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Satellites
Published in Mohammad Razani, Commercial Space Technologies and Applications, 2018
Most satellite systems employ opposite polarization states to make most efficient use of the frequencies that are available for transmission and reception. This means that two signals may share the same frequency within a satellite system, so long as they employ opposite polarization states (e.g., horizontal linear polarization and vertical linear polarization). Theoretically, each signal can be received without interference from the co-frequency signal on the opposite polarization. However, being practical devices, the Earth station and satellite antennas and their feeds are not able to perfectly separate the two polarization states, which results in a small proportion of the unwanted “cross-polar” signal being transmitted or received along with the wanted signal, causing cross-polarization interference. Since the polarization performance of the satellite antennas is fixed, cross-polarization interference is maintained at an acceptable level by ensuring that the Earth station antenna has adequate cross-polar performance (“cross-polar discrimination, XPD”). If the XPD level of an uplink antenna is less than 30 dB, antenna transmits both vertical and horizontal polarizations. Polarization discrimination between co-polar and cross-polar signals is important in a dual polarization frequency reuse satellite communication system. Figure 3.64 illustrates polarization discrimination in an antenna radiation pattern.
Satellite Link Design
Published in Jerry D. Gibson, The Communications Handbook, 2018
Peter P. Nuspl*, Jahangir A. Tehranil*
Cochannel interference arises from reuse of frequency bands by spatial or polarization isolations of the signals; CCI is regarded as being under the designer's control. The carriers in the cochannel transponders can operate at the same frequency; however, they are assigned to the transponders that operate with beams that are spatially isolated. In cross polarization, the signals have opposite polarization. The amount of cochannel interference depends on the modulation characteristics of the carriers, the relative levels and frequency separations between the carriers, and the isolations among the beams. Assuming equal powers in the beams, the beam isolations contribution for the uplink and downlink can be calculated as follows:
Electromagnetic Waves
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
J. H. Causebrook, R. V. Goodman
The use of orthogonal polarization in communications systems is an important technique by which economy of frequency spectrum usage can be improved by reducing mutual interference between systems sharing the same, or adjacent, frequency channels. This technique relies on the Cross-Polarization Discrimination (XPD) achieved by the careful design and alignment of the transmitting and receiving antennas involved.
DNG Metamaterial-Based Superstrate for Performance Enhancement of Compact Size Wideband Patch Antenna
Published in IETE Technical Review, 2023
Ananda Babu Devarapalli, Tamasi Moyra, Partha Kumar Deb
The radiation pattern of the designed antenna in the E and H-planes with and without the metamaterial superstrate layer is described in this section. The radiation pattern graphically represents space energy dispersion as a function of direction. Figure 13(a,b) shows the radiation patterns that have been simulated and measured at the resonant frequency of the designed antenna with and without a superstrate layer. In the E-plane, the radiation pattern produced by antenna is directional, while in the H-plane, it is almost omnidirectional. Cross polarization describes the radiation from the antenna in an undesired direction. Simulated and measured co and cross-polarizations with and without MTM superstrate in the E-plane and H-planes for the resonant frequency are shown in Figure 14(a,b). In the far-field measurement, the differences between the measured and simulated results should be caused by losses in the cable and adapter losses in the dielectric, and manufacturing tolerances. The performance of the designed DNG metamaterial-based antenna is compared in Table 4 with that of various recently published high-performance antennas. This analysis indicates that the proposed low-profile design has greatly improved gain, bandwidth, and efficiency. Based on the data in Table 4, it is clear that the suggested antenna has a simple structure, compact size and low cost than the previously stated ones.
Compact PIFA Antenna with High Gain and Low SAR Using AMC for WLAN/C-band/5G Applications
Published in IETE Journal of Research, 2021
Akhilesh Verma, Ravi Kumar Arya, Rajarshi Bhattacharya, Srinivasa Nallanthighal Raghava
To verify the simulated radiation patterns, we made the anechoic chamber measurements. The simulated and measured radiation patterns of the proposed AMC based PIFA antenna at 5, 5.5, and 6 GHz in for different phi-cuts are shown in Figure 7. The simulated and measured results are in good agreement. The co-polarization gain is shown by red color while the cross-polarization gain is shown by a black color lines. We note that the cross-polarization levels are high and are not desirable as it is the indication that the part of the power is getting wasted in unwanted polarization i.e. cross-polarization. In order to reduce the cross-polarization level, without changing the radiation antenna structure, upcoming publication [27] can be helpful for the readers where rectangular metasurface superstate is employed to reduce cross-polarization. Another novel and innovative way of reducing cross-polarization is by enhancing the AMC design and this technique is discussed in section 4.7.
A High Gain Ku Band Antenna with Circular Polarization Using Hybrid Choke Ring Structure
Published in IETE Journal of Research, 2021
Akhila John Davuluri, Siddaiah Polepalli
Figure 12 presents the simulated radiation patterns of Gain in E-plane and H-plane which represents the Co-pol and Cross-pol plots. Cross polarization refers to the polarization that is orthogonal to the desired polarization.