The signal samples are stored in a window divided into 2N, and in a Square-law detector each cell is composed of a signal sample, defined as:
In a square-law detector this random variable [Y.sub.0] is exponentially distributed with the following probability density function(pdf) and the average noise power is [mu]:
The radiometer is equipped with an on-chip square-law detector and with an input Dicke switch for the receiver calibration.
It consists of a square-law detector preceded by a low-noise amplifier and followed by a low-frequency integrator.
The receiver gain is determined by selecting a suitable power level [P.sub.D] at the square-law detector input:
Four detector types will be considered here: envelope detector; square-law detector; true-RMS detector; and log detector.
The response to large abrupt increases in input amplitude can be even more striking, however, because the square-law detector characteristic exaggerates the effect of the input increase.
Two straightforward detector types can be made, using microwave semiconductor diodes: the linear detector and the square-law detector. In the present case, it is very attractive to use the square-law detector; then the output voltage will be proportional to the input power and hence the input temperature.
The output of the square-law detector is multiplied by +1 or -1, depending on the position of the Dicke switch, before integration.
Each filter output from each square-law detector
is integrated in time, producing a DC voltage proportional to the integrated power density of the input RF signal over the bandpass of the filter.
The linear combination of the square-law detectors
' output voltages is generated by a properly designed operational amplifier circuit.
This six-port junction linearly combines the two input signals and, because of the square-law detectors
on its four outputs, it delivers four DC voltages.