Design and simulation of a 3-bit DMTL phase shifter for wideband applications

This paper presents a wideband distributed coplanar waveguide (CPW) phase shifter for S-band operation. A 3-bit distributed MEMS transmission line (DMTL) phase shifter is developed by periodically loading MEMS shunt switches on a CPW transmission line (TL). A total of 105 MEMS shunt switches are utilized in the design to provide phase shifts of 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315° at 2.45 GHz. Two large metal-insulator-metal (MIM) capacitors are implemented on the CPW centre conductor as DC blocking capacitors to separate the DC actuation voltage between three bit segments during operation. The high resistivity silicon substrate (ρ=10 Ω·cm) and 2 μm thick aluminium centre conductor are employed to reduce the insertion loss due to the transmission line (TL). The simulated reflection coefficients are better than -10 dB across the operating band with an average insertion loss of -2.94 dB at 2.45 GHz. The CPW transmission line has been meandered using 60° mitered bends to optimise the size of the phase shifter to result in overall size of 30 mm × 10 mm. The simulated pull-in voltage of the doubly clamped beams implemented in the design is 17.18 V. The proposed DMTL phase shifter is suitable for use in smart antenna applications, radar systems and ultra-wideband (UWB) microwave medical applications.