INTRINSIC MODES OF RADIATION IN FERRITE PATCH ANTENNAS

We have found two types of radiation modes for patch antennas loaded w ith ferrite materials. Each mode of radiation is a linear combination of normal modes of propagation in parallel plate waveguide separated b y a slab of ferrite material. We have introduced new boundary conditio ns in which only TE modes of oscillation in the patch antenna cavity r esult. According to different propagation directions relative to the a pplied dc field these TE modes are distinguished as transverse modes a nd longitudinal modes, and they possess mutually perpendicular radiati on polarizations. While the longitudinal TE modes are found to form di screte modes in the frequency domain, the radiation frequency of a tra nsverse TE mode can be continuously tuned over a wide frequency range by varying the biasing magnetic field. Circularly polarized radiations may result from simultaneous excitations of these two modes. Ferrite patch antennas of square geometry have been fabricated and tested. The measured resonant frequencies compared very well with our theory.