The bi-polar near-field antenna measuring system at Wroclaw University of Technology

This paper presents a near-field antenna measurement system that was developed in-house. The capabilities of our bi-polar system were extended by a backward-projection processing of data. The amplitude and phase distribution within the array elements can thus be reconstructed. Major applications of the presented near-field system are in research on advanced beamforming, and in investigations into large-scale integration of lightweight arrays. The results presented were obtained for planar microstrip arrays, and for a phased array operating between 5 GHz and 12 GHz.     

An electromagnetic-field method modeling of a radial line planar antenna with coupling probes

This communications describes an electromagnetic model of a radial line planar antenna consisting of a radial guide with one central probe and many peripheral probes arranged in concentric circles feeding an array of antenna elements such as patches or wire curls. The model takes into account interactions between the coupling probes while assuming isolation of radiating elements. Based on this model, computer programs are developed to determine equivalent circuit parameters of the feed network and the radiation pattern of the radial line planar antenna. Comparisons are made between the present model and the two-probe model developed earlier by other researchers.     

The temperture dependence of substrate parameters and their effecton microstrip antenna performance

In the common approach to the design of microstrip antennas, the designers rely on data provided in the manufacturers' specifications, even though such specifications are confined to standard environmental conditions. In practice, the electrical parameters of the substrates may deviate from the manufacturers' data, thus making the antenna designer adopt a deficient design strategy. In the study reported, microstrip substrates were exposed to large temperature variations and their temperature dependent properties were measured in a specialized laboratory for dielectric materials. The results include plots of the dielectric constant and dissipation factor for wide temperature ranges equivalent to those in airborne applications. On the basis of this experimental data, the substrates were divided into four categories according to their dielectric constant value and its temperature dependence. Using both manufacturers' data and the measured values, a series of microstrip dual-feed aperture-coupled patch antennas were designed for the four categories of substrates and the sensitivity of their electrical performance due to temperature variations was fully investigated     

Investigations into Operation of Single- and Multi-Layer Configurations of Planar Inverted-F Antenna

The paper presents a tradeoff analysis between single- and multi-layer (stacked) configurations of a planar inverted-F antenna (PFIA) of fixed overall height, with respect to achieving multi-band operation. The investigations focus on two bands, 800 to 1000 MHz and 1700 to 2600 MHz, which cover a frequency spectrum allocated to most of the present-day wireless systems operating below 2600 MHz. Folding and tapering of a conducting patch in the single-layer configuration, and increasing the number of conducting patches in the multi-layer layer (stacked) configuration, are used to achieve multi-band operation. The results obtained show that the stacked PIFA is able to generate many (four or more) bands within the investigated frequency spectrum. However, it faces difficulty in broadening them, as the coupling of upper plates to the ground is weakened by the presence of middle plates. At the same time, the tuning of one band adversely affects the other bands' performance. For the single-layer PIFA, the multi-band impedance characteristics are easier to adjust. A significant band widening can be obtained by proper arrangement of a conducting patch, and by introducing cuts or slits in the ground plane. In the designs presented, the antenna volume, measured by its outline, fell under 3 cm³. The resulting radiation efficiencies were 95% at the lower band (900 MHz), and 89% at the upper frequency range (2020 MHz).     

Investigations into advanced concepts of terminal and base-stationantennas

The development of essentially new terminal and base-station antennas has become one of the most important tasks in contemporary antenna engineering. Improvements in antenna technology must be accomplished regardless of progress in signal processing. Comprehensive research on such antennas has been carried on at the Wroclaw University of Technology, Poland, for several years now. There are three major fields of interest: small antennas, base-station antennas, and smart-antenna technology. The small antennas investigated-either planar or conformal-approach the physical limits of allowable dimensions. They operate with a number of systems that might involve advanced signal-processing techniques. The scope of the research also includes studies on the interactions between terminal antennas and humans