:Solar Energy Harvesting: Nanoengineered materials can improve the efficiency of solar cells, capturing more sunlight and generating more electricity.Fuel Cells: Nanocatalysts can enhance the performance and durability of fuel cells, providing a cleaner and more efficient energy source.Batteries: Nanomaterials can lead to the development of higher-capacity, longer-lasting batteries for portable devices and electric vehicles.In Electronics:Miniaturization: Nanotechnology allows for the creation of smaller, more powerful electronic devices with enhanced capabilities.Advanced Computing: Nanomaterials can enable faster processing speeds and increased memory capacity in computers.Nanophotonics: Nanostructures can manipulate light in novel ways, opening up possibilities for optical computing and ultra-high-speed data transmission.In Manufacturing:Lightweight Materials: Nanomaterials can be engineered to create lightweight, ultra-strong materials for aerospace and automotive applications.Self-Cleaning Surfaces: Nanoparticles can impart self-cleaning properties to surfaces, reducing the need for harsh chemicals and detergents.Antimicrobial Textiles: Nanomaterials can be incorporated into textiles to provide antimicrobial protection, preventing the growth of bacteria and viruses.Challenges and Ethical Considerations.While nanotechnology holds immense promise, it also presents challenges and ethical considerations that need tobe carefully addressed.Environmental Impact: The potential environmental impact of nanomaterials requires thorough assessment and responsible disposal practices.Health and Safety: The health and safety implications of nanomaterials must be fully understood and managed to ensure their safe use.Ethical Responsibility: The rapid advancement of nanotechnology raises ethical concerns about its potential use for malicious purposes or exacerbation of existing inequalities.Conclusion.The Nanotech Era presents both unparalleled opportunities and challenges. By embracing the responsible development and application of nanotechnology, we have the potential to unlock transformative solutions to some of the world's most pressing problems. From revolutionizinghealthcare to addressing the energy crisis, nanotechnology holds the key to shaping a brighter and more sustainable future.。
新探索研究生英语读写教程作文提高级范文
新探索研究生英语读写教程作文提高级范文A Research Paper on Improving Graduate-Level English Reading and Writing":The pursuit of higher education is a journey of intellectual growth, where students not only acquire specialized knowledge but also hone their language proficiency. For graduate students, the ability to effectively read and write in English is paramount, as it serves as the foundation for engaging with scholarly literature, conducting research, and communicating their findings to the academic community. However, the challenges faced by graduate students in mastering English reading and writing skills are multifaceted and require a comprehensive approach to overcome.One of the primary obstacles graduate students encounter is the sheer volume and complexity of the academic literature they are expected to engage with. The language used in scholarly journals, books, and research papers often features advanced vocabulary, intricate sentence structures, and dense, technical content. Navigating this academic landscape can be daunting, especially for students whose first language is not English. Developing effective reading strategies, such as actively engaging with the text,identifying key concepts and arguments, and synthesizing information from multiple sources, is crucial for graduate students to comprehend and critically analyze the literature in their field.In addition to the challenges of reading, graduate students must also hone their writing skills to effectively communicate their research and ideas. Academic writing in English demands a high level of precision, clarity, and organization, as well as the ability to construct well-reasoned arguments and support them with evidence. Graduate students must learn to navigate the conventions of academic writing, such as proper citation formats, the use of formal language, and the structuring of research papers and dissertations. Mastering these skills is essential for graduate students to produce high-quality written work that meets the standards of their respective fields.To address these challenges, a comprehensive approach to improving graduate-level English reading and writing skills is necessary. This approach should encompass both classroom-based instruction and individualized support, catering to the diverse needs and learning styles of graduate students.In the classroom setting, graduate-level English courses should focus on developing advanced reading and writing strategies. These courses could incorporate activities such as close reading exercises, academic writing workshops, and peer-review sessions, allowingstudents to practice and refine their skills in a supportive environment. Instructors should also emphasize the importance of critical thinking and the integration of research sources, equipping students with the tools to engage with complex academic texts and construct well-supported arguments in their written work.Alongside classroom instruction, graduate programs should also provide individualized support and resources to address the specific needs of their students. This could include one-on-one tutoring sessions, writing centers, and workshops that focus on targeted areas of improvement, such as vocabulary development, grammar, or the organization of research papers. By offering personalized guidance and feedback, graduate programs can help students identify and overcome their unique challenges, ultimately enhancing their overall English proficiency.Furthermore, the integration of technology-based learning resources can significantly enhance the effectiveness of graduate-level English reading and writing instruction. Online platforms, such as interactive tutorials, virtual writing labs, and collaborative writing tools, can provide students with flexible and accessible learning opportunities. These resources can offer immediate feedback, personalized exercises, and the ability to connect with peers and instructors, fostering a dynamic and engaging learning environment.To ensure the long-term success of graduate students, it is essential that English reading and writing instruction be embedded throughout the entire graduate curriculum, rather than being confined to a single course or program. By integrating these skills across various academic disciplines, graduate programs can reinforce the importance of language proficiency and provide students with opportunities to apply their skills in the context of their research and coursework.Moreover, the development of English reading and writing skills should not be viewed as a standalone endeavor but rather as an integral part of the broader graduate education experience. By fostering a culture that values and supports the development of these skills, graduate programs can empower students to become confident and effective communicators, better prepared to navigate the academic landscape and contribute to their respective fields.In conclusion, the improvement of graduate-level English reading and writing skills is a multifaceted challenge that requires a comprehensive and strategic approach. By implementing a combination of classroom-based instruction, individualized support, technology-enhanced learning, and the integration of language proficiency across the graduate curriculum, graduate programs can equip their students with the necessary tools to excel in their academic pursuits and effectively communicate their research andideas to the global academic community. Through this holistic approach, graduate students can unlock new avenues for intellectual growth, collaboration, and the advancement of knowledge, ultimately contributing to the continued progress and innovation within their fields of study.。
A Novel Approach for Identification...(IJITCS-V6-N4-4)
Published Online March 2014 in MECS (/) DOI: 10.5815/ijitcs.2014.04.04
I.
