Efficiency of the Image Band Suppression in Sideband Separating SIS Receivers for Radio Astronomy

The sideband separating SIS receivers are known as the most sensitive instruments for millimeter and submillimeter ground based radio astronomy. Sideband Ratio or Sideband Rejection Ration (SRR), is one of the key parameters of heterodyne receivers, because it is strongly influencing the system sensitivity. This effect takes place due to sufficient signal losses in the atmosphere or in the instrument optics, which is reducing the signal to noise ratio. To develop high performance receiver SIS sideband separating receiver with have performed a comprehensive analysis of the signal transformation in both high frequency (RF) and low frequency (IF) parts of the receiver. As result, the entire IRR pattern was simulated. It was found that SRR performance is very much restricted by reflections in RF and IF parts of the receiver. Minimization of these reflections is curtail for achieving SRR levels of 15 dB or higher. This knowledge is used in development of sideband separating SIS receiver for ground based telescope APEX and for Millimetron space mission.