18.7 GHz 4-Bit PIN diode Reflection Type Phase Shifter for radiometer phased array antenna

A design of 18.7 GHz PIN diode Reflection Type Phase Shifter (RTPS) for Ku-band soil moisture radiometer phased array antenna is presented. The compact reflective loads are designed using PIN diodes to control phase shifts. The PIN diodes are MACOM's MA4FCP200. The designs sequence is to start with modelling PIN diode equivalent circuits at 18.7 GHz. Then a quadrature hybrid coupler and PIN diode reflective loads are designed. A PIN diode in forward and reverse states is considered as lumped components when designing the reflective loads. This approach offers more freedom when designing loads with high accuracy. The phase shifter is fabricated directly on the same Taconic TLX8 laminate with the feed network, this allows producing a monolithic phased array and reduces the cost of the whole system significantly. The simulated results show that the 4-bit phase shifter can yield 4.7 dB insertion loss (IL) and the input and output return losses (RL) are higher than 15 dB at 18.7 GHz. The phase resolution is 22.5° with the root mean square (RMS) phase error of about 1°. The measured results of the prototypes of 180°and 90° bits show a good agreement between simulation and measurement. The size of the phase shifter is quite compact, just about 2.8 cm x 0.6 cm.