An Efficient Method for Synthesizing Symmetrical Directional Couplers with a Large Number of Sections

An efficient method for synthesizing symmetrical directional couplers of the coupled transmission line type has been developed. The basic operation is a transformation of the coupling from the frequency domain to the time domain, where the couplings of the individual sections are easily separated. The computations are performed by the Fast Fourier Transform which makes the method very fast and efficient even for couplers with a large number of sections. Butterworth couplers with several hundred sections has been designed by this method using a small desktop computer.