A compact UHF dual-band rat-race coupler with complex impedance load

A compact UHF dual-band rat-race coupler with complex terminated loads is proposed. The design procedure starts with design circuit with transmission line (TL) components, and design equations are also detailed in this letter for dual-band operation. Moreover, the circuit size is further reduced by replacing the TLs with lumped components. An example circuit operating at 450/900 MHz is given. The measurement shows that the circuit has the reflection coefficient at the input port less than −13 dB, the transmission coefficient greater than −5.6 dB and phase difference less than ±10° at the output ports.