Waveguide-integrated MEMS-based phase shifter for phased array antenna

This paper investigates a new concept of waveguide-based W-band phase shifters for applications in phased array antennas. The phase-shifters are based on a tuneable bilateral finline bandpass filter with 22 MEMS (microelectromechanical system) switching elements, integrated into a custom-made WR-12 waveguide with a replaceable section, whose performance is also investigated in this paper. The individual phase states are selected by changing the configuration of the switches bridging the finline slot in specific positions; this leads to 4 discrete phase states with an insertion loss predicted by simulations better than 1 dB, and a phase shift span of about 270°. MEMS chips have been fabricated in fixed positions, on a pair of bonded 300 μm high resistivity silicon substrates, to prove the principle, i.e. they are not fully functional but contain all actuation and biasing-line elements. The measured phase states are 0°, 56°, 189°, and 256°, resulting in an effective bit resolution of 1.78 bits of this nominal 2-bit phase-shifter at 77 GHz. The measured insertion loss was significantly higher than the simulated value which is assumed to be attributed to narrow-band design of the devices as the influence of fabrication and assembly tolerances is shown to be negligible from the measurement results.