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| Paper: |
The Receiver System -- cm Regime |
| Volume: |
278, NAIC-NRAO School on Single-dish Radio Astronomy: Techniques and Applications |
| Page: |
91 |
| Authors: |
Norrod, Roger D. |
| Abstract: |
The receiver front-end of a radio telescope is generally considered to encompass components that amplify, filter, and frequency convert signals, provided by the antenna, to a level and frequency range appropriate for detection. This presentation will discuss critical parts of the centimeter wave radio astronomy front-end, and factors impacting the design and performance. The feed efficiently converts propagating electromagnetic fields near a reflector antenna's focal point to a guided wave in coax or waveguide. Some types of feeds inherently detect and separate polarizations; other types require an orthomode transducer to deliver orthogonal polarizations to separate channels. Low-noise amplifiers, usually cryogenically cooled, amplify the signal and set the receiver noise level, and are followed by filters, mixers, and additional amplification. All the passive and active components add electrical noise to the signal, and models used during receiver design will be presented, explaining why loss and noise introduced in the early stages of the receiver are critical. The linear operating range of active components is limited by their power handling capacity, and how these limitations are considered will be discussed. We will also discuss stability of the receiver, and practical means of achieving the required performance. |
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