Introduction
The present day technological developments witnessed the storage of huge data and methodologies targeted towards efficient retrievals. Since this data is available are surmounting, security breaches and upholding the privacy is a major concern. These security issues are much more challenging while considering the data transfers in cloud environment or parallel processing architectures [1]. In order to handle this data efficiently concepts of mapreduce [2] is focused in the literature. This is due to its capabilities of faulttolarence and scalability together with simplicity. Another main advantage of highlighting the mapreduce concept is it facilitates the parallel processing environments which help indirectly towards huge data storage [3]. The concept of mapreduce can be easily implemented using hadoop environment [4].Many Copyright © 2014 MECS
论弗罗斯特《摘苹果之后》中的死亡隐喻
论弗罗斯特《摘苹果之后》中的死亡隐喻发布时间：2022-07-21T08:53:03.876Z 来源：《时代教育》2022年5期作者：刘沛婷[导读] 乔治·莱考夫和马克?约翰逊于《我们赖以生存的隐喻》一书中指出隐喻不仅仅是一种修辞手法，更是一种思维方式刘沛婷湖南师范大学，湖南长沙 410006摘要：乔治·莱考夫和马克?约翰逊于《我们赖以生存的隐喻》一书中指出隐喻不仅仅是一种修辞手法，更是一种思维方式，在人们的日常语言和活动中无所不在。
诗歌是高度隐喻化的体裁，本文就将以弗罗斯特的短诗——《摘苹果之后》为例，通过挖掘诗歌中的结构隐喻、方位隐喻和本体隐喻，深刻剖析弗罗斯特的死亡观建构，为该诗的解读提供新的维度，也有助于丰富该理论的应用范畴。
关键词:《摘苹果之后》；结构隐喻；方位隐喻；本体隐喻；死亡On death metaphors in Frost’s “After Apple-Picking”Peiting LiuHunan Normal University, Hunan Changsha 410006Abstract: George Lakoff and Mark Johnson put forward in their book Metaphors We Live By that metaphor is not only a figure of speech but a way of thinking, pervasive in everyday language and action. Since poetry is highly metaphorical, this thesis is to explore how Robert Lee Frost construct his insight of death through structural metaphors, orientational metaphors as well as ontological metaphors in his short poem “After Apple-Picking”, with the hope to provide a new dimension for the interpretation of the poem and to expand the application scope of the theory. Key words: “After Apple-Picking”; structural metaphors; orientational metaphors; ontological metaphors; death 1.IntroductionLakoff and Johnson in their monograph Metaphors We Live Вy, point out that metaphor not only can be understood from the figurative perspective, but is the thinking way.[1] Ungerer and Schmid hold that conceptual metaphor, as a cognitive instrument, is not just a stylistically dramatic way of expressing thoughts by means of literary language, but a way of thinking.[2] K?vecses has put that conceptual metaphor is defined as understanding one conceptual domain in terms of another conceptual domain.[3] On the basis of the cognitive approach to the understanding of conceptual metaphor, it can be divided into structural metaphor, orientational metaphor and ontological metaphor. The development of conceptual metaphor theory has brought advance to Linguistics, Anthology, Literature and so on.Robert Lee Frost commands an important place in any list of outstanding poets in the twentieth century. His poem “After Apple-picking” is written in the first person. The speaker is an orchard worker who has picked apples long and hard but is now on the verge of being overwhelmed by fatigue and the depth of the experience. On the edge of falling sleep, he remembers not only the ripe apples successfully picked but also those that fell and were considered damaged and had to be sent to the cider mill. He knows that his sleep will be troubled by the failures more than by the successes. He is not sure about the nature of the sleep he is about to drop into—whether it will be ordinary sleep, more like a hibernation, or more like death.The entire poem is a kind of extended metaphor, in which the activity of harvesting apples represents people’ life and the speaker’s falling asleep suggests human death.As a classical literary work, the study of this poem mostly focuses on its rhythm and writing devices. The analysis of multiple themes and symbols has always been the research hotspot of literature works. Li Yingxue discussed the fuzziness of the meaning of poetry from the perspective of deconstruction, and there are many scholars who explore metaphors in Frost’s other poems.[4] Few people applied it to analyze “After Apple-Picking”. Therefore, this paper is to discuss how Frost structures his thoughts on death metaphorically by describing a laborer’s picking apples. The first three chapters of this thesis illustrate Frost’s views of death through the construction of structural metaphors, orientational metaphors and ontological metaphors in “After Apple-Picking” respectively. At last it is followed by a logical conclusion of this thesis.2.Structural MetaphorsIn structural metaphor, one greatly structured and explicitly delineated concept is applied to structure another. As Lakoff and Johnson point out that one domain of conceptual metaphor is metaphorically structured in light of another. Structural metaphor allows its source domain to offer a comparatively rich knowledge structure for the target domain, that is to say, the cognitive function of structural metaphor is to enable audiences to understand the target domain by the structure of the source domain. The poem “After Apple-Picking” include two key conceptual metaphors: DEATH IS SLEEP and PEOPLE ARE PLANTS.2.1 DEATH IS SLEEPFrost chooses a laborer who is overtired with apple-picking and falls asleep to reflect his insight of death. Hence the poem can be understood as a mapping from a source domain (sleep) to a target domain (death). The mapping is tightly structured. There are ontological correspondences. The dead correspond to those who have a sound sleep. The retrospection before death corresponds to the unconscious state near sleep. The darkness corresponds to the night. The cease of life corresponds to the stillness and motionlessness of sleep. As Lakoff puts it, “people use a concrete source domain to describe an abstract target domain.”[5] Death is an abstract concept, which can be understood vividly through the concept of sleep. The word “sleep”has been repeated five times. “Winter sleep” suggests the emotion of being decayed, forlorn and silent triggered by death because winter, in the metaphoric meanings, has strong associations with death.