Radiation from planar resonators

Power radiated from microstrip-based resonators is calculated by integration of a Green´s function with assumed currents, a method that is convenient and is thought to be more accurate than previous methods used in calculations of radiation Q. Resonators consisting of two coupled microstrips excited in the odd mode are found to radiate much less than conventional single-microstrip resonators or U-shaped hairpin resonators. However, when the resonator is loaded by a semiconductor device, as in an oscillator, radiation increases. Asymmetries in the resonators, arising from output coupling or fabrication errors, introduce even-symmetric currents which radiate much more strongly than odd-mode currents. The effects of such asymmetries on radiated power are estimated. On the basis of these findings, a convenient geometry for high-power planar oscillators with low radiation is proposed