Analysis of the Wilkinson Coupler Under Different Input Conditions

In sub-terahertz receivers, it is indispensable to apply beamforming that combines multiple RF paths from the viewpoint of SNR (signal to noise ratio) improvement by increasing the directivity of the communication path. For beamforming in the case of mm-wave band application, the receiver is placed near the antenna. However, in the case of sub-terahertz band application, where the wavelength is short, the RF paths must be directly synthesized because space for a receiver is not available. It is desirable to apply a Wilkinson Coupler composed of simple passive elements to combine RF paths. When applied to beamforming, the amplitudes and phases of signals to be combined may differ greatly. It is also necessary to turn off some input signals for calibration.In this case, it is difficult to fix the impedance in the OFF state to a specific impedance. For this reason, it is desirable to have low sensitivity to the impedance in the OFF state. In this paper, we analytically confirm that the Wilkinson Coupler can operate normally even in such a special situation.