[6] Another euphemistic expression of death is “long sleep”, which is indicative of its permanence. “Human sleep” is the most evident reflection of conceptualization of death as sleep, showing that human death is what Frost has discussed. In the light of sleep, Frost’s “After Apple-Picking” is no longer a lyrical poem of a worker’s experience on the orchard farm and fatigue aftera day’s labor, but a profound thought on life and death through an extended conceptual metaphor of death as sleep.2.2 PEOPLE ARE PLANTSBoth man and tree are living beings that go through birth and wither, and the achievements of man are kin to the fruits of plants. “Apples I didn’t pick upon some bough” correspond to those unfilled dreams while apples that “struck the earth/ No matter if not bruised or spilled with stubble”correspond to people’s failed pursuits. The scent of apples refers to delight and satisfaction brought by success. In Frost’s poem, the act of apple-picking is a metaphor for the fruits the speaker has achieved in life.[7] It is universally acknowledged that success is what people desire and is something enjoyable. However, the speaker is overtired of the great harvest and wished to rest, which illustrates that the speaker has been bored with worldly sense of accomplishment and hopes to simple have a dream and a “long sleep”. Due to the sweet smell of the apple, the narrator actually falls asleep after fatigue and he enters into “long sleep”(death) with a sense of emptiness resulted from the excessive fruits he has gathered. The speaker’s experience reveals the poet’s meditation on life that it is futile people achieve a great deal of success but eventually own nothing after death. Therefore, the poet don’t ponder on human sleep for no reason but he penetrates the meaninglessness of long tough life struggles.The two root metaphors are carefully chosen to reflect Frost’s philosophy on death. This also confirms the cognitive value of metaphor, that is, vehicles(such as sleep) are usually well known to readers, and their features and structures will be mapped to relatively unfamiliar things when they interact with tenor (such as death) to help readers understand the characteristics and structures of ontology. The characteristics of sleep are mapped to the characteristics of death. Frost’ poem “After Apple-Picking” is not only a pastoral work of rural world in orchard farm but also a thought-provoking poem on death. The end of labor leaves the speaker with a sense of completion and fulfillment yet finds him blocked from success by winter’s approach and physical weariness. The futility that what people achieved as a result resembles fallen apples of no worth leads to fatigue and wish to seek relief in sleep, that is death. Therefore, this seemingly idyllic poem is in fact the ultimate exploration of human destiny through the metaphors of death as sleep and people as plants.3.Orientational MetaphorsOrientational metaphors do not structure one concept in terms of another but instead organize a whole system of concepts with respect to one another.[1] Most of them have to do with spatial orientation: up-down, in-out, front-back, on-off, deep-shallow, central-peripheral. These spatial orientations arise from the fact that we have bodies of the sort we have and that they function as they do in our physical environment. As Lakoff points out that CONSCIOUS IS UP; UNCONSCIOUS IS DOWN. HEALTH SND LIFE ARE UP; SICKNESS AND DEATH ARE DOWN. This poem employs spatial antagonism to construct death metaphor. “The Apple-Picking” involves a development from consciousness to unconsciousness. At the very beginning, the farmer is sober enough on the long two-pointed ladder sticking toward heaven. The spacial position is rather high. After the speaker has been done with apple-picking, rest is badly needed after the arduous labour. He is drowsed off and no longer in his conscious state. Frost adopts simple past tense from line8 to line17, serving as a beginning of the speaker’s dream. In the half unconsciousness of the farmer, the autumn evening bursting with the aroma of the apples has for a moment changed into a winter morning with hoary glass. In farmer’s dream, things “melted”, “fall and break”, which suggests a downward trend. Finally both woodchuck and the farmer fall asleep on the ground. The perspective of the whole poem shifts from heaven to earth, that is from top to bottom, revealing the opposition of space. A pane of glass divides the world into two parts: reality and dream. The transition from reality to dream is the manifestation of change of the speaker’s consciousness. The higher position represents reality and consciousness while the lower dream and unconsciousnessWhat’s more, the positional contrast reveals the opposition of life and death. In the first line of “After Apple-Picking”, the ladder occupies a central position in the whole picture of the poem, acting as a bridge between heaven and earth, life and death. The imagery of heaven and apples evokes the garden of Eden. The act of ascending the ladder symbolized a re-approach to heaven and eternal life while the movement down the ladder symbolizes the descent from heaven to earth, also from life to death[4]. According to Bible, picking apples is considered as corruption and degradation. As baskets of apples fall down and are spiked, they become worthless. This is true of human beings. After the farmer has finished apple-picking, fatigue and emptiness has wrapped him. His vigorous life reaches a pause, which actually means the farmer’s death. Most of fundamental concepts are organized in terms of one or more spatialization metaphors. In Frost’s “After Apple-Picking”, the poet shows the transition from consciousness to unconsciousness as well as from life to death in virtue of the binary opposition of space. The physical basis of such division is that humans sleep and die lying down and stand up when they are awaken. Therefore, the antagonism of life and death is constructed through the opposition of up and down positions, which contributes to the further construction of the root metaphors.4.Ontological MetaphorsOntological metaphor helps us understand those abstract entities through conceptualizing them as these entities and substances which are related to human’s experience. As Lakoff and Johnson point out: “our experience of physical objects and substances provides a further basis for understanding.” Ontological metaphor