A broadband 180° phase shifter with a small phase error using lumped elements

A new switched 180° phase shifter with a small phase error over a large bandwidth using lumped elements is proposed. The topology has two states, an all-pass network (APN) as the reference state, and a bandpass filter (BPF) as the phase shifting state. In the BPF, LC resonators are used to change the slope of the insertion phase to achieve a good phase alignment between the two states for a large bandwidth. Scalable parameters are provided and the theoretical performance is compared with the conventional high-pass/low-pass phase shifter and with the all-pass phase shifter. A phase error of ±3.5° is found over an octave bandwidth while the return loss remains larger than 18 dB, which is comparable with distributed designs. However, the circuit size of the proposed topology is much smaller than the distributed designs. To validate the topology, a phase shifter, centered at 1.0 GHz and with a core area of 1.6 cm², is designed and measured. The measured phase shift is 182 ± 5° and the return loss is larger than 14 dB from 0.68 GHz to 1.28 GHz. The amplitude imbalance is less than 0.25 dB.