FDTD analysis of microwave resonant structures with dielectric substrates

An analysis of resonance phenomena in capacitors, microstrip antennas and microstrip ring resonators is presented in this work. All devices are modeled using the Finite Difference Time Domain (FDTD) method. Some additions to the FDTD standard simulation procedure are developed. The key simulation results are verified experimentally.; The transients in capacitors with different types of connection are studied at microwave frequencies. It is shown that the configurations of the transient fields do not correspond to the quasi-TEM mode. The mechanism of the first resonance formation in capacitors is determined and the effect of feeding symmetry on the resonant modes is investigated. A new approach is developed to optimize capacitor design and to increase the first resonance frequency by two fold. Variation of feeding symmetry is found to be efficient in eliminating undesirable resonant modes in patch antennas.; Two components of the first higher order mode are found in leaky wave antennas: leaky and bound ones. Only a part of the power transforms into a narrow band leaky wave radiation and the balance goes to excite a bound mode in a wide frequency range. Standing waves produced by the bound mode induce radiation as an array of elementary oscillators.; Surface waves in dielectric substrate are directly visualized. It is shown that these waves can support quasi-TEM and other modes besides TM and TE modes. The radiating edges of patch antennas are not necessarily the sources of surface waves. To block the sources of surface waves low permittivity dielectric plugs are found to be efficient.; It is shown that in edge-coupled ring resonators the resonances occur due to the back and forth oscillations of the wave packet, while in side-coupled resonators the circular movement of two wave packets in two opposite directions takes place. Therefore, the resonant modes are split in the latter devices, and this effect depends on the substrate permittivity. The obtained results open an opportunity to modify the Q-factor of ring resonators. A new method of characterization dielectric materials at microwaves is proposed based on fitting the simulated S-parameter spectra of ring resonators to the measured ones.