Linear FM chirp filters in pulse compression radars

Abstract

Using a complex Fresnel integral algorithm, the authors extend results of other authors from a time-bandwidth product of 50 up to 720. They analyze a rectangular linear FM filter having a 300-MHz center frequency, 120-MHz bandwidth, and 6-μs dispersion time <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> . Two different methods of rectangular FM cosine square tapering are compared. In the first method, the tapers are of length <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> /12 at the two edges inside the dispersion time <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> , while in the second, tapers of length α <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> are added to the duration <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> (α=0.05 and 0.1). The results show that the skirt steepness, the sidelobe rejection, and the Gibbs ripples of the wave spectrum, as well as the reduction of insertion loss and the suppression of Fresnel ripples, are best at α=0.1.