Highly Flexible Broadband Multiport Reflectometer With Compact Size

In this article, a novel concept of a multiport reflectometer with compact size and high design flexibility is proposed. The circuit is composed only of several couplers in series. The accuracy of the reflection coefficient (Γ) can be customized by the ratio between the magnitude of the isolation and coupling coefficient and the phase of the transmission coefficient of each coupler. A prototype of a five-port circuit composed of three couplers is further investigated theoretically to verify the design procedure. Compared with the well-known optimal reflectometer, the proposed topology exhibits comparable accuracy for |Γ| from -5 to -15 dB and significantly higher precision for |Γ| below -15 dB. The topology of the five-port circuit is prototyped with microstrip weak couplers based on edge coupling. This reflectometer is calibrated and measured in the frequency range from 0.7 to 1.4 GHz. The error trends related to the magnitude level show excellent agreement between simulations and measurements. The total size of the circuit is as small as 0.25λ0 × 0.07λ0 at 1.05 GHz.