Coupled-Strip-Transmission-Line Filters and Directional Couplers1956 lRE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES Coupled43trip-Transmission-Line and Directional E. M. T. JONES~ AND Filters Couplers J. T. BOLLJAHN~ Summary―Tkis paper describes the theory of operation of coupled strip line tilt ers and dh’ectional couplers, and presents information from which these components may be easily designed. Low-pass, band-pass, all-pass, and all-stop filter characteristics are obtained from these coupled lines either by placing open or short circuits at two of the four available terminal pairs, or by interconnecting two of the terminal pairs. Directional couplers having perfect dk-ectivity and constant input impedance at all frequencies, and for all degrees of coupliig, are obtained by placing equal resistive loads at each of the four terminal p……