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Advanced weather radar systems to improve aviation safety
Published in Hans M. Soekkha, Aviation Safety, 2020
Pulse compression allows a radar to utilize a long pulse to achieve a large radiated energy, but simultaneously to obtain the range resolution of a short pulse. The broader the wave form the higher range resolution can be obtained and subsequent a larger number of independent estimates within the dwell time. This allows accurate weather measurements in a shorter time. An FM-CW radar is an extreme form of pulse compression and may be a good alternative, due to their low minimum range, high range resolution, together with low power and low cost [8]. A phased array antenna allows rapid beam movement using a number of T/R modules to cover the surveillance volume of an airport terminal area. A standard mechanically steered radar antenna would have extreme difficulty in searching the same volume in a timely fashion. Again in the normal weather forecasting there is no need for such short time limits as it is in “now-casting”.
P
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
pulse compression technique of correlating identically coded signals, such as chirp signals, to produce a sharply peaked correlation function, the peak width being much shorter than that of the original coded pulses by a ratio equal to the time-bandwidth of the coded signals. pulse distortion a spreading or lengthening of the temporal shape of an optical signal transmitted through an optical fiber caused by a combination of wavelength effects (dispersion) and multimode and polarization effects. Also called pulse broadening. See also signal distortion. pulse Doppler a coherent radar, usually having high pulse repetition rate and duty cycle and capable of measuring the Doppler frequency from a moving target. Has good clutter suppression and thus can see a moving target in spite of background reflections. pulse forming network (PFN) (1) a transmission line with different impedance along its length. (2) a lumped element circuit consisting of inductors and capacitors designed to deliver a square pulse.
Pulse Compression
Published in Bassem R. Mahafza, Introduction to Radar Analysis, 2017
Range resolution for a given radar can be significantly improved by using very short pulses. Unfortunately, utilizing very short pulses decreases the average transmitted power, which can hinder the radar’s normal modes of operation particularly for multi-function and surveillance radars. Since the average transmitted power is directly linked to the receiver SNR, it is often desirable to increase the pulse width (i.e., increase the average transmitted power) while simultaneously maintaining adequate range resolution (i.e., use short pulses). This can be made possible by using pulse compression techniques. Pulse compression allows us to achieve the average transmitted power of a relatively long pulse, while obtaining the range resolution corresponding to a short pulse. Two pulse compression techniques are discussed. First, we consider the correlation processing, which is predominantly used for narrowband and some medium-band radar operations. Second stretch processing (normally used for extremely wideband radar operations) is considered next.
Photonic broadband signal frequency conversion and bandwidth multiplication based on a Fourier domain mode-locked optoelectronic oscillator
Published in Journal of Modern Optics, 2021
Yalan Wang, Jin Zhang, Xiang Li, Jianghai Wo, Anle Wang, Xiaoniu Peng
Then the frequency conversion is implemented. The central frequency of the LFM signal generated by AWG is set to be 20 GHz, and the bandwidth of the signal is 1 GHz. Figure 3(a) shows the frequency down-conversion results by tuning the wavelength of the laser. The central frequency of the LFM signal is tuned from 4.6 to 11.2 GHz when the laser wavelength is adjusted from 1550.99 to 1550.94 nm. The frequency conversion range and the resolution are limited by the bandwidth of the FBG-FP filter and the free spectral range (FSR) of the OEO, respectively. Similar results are also confirmed when the central frequency of the AWG frequency is tuned at 30 GHz (see Figure 3(b)). Figure 3(c and d) show the frequency conversion results at different input frequencies. As shown in Figure 3(c and d), by tuning the central frequency of the LFM signal, the frequency of the converted signal changes correspondingly. Since we use an optical filter that is not narrow enough to select the desired optical sideband, only frequency down-conversion is demonstrated. If the CS-SSB modulation is employed in terms of the DPMZM, frequency up-conversion can also be achieved. Furthermore, by applying different modulation signal onto the MZM and utilizing the modulated optical sideband as the light source, the system can generate not only frequency-converted LFM signal, but also other arbitrary waveforms such as phase coded signal as long as Fourier domain mode locking is achieved. Figure 3(e and f) are the corresponding time-domain waveform and the pulse compression performance, the amplitude jitters are very small, and the full width at half maximum is 1.08 ns, respectively. Thus, a pulse compression ratio of ∼18865 is realized.
An adaptive filtering algorithm in pulse-Doppler radar for counteracting range-velocity jamming
Published in International Journal of Electronics, 2022
Ahmed Abdalla, Mohammed Ramadan, Yongjian Liao, Shijie Zhou
Primarily, Doppler radar is employed for the detection of moving targets whose echo region is much smaller than the relatively stationary clutter return. Moving targets are discriminated from noise, clutter, and jamming on a frequency basis by exploiting the Doppler phenomenon. Conventionally, the pulse-Doppler radar repeats the same waveform to permit efficient pulse compression and Doppler processing technique to be utilised.