Paul W. Davis

Experimental investigations into a linearly polarized radial slot antenna for DBS TV in Australia

A hybrid theoretical/experimental approach to the design of radial line slot array (RLSA) antennas for receiving direct broadcast satellite (DBS) TV programs in Australia is presented. Using this approach, 0.4-m and 0.6-m diameter linearly polarized Ku-band prototype antennas were constructed and experimentally investigated. The 0.6-m prototype incorporates reflection cancelling slots, which allow it to overcome the inherent poor return loss performance in linearly polarized RLSA antennas. Measurements show high-radiation efficiency for this form of radial slot antenna and its suitability for the DBS TV application.

Linearly polarized radial-line slot-array antennas with improved return-loss performance

The standard linearly polarized radial-line slot-array (RLSA) antenna exhibits poor return loss as seen by its coaxial feed. This paper describes techniques that improve the poor return-loss performance of this antenna, by using two interchangeable methods: i) reflection-canceling slots on the front and back surface of the antenna, and ii) beam squinting. A series of 550 mm diameter linearly polarized Ku-band prototype antennas were constructed to experimentally investigate the efficiency of each of these methods. In order to cut experimental costs, initial radiation-pattern modeling was performed theoretically, and then prototypes were developed using inexpensive aluminum foil. Measurements of the developed prototypes indicated that both the reflection-canceling and beam-squinting methods provided a substantial improvement in return loss over the desired frequency band.

Analysis of a circular patch antenna radiating in a parallel-plate radial guide

This paper investigates the use of a coaxially fed patch as a feeding element in a single-layer radial line slot antenna (RLSA) array. A field matching method is described to analyze a recessed circular cavity radiating into a radial waveguide. Using the wall impedance approach, the analysis is divided into two separate problems of the cavity and its external environment. Based on this analysis, a computer algorithm is developed for determining wall admittances as seen at the edge of the patch in the cavity, the radial admittance matrix for the two-probe feed arrangement, and the input impedance as observed from the coaxial line feeding the cavity. This algorithm is tested against the general-purpose Hewlett-Packard finite-element high frequency structure simulator as well as against measured results. Good agreement in all considered cases is noted.

Modelling and testing of radial divider/combiners

Field matching methods are used for the analysis of two types of radial waveguide power divider/combiners: one-incorporating probes, and two- including E-plane-coupled rectangular waveguides. Based on these methods, computer algorithms are developed and tested on design examples of various power dividing/combining structures.<<ETX>>

The performance of a linearly polarised RLSA antenna for different beam squint angles

In the standard design of the linearly polarised Radial Line Slot Array (RLSA) antenna, the efficiency is poor due to a high return loss. This paper investigates a method of reducing this return loss figure by squinting the main beam direction. Three prototype antennas with squint angles of 0/spl deg/ (standard broadside), 10/spl deg/ and 20/spl deg/ were produced and investigated. Measurements on these prototypes indicate a significant improvement in return loss, and an ability to accurately design the beam tilt angle.

Simplified mode-matching techniques for the analysis of coaxial-cavity-coupled radial E-plane power dividers

Two simplified mode-matching techniques for the numerical analysis of nonsymmetric waveguide E-plane radial N-ports are presented. The first model, which utilizes cartesian and cylindrical coordinate systems for interfacing rectangular waveguides to a coaxial cavity, shows excellent agreement between measurements and computer-intensive finite-element calculations. The second technique, which is based on rectangular coordinates only and thereby neglects the curvature of the coaxial cavity, achieves agreement only for transmission coefficients if the inner radius of the coaxial cavity is sufficiently large. The software for both models are operational on personal computers and require only seconds for a complete analysis. Examples are presented for a Ku-band E-plane six-port and a W-band E-plane ratrace ring. Some additional investigations on the ratrace configuration demonstrate the applicability of the models with respect to reliable component design. >

A linearly polarized radial-line slot-array antenna with a broadened beam

The beam shaping of a linearly polarized radial-line slot-array (LP RLSA) antenna is demonstrated with the production of a prototype with a broadened main beam pointed in an arbitrary direction. The method of synthesis is presented, which utilizes a simple but accurate radiation model for the RLSA antenna to predict radiation characteristics. Experimental results for a Ku-band LP RLSA antenna manufactured using the described techniques show good agreement with the theoretically predicted performance

Predicting the radiation pattern of a radial line slot array antenna

A simple but accurate method is presented to predict the radiation pattern of a single layer Radial Line Slot Array (RLSA) antenna. In this method, radiating slots are replaced by equivalent magnetic dipoles for which excitation coefficients are obtained by employing a small-coupling theory to the coaxial-probe-launched TEM radial mode. Comparison between theoretical and experimental results for 55 cm diameter RLSA antennas show that the presented method of predicting the radiation pattern works well.

Unified Design of a Single-Layer Radial Line Slot Array Antenna

A unified design of a single layer Radial Line Slot Array (RLSA) antenna of arbitrary polarisation is presented. The design addresses such tasks as the electromagnetic modelling of the feed, modelling of the radiating surface, prototyping of the feed and the radiating surface, and near-and far-field testing of the developed prototypes. The issues of beam tilting, beam broadening and shaping are also considered. The developed antennas are tested in terms of return loss, uniformity of aperture illumination, gain and radiation pattern. Iterative refinements are performed when the prototype does not meet the assumed performance specifications.

Computer algorithms for the analysis of waveguide ring hybrids

This paper presents very efficient computer algorithms for an IBM PC or equivalent, for the analysis of waveguide hybrids composed of a coaxial or radial cavity and E- or H-plane coupled rectangular waveguide ports. The case of an H-plane coupled cavity with a central coaxial port is also considered. The proposed algorithms are based on a field matching analysis and can determine a full set of scattering parameters for the hybrid at a single frequency point in a matter of seconds. The accuracy is equivalent to that offered by more sophisticated commercial software packages.