Broadband K-Q-W feed system for the 40 meters Yebes radio telescope

The optical designs of the new full Q-band (31.5-50.0 GHz) and W-band (72–116 GHz) receivers for the 40-meter radio telescope at the Yebes Observatory are presented. The design, based on converging optical paths, aims to provide simultaneous observation in both bands and it allows using a common hot-cold load system for the noise temperature calibration of each receiver. Quasioptical design techniques have been used to analytically solve the frequency independent optical systems in the focal zone of the Cassegrain radio telescope. Since such analysis is valid when the beam waist radius of the feed is constant in frequency, the feed horns have been designed to approximate as much as possible this condition. Subsequently, further analysis based on physical optics has been performed to show how these design and analysis methodology agree with experimental measurements.