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Thermal Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
What is a hot-electron bolometer? An HEB is a detector for submillimeter radiation and far-nfrared radiation (Cherednichenko and Drakinskiy 2008; Gerecht and You 2008; Jiang et al. 2009). The detector is mainly of interest for detecting radiation with a frequency above 1000 GHz, an area where heterodyne SIS (superconducting-insulating-superconducting) receivers no longer work well. The heterodyne is a signal frequency produced by mixing two alternating current signals of different frequencies. Of the two the resultant frequencies, one is equal to the sum of the two original frequencies while the other equals their difference. Either of the two newly generated frequencies may be used in receivers by proper tuning or filtering. Heterodyning is applied to frequency shifting information of interest into a useful frequency range.
Digital Coherent Optical Technologies
Published in Zhensheng Jia, Luis Alberto Campos, Coherent Optics for Access Networks, 2019
In heterodyne detection [29], the difference between the LO and transmitter laser frequency is higher than the electrical signal bandwidth and the entire optical signal spectrum is directly translated to an electrical bandpass signal centered at the fIF for further electronic processing. Such a receiver has a reduced sensitivity of >3 dB in comparison to homodyne detection, as the signal energy with homodyne detection is twice the signal energy of a heterodyned signal. The linewidth requirements are, however, about an order of magnitude less stringent in comparison to homodyne detection, which makes the realization of such a receiver simple. The main drawback of heterodyne detection is that it requires a receiver bandwidth of at least twice the bit rate. A heterodyne receiver, therefore, needs broadband photodiodes and electrical amplifiers, which makes it challenging to realize high-speed transmission.
Terahertz detectors and focal plane arrays
Published in Antoni Rogalski, Infrared and Terahertz Detectors, 2019
The primary benefit of heterodyne detection systems is that the frequency and phase information at the signal frequency νs is converted to the frequency νIF, which is in a much lower frequency band (νIF << νs) appropriate to electronics time response. This transformation (νs → νIF) is called heterodyne conversion. If the signal and LO frequencies are equal, then νIF = 0 and the beat tone degenerates to DC, and such a detection process is called homodyne conversion.
Intensity correlations of flat-topped beams in oceanic turbulence
Published in Journal of Modern Optics, 2020
In this paper, we have formulated and evaluated the intensity correlations at the receiver plane of flat-topped Gaussian laser beam in oceanic turbulence. To our knowledge, there exists no study in the literature on the intensity correlations of any type of beam in oceanic turbulence. Our results can be used in the design of oceanic telecommunication links and imaging systems, specifically when heterodyne detection is employed. As known, heterodyne systems are used in selecting the intended channel in a wireless environment in which multichannel is broadcast. Such systems employ frequency mixing where the received field at the carrier frequency is mixed with the field of the local oscillator generated at the receiver. After mixing, the receiver signal at the carrier frequency is converted to a signal at the intermediate frequency (IF) which is more easily processed than the original signal at the carrier frequency. The intensity fluctuations occurring at the photodetector output are related to the mixed field which has several terms, also involving the intensity correlation. Thus, in finding the performance of a heterodyne optical communication system employing flat-topped incidence and operating in the turbulent ocean, intensity correlations evaluated in this paper will help to be useful.
Surfing the Radio Spectrum Using RTL-SDR
Published in IETE Journal of Education, 2019
Antonios Valkanas, Divyanshu Pandey, Harry Leib
Assume is the RF signal after LNA and bandpass filtering. A general form of a passband signal comprising of in-phase and quadrature components and respectively can be written as where is the carrier frequency. Let the local oscillator frequency be , and let the phase offset between the transmitter and the receiver be , then the output of the mixer , can be written as The output of the mixer after passing through an IF bandpass filter transforms the signal into a low intermediate frequency (IF) denoted as . If , it is called high side injection (HSI) of oscillator and if , it is called low side injection (LSI). By converting to a fixed IF frequency, the super-heterodyne receiver provides improved selectivity. Another signal at called the image response can be down converted to the intermediate frequency if the RF bandpass filter is not narrow enough. Hence the image signal can superimpose with the desired signal. This is illustrated in Figure 3.
Modified FMCW system for non-contact sensing of human respiration
Published in Journal of Medical Engineering & Technology, 2020
Aloysius Adya Pramudita, Fiky Y. Suratman, Dharu Arseno
The in-phase quadrature (IQ) demodulation was commonly applied as a method for detecting phase of the signal. IQ demodulator usually was placed at the receiver circuit part. Homodyne and heterodyne systems are types of receiver that can be employed in realising the IQ demodulation. The application of homodyne quadrature system for Doppler radar had been investigated in detecting the respiration and heartbeat [23]. However, the direct conversion to dc and baseband amplification exhibited the additional noise. In this method, the presence of dc offset was compensated, while the dc information required for arctangent demodulation was captured before being compensated. Heterodyne system had been widely employed in telecommunication and radar receiver in which the radio frequency (RF) signal was down-converted to immediate frequency (IF). This system became another solution for the dc offset and low frequency noise problems [24]. In developing the proposed method, the IQ demodulation was elaborated as phase data extraction from the LPF output. In a number of previous research, the IQ demodulator was employed as a part of RF circuit part of the radar [23–27]. Power consumption issue respecting the IQ additional demodulator in RF hardware also needs attention in the implementation. The analogue correlator had proposed to replace the IQ demodulator for reducing the power consumption [28]. To minimise the hardware modification of conventional FMCW system, the IQ demodulation was implemented in proposed method as post-processing computation of LPF output sequence. A sinusoidal signal using as reference signal to perform the IQ demodulation could be synthesised from the LPF output. The frequency of reference signal was obtained by detecting the beat frequency from the LPF output. Furthermore, the FFT was used to determine the LPF output frequency and then the reference sinusoidal signal could be synthesised easily by the frequency synthesiser (Figure 5).