S.D. Targonski

Design of millimeter wave microstrip reflectarrays

This paper discusses the theoretical modeling and practical design of millimeter wave reflectarrays using microstrip patch elements of variable size. A full-wave treatment of plane wave reflection from a uniform infinite array of microstrip patches is described and used to generate the required patch-design data and to calculate the radiation patterns of the reflectarray. The critical parameters of millimeter wave reflectarray design, such as aperture efficiency, phase errors, losses, and bandwidth are also discussed. Several reflectarray feeding techniques are described, and measurements from four reflectarray design examples at 28 and 77 GHz are presented.

Design of wideband circularly polarized aperture-coupled microstrip antennas

Two variations of a novel feeding technique for a wideband circularly polarized aperture-coupled microstrip antenna are described. Prototype designs for wideband linearly polarized elements are first presented, and then used for circularly polarized designs. Techniques used for design of the feed network are detailed, for both series feed and parallel feed versions. Experimental results are shown for each antenna, and results for the two designs are compared. The impedance and axial ratio bandwidths for these antennas are among the best yet achieved for microstrip antenna elements. Several design variations are also discussed. >

A shaped-beam microstrip patch reflectarray

This paper describes a microstrip reflectarray antenna designed to produce a shaped-beam coverage pattern using phase synthesis. The concept is demonstrated with a Ku-band linearly polarized reflectarray designed to provide coverage of the European continent and measured results are compared to those obtained for a previously designed shaped-reflector antenna designed for the same coverage specifications. Results validate the shaped-beam reflectarray concept, although there are disadvantages to the reflectarray such as narrow bandwidth and reduced aperture efficiency that may offset the mechanical and cost advantages of the flat surface of the reflectarray.

Analysis and design of a microstrip reflectarray using patches of variable size

In a great number of microwave applications a highly directive antenna with a main beam scanned to a certain angle is required. To achieve this a certain aperture illumination with progressive phasing is used. The two primary ways to do this are reflectors and arrays. The reflector antenna uses its geometry to create the desired phase across the aperture, while the array employs distinct elements fed with progressive phasing. Reflector antennas are advantageous in the fact that they typically exhibit large bandwidth and low loss. The main disadvantage of the reflector is the geometrical constraint it imposes on the design. The most popular reflector, the parabolic reflector, also exhibits inherently high cross polarization levels. Microstrip patch arrays are lightweight, low-profile antennas that are capable of low cross polarization levels but typically have small bandwidth and fairly large loss at microwave frequencies. The more attractive features of reflectors and arrays are combined in the reflectarray. The steps taken in the design of a microstrip reflectarray using patches of variable size are outlined. Measured and theoretical results are shown for the finished design, and several important performance criteria are compared with the microstrip reflectarray.

A shared-aperture dual-band dual-polarized microstrip array

This paper describes the design and testing of a prototype dual-band dual-polarized planar array operating at L- and X-bands. The primary objectives were to develop new antenna technology with dual-band and dual-polarization capability in a shared aperture, featuring low mass, high efficiency, and limited beam scanning. The design of a prototype planar microstrip array of 2/spl times/2 L-band elements interleaved with an array of 12/spl times/16 X-band elements that meets these requirements is discussed in detail and measured results are presented. The array is modular in form and can easily be scaled to larger aperture sizes.

Aperture-coupled microstrip antennas using reflector elements for wireless communications

The design advantages provided by aperture-coupled microstrip patches can be very useful in wireless communications applications. A way to improve the front-to-back ratio is to place a microstrip antenna element behind the aperture as a reflector. Proximity coupling between the feed line and the reflecting element is negligible due to the thick foam substrate used, allowing use of the reciprocity method of analysis. Also, the directive patch elements are shielded from the reflector by the ground plane. Therefore, only interactions between the reflector and the aperture need to be modeled, resulting in a simple analysis. For aperture-coupled patch designs with a front-to-back ratio of 10 dB or greater, the introduction of a reflecting element has a negligible effect on the input impedance of the antenna. Therefore, a reflector element can readily be incorporated into existing designs.

Analysis and design of millimeter wave microstrip reflectarrays

The reflectarray combines features of reflector and array antennas. Reflectarrays are illuminated by a feed antenna which excites an array of radiating elements comprising a reflecting surface, and these elements produce a radiated field. Some types of reflectarrays, including the microstrip reflectarray, also produce a specularly reflected field component, as in the case of a reflector antenna. The total field then consists of the radiated field from the patches and the specular reflection. The design and analysis of two millimeter wave microstrip reflectarrays, operating around 27-28 GHz, are discussed. The first design utilises a corrugated conical horn feed and square patch radiating elements to accommodate dual polarisation. The main beam is steered to 25/spl deg/ off broadside in the vertical plane. The second design uses rectangular patches for linear polarization, and a backfire feed which greatly simplifies the feed supporting structure, and a broadside main beam. Measured patterns, gain, and a loss budget are presented and the performance is compared with typical microstrip array antennas. The generation of cross-polarized components of the radiated field is also discussed.

A novel wideband circularly polarized aperture coupled microstrip antenna

The authors describe two variations of a novel aperture feeding technique for circularly polarized microstrip antennas. Measured results for a series-fed crossed-slot microstrip antenna are shown. Experimental results are shown that demonstrate an axial ratio bandwidth of 15% and an impedance bandwidth in excess of 20%.<<ETX>>

An L/X dual-band dual-polarized shared-aperture array for spaceborne SAR

Spaceborne synthetic aperture radar antennas have many special electrical requirements, such as operation at multiple frequencies with multiple polarization ability, with fairly wideband operation being required at these frequencies. They are also required to be electrically large, giving rise to issues such as low mass, easy and reliable deployability, and low cost. This paper describes the results of a prototype SAR array developed with these considerations in mind. The prototype antenna is a dual-frequency array operating at L and X bands, with dual linear polarization capability at both bands. This array shares the same radiating aperture for both bands and both polarizations. The prototype antenna described can also be used as a single module in a much larger array.

Effect of random positioning errors on the input impedance of an infinite array of printed dipoles

In order to to study the effect of random positioning errors in an infinite array an impedance analysis must be done. The authors present the first solution and data for the expected value of the input impedance of an infinite array of printed dipoles on a dielectric substrate. Theory is introduced, and results for several cases are presented and discussed. It is shown how scan blindness can be removed from an infinite array of printed dipoles by randomizing the positions of the elements in the E-plane and by analyzing the structure by an impedance approach.<<ETX>>