H Pues

An impedance-matching technique for increasing the bandwidth of microstrip antennas

The nature of the inherent narrow bandwidth of conventional microstrip patch antennas is considered. It is observed that, except for single-feed circularly polarized elements, their bandwidth is limited only by the resonant behavior of the input impedance and not by radiation pattern or gain variations, which usually are negligible over a moderate 10 to 20% bandwidth. Therefore, broadband impedance matching is proposed as a natural to increase the bandwidth. The maximum obtainable bandwidth is calculated using Fanos broadband matching theory. It is found that by using an optimally designed impedance-matching network, the bandwidth can be increased by a factor of at least 3.9, the exact value depending on the degree of matching required. A transmission-line prototype for a proper matching network is developed. The translation of this prototype network into a practical structure (e.g. a microstrip or stripline circuit) is considered. Practical design examples and experimental results which clearly show the validity of the technique are given. >

Calculation of the Bandwidth of Microstrip Resonator Antennas

In this paper one presents an analysis of the bandwidth of microstrip resonator antennas in function of the antenna parameters. Starting from the general expression for the quality factor of a resonator, it will be proved that the bandwidth of a microstrip resonator antenna is directly proportional to the thickness of the substrate, to the square of the resonant frequency and inversely proportional to the square root of the relative permittivity of the substrate material. Comparing the theoretical results with experimental data one finds a good agreement.