Design of Large Bandwidth Phase Shifters Using Common Mode All-Pass Networks

The design of digital phase shifters with bandwidths from 2:1 up to 20:1 using common mode all-pass networks (APNs) is presented. Because of the inherently large return loss value of the APNs, the phase shift response is not affected by the return loss and therefore the phase shift can be treated separately. The common mode APNs enable the use of standard switches and low cost fabrication. By properly designing the common mode APN phase shifter, an equal ripple phase shift response over a very large bandwidth can be realized. As an example, a 3 b 360^° phase shifter covering a bandwidth of one decade (10:1) is designed using discrete components on PCB. An RMS phase error less than 10^°, a return loss larger than 10 dB, and an amplitude imbalance less than 1.5 dB are measured from 100 MHz to 940 MHz.