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

Abstract

The radiation from the probe feed of a microstrip patch can contribute significantly to the cross-polarisation radiation or to pattern distortion, especially if the patch is fabricated on a relatively thick, low-perinittivity substrate. By introducing a second probe, which is fed out of phase with the original probe, this unwanted radiation can effectively be suppressed. To demonstrate this technique, two L-band patches were fabricated, one with and one without the extra probe. The dual probe-fed patch produced more symmetrical radiation patterns and had a reduction in the peak cross-polarisation level of nearly 20 dB. The unwanted radiation is effective]y suppressed over a bandwidth of > 10%.