Microstrip lumped element quadrature couplers for use at microwave frequencies

The design of a 3 dB lumped-element quadrature coupler suitable for a microstrip environment is described in the paper. The circuit exhibits ideal quadrature, return loss and isolation performance, with a coupling characteristic making it suitable for up to 20% bandwidths. The design of the circuit is simple, requiring the specification of only two components in addition to the microstrip connecting lines. The performance of two couplers is described. The first, centred at 1.27 GHz, shows an excess loss of 0.2 dB at the centre frequency, with a return loss of better than 25 dB, an isolation of better than 30 dB and a phase deviation from quadrature of less than 1° over a 20%, bandwidth. The second, centred at 6.4 GHz, shows an excess loss of 0.5 dB, a return loss and isolation both better than 25 dB, and a phase deviation from quadrature of less than 2° over a 20% bandwidth