Investigations on microstrip antennas with dielectric superstrates

Abstract

Microstrip patch antennas are attractive for use in fast moving vehicles such as missiles, airplanes and satellites. In these applications, the antenna is often covered with a dielectric superstrate for protection against the environmental effects such as snow, raindrops, etc. When microstrip antennas are covered with protective dielectric superstrate, the antenna resonant frequency, bandwidth, gain and other parameters are altered, resulting in detuning, which may seriously degrade the system performance. As the bandwidth of microstrip antennas is inherently low, it is important to determine the effect of dielectric superstrate on the resonant frequency and other parameters of patch antennas, in order to introduce appropriate corrections in the design of antenna. In view of this, the planar microstrip patch antennas like rectangular, square, circular antennas with linear polarization are designed at center frequency of 2.4 GHz (ISM band) and E-shaped and U-slot patch antennas with circular polarization are designed at 2.0 GHz on Arlon diclad 880 substrate having dielectric constant (and#8712;and#119903;)=2.2 and thickness (h)=1.6 mm. The characteristics of all these patch antennas have been evaluated by simulation using Ansoft EM-simulator HFSS, version 13.0. The simulated results are obtained for superstrates having dielectric constant (and#8712;and#119903;) =2.2, 3.2, 4.8, 10.2 and thickness (h) =1.6 mm, 3.2 mm, 1.6 mm and 0.8 mm for various heights of the superstrates above the patch antennas. Also, measurements were carried out to substantiate the simulated results for typical cases: i) Without superstrates ii) Superstrate touching the patch antenna iii) Superstrate at a height giving the optimum values. Also, a special type of non-planar wideband unidirectional antenna namely, electro-magnetic dipole (EMD) antenna is designed at 3.0 GHz and the effect of superstrate on the performance of EMD antenna is studied.