Ultra-Wideband FSS-Based Antennas

As antennas are indispensable elements in wireless systems, it is necessary to provide UWB antennas suitable for UWB systems. The most proposed UWB antennas have omnidirectional radiation, which provides the wide coverage area that is highly demanded by many conventional UWB applications. However, directional radiation is more beneficial for other UWB applications and it may even be beneficial for the conventional UWB omnidirectional applications in some environments that contain many sources of interference and distorting objects, where the omnidirectional radiation leads to high interference and loss of power in undesirable directions. Consequently, an immense research has addressed the issue of realizing UWB planar antennas with unidirectional radiation characteristics. Basically, the main technique used to create unidirectional radiation patterns is employing cavity-baking reflectors to redirect the back radiation, hence increasing the gain of the radiators. In addition, these reflectors can decouple the mounted radiator from the surroundings that can damage its characteristics. Therefore, we suggest the employment of UWB reflectors to achieve UWB planar antennas with directional radiation. Our research for designing optimal UWB reflectors has led to the investigation in the field of frequency selective surfaces (FSSs), which are valuable structures and can be of great interest to a wide range of applications especially UWB applications. Subsequently, the main aim of this chapter is to give a review of the fundamental uses of FSSs in antenna engineering and the basic physical concepts that have been employed to serve the purpose of enhancing antennas’ performances using FSSs with a variety of features and characteristics. Furthermore, it is geared toward the presentation of our proposed UWB FSS-based antennas. First, we use basic FSSs such as the capacitive and its complementary inductive FSSs to design UWB reflectors that can serve improving and stabilizing the gain of UWB antennas. Thereafter, a proposed UWB single-layer FSS is used to serve the same purpose. Then, the FSS is integrated and designed together with UWB radiator, which resulted in lower profile along with good performance

Applications of circularly polarized crossed dipole antennas

© 2014 IEEE. Circularly polarized crossed dipole antennas are presented in this paper. A compact crossed dipole is realized with the use of a meander line and a barbed end in each dipole arm. A vacant-quarter printed ring is used as a 90° phase delay line to achieve circularly polarized radiation. For multi-band applications, each dipole arm is divided into multi-branches with different lengths to obtain multiple resonances. These radiators can be equipped with different reflectors, such as a finite planar metallic conductor, a cavity-backed metallic conductor, and a finite artificial magnetic conductor to obtain the desired antenna radiation characteristics. These antennas are quite practical for many wireless communication systems, such as satellite communications, global positioning systems, wireless local area networks, and radio-frequency identification devices

