Design and development of multi-frequency comb generator for space borne microwave active sensors

An integral part of space borne active remote sensors like scatterometer is the Frequency Generator unit (FG) which caters to the requirement of coherent, highly stable, multiple frequency signals required for the operation of the payload right from clock generation, LO signals to linear frequency transmit signal. At the heart of FG is a comb generator which simultaneously generates some of the required frequencies. This paper presents the design and development of an active frequency multiplier designed using BJT device, with multi frequency output. The comb-generator like active multiplier generates X5, X10 and X17 multiplies of the input frequency simultaneously. Desired signal at 250 MHz, 500 MHz and 850 MHz are generated using a 50 MHz input from a stable crystal source. It features a low input power and low added phase noise. Size of the designed hybrid MIC on 25 mil substrate is 33.5 times 12.7 mm. It also offers rejection to adjacent harmonics to ease the design of subsequent filters. This paper discusses the topology selection, its merits and demerits. It is followed by simulation techniques and critical issues addressed during design. Finally it shows the measured results of the comb generator which has successfully passed through environmental stress screening.