Gordon Mayhew-Ridgers

Single-layer capacitive feed for wideband probe-fed microstrip antenna elements

In this paper, it is shown how a single-layer capacitive feeding mechanism, consisting of a small rectangular probe-fed patch, which is capacitively coupled to the radiating element, can be used to obtain wideband operation for probe-fed microstrip antennas on thick substrates. The main advantages of this feeding mechanism are that all the elements reside on a single layer and that it is very easy to fine-tune the input impedance. Calculated as well as measured results for rectangular, circular and annular-ring geometries are included.

On primary incident wave models for pyramidal horn gain calculations

A few widely used primary incident wave models for pyramidal horn antenna analysis are compared on the basis of gain calculations. The analysis is based on edge-wave diffraction theory, as presented in a previous publication, with some modifications made to the underlying theory. It is shown that these models agree well for high-gain horns with small flare angles, but that the differences are more profound for lower gain horns, where the flare angles are larger. The accuracy of the various models are studied by comparing the results to actual measurements. The respective effects of amplitude and phase variation in the primary incident wave are also illustrated.

Horn antenna analysis as applied to the evaluation of the gain-transfer method

An important condition that has to be satisfied when implementing the gain-transfer method is that the fields in the test zone of the measurement facility should be as close to the plane wave as possible. In this paper, the effect of amplitude and phase deviation from a perfect plane wave, on gain measurements for microwave aperture antennas, conducted via the gain-transfer method, is determined and quantified. The pyramidal horn antenna is used as a basis for all calculations as it is the universal standard for microwave antenna gain measurements. Coupling, between the antenna being illuminated and the test zone fields, is evaluated by means of the reciprocity theorem. Test zone field variations are simulated and the effect thereof, on the predicted measured gain, is illustrated.

Efficient full-wave modeling of patch antenna arrays with new single-layer capacitive feed probes

This paper introduces a new variation on the capacitive feed probe for patch antennas on thick substrates. It consists of a small circular probe-fed capacitor patch that is situated next to the resonant patch. This configuration can bring about significant savings in terms of manufacturing cost, but also lends itself to a very efficient full-wave analysis. As such, the main focus of this paper is a spectral-domain moment-method formulation, which was specifically developed for the analysis of large, but finite, arrays of these antenna elements. Entire-domain and subdomain basis functions are combined in an efficient way to minimize the computational requirements, most notably computer memory. It is shown that, for general antenna array configurations, memory savings of more than 1000 times can be achieved when compared with typical commercial software packages where only subdomain basis functions are used. A number of numerical and experimental results are also included in order to verify the spectral-domain moment-method formulation and to illustrate various applications of the new antenna element.

Entire-domain versus subdomain attachment modes for the spectral-domain method of moments analysis of probe-fed microstrip patch antennas

Two different attachment modes that are widely used within the spectral-domain method of moments (MoM) analysis of probe-fed microstrip patch antennas are investigated and compared. Either of these attachment modes, the one being an entire-domain mode and the other a subdomain mode, is required for the accurate analysis of probe-to-patch junctions when used together with the MoM. In this paper, more light is shed on the ability of either approach in modeling microstrip patches of various sizes, residing on planar multilayered substrates, ranging from quite thin to relatively thick. Through a comprehensive comparison between numerical and experimental results, it turns out that the subdomain approach is somewhat more versatile than the entire-domain approach.

Accurate Gain Measurements for Large Antennas Using Modified Gain-Transfer Method

The classic gain-transfer method assumes a uniform plane wave incident over the apertures of the gain-transfer standard (typically a standard-gain horn) as well as the antenna under test. Variations in the incident field over the quiet zone of an antenna test range can produce large errors in the estimated gain of the antenna under test. These errors can be significant, especially when there is a large difference in aperture dimensions between the antenna under test and the standard-gain horn. In this letter, a modified gain-transfer method is described to reduce errors in gain measurements when antennas significantly larger than the standard-gain horn are measured in a test range using the gain-transfer method. The aperture of the antenna under test is usually much larger than that of the standard-gain horn, and therefore these antennas will typically be exposed to different variations in the incident field. Measured results are presented to illustrate accurate gain measurements for antennas significantly larger than the standard-gain horn.

Analysis of antenna location and polarization on Indoor cellular MIMO performance

As it is well known, MIMO channel capacity is dependent on favorable channel conditions. The antenna component is an integral part in the propagation channel, and certain antenna radiation parameters would influence the channel conditions. The impact of various antenna configurations on an indoor MIMO Radio Channel is investigated by measurement and simulation. Various antenna locations with single and dual polarized configurations in an indoor scattering environment are evaluated. A single dual-polarized omnidirectional antenna is found to provide similar or better performance results related to two spatial de-correlated singular-polarized antennas.

Reducing cellular interference in the Karoo Radio-Astronomy Reserve

This paper describes some of the developments and activities that have been undertaken to significantly reduce the extent of cellular interference in South-Africas Karoo Radio-Astronomy Reserve. The main contribution is a new omnidirectional base-station antenna with a single deep null in its radiation pattern. Such an antenna can significantly suppress the interference from a cellular base station along a specified direction, while still retaining much of the coverage in other directions around the base station. The use of femtocells over VSAT links has also been investigated as an alternative way to provide cellular services where coverage will be lost to solve interference issues.

Attachment modes for spectral-domain moment-method analysis of probe-fed microstrip patch antennas

Different attachment modes for use within the spectral-domain moment-method analysis of probe-fed microstrip patch antennas are investigated. These modes are used for the accurate analysis of probe-to-patch junctions and, in this paper, two of the most widely used approaches are compared in terms of their ability to model patches of various sizes on substrate materials ranging from quite thin to relatively thick. It finally turns out that the subdomain approach is somewhat more versatile than the entire-domain approach.

Accuracy of the gain-transfer method for a standard gain antenna and a test antenna with equal aperture dimensions

When implementing the gain-transfer method to measure the gain of an antenna, it is tempting to assume that there should be no measurement errors due to non-plane wave effects in the test zone fields, given that both the test antenna and the standard gain antenna have equal aperture dimensions. The reasoning behind this is that both antennas are exposed to the same amplitude and phase variations in the test zone fields, and therefore the measurement errors should cancel out. However, in this paper it is shown through simulated gain measurements, that equal aperture dimensions can indeed result in significant measurement errors if the incident wave is not plane.