A PCB-compatible 3-dB coupler using microstrip-to-CPW via-hole transitions

A 3-dB coupler by implementing microstrip-to-coplanar waveguide (CPW) via-hole transitions is proposed. The proposed coupler, with the advantages of wider coupled line widths and spacing without using any bonding wires, can eliminate the uncertain factors of conventional Lange couplers caused by the printed circuit board (PCB) manufacturing processes. The proposed coupler can be easily fabricated on a single-layer PCB substrate instead of using multilayer substrates. Good agreements between the simulation and the measurement in the frequency range from 0.45 to 5 GHz can be achieved. The measured results at the center frequency of 2.4 GHz have the return loss better than -15dB; the insertion loss of coupled and direct ports is about 3/spl plusmn/ 0.2dB and the relative phase difference of 89/spl plusmn/0.3/spl deg/. The dimension of the coupler is 3.1cm /spl times/ 1.8cm.