A microwave delay module for radar test applications

This paper describes a delay module designed for a wide range of radar systems including pulsed Doppler and synthetic aperture. It is based on the use of a single port, bulk acoustic wave delay line using spinel (MgAl2O4) as the delay medium. Longitudinal acoustic waves, generated by a zinc oxide thin film transducer, are converted on reflection into the required low loss, shear waves. The delay line is fed from a 4 port circular and input and output PIN diode switches reduce noise and prevent unwanted echoes from degrading the delayed signal. The module also includes a PIN temperature compensating attenuator. A typical module operates in S-band with a bandwidth of 500 MHz and has an insertion loss of no more than 65 dB over a temperature of -10 to +70 C for a delay of 22 micro seconds.