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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