Investigation of Distributed Capacitance Loading Effect on Miniaturization of Switched-Line Phase Shifter Dimensions

This paper deals with effect of periodic capacitance loading on the transmission line length of a switched line phase shifter. It has shown that the decrement in transmission line length due to capacitance loading can be 4 times greater than conventional switched-line phase shifter. This decrement is depended on effective dielectric constant and the ratio of unloaded to loaded impedance of t-line. For this reason we have utilized true-time delay (TTD) phase shifter equations to evaluate effects of distributed capacitance loading on t-line length and cut-off frequency of loaded switched-line. It has shown that the cut-off frequency is related to phase of a section of periodic capacitance loading t-line and can be very greater than operating frequency that results in better linearity and bandwidth. For this reason, a one-bit phase shifter is designed at 10 GHz and simulated to show the effects of these changes on phase and scattering parameters of switched-line phase shifter. The one-bit phase shifter has an average return loss of 20 dB and insertion loss of 2.5dB at 10 GHz. The relations and simulation results show the feasibility of proposed structure. One-bit phase shifter with new structure designed at 10 GHz has equipped an area of 10 mm².