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Target Measurements Using Radar Networks
Published in Hai Deng, Zhe Geng, Radar Networks, 2020
Amplitude-comparison monopulse radar transmits a pulse at the predicted position of the target, and the target echo is received with two squinted beams that are separated in angle by a fraction of the beamwidth (Blair, 2010). It determines the target DOA relative to the antenna boresight with the in-phase part of the monopulse ratio, which is obtained by dividing the difference of the two offset received signals by their sum. If DOA estimation in both azimuth and elevation is desired, four squinted beams are used to receive the target echo, and two monopulse ratios are formed. It is also worth mentioning that when two targets are closely spaced with respect to the resolution of the amplitude-comparison monopulse, the measurements from them can merge into one single measurement and lead to significantly declined DOA estimation performance. To address the problem of unresolved targets, several approaches have been proposed in literatures (Blair & Brandt-Pearce, 2001; Wang et al., 2004; Zhang et al., 2005).
Theories of Synthetic Aperture Radar
Published in Maged Marghany, Automatic Detection Algorithms of Oil Spill in Radar Images, 2019
where eα is the antenna’s aperture efficiency(eα=AeAphysical), in this sense, Equation 6.5 shows that the antennas with large effective apertures are high gain antennas with small angular beam widths. In other words, the receiving antennas, are furthermost precise to radio waves approaching from one direction and are considerably less precise to ones propagating from other directions. Since transmitting antennas, furthermost of their radiation is emitted in a fine beam in one direction, and tiny in other directions. Even though these terms can be depleted as a function of direction, when no direction is identified, the gain and aperture are assumed to denote the antenna’s axis of maximum gain or the antenna boresight. In this context, the antenna boresight is the alignment of equilibrium of the parabolic dish, and the antenna beam pattern, i.e., the main lobe, which is symmetrical approximately of the boresight axis. In this regard, the majority of antennas boresight axis is permanent by their form and cannot be reformed (Fig. 6.3) [83–85].
Background Material
Published in Wen-Qin Wang, Multi-Antenna Synthetic Aperture Radar, 2017
The presence of range and azimuth (or Doppler) ambiguities in SAR imaging is an important problem. When the PRF is set too high, the radar return from two successive pulses will overlap at the receiver and there will be range ambiguities. This type of ambiguity is referred to as range ambiguity. When the PRF is set too low, on the other hand, there will be returns from the targets that have the same Doppler history as the signal due to aliasing. These targets appear as if illuminated by a portion of the physical antenna beam away form the antenna boresight in azimuth. These returns are referred to as azimuth ambiguities.
A high-gain filtering DRA array for millimeter wave communication
Published in Electromagnetics, 2022
Lanlan Jiang, Wei Luo, Zihao Wang, Yi Ren
Figure 16 shows the simulated and measured E-plane and H-plane radiation patterns of the proposed DRA at 26.94 GHz and 27.85 GHz respectively. The stable measured radiation patterns are similar to the simulated results. And the measured cross polarization discrimination (XPD) is better than 20 dB in the antenna boresight direction. Since the spacing of elements between the Y direction is slightly larger than that in the X direction, side lobes are generated in the E-plane pattern. Table 4 lists several important parameter comparisons between the proposed filtering DRA and the reported filtering DRA (Hu et al. 2018; Liu et al. 2020; Tong et al. 2019; Wang et al. 2021). It shows that the proposed DRA array takes advantage of higher gain and better out-of-band suppression.
A low profile miniature RFID tag antenna dedicated to IoT applications
Published in Electromagnetics, 2019
Bilal Aslam, Muhammad Kashif, Muhammad Awais Azam, Yasar Amin, Jonathan Loo, Hannu Tenhunen
Figure 6 shows the performance of the proposed tag antenna on metal sheets of various sizes. The thickness of the sheet in each case is pinned at 5mm for consistent analysis. According to Figure 6a, a shift in the centre frequency is observed for sheets larger than the size of the tag antenna. However, the maximum centre frequency variation is within 1% and the bandwidth improves slightly of their respective values in the free space. Figure 6b illustrates the tag antenna boresight gain as a function of the size of the metallic platforms. A marked improvement in antenna gain (3 to 4 times of that in free space) is observed when the mounting metallic sheet is larger than the tag antenna. The phenomenon behind this is very simple. The metallic sheets actually become a part of the antenna structure and act as a ground plane. Therefore, the gain improvement can be attributed to the increase in the size of the effective ground plane.
Shaped beam horn antenna for enhanced gain at edge of global coverage
Published in International Journal of Electronics Letters, 2019
Ramesh Chandra Gupta, Milind Bhagwan Rao Mahajan, Rajeev Jyoti
The Gain and XPD contour are plotted for satellite location 75°E and antenna boresight at 75°E and 0°N. Figure 6 shows EoC Gain contour of the shaped beam global horn antenna at frequency 10.7 GHz and 11.2 GHz for Linear Horizontal polarisation. It can be seen that minimum EoC Gain is 18.3 dB for both frequencies for global coverage. The maximum gain contour at 10.7 GHz is at the centre of the beam, while the maximum gain contour at higher frequency 11.2 GHz is away from the centre. This is due to dispersive nature of the higher order modes. The maximum and minimum gain within global coverage at different frequencies are computed and listed in Table 3.