Characteristics of switchable ferrite microstrip antennas

Switchable antennas consisting of microstrip elements with an in-plane biased ferrite cover layer are introduced. Their radiation and radar cross section (RCS) properties are examined through a full-wave moment-method analysis. For microstrip antennas with a ferrite cover layer, the presence of a decaying extraordinary wave in the ferrite layer can reduce or prohibit incident fields from reaching the antenna resulting in significant RCS reduction. For antenna radiation, most of the power will be converted into magnetostatic waves and little radiates into the air. Under such circumstances, the antennas are “off,” in the sense that they are effectively absent as radiators or scatterers. The aim of this paper is, through the use of an accurate full-wave analysis, to investigate the properties of the switchable microstrip antennas. Both the cases of strip dipoles and rectangular patches are analyzed. The effects of the cover-layer thickness, bias-field strength, and the existence of both ordinary and extraordinary waves on the switchable antenna properties are discussed     

Microstrip antennas

Microstrip antennas have been one of the most innovative topics in antenna theory and design in recent years, and are increasingly finding application in a wide range of modern microwave systems. This paper begins with a brief overview of the basic characteristics of microstrip antennas, and then concentrates on the most significant developments in microstrip antenna technology that have been made in the last several years. Emphasis is on new antenna configurations for improved electrical performance and manufacturability and on advances in the analytical modeling of microstrip antennas and arrays     

Broad-band cavity-backed and capacitively probe-fed microstrippatch arrays

A hybrid full wave method for the analysis of probe-fed infinite phased arrays of single and stacked microstrip patches, backed by metallic cavities, is applied to investigate the combined utilization of the capacitive probe-feeding technique and the cavity enclosure of microstrip patches. The goal is to obtain broad-band microstrip antennas on thick substrates without the limitations due to the generation of surface waves of the conventional microstrip antennas on infinite substrates. A design procedure for the capacitive coupling is investigated and theoretical results for the active input impedance and radiation characteristics of different wide-band antenna designs are presented     

Integration of a Microstrip Circulator With Planar Yagi Antennas of Several Directors

An integration methodology is presented to design antenna systems incorporating a ferrite circulator. Two integrated systems comprised of a microstrip circulator and Yagi planar–type antennas are presented as validation of the proposed methodology. Excellent pass band characteristics are observed in the experimental and numerical data for both systems. Furthermore, one system is magnetically tuned to realize 30 dB isolation over a bandwidth of 850 MHz. Both systems maintain excellent return loss and show improved insertion loss specifications even though the ferrite is biased into partial saturation. Extensive measurement data of the ferrite material and system network parameters are provided to corroborate the claims made herein.      

Microstrip antennas and arrays on chiral substrates

Results are presented for isolated microstrip antennas and infinite arrays of microstrip antennas printed on chiral substrates, computed from full-wave spectral domain moment method solutions. Data for resonant length, impedance, directivity, efficiency, cross-polarization level, and scan performance are compared to results obtained for a dielectric substrate of the same thickness and permittivity. It is concluded that, from the point of view of antenna characteristics, there does not seem to be any advantage to using chiral antenna substrates, while there are disadvantages in terms of increased cross-polarization levels and losses due to surface wave excitation     

Analysis and design of aperture-coupled microstrip patch antennasand arrays fed by dielectric image line

This paper presents the analysis and design of aperture-coupled microstrip patch antennas and arrays fed by an dielectric image line. A theory based on the cavity model of the microstrip patch antenna and the change in the modal voltage of the image line at the aperture was developed to analyze the single element aperture-coupled microstrip patch antenna. The theory developed was combined with the array theory to design linear traveling wave arrays at X-band and Ka-band frequencies. The required taper in the excitations of the individual patches of the array was achieved by varying the aperture dimensions. Experiments show very good results for the antennas and the arrays     

Polarisation switchable microstrip array antenna using proximity feeding technique

A polarisation switchable microstrip array antenna is presented. This array consists of square patch antennas coupled in close proximity to a microstrip line. The polarisation state can be switched electrically by short- or open-circuiting the end of the feedline using a PIN diode. Fundamental characteristics of the proposed array are investigated by measurements performed at S-band to demonstrate the proposal.     

Circular microstrip antenna on ferrimagnetic substrate

A theoretical analysis of circular microstrip antenna on a ferrimagnetic substrate predicts significantly reduced resonant radii and improved bandwidth as compared to those of similar antennas built on purely dielectric substrates, when operated in the lower range of UHF. The impedance characteristics, return loss, and radiation pattern studied experimentally for antennas built upon a typical ferrite substrate are found to be in good agreement qualitatively with the theoretical results.     

Millimeter wave components for electronically controllable antennas

Many present and future military and commercial systems operating at millimeter wave frequencies require the use of sophisticated electronically controllable antennas for maximum capability and flexibility. Electronic control of the antenna pattern is provided by electronically switchable phase control of each radiating element such as that achieved in phased array antennas or via electronically reconfigurable antenna feeds referred to as beam forming networks (BFN). Multibeam antennas provided by BFN'S can be realized using switches, variable power dividers (VPD), and phase shifters. Ferrite materials and associated application technology are being utilized to achieve these switchable RF control components at millimeter wave frequencies. The performance achievable in ferrite switchable circulators, variable power dividers and phase shifters in the frequency region from 20 to 100 GHz is discussed.     