could be classified into three types, which are entity and substance metaphor, container metaphor and personification.Firstly, an invisible abstract concept, in entity and substance metaphor, is considered as a visible concrete object. Human being expresses abstract concepts as these entities and substances which are related to human’s experience. Death is an abstract concept, which can be understood thanks to another common concept—sleep. The dark and bleak state of death is implied by night in winter. The poet also tries to clarify the hibernation of hamsters and the long sleep of human beings: one is short seasonal rest and the other is an eternal stop of motion. In this way, the characteristics of death are no longer vague. The first root metaphor of death as sleep receives deeper and more detailed illustrations. Similarly, human achievements becomes a measurable entity like apples in “ After Apple-Picking”. Through these well-known common things, the original abstract concept can be elucidated. The essence of metaphor lies in the comparison between two entities.Secondly, container metaphor is a kind of ontological metaphor in which an invisible abstract concept is regarded as a container which has a surface owning scope and range with an in-out orientation. In Frost’s poem, the farmer’s dream and sleep is a container, where he can see “magnified apples”, feel “the pressure of ladder-round”. The farmer’s falling into dreams shows the motion from one space to another space. The state of farmer can be classified into “in sleep” and “out of sleep”, which symbolize death and life respectively.Lastly, personification specifies the physical object as being a man, which can make people to comprehend these different physical objects in light of human characteristics, motivations and activities. In Frost’s poem, apple “struck the earth” and long sleep can “come on” are all personification. They are extensions of ontological metaphors and that they allow us to make sense of phenomena in the world on the basis of our own goals. It is carefully chosen to endow this poem a dynamic effect so that the theme of this poem can be effectively conveyed. All in all, the understanding of a poetic metaphor is a cognitive process.[8] Ontological metaphor makes us understand abstract concepts by use of concrete concepts. The poet uses sleep to explain death, making the abstract concept simplified and concrete. In the poem, the dream not only reflects the structural metaphor, but also reflects the container metaphor. It forms a contrast between “in dream” and “out of dream” so as to further strengthen the difference between life and death. Apple has bruises, and Death actively does come in. These anthropomorphic expressions embody the metaphorical nature of language and the symbolic nature of death. As a result, metaphor of death in this poem has been justified.5.ConclusionThe exploration of the relationship between Frost’s view of death and Lakoff’s cognitive metaphors will undoubtedly help readers to guard against deceptive surface meanings when interpreting and appreciating Frost’s poems, and to explore the profound life philosophy reflected in his poems through metaphorical thinking and active participation.Through dividing metaphors in Frost’s “After Apple-Picking” according to Lakoff’s classification, the way of constructing poem’s theme is evidently revealed. At the first glance, it seems to be a lyrical poem, but it actually a poem of death after further analysis. Frost implicitly depicts life actions as apple picking activities, apples are symbols of human achievements, and death is similar to long sleep, which are structural metaphors, through which the characteristics of abstract concept death can be easily understood. Moreover, the orientational metaphors constitute to the body of this poem. The up-down spatial position divides the farmer’s state into consciousness and unconsciousness, also a reflection of human’s state of life and death. The contrast between in-out categories reflects the whole poem’s structure: it shifts from reality to dream. Since the farmer’s dream is explained as a container, the state of dreaming metaphorically stands for death. Therefore the whole poem is based on structural metaphors of death is sleep and people are plants, which are illustrated with orientational metaphors and ontological metaphors.However, the thesis still has some limitations due to the author’s slim analysis. It can be better with more logical illustrations and evidences. But it is no doubt that the thesis provides a new perspective of discussing Frost’s poem. It expands the application scope of Lakoff’s conceptual metaphor and enriches its practice, and produces referential meaning to literature appreciation. References[1]Lakoff, G & M. Johnson. Metaphors We Live By[M]. Chicago: The University of Chicago Press.1980.[2]Ungerer, F & H. J. Schmid. An Introduction to Cognitive Linguistics.[M]. Beijing: Foreign Language Teaching and Research Press. 2008.[3]K?vecses, Z. Metaphor: A practical introduction[M]. New York: Oxford University Press.2002.[4]李应雪. 一个解构批评的范本——析罗伯特·弗洛斯特诗歌《摘苹果之后》意义的模糊性[J]. 宁夏大学学报(人文社会科学版), 2007(04): 78-81.[5]Lakoff, G. The Invariance Hypothesis: is abstract reason based on image-schemas?[J]. Cognitive Linguistics, 1990(01): 39-47.[6]Huo, Lirong. Comments on “After Apple-Picking”[J]. Overseas English, 2012(01): 196-197.[7]赵志宇. 罗伯特·弗洛斯特的《摘罢苹果》[J]. 文学语言学研究, 2007(02):70-71.[8]胡壮麟. 诗性隐喻[J]. 山东外语教学, 2001(03): 3-8.。
希望研制出治疗癌症的药物作文
