A design of phase shifter with constant insertion loss

Abstract

Analog phase shifters are widely used in radar systems and communication systems to achieve linear phase control. To obtain linear phase control in 1-port network, a phase shifter is required constant return loss variation. Normally the phase shifting characteristic be obtained by variation of junction capacitance of varactor diode. The core circuit of the proposed reflection type phase shifter (RTPS) consists of single varactor diode and λ/4 transmission line terminated two varactor diodes. The return loss variation of the proposed phase shifter can be minimized by controlling the impedance of the transmission line. To obtain constant return loss over the phase variation of core circuit, the characteristic impedance of transmission line must be selected by parasitic components of varactor diode. Parasitic components of the varactor diodes can be extracted by Deloach method. Two core circuits are used at through and coupling ports of the proposed RTPS and the isolation port is open. RTPS is composed of 90° hybrid coupler and termination load. For an experimental validation, RTPS was fabricated on epoxy substrate with a dielectric constant (e r ) of 4.4 and a thickness (h) of 31 mils at 2.14 GHz. The SMV 1233–011LF varactor diode and S03A2500N1 90° hybrid coupler are used. As shown the Fig. 1, the phase variation of the fabricated phase shifter is 358.21° with the insertion loss variation of −2.27 ± 0.19 dB. Fig. 2 shows measured phase results on the rectangular chart.