Tuning procedure in microstrip antennas on ferrite substrate

Microstrip antennas on ferrite substrate are superior to the conventional flushmount antennas since they are truely thin antennas, requiring no cavity backing. The microstrip antenna on ferrite substrate behaves as a good resonator. At high frequencies (above 300 MHz) the tensor permeability of the magnetic material is not constant unlike at low frequencies. This effective permeability, which can be obtained by putting the value of relative permeability in the Pucel and Masse (1972) formula for a particular w/h ratio of the antenna, is frequency dependent and also varies with d.c. magnetic bias field. The exploitation of this feature through application of d.c. axial magnetic field along with excitation frequency is the principle behind the magnetic tuning of the microstrip antenna on the ferrite substrate