希望研制出治疗癌症的药物作文英文回答：In the relentless quest for medical advancements, the development of drugs to combat the scourge of cancer stands as a paramount endeavor. The intricate nature of cancer poses formidable challenges, demanding innovative approaches and a profundo understanding of its underlying mechanisms.One promising avenue lies in the exploration of targeted therapies. These drugs are designed to selectively inhibit the specific molecular pathways that drive cancer growth and progression. By precisely targeting these pathways, targeted therapies can minimize damage to healthy cells, thereby reducing treatment-related side effects. Research in this field has yielded promising results, with several targeted therapies already approved for clinical use.Another promising strategy involves harnessing the immune system's ability to combat cancer. Immunotherapies work by stimulating the immune system to recognize andattack cancer cells. These therapies have shown efficacy in treating various cancer types, particularly in combination with other approaches. By bolstering the body's owndefenses against cancer, immunotherapies offer thepotential for long-lasting remissions and even cures.Furthermore, the development of personalized medicine holds great promise in the fight against cancer. Bytailoring treatments to individual patients based on their unique genetic profile, personalized medicine aims to enhance treatment efficacy while minimizing adverse effects. This approach involves analyzing a patient's tumor toidentify specific genetic mutations or molecular characteristics that can be targeted by specific therapies.In addition to these promising avenues of research, continued investment in basic science is crucial. Fundamental research into the molecular mechanisms ofcancer will provide a deeper understanding of diseasepathogenesis, paving the way for the development of novel therapeutic strategies.The development of effective cancer drugs requires a concerted effort involving researchers, clinicians, and pharmaceutical companies. Collaboration and knowledge sharing are essential to accelerate progress and bring new treatments to patients as quickly as possible.中文回答：概述：攻克癌症是医学界孜孜不倦的追求，研制出有效的抗癌药物是其中重中之重。
应用荧光实时定量PCR方法检测重组慢病毒滴度及其感染效率（精品）
生命科学研究2009年慢病毒载体是目前应用最广泛的基因运载工具之一，在基因治疗研究和转基因动物的制备中已显示出其广阔的应用前景．慢病毒载体是一种反转录病毒载体，其中以人类免疫缺陷性病毒（HIV -1）载体研究最为深入．与传统的小鼠白血病病毒载体（MuLV ）偏爱整合入基因5′端相比，慢病毒载体均匀分布于基因组内，从而降低了其激活原癌基因的几率［1~3］．重组慢病毒载体既能感染分裂期细胞，也能感染非分裂期细胞［4］．它可携带较大的外源基因（约8kb 左右）并稳定整合和表达［5］，加之其诱发的宿主免疫反应相对较小［6］，使得重组慢病毒载体具有较为广阔的应用应用荧光实时定量PCR 方法检测重组慢病毒滴度及其感染效率马海燕，方彧聃，张敬之*（上海交通大学医学院，上海市儿童医院上海市医学遗传研究所，中国上海200040）摘要：慢病毒载体已经广泛应用于动物模型中基因治疗的研究和转基因动物的制备，而准确地测定重组慢病毒的滴度和感染效率是其关键步骤．通过荧光实时定量PCR 的方法定量分析重组慢病毒的颗粒数以及病毒的活性滴度，并以GFP 报告基因的方法作为对照来验证定量PCR 方法的准确性．研究结果显示，应用荧光实时定量PCR 法与GFP 报告基因法测定得到的病毒活性滴度成正相关，而且前者可以更加准确地测定病毒滴度和病毒感染效率．关键词：慢病毒载体；荧光实时定量PCR ；病毒滴度；整合拷贝数；感染效率中图分类号：Q331文献标识码：A文章编号：1007-7847（2009）05-0394-05A Novel Method for the Determination of Recombinant LentiviralTiter and Infectivity by qRT -PCRMA Hai -yan ，FANG Yu -dan ，ZHANG Jing -zhi *（School of Medicine ，Shanghai Jiaotong University ，Shanghai Children ’s Hospital ，Shanghai Institute of Medical Genetics ，Shanghai 200040，China ）收稿日期：2009-03-18；修回日期：2009-05-16基金项目：国家高技术研究发展计划项目（2007AA021206）；国家自然科学基金资助项目（30870943）；上海市自然科学基金资助项目（08ZR1412100）作者简介：马海燕（1983-），女，山东淄博人，硕士研究生，主要从事病毒载体在转基因动物制备中的应用研究；*通讯作者：张敬之（1959-），男，上海人，上海交通大学医学遗传研究所副教授，博士，主要从事分子病毒学研究，Tel ：021-********，E -mail ：********************.Abstract ：Lentiviral vector is being widely used in the study of gene therapy in animal models and in generating transgenic animals.However ，determination of lentiviral particles and their infectivity is essential before their being used.Such a requirement can be accurately achieved by qRT -PCR.Refered by infectious units got from GFP reporter assay ，it showed a positive correlation between the two approaches.A reliable ，accurate and rapid method is therefore established for the determination of the recombinant lentiviral titer and the infectivity.Key words ：lentiviral vector ；qRT -PCR ；viral titer ；integration copy number ；infectivity（Life Science Research ，2009，13（5）：394～398）第13卷第5期生命科学研究Vol．13No．52009年10月Life Science Research Oct.2009第5期前景．无论何种目的使用重组慢病毒，都有必要准确地检测病毒滴度．目前，重组慢病毒滴度的检测方法有：依赖于报告基因的GFP荧光检测法、检测慢病毒外壳蛋白p24的抗原-抗体法（ELISA 法）和检测其逆转录酶活性的酶学法等．这些方法多存在耗时、费力、检测成本较高、病毒用量多、不适于非报告基因载体等缺点．所以，建立一种快速、简便、准确的慢病毒滴度检测方法，是非常有必要的．在此，我们介绍一种利用实时定量PCR测定重组慢病毒滴度的方法．该方法通过在载体的长末端重复序列区（LTR）设计定量引物，利用荧光实时定量PCR测定重组慢病毒中LTR拷贝数来测定病毒颗粒数和有效感染的病毒颗粒数．通过与GFP报告基因测定法的比较验证，证明该测定方法准确可靠．并且，通过慢病毒颗粒数与实际有活力病毒滴度的比较，可以计算得到重组慢病毒感染效率．多次重复实验证明，该方法具有快速、准确的优点，非常适用于非报告基因载体的病毒滴度及其感染效率的测定．1材料与方法1.1材料组成慢病毒载体的3个质粒FUGW（即含eGFP基因的转基因质粒），△8.9（编码结构和非结构蛋白基因质粒）和VSVG（外壳蛋白质粒）由美国Marine Medical Center Research Institute王征宇博士惠赠；293T细胞（人胚肾细胞）购自美国ATCC（American Type Culture Collection）细胞库；ProFection购自Promega公司；胎牛血清（FBS）、培养液和Hanks液及Salmon Sperm DNA 购自Gibco BRL；STE配方为10mmol/L Tris pH 7.6，1mmol/L EDTA pH8.0，0.1mol/L NaCl．1.2FUGW病毒的制备当293T细胞长至70%饱和度时，用磷酸钙法转染，按照Promega公司的ProFection Kit说明书操作，其中FUGW15μg，△8.910μg，VSVG7.5μg，转染6h后换完全培养液（含10% FBS的DMEM），并在37℃，5%CO2培养约60h．上述病毒培养上清液经离心、过滤后，50000g 超速离心1.5h后弃上清，在病毒沉淀上加少量Hanks液，获得病毒浓缩液，-80℃保存待用．1.3病毒RNA的提取取2μL病毒浓缩液进行DNase处理，体系中加入5μL10×DNase I Buffer、2μL DNase I （5U/uL，Takara Bio Inc，Shiga，Japan）、2μL RNase inhabitor（Takara Bio Inc.，Shiga，Japan），用DEPC水定容至50μL反应体系，37℃45 min．DNase处理后的混合液，加入350μL STE、20μL10%SDS和5μL蛋白酶K（20g/L，AMRESCO，Solon，OH），56℃15min水解．最后等体积酚、氯仿抽提，两倍体积无水乙醇沉淀，冻干后，20μL DEPC水溶解．1.4反转录反应病毒RNA在酚/氯仿抽提、无水乙醇沉淀前，需经过DNase I处理，以避免DNA污染．根据产品说明书，取1μg RNA、20pmol RT-PCR 下游引物（5′-GAGAGCTCCCAGGCTCAGATC-3′）、2μL5×RT Buffer、1μL MLV酶（Takara Bio Inc，Shiga，Japan）、水补足至10μL体系，37℃1h．1.5实时定量PCR分析病毒颗粒数为了测定制备的慢病毒的病毒颗粒数，应用实时定量PCR测定病毒LTR拷贝数.其中，引物和探针序列见表1．在反应体系中，引物900 nmol/L，探针250nmol/L，2.5μL10×Ex-Buffer，15μmol Mg2+，2.5μmol dNTP，1U ExTaqE，5μL样本，总反应体系为25μL体积．实时定量PCR仪（Corbett Life Science RG-3000，Sidney，Australia）上反应：95℃5min变性，95℃30s，59℃30s，40个循环，59℃520nm处检测荧光值．软件分析荧光检测数据．1.6不同剂量FUGW病毒感染293T细胞取病毒浓缩液，按10倍稀释法，取0.1、0.01、0.001μL病毒浓缩液（即用实时定量PCR 检测法，定量慢病毒颗粒数为：6.32×107、6.32×106、6.32×105），用含有8mg/L Polybrene促感染（Sigma-Aldrich，Inc，St.Louis，MO）且不含血清的培养液逐级稀释后，感染293T细胞（1.5×106/孔），37℃2h.然后，加入完全培养液培养细胞2d，表1实时定量PCR引物及探针序列Table1The sequences of primer and probe of Real-time PCRLTR-FLTR-PLTR-ProbePrimer Sequences5′-ACAGCCGCCTAGCATTTCAT-3′5′-GAGAGCTCCCAGGCTCAGATC-3′5′-ACATGGCCCGAGAGCTGCATCC-3′马海燕等：应用荧光实时定量PCR方法检测重组慢病毒滴度及其感染效率395生命科学研究2009年图1定量PCR 反应荧光强度曲线Fig.1Fluorescence intensity curve of Real -time PCR图2定量PCR 标准曲线Fig.2Standard curve of Real -time PCR至荧光显微镜下观测绿色荧光蛋白表达情况．1.7病毒感染细胞内DNA 的提取细胞经2d 培养后，用胰酶将细胞消化，收集入1.5mL EP tube 中，200g ，5min ，将细胞沉淀下来．加入200μL STE 、20μL 10%SDS 、10μL 蛋白酶K ，混匀后，37℃4h.加入等体积酚，振荡混匀，15000g ，离心12min ；吸取上清，加入等体积的氯仿，振荡混匀，15000g 离心6min ；吸取上清，加入1/10体积3mol/mL NaAc ，两倍体积的无水乙醇，-20℃沉淀1h 以上；混合液15000g ，4℃离心20min ；弃上清，沉淀风干，100μL TE 溶解．1.8实时定量PCR 测定重组载体整合拷贝数为了测定被感染的293T 细胞内重组载体的整合，用实时定量PCR 检测上述被抽提的基因组DNA 中LTR 的拷贝数．具体方法同1.5．2结果2.1实时定量PCR 检测病毒颗粒数本实验中，定量PCR 引物设计在LTR 区，由于一个慢病毒含有两个病毒基因拷贝，因此，在计算病毒颗粒数时，LTR 拷贝数除以2即为病毒颗粒数.应用实时定量PCR 检测到病毒LTR 拷贝数为1.26×1012/mL ，定量PCR 反应荧光强度曲线及标准曲线见图1、图2.通过计算，得到病毒颗粒数为6.32×1011/mL ．此时计算得到的病毒颗粒数为所有收集到的病毒颗粒总数，既包括有感染效力的病毒，也包括无感染效力的病毒．