Series vs Parallel Reflection-Type Phase Shifters

A performance comparison between series and parallel resonant circuits in the Reflection-Type Phase Shifter (RTPS) configuration is presented in this article. Initially, equations are derived to theoretically assess the fundamental limits of both configurations, in terms of the optimum values of the required resonant inductances and, subsequently, the maximum obtainable phase shifts of both configurations, as a function of the reactive parameters of the varactor diode. Then, based on these predictions, two sets of three RTPSs (three series-circuit and three parallel-circuit) operating at a center frequency of 2.3 GHz are designed, simulated, fabricated and their performance was measured and compared with the theoretically predicted results. For each set of the RTPS, the intrinsic parameters of the varactor diode (minimum capacitance and tuning ratio) are altered by the addition of a lumped element. This is done in order to adequately assess the performance of phase shifters for different characteristics of the active element. Then, based on the derived equations, the corresponding RTPS is designed so as to provide maximum phase shift. The theoretical analysis indicates that the parallel resonant configuration is inherently more capable of providing higher values of shift compared to its series resonant circuit counterpart, reaching 360° in the limit case. The measurement results largely confirm these theoretical findings, and the parallel RTPS configuration is shown to outperform the series RTPS configuration under most conditions. Results are discussed in detail.