Ultra-Wideband Spurious Radiation Suppression in Microstrip Antennas Using Integrated Uniplanar Compact Coupling Structure With Controllable Transmission-Zeros Matching Approach

A design of microstrip patch antenna with ultra-wideband spurious suppression, up to nine times the operating frequency (
${f}_{c}$
), is presented using transmission line (TL)-based compact uniplanar coupling structure (CS) without ground plane structures and via holes. The input–output cross coupling in the CS results in wide stopband with multiple transmission zeros (TZs) ensuring good rejection level, where the characteristics are controlled by just three impedances. Design equations are derived analytically using TL model analysis. The achieved 20-dB stopband bandwidth (>140%) and size
$0.324\lambda _{g} \times 0.03\lambda _{g}$
(
$\lambda _{g}$
at cutoff frequency) of the CS are superior to the reported designs. Besides, the CS is flexible to use on the microstrip feed line of the antenna. For validation purposes, a prototype antenna at
${f}_{c}= {3.04}$
GHz, having suppressed spurious response up to 28 GHz (
$> 9{f}_{c}$
), is fabricated and the measured results are demonstrated.