Microstrip antennas on ferrites

There is much interest in the use of ferrite substrates for microstrip patch antennas. The high dielectric constant of the ferrite brings about a reduction in the antenna dimensions. When biased with a magnetic field the antennas exhibit a number of novel properties. These include frequency tuning over a 15-40% range, the generation of two opposite hands of circular polarisation and beam steering possibilities. This paper discusses two aspects of circular microstrip antennas on ferrite substrates. The first is spectral domain modelling of the frequency tuning characteristics for a circular patch on a ferrite. Details of the model together with a comparison with experimental results are given. Phased arrays often use ferrite phase shifters to change the phase of individual elements and produce electronic beamsteering. We demonstrate a simple but effective means of controlling the beam angle from 2 and 4 element arrays where the patch elements are fed by a microstrip line on a ferrite substrate. Biasing the ferrite causes a shift in the phase length of the line hence varying the beam angle.