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Ultra-Wideband Radar Receivers
Published in James D. Taylor, Introduction to Ultra-Wideband Radar Systems, 2020
James D. Taylor, Elizabeth C. Kisenwether
One objective in radar performance is to increase the range resolution. If we use a sine wave pulse of duration τ, then the range resolution will be cτ/2. Short pulse lengths mean high output power for a given radiated energy, which means practical implementation problems. One approach to increasing range resolution and accuracy is to use a long waveform which is a nonsinusoidal wave, or a coded pulse train, which will only correlate when there is an exact coincidence of reference and received waveform. We showed this earlier in Figure 10.23C with the autocorrelation of the chirped waveform. Now, let us look at the approaches using Barker codes and complementary (or Golay) codes. The Barker code only correlates at one instant and is a discrete interval version of the chirped waveform. The complementary (Golay) code uses two coded sequences which have sidelobes of the same size, but opposite sign. When complementary correlations add, the result is a large value output and zero time sidelobes.
The Matched Filter Receiver and the Ambiguity Function
Published in Bassem R. Mahafza, Introduction to Radar Analysis, 2017
Barker code is one of the most commonly known codes from the binary phase code class. In this case, a long pulse of width Tp is divided into N smaller pulses; each is of width τ0 = Tp/N. Then, the phase of each subpulse is chosen as either 0 or π radians relative to some code. It is customary to characterize a subpulse that has 0 phase (amplitude of +1 volt) as either “1” or “+.” Alternatively, a subpulse with phase equal to π (amplitude of −1 volt) is characterized by either “0” or “−.” Figure 7.15 illustrates this concept for a Barker code of length seven. A Barker code of length N is denoted as BN. There are only seven known Barker codes that share this unique property; they are listed in Table 7.1. Note that B2 and B4 have complementary forms that have the same characteristics.
Super Deltaflex − Advanced development of transit time acoustic flow measurement
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
The transmitter signal is a pulse sequence of a phase modulated carrier (PSK = phase shift keying) of 200 kHz with about 1.5 ms length, sent in both direction, first from TD1 to TD2 and a second time reverse. The modulation of the pulse sequence is a special Barker Code, designed to allow pulse compression in order to obtain a better signal to noise ratio S/N.
LFM-Chirp-Square pulse-compression thermography for debonding defects detection in honeycomb sandwich composites based on THD-processing technique
Published in Nondestructive Testing and Evaluation, 2023
Guozeng Liu, Weicheng Gao, Wei Liu, Jianxun Xu, Rui Li, Weiliang Bai
According to the different thermal excitation method, optical thermography infrared NDT technique is mainly divided into pulse thermography (PT), lock-in thermography (LT), pulsed phase thermography (PPT) and frequency modulation thermography (FMT) [5,6]. Pulse compression thermography (PuCT) [7] is a new active infrared NDT technique, its excitation signal is divided into two-phase coded signal (Barker code) and frequency modulation coded signal (chirp signal). The Barker code is a two-phase coded signal with a fixed sign value that can only take + 1 or −1, which has great ideal autocorrelation characteristic. It is conducive to extracting characteristic signals, suppressing noise and improving defect identification results using PuCT technique with Barker code. However, as a pulse compression signal, FM coded signal (chirp signal) is relatively easy to implement. Furthermore, linear and non-linear frequency-modulated pulse-compression [8] can flexibly change the frequency of the excitation signal when identifying defects, effectively detecting defects in different depth ranges of interest.
Photonic generation of binary and quaternary phased-coded microwave pulses with tunable frequency multiplication factor
Published in Journal of Modern Optics, 2020
Xiong Luo, Lan Yu, Anle Wang, Jianghai Wo, Yalan Wang, Jin Zhang, Ranran Liu, Haida Yang
13-bit Barker code commonly used in radar systems is employed as the binary coding sequence. The coding signal has a 32-bit fixed pattern ‘0, 0, … , 0, −1, −1, −1, −1, −1, +1, +1, −1, −1, +1, −1, +1, −1’ (19-bit ‘0’ plus 13-bit Barker code) operated at a coding rate of 5 Gb/s. Corresponding electrical modulation signal ‘’ is shown in Figure 3(a). The generated frequency-quadrupled binary phase-coded microwave pulse train with a time duration of 23 ns is indicated in Figure 3(b). The repetition period and duty cycle of the generated pulse train are 6.4 ns and 13/32, respectively. Figure 3(c) shows the waveform of the generated binary phase-coded microwave pulse in a time range from 3 to 7 ns. The intra-pulse waveform has a period approximately 50 ps, which corresponds to a frequency of approximately 20 GHz. Figure 3(d) illustrates the phase information extracted from Figure 3(c) by Hilbert transform. Approximately phase jumps can be observed and the jump points fit well with the level-jump points in Figure 3(a). To investigate the pulse-compression capability of the generated binary phase-coded pulses, autocorrelation of the pulse in Figure 3(c) is calculated by MATLAB. The result is shown in Figure 3(e), and the zoom-in view over the time span of −0.3–0.3 ns is shown in Figure 3(f). As can be seen, the peak-to-sidelobe ratio (PSR) and the full width at half-maximum (FWHM) of the compressed pulse are 10.58 dB and 0.203 ns, respectively. Thus, a pulse compression ratio (PCR) of 12.8 is achieved, which is close to the theoretical value of 13. The results indicate that the generated binary phase-coded microwave pulses have a great compression capability.
Application of pulse compression technique in metal materials cracks detection with LF-EMATs
Published in Nondestructive Testing and Evaluation, 2023
Min He, Wenze Shi, Chao Lu, Yao Chen, Liping Zhao, Dexiu Dong, Guangdeng Zeng
The Barker code is a binary code set with special laws proposed by BARKER in the early 1950s, which is an acyclic sequence and its code elements can only take +1 or −1. This code has good autocorrelation and noise suppression characteristics and is considered an effective coding method to obtain the minimum time-domain partials [26,27]. The longest known Barker code is 13 bits, and its sequence is [1,1,1,1,1–1,-1,1,1,-1,1,-1,1] [28], and the sinusoidal pulse is used as the code element of the Barker code signal, which is used as the excitation current of the EMAT.