Reflection Suppression through Modal Filtering for Wideband Antenna Measurement in a Non-Absorbent Environment

Abstract

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.