Passive Reciprocal high-pass/low-pass 4-bit phase shifter at 2.45 GHz

This paper presents the design, fabrication and measurement of a low cost, reciprocal 4-bit phase shifter at 2.45 GHz ISM band using COTS components. High-pass/low-pass filters in π configuration are used to implement the phase shifter bit sections. SPDT switches are realized with BAP51 dual PIN diodes, with resonant inductors in the off-state to provide high isolation. The driver circuit consisting of 74AHC240 octal buffer/inverter was implemented to switch the PIN diodes and control the phase states. A compact layout of the 4-bit phase shifter and driver circuitry was fabricated on a 4-layer FR4 substrate. The total size of the PCB board was 4.9×5.3 cm. The measurement results showed an RMS phase error better than 4.1°, insertion loss better than 8.8 dB and return loss better than 13 dB. The maximum power consumption of the 4-bit phase shifter was 80 mW.