Two-Dimensional Planar Array for Digital Beamforming and Direction-of-Arrival Estimations

A compact uniplanar design of 2-D antenna arrays is presented for digital beamforming (DBF) and direction-of-arrival (DOA) estimations. The array is based on switchable microstrip slot antennas that are series fed in one dimension and parallel fed in the other dimension. In conjunction with spatial multiplexing of local elements (SMILE) techniques, the array is able to use both the series- and parallel-fed antennas for 2-D beamforming and DOA estimations. The combination of series and parallel feeding provides a simple way of constructing 2-D DBF arrays with a simple and uniplanar feed network. Other advantages are its low cost and compatibility with a microwave integrated circuit process for the receiver system. A 4 $times$ 4 receiving array test bed at a 5.5-GHz operating frequency is fabricated, and DBF and DOA tests on this test bed are successfully demonstrated.      

Active Frequency-Tune Beam-Scanning Leaky-Wave Antenna Arrays

X-band active beam-scanning leaky-wave antenna arrays, including 1 × 1,1 × 2 and 1 × 4 prototypes, have been demonstrated. These antennas integrated one or several microstrip leaky-wave antenna elements with a single varactor-tuned HEMT VCO as an active source. Measured results on experimental antennas indicate that the beam scanning angle of the 1 × 1 antenna close to 40° can be achieved and the scanning range of 1 × 2 and 1 × 4 antenna arrays are both close to 32°. Furthermore, reflected wave due to the open end of each leaky-wave antenna element has been suppressed by the symmetric configuration of this antenna array and the antenna efficiency increases. When comparing with the measured radiation pattern of the single element antenna, we found that the 1 × 2 and 1 × 4 antenna arrays can effectively suppress the reflected power by more than 5.5 dB and 10.5 dB, respectively, at 10.2GHz. The power gain are more than 2 dB and 3.16 dB higher than the single element antenna with a measured EIRP of 18.67 dBm.     

An analysis of antenna coupling between arrays on a polyhedronstructure

Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Keller's GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations     

Lens-coupled imaging arrays for the millimeter- andsubmillimeter-wave regions

The authors have been developing four kinds of lens-coupled antenna imaging arrays for operation at millimeter- and submillimeter-wave frequencies. Dipole antennas, Yagi-Uda trap-loaded antennas, and microstrip patches are compared from the viewpoint of matching with detectors and optical systems. The radiation patterns and input impedance of each antenna have been calculated and measured to attain the optimum matching using model experiments. The trap-loaded antenna arrays have been successfully applied to plasma diagnostics at the Tsukuba GAMMA 10 tandem mirror     

Correlation and channel capacity of MIMO systems employing multimode antennas

A novel way of exploiting higher modes of antennas as diversity branches in multiple-input-multiple-output (MIMO) systems is introduced. Essentially, antennas employing multiple modes offer characteristics similar to an antenna array, through multiple modes and using only a single element. The physical mechanism that yields different received signals is the fact that each mode has a different radiation pattern. Analytical expressions for the correlation between signals received by different modes are presented for a biconical and a circular microstrip antenna that employs higher order modes. It is found that the correlation is low enough to yield a significant diversity gain. Furthermore, the channel capacity of a MIMO system using a multimode antenna, i.e., an antenna employing multiple modes, is found to be comparable to the capacity of an array. Since only one element is needed, the multimode antenna offers several advantages over traditional arrays, and is an interesting antenna solution for future high capacity MIMO systems.     

A reconfigurable microstrip antenna for switchable polarization

A novel reconfigurable microstrip antenna with switchable polarization sense is proposed. The proposed antenna has a simple structure, consisting of a corner-truncated square radiating patch, four small triangular conductors, and a microstrip line feed. Using independently biased PIN diodes on the patch, it can produce linear polarization, or left- or right-hand circular polarization according to bias voltages. From the measured results, low cross-polarization levels when operated in the linear state and good axial ratios in the circular state are observed.     

有源微带天线阵列的实验研究

本文提出了一种混和集成型有源阵列天线结构，并对这一结构进行了空间功率合成的实验研究。功率源采用微带型振荡电路；天线采用矩形微带贴片阵列，二者通过背馈相连。贴片天线阵间的互耦使振荡单元间实现注入镇定，各单元的辐射功率在空间实现合成。在Ｘ波段成功地实现了四单元有源阵列的互锁和空间功率合成。本文报导了实验结果并给出了一些有意义的结论     

相控阵天线的设计与FDTD分析

基于工作频率在1.79 GHz的微带天线,首先研究了移相器的设计方法,然后利用两种不同方法实现的移相器,分别设计出了相控阵天线。通过FDTD进行建模和仿真实验,计算了相控阵天线在不同扫描角的远场辐射方向图,分析了实验误差,得出了结论,所设计的相控阵天线结构简约,主瓣尖锐,最大扫描角大于45°。     

宽带毫米波微带天线的设计与分析

根据微带天线的设计技术要求,介绍了微带天线带宽的影响因素。在矩形毫米波微带天线设计与分析的基础上,分别设计出 C 型和 W 型两种宽带毫米波开槽微带天线。利用仿真软件对3 种天线的输入回波损耗、驻波系数、相对带宽和方向性等技术参数进行仿真优化和比较分析。仿真与实验结果表明,3 种天线的设计均满足技术要求,C 型和 W 型开槽微带天线较矩形微带天线的相对带宽大幅提高,且具备良好的定向辐射特性。     

面向RFID应用的几种2.45 GHz微带天线的分析比较

随着RFID的广泛应用,微带天线已经成为RFID中不可缺少的一部分,常见的微带天线有单偶极子和双偶极子天线。根据目前RFID的应用,提出了几种基于2.45 GHz的板载天线,同时结合天线的基本理论对这几种结构进行了分析,并通过HFSS软件进行仿真比较。通过对仿真结果的分析,讨论了各种微带天线的优缺点,为RFID的应用提供了参考。