Suppression of unwanted probe radiation in wideband probe-fed microstrip patches

The radiation from the probe feed of a microstrip patch can contribute sign ificantly to the cross-polarisation radiation or to pattern distortion, esp ecially if the patch is fabricated on a relatively thick, low-perinittivity substrate. By introducing a second probe, which is fed out of phase with t he original probe, this unwanted radiation can effectively be suppressed. T o demonstrate this technique, two L-band patches were fabricated, one with and one without the extra probe. The dual probe-fed patch produced more sym metrical radiation patterns and had a reduction in the peak cross-polarisat ion level of nearly 20dB. The unwanted radiation is effectively suppressed over a bandwidth of > 10%.