낮은 높이의 광대역 원형 편파 배열 안테나 시스템을 위한 다층 적재된 실시간 지연 회로와 위상 조절 반사판 설계

학위논문(박사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2020. 2. 남상욱.본 논문에서는 낮은 높이의 광대역 배열 안테나 시스템을 구현하기 위해 필요한 핵심 기술 개발에 관해 연구하였다. 레이더, 전자전, 무선 통신과 같이 많은 분야에서 활발히 사용되는 있는 배열 안테나는 산업이 고도화되면서 요구하는 시스템 스펙이 더욱 고급화되고 있다. 그 중 무인 비행체, 미사일 등과 같은 고속 이동체의 곡면에 배치할 수 있도록 하기 위해서는 낮은 높이의 안테나 설계가 필요한데, 특히 낮은 높이의 광대역 안테나는 구조적으로 설계에 큰 어려움이 있다. 이 논문에서 목표로 정한 응용 분야는 전자전에서 빔포밍을 이용하여 적의 위치를 탐색하고 해당 위치로 특정 주파수의 큰 전력의 신호를 전송하는 전파 방해기이다. 전파 방해기는 광대역의 주파수 대역 내에서 선택적으로 주파수를 선택하여 사용할 수 있도록 설계되어야 하므로 광대역으로 동작하는 시스템 구현이 필요하다. 낮은 높이의 광대역 배열 안테나 시스템는 크게 광대역 빔조향 네트워크와 낮은 높이의 광대역 배열 안테나로 구분할 수 있다. 본 논문에서는 각 부분에서의 문제를 분석하고 이를 해결하여 설계 및 구현하는 방향으로 연구를 진행하였다. 수행된 연구의 내용은 아래와 같다. 첫 번째로, 광대역 빔조향 네트워크를 구성하는 가장 핵심 요소인 실시간 지연회로를 구현할 때 필요한 기술을 개발하였다. 먼저 실시간 지연회로의 중요한 성능 지표인 지연 시간 특성에 영향을 줄 수 있는 3가지 요소들에 대해 분석하였다. 첫 번째 요소는 off 상태에서 보이는 커페시터에 의한 공진이다. 실시간 지연회로에서 공진이 발생하면 전체 시스템 성능이 악화될 수 있기 때문에 30 dB 이상의 격리 특성을 갖는 스위치를 사용하여야 한다. 두 번째로 분석한 요소는 불연속에 의해 나타나는 반사파로 이는 실시간 지연회로와 전체 시스템을 구성할 때 매칭이 필수적으로 수행되어야 하는 이유가 된다. 마지막으로 분석한 요소는 안테나 임피던스에 의한 반사 손실이다. 광대역 안테나의 임피던스는 주파수에 따라 변하게 되는데 이는 안테나에 인가되는 신호의 위상을 변화시켜 배열 안테나 시스템 성능에 영향을 줄 수 있다. 몬테 카를로 시뮬레이션을 통해 안테나 임피던스 변화에 따른 위상 오차가 빔조향각과 사이드 로브 레벨에 얼마나 영향을 주는지 확인하였다. 배열 안테나를 설계하여 해당 안테나의 능동 반사 계수를 통해 이를 검증하였다. 실시간 지연회로의 설계를 진행할 때 추가적인 이슈는 소형화가 있다. 앞에서 분석한 3가지 요소를 고려하여 7-bit 적층 실시간 지연회로를 설계하였다. 제작 및 측정을 통해 설계한 실시간 지연회로가 손실에 따른 지연시간, 높은 bit 수, 저전력의 장점을 가지는 것을 확인하였다. 마지막으로 광대역 안테나 시스템을 구성하여 제작된 실시간 지연회로를 검증하였다. 측정을 통해 제작된 광대역 안테나 시스템이 3:1 대역에서 빔 스퀸트 현상 없이 빔조향이 가능함을 확인하였고 소형화된 실시간 지연회로가 제대로 동작함을 검증하였다. 두 번째로, 낮은 높이의 광대역 안테나를 구현에 필요한 기술로 광대역 안테나 가까이 반사판을 배치하여 단방향 빔을 형성할 때 발생하는 문제점을 분석 및 극복하였다. 낮은 높이의 광대역 배열 안테나에 가장 적합한 안테나는 구현이 쉽고 소형화에 장점이 있는 스파이럴 안테나이다. 양방향 패턴을 갖는 스파이럴 안테나는 단방향 패텅을 만들어 주기 위해 반사판이 필요한데 해당 반사판으로 인해 매칭과 축비에 문제가 생기는 큰 단점이 있다. 본 논문에서는 먼저 반사판이 축비를 악화시키는 이유에 대해 분석하였다. 분석을 기반으로 축비 개선을 위해 varactor를 사용한 polarization-dependent 위상 조절 반사판을 제안하였다. polarization-dependent 위상 조절 반사판이 효과적으로 축비를 개선하는지 확인하기 위해 스파이럴 안테나와 함께 배치하여 설계하였다. 주기 구조를 통해 무한 배열 시뮬레이션을 진행하여 원하는 주파수 대역에서 축비가 효과적으로 개선되는 것을 확인하였다. 이를 구현하기 위해 dummy를 추가한 4 x 4 배열 안테나를 최종 설계하였다. 주기 구조 시뮬레이션과 높은 일치성을 보여 제작 및 측정을 진행하였다. 제작된 안테나의 반사 손실은 원하는 대역 모두에서 -10 dB 이하의 값을 가졌다. 축비, 이득, 패턴 모두 시뮬레이션과 거의 일치한 측정 결과를 얻을 수 있었다. 이를 통해 polarization-dependent 위상 조절 반사판이 효과적으로 축비를 개선하는 것을 검증하였다. 마지막으로 빔조향 특성을 확인한 결과 polarization-dependent 위상 조절 반사판을 적용하면서 손실없이 빔폭 내에서 1.5 dB 아래의 우수한 축비 값을 가지며 -30도에서 30도까지 빔조향이 가능함을 확인하였다. 결론적으로, 본 논문에서는 낮은 높이의 광대역 안테나 시스템을 구현할 때 극복해야 하는 두가지 주제에 대해 분석 및 해결하였다. 정확한 분석 및 적절한 해결 방안을 찾을 수 있었고 이를 통해 광대역 빔조향 네트워크와 낮은 높이의 광대역 배열 안테나에 적용하여 설계하였다. 최종적으로 측정 및 검증을 통해 전체 과정의 타당성을 검증하였다.In this thesis, two essential technologies to realize a low profile wideband phased array antenna system are described. Phased array antennas, which have been actively used in military and civil applications such as radar, electronic warfare (EW), and wireless communications, are becoming more advanced as the system specification demanded by the industry. Especially, low-profile wideband phased array antennas are actively studied. It has been a challenge to design wideband and low-profile antennas, which can be surface-mounted on airborne applications such as missile, aircraft, and unmanned aerial vehicle (UAV) to reduce air resistance. Target application in this thesis is jammer in electronic warfare which is to search the enemy's position and shoot a signal of a large power of a certain frequency to the position by beamforming, so it is designed to selectively choose a frequency in a wide band. The low-profile wideband array antenna system for the application consists of a wideband beamforming network and a low-profile wideband array antenna. In this thesis, we analyzed the issues and problems in each part and overcame them to design and implement the low-profile wideband antenna system. The contents of the study carried out are as follows. At first, design considerations and procedure of wideband beamforming network is presented. Three factors that can affect group delay variation are analyzed, which is the most important performance indicator of the true-time delay line (TTD). First factor that affects group delay characteristic is off-state capacitor resonance. To minimize degradation of TTD performance due to the resonances, switches with an off-state isolation of more than 30 dB are required. Second factor is reflected wave due to discontinuity, so that matching must be accomplished in design of TTDs and all system. The last factor is the phase error caused by the reflection coefficient due to the antenna impedance. Monte Carlo