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ALMA MEMO #416

The Relative Sensitivity of Full-Wave and Half-Wave Detectors in Radio Astronomy

A. R. Thompson (NRAO) and D. T. Emerson (NRAO)

2002/04/03




Keywords: sensitivity, linear detectors, square-law detectors, half-wave, full-wave

The sensitivity in the measurement of Guassian noise power using a half-wave detector can suffer degradation relative to that of a full-wave detector, in cases where the bandwidth of the input waveform is not small compared to the center frequency. There are two physical mechanisms that suggest a basis for this effect. The half-wave detector responds to only half of the input waveform, resulting in possible loss of information. Also, in the half-wave detector a component of the input spectrum feeds through the diode and adds to the noise that is subsequenctly filtered by averaging at the detector output. This feedthrough component does not occur in full-wave detectors. The phenomena are examined using an analytic method developed by Nuttall (1986), and also by numerical simulation. The results for both linear and square-law characteristics are considered, and formulas and graphs for estimating the magnitude of the effects are given.


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Last modified: 2002-04-03

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