A K-Band Ground-Backed CPW Balanced Coupler and Integrated Antenna Feed

This paper reports on the performance of a K-band finite-width ground-backed CPW balanced coupler. The use of the coupler as a balanced feed for a slot and patch antenna is investigated. The designs are uniplanar and the circuit does not require vias or airbridges. The return loss of the coupler is less than 10 dB over a 12% bandwidth from 17.1 to 19.2 GHz with a 2-dB average insertion loss over the pass band. The 2:1-VSWR bandwidths of the transition-fed slot and patch antenna are 3.3% and 3.1% respectively.