为了测定制备得到的病毒实际滴度（即单位体积内有感染效力的病毒颗粒数），我们将不同剂量病毒感染细胞，分别用GFP 报告基因法和定量PCR 法测定病毒滴度．2.2实时定量PCR 检测病毒载体整合拷贝数，计算病毒滴度取病毒浓缩液，按照10倍稀释，分别取0.1、0.01、0.001μL 病毒浓缩液感染1.5×106293T 细胞，感染2d 后，应用实时定量PCR 检测不同病毒量感染的细胞DNA 中LTR 整合拷贝数，结果显示，0.1、0.01、0.001μL 病毒感染的细胞中外源基因整合的拷贝数分别为5.32×106、9.28×105、4.48×104.定量PCR 的系统参数为：R =0.99，R ∧2=0.99，Efficiency =1.01，各参数值表明实验检测的准确性和可信性．当一个病毒感染细胞并将外源基因整合入基因组后，由于其末端发生跳跃过程，使得每条DNA 单链上含有两个完整的LTR ，因此，在被整合的细胞基因组，一个慢病毒颗粒=LTR 拷贝数/4．通过计算，得到病毒滴度为（1.59±0.64）×1010IU /mL ．2.3GFP 报告基因检测法测定病毒滴度同时将0.1、0.01、0.001μL 病毒浓缩液感染2d 后的细胞，置于荧光显微镜下观测．镜检结果显示，GFP 阳性细胞数逐级递减，0.1、0.01、0.001μL 病毒量感染的细胞中，GFP 阳性率分别为52%、6%、0.5%，呈现较好的倍比关系（图3）．通过公式：病毒滴度=感染细胞数×GFP 阳性率×病毒稀释倍数÷病毒量，得出病毒滴度为（8.10±0.79）×109IU/mL ．2.4GFP 报告基因检测法与定量PCR 检测法所得病毒滴度比较，验证定量PCR 检测法准确性通过比较GFP 报告基因检测法和实时定量510152025303510^-110^-210^-3N o r m f l u o r eCycle numberThreshold·····10^410^510^610^710^810^940302010R =0.99980R ^2=0.99960Efficiency=0.96M =0.293B =13.087Concentration （Copy number ）T h r e s h o l d c y c l e396第5期注：病毒感染293T 细胞数为1.5×106.Notes ：293T cells in each well are:1.5×106.图3逐级稀释的慢病毒感染293T 细胞后GFP 的表达情况（A ）0.1μL 病毒感染细胞；（B ）0.01μL 病毒感染细胞；（C ）0.001μL 病毒感染细胞.Fig.3GFP expression in infected 293T cells after 10fold dilution （A ）293T cells infected by 0.1μL virus ；（B ）293T cells infected by 0.01μL virus ；（C ）293T cells infected by 0.001μL virus.PCR 检测法（表2），可以看出，与我们预期结果一致，实时定量PCR 法检测结果与GFP 报告基因检测法检测结果成正相关．多次重复实验结果均表明，两者的检测结果成稳定的正相关性．而且，实时定量PCR 检测法不依赖GFP 蛋白正常表达，对整合入宿主基因组但不能正常表达的病毒仍然能够在其检测范围之内，因此，实时定量PCR 的检测结果更接近实际值，能够更加准确的检测病毒滴度．（A ）（B ）（C）表2GFP 报告基因检测法与定量PCR 检测法测得病毒滴度比较Table 2Comparison of lentivirus titer determined by GFP reporter assay and qRT -PCR approachDose of viral particles6.3×107 6.3×106 6.3×105GFP reporter assay Percentage of GFP +cells Infectious units qRT -PCR assayInfectious units52.0%7.8×1051.3×1066.0%9.0×1042.3×1050.5%7.5×1031.1×1042.5荧光实时定量PCR 法测定病毒实际感染效率通过计算公式：感染效率=有效感染病毒数/感染细胞总病毒颗粒数×100%，得到该实验中慢病毒的感染效率为：2.65±1.07%．3讨论慢病毒载体的研究，目前以HIV -1最为深入．慢病毒载体构建的基本原理是将HIV -1基因组中的基本骨架与编码其功能蛋白相分离，分别改建成载体质粒和表达包装蛋白的质粒，并将两种成分共转染入细胞，从中获得只有一次感染能力而没有复制能力的HIV -1载体假病毒［7］，从而提高了其应用的安全性.近年来，越来越多的研究者利用慢病毒载体系统作为在动物模型研究基因治疗的导入系统，并取得良好的效果［8~10］．与此同时，利用慢病毒载体介导制备转基因动物的研究也得到发展，慢病毒载体介导成功制备了转基因小鼠［11，12］、转基因猪［13］、转基因牛［14］等动物，为基因工程领域的研究奠定基础．由于慢病毒载体的基因转导效率主要取决于病毒滴度，这就使得慢病毒滴度及其感染效率的检测变得很重要．目前，通行的慢病毒滴度检测方法有：1）p24等抗原酶联检测法（p24ELISA 方法）.其缺点是：商业化的ELISA 试剂盒往往太贵，约6000元人民币一盒.而且蛋白含量检测结果不能直接反映其拷贝数；2）使用报告基因系统，无法检测其真实颗粒数及不携带报告基因的假病毒滴度；3）检测逆转录酶活性，用量马海燕等：应用荧光实时定量PCR 方法检测重组慢病毒滴度及其感染效率397生命科学研究2009年大，操作复杂及准确性差．本文所阐述的通过实时定量PCR法测定LTR拷贝数来检测病毒滴度的方法，能在提高慢病毒滴度检测准确性的同时，缩短检测时间、减少检测成本.相比传统检测方法，实时定量PCR 检测法有以下特点：1）由于本检测方法中，实时定量PCR的检测引物设计在慢病毒载体的LTR区，因此检测不依赖于所携带的外源基因；2）传统的GFP报告基因检测方法依赖绿色荧光蛋白的表达，对于外源基因整合入宿主基因组中但由于基因沉默而未能表达GFP蛋白的细胞无法检测，致使滴度测定不能准确地反应病毒的感染效率；而实时定量PCR检测法不依赖GFP报告基因的功能表达，因此其准确程度更高；3）报告基因检测法，因其感染和表达效率随宿主细胞而异，而利用实时定量PCR方法，直接检测病毒的颗粒数和整合入宿主基因组内的外源基因的拷贝数，从而大大提高了其检测的准确性．目前，临床上及实验室所应用的定量PCR方法，通常是检测整合入宿主细胞的基因拷贝数，因此，是对有活力病毒滴度的测定．而本文所介绍的方法，是通过直接裂解病毒，利用荧光实时定量PCR检测总的病毒颗粒数，并结合传统的慢病毒活力滴度的检测方法，对病毒颗粒的感染效率进行检测．所以本方法更适于被应用于研究病毒制备、感染过程中各因素对病毒感染效率的影响．病毒浓缩和感染过程中，由于受超离的压力、反复冻融、受体细胞易感性、病毒自身半衰期等诸多因素影响，使得有效的病毒数要低于其总颗粒数．为了确定实验中病毒的用量，需要预测病毒的实际感染效率．利用本文所介绍的实时定量PCR方法，检测慢病毒颗粒数及有活性的病毒滴度，通过计算有活力的病毒颗粒和总病毒颗粒的比值，我们可以得到每次制备的病毒的感染效率．在我们的实验中，所得到的病毒在293T细胞的实际感染效率为4%左右．而且多次实验表明，反复冻融对病毒感染效率具有很大影响.病毒实际感染效率的测定，为我们在进行具体实验中确定病毒用量具有实际指导意义．经本实验室多次重复试验，结果均表明荧光实时定量PCR法是一种高效、准确、快速的检测重组慢病毒滴度及其感染效率的方法，为重组慢病毒载体的应用奠定了基础．致谢：感谢任兆瑞教授对本文的悉心指导．参考文献（References）:[1]WU X，LI Y，CRISE B，et al.Transcription start regions inthe human genome are favored targets for MLV integration[J].Science，2003，300：1749-1751.[2]DEPALMA M，MONTINI E，SANTONIDESIO F R，et al.Promoter trapping reveals significant differences in integrationsite selection between MLV and HIV vectors in primaryhematopoietic cells[J].Blood，2005，105（6）：2307-2315. [3]SCHRODER A R，SHINN P，CHEN H，et al.HIV-1integration in the human genome favors active genes and localhotspots[J].Cell，2002，110：521-529.[4]JAKOBSSON J，ERICSON C，JANSSON M，et al.Targetedtransgene expression in rat brain using lentiviral vectors[J].Neurosci Res，2003，73（6）：876.[5]张敬之，郭歆冰，谢书阳，等.用慢病毒载体介导产生绿色荧光蛋白（GFP）转基因小鼠[J].自然科学进展（ZHANGJing-zhi，GUO Xin-bin，XIE Shu-yang，et al.Production oftransgenic mice carrying green fluorescence protein gene by alentiviral vector-mediated approach[J].Progress in NatureScience），2006，16（8）：827-832.[6]STEWART S A，OYLOCHOOM D M，PALLISER D，et al．Lentivims-delivered stable gene silencing by RNAi in primarycells[J].RNA，2003，9（4）：493-501．[7]刘茵.慢病毒载体在转基因动物研制中的应用[J].国际遗传学杂志（LIU Yin.Application of lentiviral vectors intransgenic animal development[J].Int J Genet），2007，30（5）：374-377.[8]MAY C，RIVELLA S，CALLEGARI J，et al.Therapeutichaemoglobin synthesis in beta-thalassaemic mice expressinglentivirus-encoded human beta-globin[J].Nature，2000，406（6791）：82-86.[9]HAN X D，LIN C，CHANG J，et al.Fetal gene therapy ofα-thalassemia in a mouse model[J].PNAS，2007，104（21）：9007-9011.[10]LI W，XIE S Y，GUO X B，et al.A novel transgenic mousemodel produced from lentiviral germline integration for thestudy ofβ-thalassemia gene therapy[J].Haematologica，2008，93（3）：357-362.[11]LOIS C，HONG E J，PEASE S，et al.Germline transmissionand tissuespecific expression of transgenes delivered bylentiviral vectors[J].Science，2002，295：868-872.[12]PFEIFER A，IKAWA M，DAYN Y，et al.Transgenesis bylentiviral vectors：lack of gene silencing in mammnlianembryonic stem cells and preimpalntation embryos[J].ProcNatl Acad Sci U S A，2002，99：2140-2145.[13]HOFMANN A，KESSLER B，EWERLING S，et al.Efficienttransgenesis in farm animals by lentiviral emtovora vectors[J].EMBO Reports，2003，4：1054-1060.[14]HOFMANN A，ZAKHARTCHENKO V，WEPPERT M，et al.Generation of transgenic cattle by lentiviral gene transfer intooocytes[J].Biol Reprod，2004，71：405-409.398。
悬置带线滤波器和多工器研究
摘要摘要随着科学技术的不断进步，无线通信技术也得到了蓬勃的发展，尤其在微波和毫米波方面，由于人们日益增长的需求促使了大量高效实用的设计理论和工程技术被不断提出来。
然而在无线通信技术中，保证通信信号的质量一直都是至关重要的，所以能够高效的完成信号选择作用的滤波器和多工器也就理所当然成为了无线通信技术发展进步中至关重要的一部分。
近年来，无线通信设备在保证高效性能的基础上对其小型化的要求越来越高，所以这就造成了目前滤波器和多工器的研究方向主要集中在保证其低损耗和高选择性的性能基础实现物理结构的小型化。
悬置带线的传输线结构是上世纪80年代才被提出来的一种新型的传输线结构，它可以看作是一种特殊的带状线结构，但其独特的物理结构使其与微带线相比有着非常明显的低损耗的优势，而与金属同轴和波导结构相比又有着容易实现小型化和容易被集成的长处。
与此同时，该传输线的基本物理结构是金属腔体包围着空气环绕的介质基板构成，所以该传输线结构所设计的器件就有着低温漂和高功率容量的特点。
由此看来，对悬置带线设计的滤波器和多工器进行深入的研究是有着远大前景和重大意义的。
本文首先了解了滤波器和多工器的研究背景，对其在国内外的研究现状进行了调研，并在此基础上分析了目前在通信技术中滤波器件的发展趋势。
然后，对悬置带线滤波器件的研究现状和发展方向也做了深入的调研和详细的分析。
继而在此基础上，以广义Chebyshev函数滤波器耦合矩阵的综合为设计理论，完成了悬置带线带通滤波器、双工器以及四工器的设计。
