Frontend and Receiver Technology for Microwave and Sub-Millimeter Receivers up to 800 GHz
Czekala, H; Rose, T; Walber, A; Zimmermann, R
RPG Radiometer Physics GmbH

Radiometer Physics GmbH (RPG) recently has made significant advances in the performance of receiver frontends at various frequency bands. Depending on the input frequency the receiver design is optimized for best noise performance, system stability, and robustness against radio frequency interference.

Up to 119 GHz, a direct detection design is usually showing better performance than heterodyne receivers. RPG is using MMICs from the Fraunhofer Institute for Applied Solid-State Physics (IAF Freiburg, Germany) to build compact and reliable low noise amplifiers (LNA) with a noise temperature of 450 K at 90 GHz. These direct detection receivers allow compact system integration and provide inherent robustness to all RFI except for direct in-band sources. Direct detection frontends up to W-band are equipped with a noise injection section and a magnetical Dicke switch in between the feedhorn and the LNA. With these features, the receivers are auto-calibrating and the frontend stays on scene all time.

Fully equipped radiometers (including optics, feed, noise injection, Dicke Switching, LNA and detector) have noise temperatures of 280 K (550 K, 900 K) at 20 to 30 GHz (50 to 60 GHz, 90 GHz).

The magnetically switched Faraday rotators act as terminations with better than 30 dB isolation and input match, while having less than 1 dB insertion loss. Additionally, these devices are used for power levelling in the W-band and beyond.

At 183 GHz and higher up towards sub-millimeter applications, the heterodyne detection still performs better than low-noise amplification at the signal input. Using sub-harmonic mixers designed at RPG, we obtain noise temperatures of 400 K at 183 GHz for the DSB mixer. The complete frontend has 800 K. A noise source at 183 GHz delivers 5000 K of power and is coupled to the system with a 10 dB coupler. When adding the noise injection to the system, the system noise is roughly 1100 to 1400 K, depending on the IF channel within the 0.1 GHz to 9 GHz IF bandwidth.

The sub-harmonic heterodyne receiver frontends at 280 GHz and 425 GHz have system noise temperatures of 900 and 2700 K, respectively, for the complete system. Similar receivers for 600 and 800 GHz are currently optimized.