FULL CHARACTERIZATION OF VARACTOR-LOADED, PROBE-FED, RECTANGULAR, MICROSTRIP PATCH ANTENNAS

A thorough investigation of the radiation characteristics of a probe-f ed microstrip patch loaded with a varactor diode is presented. The the oretical analysis used to model this structure incorporates the full-w ave spectral domain integral technique in conjunction with an equivale nt circuit model of the varactor diode. Attachment modes are used to a ccurately model the current through the feed and load. Very good agree ment between theory and measurement was obtained. From this investigat ion, the advantages and drawbacks of using varactor diodes to improve the radiation characteristics of a microstrip patch antenna were estab lished. It was shown that large effective bandwidths can be achieved u sing varactor diodes, although at the expense of reduced antenna effic iency and increased cross-polarisation levels.