Experimental verification: As is well known, vertically polarized waves need to be received by antennas with vertical polarisation characteristics, while horizontally polarized waves need to be received by antennas with horizontal polarisation characteristics. When the polarisation direction of the incident wave is inconsistent with that of the receiving antenna, the received signal energy will decrease, which means polarisation loss will occur. When the polarisation direction of the receiving antenna is completely orthogonal to the polarisation direction of the incident wave, for example, if a horizontally polarized antenna is used to receive a vertically polarized incident wave, the antenna will not receive the energy of the incident wave at all. In this case, the polarisation loss is the maximum, which is called complete polarisation isolation [16]. This section conducts experiments based on the principle of polarisation mismatch.
Considering the issue of excessive computational complexity and long simulation time when simulating array antennas, we used the horn antenna as the ultra-wideband antenna for simulation. The simulation diagram and simulation results are shown in Figure 5. Over the entire operating frequency range, when PRS is placed between two horn antennas, the coupling between the antennas decreases by an average of 20dB. From the simulation results, it has been proven that the use of polarisation mismatch principle for antenna decoupling is effective, and it has also demonstrated the decoupling ability of the PRS designed in this paper in ultra-wideband.
The processed sample is shown in Figure 6 (b), with a length and width of 400mm and a thickness of 6mm. The medium is the F4BM-2 sheet with a relative dielectric constant of 2.2. This experiment was conducted using the free space method. The experimental scene is shown in Figure 6 (a). The polarisation rotating surface is placed between coplanar array antennas spaced 1m apart. Since a single pair of array antennas cannot cover the entire frequency band, the experiment is divided into two frequency bands: 6GHz ~ 12GHz and 12GHz ~ 18GH. For the same reason, the experimental results are also divided into two parts. Figure 7 is a schematic diagram of the coupling comparison between array antennas before and after simulated PRS. In the entire frequency band from 6GHz to 18GHz, PRS can reduce the coupling of the array antenna by an average of 20dB. Since the antennas used in the simulation are different from those used in the experiment, the result curves are also inconsistent. However, from the perspective of decoupling capability and decoupling bandwidth, it is very consistent with the simulation results, which effectively proves the decoupling capability of PRS between ultra-wideband antennas.
Conclusion: Based on the principle of polarisation mismatch, a PRS with polarisation conversion rate higher than 99% was designed and manufactured from the perspective of polarisation. Moreover, the dual-size combined ring is cleverly used to extend the operating bandwidth to an ultra-wide frequency band of 4.8GHz~18.2GHz. In this paper, the PRS is applied between the ultra-wideband horn antenna and the array antenna. The simulation and experimental results consistently prove its superior performance in decoupling capability and operating bandwidth. In short, this PRS provides a new perspective and method on how to decouple ultra-wideband antennas.
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