那么，本文的工作主要包括以下几个方面：1.对基于广义Chebyshev函数滤波器的综合理论进行研究。
以广义Chebyshev 函数为逼近函数的所设计的滤波器最大的特点就是可以引入交叉耦合，从而能够优化滤波器的传输特性。
这里从特征多项式的推导出发，进而完成滤波器初始耦合矩阵的综合，然后通过旋转消元实现自定义拓扑结构耦合矩阵的综合，为之后设计带有交叉耦合滤波器时进行耦合矩阵的综合提供了理论基础。
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL.51,NO.3,MARCH 2003421A Novel Approach for Miniaturizationof Slot AntennasReza Azadegan ,Student Member,IEEE,and Kamal Sarabandi ,Fellow,IEEEAbstract—With the virtual enforcement of the requiredboundary condition (BC)at the end of a slot antenna,the area occupied by the resonant antenna can be reduced.To achieve the required virtual BC,the two short circuits at the end of the resonant slot are replaced by some reactive BC,including inductive or capacitive loadings.The application of these loads is shown to reduce the size of the resonant slot antenna for a given resonant frequency without imposing any stringent condition on the impedance matching of the antenna.In this paper,a procedure for designing this class of slot antennas for any arbitrary size is presented.The procedure is based on an equivalent circuit model for the antenna and its feed structure.The corresponding equiv-alent circuit parameters are extracted using a full-wave forward model in conjunction with a genetic algorithm optimizer.These parameters are employed to find a proper matching network so that a perfect match to a 50 line is obtained.For a prototype slot antenna with approximate dimensions of 0(gineering 48109UDigita422IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL.51,NO.3,MARCH2003 Although this method of miniaturization is susceptible to sur-face wave excitation,it might be found beneficial,especiallywhen the electrical thickness of the substrate is small comparedto the wavelength.It is worth mentioning that this type of an-tenna miniaturization is not immune to the aforementioned ad-verse effects such ashighon a substratehaving(1)Fig.1.Magnetic current distribution on a half wavelength and inductivelyterminated miniaturized slot antenna.wherealong the length of a modified slot antenna can be maintainedthe same asthe slot antenna,then it is possible to makea smaller slot antenna.Any size reduction of interest can beachieved so long as the appropriate BCs are in place at the properlocation on the slot.Fig.1illustrates the idea where it is shownthat by imposing a finite voltage at both ends of a slot,the de-sired magnetic current distribution on a short slot antenna canbe established.To create a voltage discontinuity,one can use a series induc-tive element at the end of the slot antenna.It should be pointedout that terminating the slot antenna with a lumped inductanceor capacitance is not practical since the slot is embedded in aground plane,which can in fact short-circuit any termination.To circumvent this problem,a lumped inductor could be phys-ically realized by a compact short-circuited slotted spiral.Toensure inductive loading,the length of the spiral slot must beless than a quarter wavelength.Instead of a single inductive el-ement at each end,it is preferred to use two inductive slotlinesopposite of each other[see Figs.2(c)and3].Since these twoinductors in the slot configuration are in series,a shorter slot-line provides the required inductive load at the end of the slotantenna.Another reason for choosing this configuration is thatthe magnetic currents flowing in opposite directions cancel eachother’s fields on the planes of symmetry,and thereby,minimizethe near-field coupling effect of the inductive loads on the de-sired current distribution along the radiating slot.It should be noted that the mutual coupling within the spiralslotline reduces the effective inductance,and therefore,alonger spiral length compared with a straight section[Fig.2(c)]is needed to achieve the desired inductance.To alleviate thisadverse effect,a narrower slot width must be chosen for thespiral slotline.AZADEGAN AND SARABANDI:MINIATURIZATION OF SLOT ANTENNAS423Fig.2.Transmission line model of a slot antenna (a)half-wave slot antenna.(b)Inductively terminated slot antenna.(c)Two series inductiveterminations.Fig.3.Proposed antenna geometry fed by a two-port microstrip feed.This two-port geometry is used to find out the exact resonant frequency of the inductively loaded slot.B.Antenna FeedA microstrip transmission line is used to feed this antenna.The choice of the microstrip feed,as opposed to a coaxial line,is based on the ease of fabrication and stability.This feed struc-ture is also more amenable to tuning by providing the designer with an additional parameter.Instead of short-circuiting the microstrip line over the slot,an open-ended microstrip line with an appropriate length extending beyond the microstrip-slot crossing point (additional parameter)can be used.A coplanar waveguide (CPW)can also be used to feed the antenna providing the ease of fabrication,whereas it is moreTABLE IS LOTLINE C HARACTERISTICS FOR T WO D IFFERENT V ALUES OF S LOT W IDTHw ,AND THE D IELECTRIC C ONSTANT OF "fo w h hh f mm mi fo h h fi h m mo m h h fu w m h fo fi h w h fi h mfo h me fo w wi hfwi hfh mw m h h f m424IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL.51,NO.3,MARCH2003 slotlinebymm.Referring toFig.3,the vertical dimension(alongthe55mm,which isabout.Since the dielectric constant and the thicknessof the substrate chosen for this design are very low(microstrip line.The two-port structure is constructed tostudy the resonant frequency of the antenna as well as the tran-sition between microstrip and the slot antenna.The microstripline is extended well beyond the slot transition point so that theport terminals do not couple to the slot antenna.The radiatingslot length is chosen tobetransmission line.Fig.5showsanFig.4.S-parameters of the two-port antenna shown in Fig.3.Fig.5.Topology of the equivalent circuit for the two-port antenna.equivalent circuit model for the two-port device when the tran-sition between microstrip and slot line is represented by an idealtransformer with a frequency dependent turn ratio(AZADEGAN AND SARABANDI:MINIATURIZATION OF SLOT ANTENNAS425Fig. 6.Y -parameters of the two-port antenna after deembedding the microstrip feed lines.as well as the mutual coupling between the radiator section and the rectangular spirals should also be included in the equivalent circuit.A.Equivalent-Circuit ModelIn this section,an equivalent