High directivity microstrip couplers

This paper describes the design method and realization of high directivity planar couplers realized in microstrip line technology. The basic idea is that coupling between two transmission lines is present at two points only. The coupling is realized by SMD capacitances soldered to the lines. The presented type of couplers is in close relation to two hole waveguide coupler. The proposed couplers have narrow bandwidth. Several couplers with 3, 6, 10 and 15 dB couplings have been designed and realized at frequency 1.3 GHz. In each case directivity is better than 30 dB. Couplers are planar, compact and easy to realize.