A 9 Bit DIFM Receiver for Ka-Band

A digital instantaneous frequency measuring receiver (DIFM) has been built at Ka-band with a frequency resolution of 25 MHz (9 bit) using a five discriminator binary system digitised to 11.25 degrees. Absolute frequency accuracy is dispersion limited to 100 MHz. A simplified system block diagram is shown in fig. 1. Advanced technology is used in each of the three sections to obtain a compact unit with a performance limit set by the inherent frequency dispersion in the microstrip discriminator circuitry. This paper describes the design. construction and performance of the complete DIFM receiver with special attention given to the CAD techniques based on circuit modelling to allow microwave discriminator design to be carried out under conditions of severe frequency dispersion.