An accurate six-port microstrip reflectometer

This paper describes the properties of a novel 8-port coupler which has been assembled out of three 4-port interdigitated couplers. The procedures used in the design of this coupler, as well as in the derivation of its essential parameters are demonstrated. The scattering matrix of the proposed coupler is derived by using the signal flow graph (SFG) technique. The 8-port coupler has been modified with proper terminations in order to produce a working six-port reflectometer. Detailed SFG analysis of this reflectometer reveals that it is inherently of a broad-band character. This reflectometer has been fabricated, calibrated and tested at the X band.