A. Sambell

Dual-polarized broad-band microstrip antennas fed by proximity coupling

This work presents a novel broad-band dual-polarized microstrip patch antenna, which is fed by proximity coupling. The microstrip line with slotted ground plane is used at two ports to feed the patch antenna. By using only one patch, the prototype antenna yields a bandwidth of 22% and 21.3% at the input port 1 and 2, respectively. The isolation between two input ports is below -34 dB across the bandwidth. Good broadside radiation patterns are observed, and the cross-polar levels are below -21 dB at both E and H planes. Due to its simple structure, it is easy to form arrays by using this antenna as an element.

Polarization-agile antennas

A polarization-agile antenna is a type of antenna the polarization state of which can be changed dynamically, i.e., it can have either linear (vertical or horizontal) or circular polarization (left hand or right hand), depending on the requirements of its specific application. This special characteristic offers great flexibility for antenna systems, because a single antenna could be used to satisfy the different requirements of several systems. This paper gives a comprehensive review of polarization-agile antennas. The basics of polarization in antennas and polarization-agile antennas are explained. Various examples of recent developments are then provided, and the antenna configurations and design principles are illustrated and discussed. Finally, the future development of polarization-agile antennas for wireless systems is discussed

A SIMPLE BROADBAND PRINTED ANTENNA

—This paper presents a simple broadband proximity-coupled microstrip patch antenna. A circular patch is used as the main radiator, and an H-shaped shot is cut in the ground plane below the feed line. A stepped-width microstrip line is used to feed the patch through proximity coupling. By using a single patch, the prototype antenna achieves an impedance bandwidth of 26%. Low cross-polar levels below −20 dB are observed in both E-and H-planes. The broadband antenna is planar, small size, simple in structure, low in cost, and easy to be fabricated, thus attractive for practical applications.

High-efficiency power amplifier design including input harmonic termination

This letter presents the design of a high-efficiency Class-F power amplifier in pseudomorphic high electron mobility transistor technology using a novel load-pull/source-pull simulation-based approach. The second harmonic input termination is shown to have a critical influence on performance, which is justified by the shape of the simulated waveforms. Experimental validation is carried out on a 2-GHz practical circuit using a medium-power packaged device. Two cases are compared both theoretically and experimentally: for the best and worst case second harmonic input terminations, 76% and 42% saturated power-added efficiency are measured, respectively. In addition, the worst case termination degrades the saturated C/I3 by 7.5dB.

FDTD Analysis of a Dual-Frequency Microstrip Patch Antenna

Characteristics of a single-layer, dual-frequency microstrip patch antenna, which uses a T-strip loaded rectangular microstrip patch, are studied. This antenna is easy to achieve good impedance matching at both frequencies by tuning the feed position and other design parameters. Another advantageous aspect is that it has high polarization purity. A detailed parameter study is performed and the theoretical analysis is based on the finite-difference time-domain (FDTD) method. The FDTD programs are developed and validated by measurement results. The effects of various antenna parameters on two resonant frequencies, frequency ratio, and radiation pattern characteristics of the antenna are analyzed and discussed. It is shown that various frequency ratios (1.5–2.49) can be obtained by varying the design parameters of this antenna. Similar radiation patterns with same polarization are obtained at two resonant frequencies. Several design curves are presented. 156 Gao, Li, and Sambell

Low-Cost Broadband Circularly Polarized Printed Antennas and Array

This paper presents the design, simulation, and measurements of two low-cost broadband circularly polarized (CP) printed antennas: an element and an array at 2 GHz. To realize the broadband circularly polarized antenna element, a circular microstrip patch is electromagnetically coupled by crossed slots cut in the ground plane, which is fed by an L-shaped microstrip feed. Two orthogonal modes in the patch are excited by using the crossed slots, and a single L-shaped feed provides a 90deg phase shift between two orthogonal slots. The antenna element achieves a 9.6% bandwidth for an axial ratio (AR) below 3 dB and a voltage standing wave ratio (VSWR) below 1.5. To further improve the performance, a sequentially rotated feed network is designed for a 2 times 2 array. The axial ratio value of the array is below 3 dB within a 27.2% bandwidth, from 1.75 GHz to 2.3 GHz. The return loss is above 10 dB within a 41% bandwidth, from 1.62 GHz to 2.45 GHz. Details of the proposed antenna element and the array design are described, and both the simulation and the experimental results are presented and discussed.

An indirect holographic method for determining antenna radiation patterns and imaging antenna fields

This work describes a new technique for the determination of antenna radiation patterns and the imaging of antenna aperture fields. It uses an indirect holographic method to record simple intensity patterns formed by a combination of the antenna near field signal and an offset reference signal and is similar to methods employed at optical frequencies. This is as an alternative to the traditional direct holographic method of measuring complex amplitude and phase values. It outlines how previous practical difficulties, which have prevented this method being usefully employed at microwave frequencies, can be overcome by the synthesis of an offset reference plane wave. It describes how far field antenna radiation patterns can be obtained from knowledge of the resultant intensity pattern and how the information contained within this pattern can be further processed to provide images of the antenna aperture fields. It includes the results of mathematical simulations which strongly support the ideas outlined. Currently, an experimental system is being assembled to provide practical measurements and preliminary experimental results are expected to be available shortly.

Low-cost dual-polarized printed array with broad bandwidth

This work presents a novel design of low-cost broad-band dual-polarized microstrip arrays. The antenna uses the slot-coupled feed for one polarization, while the microstrip line feed with slotted ground plane is used for the other polarization. It can make good use of the space on both sides of the ground plane, as the feed circuits for two orthogonal polarizations are placed on each side of the ground plane, respectively. The prototype four-element array designed at C band yields a bandwidth of more than 14% at both ports, and isolation below -30 dB. Good broadside radiation patterns are observed, and the cross-polar levels are below -20 dB at both E- and H-planes.

Microwave Class-F and Inverse Class-F Power Amplifiers Designs using GaN Technology and GaAs pHEMT

This paper presents the designs and results of two high-efficiency harmonics-tuned microwave power amplifiers (PA): the first one is a 2 GHz class-F PA in monolithic integrated circuit (MMIC) by using GaN HEMT technology, and the other one is a 2.45-GHz inverse class-F PA using packaged GaAs pHEMT devices with PCB technology. In the class-F MMIC PA, field-plated GaN HEMT device is used for high-power performance. The 2.0-GHz class-F MMIC PA achieves a PAE of 50%, 38 dBm output power, and 6.2 W/mm power density. The inverse class-F PA at 2.45 GHz achieves 22.6 dBm output power and 73% PAE at 3 dB compression, and has very low cost

Microwave indirect holographic imaging using an adaptation of optical techniques

Indirect holography provides a quick and inexpensive three-dimensional (3-D) imaging technique at optical frequencies which has not been directly adapted to microwave imaging. This letter describes a technique whereby a radiated offset reference plane wave can be electronically synthesized allowing this technique to be used at microwave frequencies. In this letter, this technique has been applied to the problem of determining antenna radiation patterns and reconstructing complex near fields. Early experimental results compare favorably with results taken using traditional methods.