This study describes a method for designing miniaturised frequency selective rasorbers (FSRs) with a transmission band located between two adjacent absorption bands. The proposed FSR composes of a bandpass frequency selective surface at the bottom and an absorptive surface (APS) with lumped resistors and parallel LC resonators printed on the top. The absorptive surface is a 2.5‐dimensional geometry for the purpose of miniaturisation. The mounted parallel LC resonators mounted in the APS are utilised to implement the transmission characteristics of the proposed FSR while the constructed lumped resistors in the APS are used to realise the absorption performance. A prototype is fabricated and measured in an anechoic chamber under the guidance of a free‐space measurement system to verify this method. Experiments show that the proposed FSR has a transmission band at the centre frequency of 7.24 GHz and over the bands from 4.85 to 6.82 GHz and from 8.05 to 9.36 GHz, both reflection and transmission coefficients are less than −10 dB. The performances of the proposed FSR with different incident angles and polarisations are also investigated and results show that it is insensitive to electromagnetic wave polarisations and has a stable performance when the incident angles up to 45°.
In order to reduce the influence of multi-path effects on the measurement results of wideband antennas, this paper proposes a method for suppressing interference in wideband antenna measurements based on modal filtering technology. This paper introduces the theory and operation process of modal filtering, establishes the relationship between the distribution of modal coefficient terms and the location of the antenna and external interference sources, and clearly reveals the principle of filtering interference through modal filtering. It is pointed out that each location of interference sources corresponds to different pattern items. Filtering out the power of the pattern term generated by the interference source is equivalent to filtering out the interference caused by the interference source. The sources filtered by this technology are external sources that are spatially separated from the antenna, including external sources, environmental reflections, and device reflections, among others. This feature makes it possible to be used for testing in a non-absorbent environment. Its ability to operate at almost any frequency makes it ideal for suppressing interference effects in wideband antenna measurement. This paper demonstrates a recent advance wherein modal filtering techniques are used in interference suppression for wideband antenna non-absorbent measurement. In the full bandwidth range of the wideband antenna, we verify the method through numerical simulation analysis and practical measurement. In the numerical simulation, we obtain that 15 dB interference can be filtered out at the −25 dB level and 5 dB interference can be filtered out at the −35 dB level. In the experiments, within the broadband antenna bandwidth, we found that 2.5 dB can be filtered at the −10 dB level at 4 GHz, 3 dB is filtered at the −10 dB level at 6 GHz, and 5 dB is filtered at the −10 dB level at 7.5 GHz. All of the above results prove that the proposed method can effectively suppress the multi-path interference in wideband non-absorbent antenna measurement and improve the measurement results.
A new method for solving the excitation amplitude and phase of wide-band phased array antenna is presented, in which spherical wave expansion and mode filtering (SWEMF) techniques are applied for the first time. Different from the previous methods that are required of matrix inversion or optimization iteration, the proposed SWEMF method is a forward calculation process. Thus, the solution is unique, and the result is closer to the true value. On the other hand, the SWEMF method only needs the total radiated field data of the array antenna in a small angular domain to ensure that the operation is simple and efficient. The effectiveness of the SWEMF method is successfully verified by examples of low sidelobe planar and linear arrays. The mean square error of the excitation amplitude can reach −38.88 dB. The range of excitation amplitude error is 0.05 v, and the excitation phase error is within 5.2°. This method takes about 60 s to calculate amplitude and phase at any one time. The feed amplitude and phase can be only calculated with the data in a small angular domain, and when the amount of data is small.
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