Field-simulation-based strategy for designing microstrip filters

The insertion loss spectrum of a microstrip open-loop square ring band-pass filter is analyzed by using the Finite Difference Time Domain (FDTD) field simulations. Visualization of standing waves at resonant frequencies guides the placement of stepped impedance sections or capacitive loads at electric field maxima. Strategic load placement enables us to modify selected resonant modes, to monitor efficiently center and attenuation pole frequencies, to affect the shape and width of the pass-band, and to alter the input impedance. The presented approach is useful for miniaturizing various types of microstrip filters and antennas and optimizing their performance.