Finite difference time domain analysis of microstrip antenna-circuit modules
Compact microstrip antenna-circuit modules, which could be used as front-ends for future wireless systems applications, require electromagnetic modelling due to the close interaction of the circuit with the antenna. Spectrum crowding and EMC/EMI issues call for modelling of the radiation of such modules. Coupling through fringing fields and the nonlinearities of active devices must be addressed. In this work, the FDTD method was used because it can provide the framework for inclusion of circuit elements in a full wave calculation. A software tool was developed and validated based on this method. The modules studied were chosen due to their compactness and their merit as system components. A module with simultaneous transmit-receive operation integrating an active circulator (using amplifiers in a ring-like arrangement) and a quarter wavelength antenna was analysed. Coupling effects were identified and their impact on the radiation patterns was shown. Electronically tuneable microstrip patch antennas using varactor diodes were also studied. Tuning range and harmonic radiation were demonstrated. Single and dual device Gunn oscillator antennas were analysed and their radiation patterns were calculated for the first time. All of our results were in agreement with experimental findings.