Radiation from a dielectric disk near a lossy dielectric plane

We calculate how the radiation pattern, the quality factor Q, and the resonant frequency of a dielectric disk resonator are altered from that of free space when the resonator is brought in close proximity to a lossy dielectric plane. The calculations are compared with measurements performed at frequencies near 10.4 GHz on a sapphire disk resonator that is within a wavelength of a copper backplane. As the resonator approaches the backplane, the resonant frequency increases and the radiated power is suppressed, enhancing the Q of the resonance by a factor Q_e. Experimentally, the Q of the resonator is enhanced by an optimum value of 4.5 when the midplane of the disk is about 0.5 cm above the copper backplane. Here the resonant frequency is shifted to 10.45 GHz.