Development of the Measurement System of Image Rejection Ratio for the Sideband-Separating Receiver

We developed a measurement system of image rejection ratio for the sideband-separating receiver. This system comprises a horn moved by a motor slider, a harmonic mixer and a signal generator. We have installed the system on the Nobeyama 45-m millimeter telescope and compared the image rejection ratio measured by this system with that obtained from molecular line observations of celestial objects. We confirmed that we can measure image rejection ratio with an accuracy of ±10% with our system. By using the system, we can tune the applied bias voltage of mixer chips to the best performance of image rejection ratio and accurate calibration of the intensity of molecular line observations becomes possible. This is the first IRR measurement system developed for practical use with the 2SB receiver system.