Investigation and optimization of a waveguide slot antenna array by finite-difference time-domain method

Classical planar waveguide slot antenna arrays are well-known and widely used in the frequency range from 4 to 14 GHz. Among the advantages of this type of antennas are low level of cross-polarisation (-35 dB or better is achievable), high levels of radiated power, low losses and simplicity. The main problem is that due to the resonant nature of the slots and their waveguide serial feed in the frequency band of this arrays are usually limited by several percent. Often different tuning posts, E-plane shorted stubs and metal plates are applied to obtain an improvement of the characteristics in the frequency range. The method of moments (MoM) was used before to analyse such arrays. But the MoM can be hardly implemented in the cases, when more complicated waveguide structures together with radiating slots are to be studied. In this paper the finite-difference time-domain method (FDTD) method was used. Due to it's high flexibility it gives the opportunity to investigate different complex structures accurately and at a high speed. Coupling between slots through the free space and waveguide and the coupling between slots and waveguide's discontinuities are taken into account.