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Radar Waveforms
Published in Hai Deng, Zhe Geng, Radar Networks, 2020
It could be seen that for large time-bandwidth product, i.e. BT ≫ 4, the first null of |χ(τ, 0)| occurs at τ = 1/B. And the pulse compression ratio is defined as T/(1/B) = BT. Therefore, we could conclude that adding linear frequency modulation improves the range resolution of the signal by a factor equal to BT. However, the sidelobes are still strong. Two basic approaches to sidelobe suppression are amplitude weighting and frequency weighting, i.e. nonlinear frequency modulation (Levanon & Mozeson, 2004). Assume that the pulse width of a down-chirp LFM pulse is 1 s and the bandwidth is 10 Hz. The AF of the LFM pulse with duration and zero-Doppler/zero-delay cuts are plotted in Figure 3.3. It could be seen that the mainlobe of the zero-Doppler cut of the AF shown in Figure 3.3c is much narrower than the one shown in Figure 3.1c, which proves that the LFM pulse provides finer range resolution compared to unmodulated pulse.
S
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
Si/SiGe/SiGeC silicon-based alloy system providing band offsets that enable heterostructures that can be utilized for heterojunction transistor design and quantum confinement. sideband the signal produced when a carrier signal is modulated. They may be one single sideband, one set of upper and lower sidebands, or a series of sidebands whose number is dependent on the modulation index of the modulation system being used. sidelobe a lobe in an antenna radiation pattern apart from the main lobe and any grating lobes. Sidelobes have peak amplitudes less than that of the main lobe. side lobe level the ratio of a local maximum in a radiation pattern to the global maximum (main beam) of the radiation pattern. sidelobe level (SLL) the peak amplitude of a sidelobe relative to the peak amplitude of the main lobe. The SLL is usually expressed as the number of decibels below the main lobe peak. Siemens, Ernst Werner von (1816-1892) Born: Lenthe, Hanover, Germany Best known for the German and British companies that bear his name. Siemens was a strong believer in basic research, as well as an avid inventor. His early inventions included an improved gutta-percha wrapped telegraph cable that allowed his companies to secure a number of lucrative cable contracts. His discovery of the dynamo principle, and his use of this in heavycurrent applications, allowed his companies to
From launch to transmission: satellite communication theory and SNG
Published in Jonathan Higgins, Satellite Newsgathering, 2012
This means not interfering with adjacent satellites to the intended one, and therefore the radiation pattern from the antenna has to be accurately defined. Due to the relative difference between the wavelength of satellite frequencies and the typical range of antenna sizes, no parabolic antenna can be manufactured to produce a completely perfect radiation pattern, which would be a single focused beam, but always has a main ‘lobe’ (centered on the boresight) and a number of ‘sidelobes’ radiating out from the antenna, as shown in Figure 2.40. The sidelobes can potentially interfere with adjacent signals on the satellite, and one of the aims of good antenna design is to seek to minimize the sidelobes while maximizing the main lobe. Typically, up to 70% of the signal energy will be on boresight – this is a measure of the efficiency of the antenna. Too much energy in the sidelobes will reduce energy in the main lobe signal and will interfere with signals on adjacent satellites. Hence, the requirement to meet a performance target based on 2° satellite spacing.
A compact RHCP and LHCP truncated corner patch series-fed array antenna
Published in International Journal of Electronics Letters, 2023
H. Zakeri, M. Parvaneh, G. Moradi
A conventional method for achieving circular polarisation is truncating the patch corners (Bouca et al., 2020; A. Chen et al., 2011; Falade et al., 2020; Khan et al., 2014). The features such as simple design, low radiation losses, and beam steering capability in the feeding network are the most important advantages (A. Chen et al., 2011). A single patch dual-CP antenna element is reported in -band satellite communication (Khan et al., 2014). Using disparate patch elements and the isolation between the two ports is another solution to have LHCP and RHCP (?). By this technique, the antenna can produce a dual-band orthogonal circular polarisation. However, realising LHCP and RHCP by using disparate patch elements and the isolation between the two ports is enhanced by this method. Furthermore, a symmetrical series-fed truncated patches antenna is used to reduce sidelobe level (SLL) and clutters (Im et al., 2010).
A novel wideband reflectarray using sub-wavelength Archimedes spiral unit cell
Published in Electromagnetics, 2022
Zhiyuan Yang, Jie Zhang, Yufeng Liu, Wenmei Zhang, Qiang Zhang, Yang Gao, Zongwei Tong
Figure 13 shows the measured and simulated normalized radiation patterns of the designed reflectarray antenna in the E- and H-plane at 5.8 GHz. As shown in the figure, good agreement has been observed between measurement and simulation in E-plane. However, the measured main lobe of the H-plane is somewhat wider than the simulated one, which is mainly caused by the influence of the supporting brackets. The measured E- and H-plane sidelobe levels are less than −15 dB and −19 dB, respectively. It can be also seen that the cross-polarization levels are less than −29 dB and −25 dB, respectively. The low cross-polarization is mainly due to the mirror-symmetric arrangement of elements and the cross-polarization components along the horizontal and vertical directions can cancel each other.
Underlying topography and forest height estimation from SAR tomography based on a nonparametric spectrum estimation method with low sidelobes
Published in International Journal of Digital Earth, 2022
Youjun Wang, Xing Peng, Qinghua Xie, Xinwu Li, Xiaomin Luo, Yanan Du, Bing Zhang
In addition, we also calculated the normalized sidelobe levels of the five methods for SNR levels ranging from −5 dB to 20 dB (as shown in Figure 5). The normalized sidelobe level is represented as the normalized area between the backscattering power curve and the x-axis on the non-main lobe interval. As can be seen in Figure 5, the sidelobe level of the G-Pisarenko method is less than half that of the other methods when the noise is strong (i.e. SNR = −5 dB). With the increase of the SNR, the G-Pisarenko method maintains the obvious advantage of the low sidelobe level, and no sidelobes are apparent at the range of [15, 20] dB. The above analysis demonstrates that the G-Pisarenko method greatly reduces the sidelobe effect in TomoSAR.