Application of fiber-optic delay lines in radar phase noise measurement

A critical parameter in the performance of airborne radars is the phase noise of the radar´s carrier frequency. Low phase noise is important for accurate long range detection of a target. Many phase noise test sets utilize waveguide delay lines as part of the test circuit. Because of its size, weight, and signal attenuation, the waveguide delay line has length limitation. Replacing waveguide with fiber-optic delay line allows for a major reduction in size and weight, as well as an added ability to improve the sensitivity of the test set in measuring phase noise close to the radar´s carrier frequency. This paper describes characteristics of waveguide and fiber-optic delay line based phase noise test sets. The advantages and disadvantages of both types of delay lines are discussed along with recommendations for the use of one versus the other as well as a combination of both