Broadband Modified Proximity Coupled Patch Antenna with Cavity-Backed Configuration

A modified proximity-coupled microstrip patch antenna with broad impedance bandwidth is proposed by incorporating proximity-coupled patch antenna into the rectangular open-ended microstrip feed line on a cavity structure. First we design a proximity-coupled microstrip antenna to have a wide bandwidth in the lower band centered at 7 GHz using a cavity-backed ground. To broaden the bandwidth of the antenna to the upper band, we then apply a rectangular open-ended microstrip feed line, adjusting the relative position to the cavity to generate an additional resonance close to 10 GHz. The combination of lower and upper band design results in a broadband antenna with dimensions of 30 mm x 30 mm x 9 mm (0.9 lambda(0) x 0.9 lambda(0) x 0.27 lambda(0)) is designed where lambda(0) corresponds to the free space wavelength at a center frequency of 9 GHz. The measurement results verify the broad impedance bandwidth (VSWR <= 2) of the antenna at 77% (5.6-12.6 GHz) while the broadside gain is maintained between 6 dBi and 8 dBi within the operational broad bandwidth.