simulations were performed to investigate the effect of phase delay error on the beam steering angle and side lobe level due to antenna impedance. And the actual antenna is designed to verify the effect of the phase delay error on the antenna impedance. Considering these factors 7-bit multistacked TTD was designed and fabricated for miniaturization which is an additional issue when designing a TTD. Fabrication and measurement were performed and our approach shows an improved performance regarding a figure of merit defined as the relative delay divided by the insertion loss at the longest delay state, a large number of bits of resolution, and low power consumption. Finally, a wideband antenna system was constructed to verify the fabricated TTD. Beam steering is performed without beam squint within the 3 : 1 bandwidth, which verify that the miniaturized TTD is capable of wideband beam steering. Second, to solve performance degradation problems when forming a unidirectional beam by attaching a perfect electric conductor (PEC) reflector close to the wideband antenna is described for low-profile wideband phased array antenna systems. The most applicable type of antennas for low profile wideband antenna array is spiral antenna which has advantages of simple manufacture process and miniaturization for array. Spiral antenna has the disadvantage of requiring a reflector for unidirectional patterns due to its bidirectional circular polarized pattern. We analyzed the reason why the axial ratio (AR) could be deteriorated by the reflector first. Based on analysis, a polarization-dependent phase tunable reflector is proposed to implement the required reflection phase of x and y using varactors for improvement of AR. To verify that AR is effectively improved by the polarization-dependent phase tunable reflector, spiral array antenna backed by the polarization-dependent phase tunable reflector was designed and fabricated. Periodic boundary simulation for infinite array and simulation of 4 x 4 array with dummy were performed. A 4 x 4 array with dummy of the fabricated array with polarization-dependent phase tunable reflector for measurement. Fabricated array antenna has a reflection coefficient of less than –10 dB in the entire target band. All measurement results and simulation results have high consistent. AR improvement was achieved through the measurement results by changing bias voltage applied to varactors on polarization-dependent phase tunable reflector. According to this measurement process and results we implemented a spiral array antenna capable of beam steering from -30˚ to 30˚ with excellent circular polarization (CP) characteristics with an AR value of less than 1.5 dB within the 3 dB beamwidth without loss by applying polarization-dependent phase tunable reflector. In conclusion, we investigated and analyzed two issues to overcome for implementation of a low-profile wideband antenna system. Through accurate analysis, appropriate solution could be found and applied to design of wideband beamforming network and low-profile wideband array antenna. Fabrications and measurements were conducted to prove the validity of the entire process.Chapter 1. Introduction 1 1.1. Motivation 1 1.2. Organization of the Dissertation 4 Chapter 2. Wideband Beamforming Network 5 2.1. Analysis of factors that affects group delay variation in TTD 6 2.1.1. Accurate group delay measurement technique in vector network analyzer 6 2.1.2. Off-switch capacitor resonance 10 2.1.3. Reflected wave due to discontinuity 13 2.1.4. Antenna impedance variation over frequency 16 2.2. Design of 7-bit multistacked true-time delay for miniaturization 26 2.2.1. Design considerations 27 2.2.2. TTD resolution and number of bits 30 2.2.3. Optimal design of signal vias 32 2.2.4. Fabrication and measurement results 36 2.2.5. Verification of TTD 40 2.3. Conclusion 53 Chapter 3. Low-profile Wideband Antenna 55 3.1. Analysis of AR deterioration backed by reflector 57 3.2. Improvement of AR with polarization-dependent phase tunable reflector 63 3.2.1. AR improvement through reflector with ideal reflection phase 63 3.2.2. Practical design issues of reflector with varactors 68 3.2.3. AR improvement through 1D phase tunable reflector 76 3.2.4. AR improvement through 2D phase tunable reflector 79 3.3. Design of spiral antenna array backed by polarizationdependent 1D phase tunable reflector 83 3.3.1. Periodic boundary simulation for infinite array 84 3.3.2. 4 x 4 array simulation with dummy 87 3.4. Fabrication and measurement results 90 3.5. Conclusion 107 Bibliography 110 Abstract in Korean 115Docto

Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

Printed Quasi-Yagi Antennas Using Double Dipoles and Stub-Loaded Technique for Multi-Band and Broadband Applications

© 2013 IEEE. Double dipoles on a single-layer substrate are utilized to construct a triple-mode printed quasi-Yagi antenna for the multi-band and broadband antenna applications. A stub-loaded dipole generating two resonant modes (i.e., lower dual-mode dipole) is allocated on the underside of a simple dipole (i.e., upper single-mode dipole) introducing the third resonant mode. Using these three resonant modes, three compact printed quasi-Yagi antennas, i.e., tri-band, dual-band, and broadband printed quasi-Yagi antennas, are designed with the same antenna prototype but different parameter values. Seen from the measured results, all of these three antennas have good unidirectional radiations, high radiation efficiencies, and low cross-polarization levels at the operating frequencies within the impedance bandwidths

2009 Index IEEE Antennas and Wireless Propagation Letters Vol. 8

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index

2008 Index IEEE Transactions on Control Systems Technology Vol. 16

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author\u27s name. The primary entry includes the coauthors\u27 names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author\u27s name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index

Multi resonance patch antenna with multiple slits

In this paper, we have presented a new design of a multi resonance patch antenna with multiple slits. Slits are located on the three sides of the designed antenna. It is simulated in a planar 3D electromagnetic simulation program, called Sonnet Software, designed on the Aluminum (96%) substrate and operates at three frequencies with reflection coefficient (S11) values lower than -10 dB. Values for the operating frequencies are 4.14, 5.52, 9.24 GHz. Electric field theta polarized gains for these three frequencies are; 8.09, 8.35, and 8.39 dBs respectively. Cross polarization levels are well below -10 dB. A parametric study was conducted by changing the gap size and the dielectric thickness. As a result of the parametric study, it is seen that fabrication tolerances of the antenna are good enough

Microwave System for the Early Stage Detection of Congestive Heart Failure

Fluid accumulation inside the lungs, known as cardiac pulmonary edema, is one of the main early symptoms of congestive heart failure (CHF). That accumulation causes significant changes in the electrical properties of the lung tissues, which in turn can be detected using microwave techniques. To that end, the design and implementation of an automated ultrahigh-frequency microwave-based system for CHF detection and monitoring is presented. The hardware of the system consists of a wideband folded antenna attached to a fully automated vertical scanning platform, compact microwave transceiver, and laptop. The system includes software in the form of operational control, signal processing, and visualizing algorithms. To detect CHF, the system is designed to vertically scan the rear side of the human torso in a monostatic radar approach. The collected data from the scanning is then visualized in the time domain using the inverse Fourier transform. These images show the intensity of the reflected signals from different parts of the torso. Using a differential based detection technique, a threshold is defined to differentiate between healthy and unhealthy cases. This paper includes details of developing the automated platform, designing the antenna with the required properties imposed by the system, developing a signal processing algorithm, and introducing differential detection technique besides investigating miscellaneous probable CHF cases