Design of a UWB phase shifter using shunt λ/4 stubs

In this paper a novel phase shifter covering the whole UWB frequency range with small phase error is presented. The proposed topology employs a single layer substrate and is easy to fabricate. The phase shifter uses shunt quarter wavelength stubs in the resonator branches and transmission lines (TLs) in the reference branches to achieve phase shifts ranging from 20deg to 70deg while keeping the return loss above 10 dB. The shunt stubs are used to control the phase response. An additional half wavelength TL is inserted in the large phase shifts to improve the return loss. As examples 22.5deg and 45deg phase bits are designed and fabricated. Theoretical phase errors of plusmn2deg and plusmn3deg are obtained for the 22.5deg and 45deg phase bits respectively. The measured phase shifts of the two phase bits are 23.6deg plusmn 2.7degand 45.8deg plusmn 4.5deg with return losses better than 11 dB and 13.4 dB from 3.1 GHz to 10.6 GHz respectively. The measured amplitude imbalances are less than 0.3 dB.