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Radar Detection
Published in Bassem R. Mahafza, Introduction to Radar Analysis, 2017
The performance difference (measured in SNR) between the linear envelope detector and the quadratic (square law) detector is practically negligible. Robertson (1967) showed that this difference is typically less than 0.2dB; he showed that the performance difference is higher than 0.2dB only for cases where nP > 100 and PD < 0.01. Both of these conditions are of no practical significance in radar applications. It is much easier to analyze and implement the square law detector in real hardware than for the envelope detector. Therefore, most authors make no distinction between the type of detector used when referring to non-coherent integration, and the square law detector is almost always assumed. The analysis presented in this book will always assume, unless indicated otherwise, non-coherent integration using the square law detector.
Applications of superconductivity
Published in J. R. Waldram, Superconductivity of Metals and Cuprates, 2017
One of the simplest applications is to use a low-capacitance weak link as a detector or mixer by biasing it into the phase-slip state just above the zero-voltage step (Figure 18.7(a)). We saw in Section 6.3 that application of an r.f. current depresses the zero-voltage step, and, as the figure shows, this leads to a corresponding change in the d.c. voltage developed across the device. For small r.f. amplitudes the depression in the step height is quadratic in the r.f. current, and of order (Ir.f./IJ)2. We therefore have once again a square-law detector, with a change in the d.c. output voltage proportional to the square of the r.f. signal.
Detecting Microwaves
Published in Iain H. Woodhouse, Introduction to Microwave Remote Sensing, 2006
After down-conversion, amplification and filtering, the signal can then be detected by some electrical component (such as a diode) which is designed to convert the microwave energy into an electrical signal. The most common kind of detector is a square-law detector which produces an output voltage proportional to the power of the wave. It is called a square-law detector since the instantaneous voltage of the wave itself is E(t) (the amplitude) but the output voltage of the detector is proportional to E2(t), the power of the wave.
Chirped-pulse millimetre-wave spectrometer for the 140–180 GHz region
Published in Molecular Physics, 2018
C. Lauzin, H. Schmutz, J. A. Agner, F. Merkt
An advantage of our spectrometer is that it can easily be modified to record either FS [24,34,35] or frequency-modulation (FM) (see, e.g. [36]) millimetre-wave spectra of the samples under the same supersonic-expansion conditions, the same excitation geometry and the same millimetre-wave power in the range 2–5 mW. For such measurements, the transmitter arm was left unaltered but the receiver was replaced by a square-law detector, i.e. an unbiased semiconductor diode (Farran, WDP-06). To illustrate this advantage, Figure 5 displays a CP-FT spectrum (bottom panels), an FM spectrum (middle panels) and an FS spectrum of NO in the vicinity of the strong 6-5 pure rotational transition of 14N14N16O. The FS and FM spectra have the characteristic line shapes for these techniques. In contrast to the CP-FT spectrum, these spectra do not reveal two distinct Doppler components although the same volume is probed. It thus appears that molecules located in the densest part of the beam close to the propagation axis are discriminated against in the CP-FT spectrum (see also Section 3.1). We do not have a conclusive interpretation of this difference but suspect that it may be caused by the collision-induced loss of coherence in the densest part of the beam, to which only the CP-FT method would be sensitive.