Ka-band reliable and compact 3-bit true-time-delay phase shifter using MEMS single-pole-eight-throw switching networks

This paper presents a radio frequency micro-electromechanical system (RF MEMS) based 3-bit phase shifter using MEMS single-pole-eight-throw (SP8T) switches. Devices are fabricated on 635 µm alumina substrate utilizing on the coplanar waveguide (CPW) transmission line. Single switch dimensions are 0.14 × 0.23 mm2 which is much smaller than Si-on-insulator switches. The symmetric and compact SP8T switch is the primary building block of the 3-bit phase shifter. The SP8T switch results in isolation levels of 31–15 dB, return loss of 33–18 dB and insertion loss of 0.6–1.9 dB, respectively, at 26–40 GHz. Later, two SP8T switches are connected back to back to develop the 3-bit phase shifter using different delay lines at 35 GHz. Finally, the phase shifter provides average return loss of better than 14 dB and average insertion loss of 4.4 dB over the 34.75–35.25 GHz. Measured average phase error is less than 0.98° at 35 GHz. The total area of the fabricated 3-bit phase shifter is 5.95 mm2. SP8T switches are capable of handling 0.1–1 W of power up to 100 million cycles which is sufficient power handling capability for wireless communication systems. Reliability of the phase shifter is extensively characterized with different incident RF powers at room temperature (25°C) and discussed in detail. To the best of the authors' knowledge, this is the first reported MEMS 3-bit phase shifter in the literature that has used a minimum number of switching elements per phase state.