RADIATION MODES IN CIRCULAR PATCH ANTENNAS

We have formulated exact solutions of the normal modes in the microstr ip patch antenna possessing circular geometry. The theory makes use of a new Green's function in conjunction with current potential analysis . The calculations demonstrate that the magnetic wall confinement boun dary conditions as formulated in past theories hold approximately true if the surface wave loss is minimal compared to other losses: dielect ric loss, conductor loss, and radiation loss. For practical path anten nas the normal modes are not confined locally near the microstrip patc h. Rather, they are composed of propagation surface waves which extend far beyond the region containing the patch antenna. We term these nor mal modes as leaky modes, since they resemble the leaky modes found in dielectric image guides. Measurements by us of the radiation mode fre quencies and the intrinsic Q-values of the microstrip patch antennas c ompared very well with theory.