High directivity couplers realized in microstrip line technology

This paper describes the design 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 capacitances soldered to the lines or realized as interdigital capacitors. The presented type of couplers is in close relation to two hole waveguide coupler. The proposed couplers are narrowband ones. Several couplers with 3, 6, 10 and 15 dB couplings have been designed and realized. Lumped SMD capacitors have been used. In each case directivity is better than 30 dB. Couplers are planar, compact and if required can be easily tuned for needed parameters.