circuit model for the proposed antenna is developed.This model is capable of predicting the slot radiation conductance and the antenna input impedance near resonance.This approach provides very helpful insight as to how this antenna and its feed network operate.As mentioned before,this model is also needed to find a proper matching network for the antenna.Near resonant frequencies,the slot antenna can be modeled by a simple second order RLC circuit.Since the voltage across the slot excites the slot antenna at the feed point,it is appropriate to use the shunt resonant model for the radiating slot as shown in Fig.5.The coupling between the microstrip and the slot is modeled by a series ideal transformer with a turnratio-pa-rameters of the two-port microstrip-fed slot antenna where the location of deembedded ports are shown in Fig.3.Note that these two ports are now defined at the microstrip-slot junction.TABLE IIT HE P ARAMETERS OF THE G ENETIC A LGORITHM OPTIMIZERTABLE IIIT HE E QUIV ALENT C IRCUIT P ARAMETERSOFTHE M ICROSTRIP F ED S LOT ANTENNAAccording to the lumped element model of Fig.5,the-parameters over 40frequency points around the res-onance is used as the objective (fitness)function of the opti-mization problem.We ran the program with different random number seeds to ensure the best result over the entire domain of the parameters space.Also,the parameters were constrained only to physical values in the region of interest.The parameters of the GA optimizer are shown in Table II.Table III shows the extracted equivalent circuit parameters after 50,000iterations.The426IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL.51,NO.3,MARCH2003parison between the full-wave simulated S-parameters of theantenna and that of the equivalent circuit.Fig.8.The required terminating admittance for the second port of the two-portmodel in order to match the antenna to a50- line.Fig.8shows the spectral behavior ofline.As seen in this figure and suggested by Table IV,thefeed line has been extended a short distance beyond the slot line.The width of the microstrip,where it crosses the slot,is reducedso that it may block a smaller portion of the radiating slot.It isworth mentioning that the effect of the feed linewidth on its cou-pling to the slot was investigated,and it was found that as longas the linewidth is much smaller than the radiating slot length,the equivalent circuit parameters do not change considerably.As mentioned,the antenna has been simulated using a com-mercial software(IE3D)[20].Using this software,the returnloss(AZADEGAN AND SARABANDI:MINIATURIZATION OF SLOT ANTENNAS427Fig.10.Measured and simulated return loss of the miniaturizedantenna.Fig.11.A photograph of the fabricated antenna.order to experimentally validate the design procedure,equiva-lent circuit model,and simulation results,the antenna was fabri-cated on a 0.787-mm-thick substratewith1%)from what is predicted by the numer-ical code.The errors associated with the numerical code could contribute to this frequency shift.This deviation can also be at-tributed to the finite size of the groundplane,for this prototype,knowing that an infinite ground plane is as-sumed in the numerical simulation.The shift in the resonant fre-quency resulted from the finite size of the ground plane for slot antennas is discussed in [15].The far-field radiation patterns of the antenna were measured in the anechoic chamber of The University of Michigan.The gain of the antenna was measured at the bore-sight directionTABLE VA NTENNA C HARACTERISTICS AS A F UNCTION OF T WO D IFFERENT S IZE G ROUND P LANES C OMPARED W ITH THE S IMULATED R ESULTS FOR THE S AMEA NTENNA ON AN I NFINITE G ROUND PLANEFig.12.Simulated radiation pattern of the miniaturized antenna.under polarization-matched condition using a standard antenna whose gain is known as a function of frequency.The gainofdB.This value of direc-tivity is very close to that of a dipole antenna.Based on the def-inition of the antenna gain [16],under the impedance matched condition,one might expect to measure the maximum gainofdB428IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION,VOL.51,NO.3,MARCH2003(a)(b)Fig.13.Measured radiation patterns of the antenna with a small (0:2)and a larger (0:5 )Ground Plane (GP):(a)H plane pattern.(b)E plane pattern.tern diminishes and the pattern approaches that of an isotropic radiator.The reduction in the directivity of the slot antenna with a finite ground plane can also be attributed to the radiation from the edges and surface wave diffraction [27].To further study the effect of the size of the ground plane,the same antenna with aslightly larger ground plane()was fabricated and measured.Table V shows the comparison between the ra-diation characteristics of these two antennas and simulated re-sults.As explained,when the size of the antenna ground plane increases,the gain of the antenna increasesfrom-field,,to vanishalong the radiating slotat-field is discontinuous.This nullin the E plane is the result of the cancellation of fields,which are radiated by the two opposing magnetic currents.The equiv-alent magnetic currents,flowing in the upper and lower side of the ground plane,are in opposite directions and consequently,their radiation in the point of symmetry at the E plane cancel each other.However,in the case of an infinite ground plane,the upper and lower half-spaces are isolated,and therefore,the E plane radiation pattern remains constant.Moreover,an increase in the measured cross-polarized com-ponent is observed as compared with the simulation results.Al-though it may seem that there is a considerable cross-polariza-tion radiation due to the presence of spiral slots at the termi-nations,there is no such component in the principal planes as well asthewas designed at300MHz and perfectly matched to a50was used to ensure that the dielectric material wouldnot contribute to the antenna miniaturization.An equivalent cir-cuit for the antenna was developed,which provided the guide-lines necessary for designing a compact lossless matching net-work for the antenna.To validate the design procedure,a proto-type antenna was fabricated and measured at 300MHz.A per-fect match for this very small antenna was demonstrated with a moderate gain ofAZADEGAN AND SARABANDI:MINIATURIZATION OF SLOT ANTENNAS429。