Continuously Tunable True- Time- Delay Phase Shifter Using Switchable Varactor- Tuned Transmission Lines

This work reports on a continuously tunable truetime-delay phase shifter using switchable varactor-tuned transmission lines. The phase shift tuning range is extended by using p-i-n diodes to switch different varactor-tuned transmission lines without increasing the capacitance tuning range. Two phase shifters are fabricated on a 0.787 mm-thick Rogers RT/Duroid 5880 substrate with ε_r = 2.2 and tanδ = 0.0009. For a 1-unit phase shifter, the measured phase shift is about 28° at 1 GHft with insertion loss of less than 1.4 dB, and return loss of better than 15 dB. For a cascaded 2-unit phase shifter, the measured phase shift is about 49° at 1 GHft with insertion loss of less than 1.5 dB and return loss of better than 15 dB.

I. Introduction

As key components of phased-array antennas, phase shifters [1] are required to be low loss, broadband, small size, and fast. In the past years, various phase shifters were designed by adopting the switched-line configurations [2], couplers with variable loads [3], LC switching networks [4] and distributed loaded lines [5], [6] to change the phase shift. The phase shift can be electronically tuned by microelectromechanical system (MEMS) switches [2], CMOS switches [4], magnetic or ferroelectric components [6] and solid-state varactors or switches [3], [5], [7]. Diode phase shifters are widely employed because of their fast switching time, low weight, and low cost.