An ultra compact C-band 5-bit MMIC phase shifter based on all-pass network

An ultra compact 5-bit MMIC phase shifter, operating in the C-band, is presented. The proposed phase shifting circuit utilizes the lumped-element all-pass network topology. The transition frequency of the all-pass network which determines the size of the circuit is set to be much higher than the operating bandwidth, which results in an extremely small chip size of the phase shifter in a relatively low frequency range. The MMIC phase shifter has been successfully fabricated with a die size of 1.72mm x 0.81mm (1.37mm(2)) and achieved a fractional bandwidth of 10%, demonstrating an insertion loss of 5.7 dB +/- 0.8 dB and an RMS phase shift error of less than 2.3 degrees in the C-band. To our knowledge, the MMIC phase shifter is the smallest among the reported digital phase shifters which cover a total phase shift of 360 degrees for the C-band.