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Orthogonal Circular Polarized Transmitter and Receiver Antennas for Mitigation of Mutual Coupling in Monostatic Radars

Shobha Sundar Ram, Akanksha Sneh

TL;DR

The paper tackles the mutual coupling challenge in through-wall monostatic radars by proposing orthogonal circular polarization using quadrifilar helix antennas (QHA). The authors design and compare QHA variants (printed and wire) to broadband Vivaldi and horn antennas, showing that orthogonal polarization can reduce direct Tx–Rx coupling while preserving first-bounce target reflections, with an emphasis on a resonant region near $3.4$ GHz and bandwidths exceeding $1$ GHz. Experimental measurements demonstrate an approximate $8~\mathrm{dB}$ reduction in mutual coupling at $3.4$ GHz for OP configurations, enabling higher transmit power ($+3~\mathrm{dBm}$) and improved target detection behind walls, validated through $S_{21}$ measurements and a trihedral target behind an $18$-inch wall. The work concludes that the QHA, owing to its compact size, high gain, wide bandwidth, and low axial ratio, is well-suited for practical, portable TWR systems, with polarization reversal on odd reflections aiding target visibility.

Abstract

Through-wall radar systems require compact, wideband and high gain antennas for detecting targets. Building walls introduce considerable attenuation on the radar signals. When the transmitted power is raised to compensate the through-wall attenuation, the direct coupling between the transmitter and receiver can saturate the receiver because of which weaker reflections off the target may remain undetected. In this paper, we propose using transmitter and receiver antennas of orthogonal circular polarization to reduce the direct coupling between the transmitter and receiver while retaining the first bounce off the target. In our paper, we demonstrate that the quadrafilar helical antenna (QHA) is a good candidate for this operation since it is characterized by a small size, wide frequency band of operation, high gain and low axial ratio over a wide field of view. We compare the reduced mutual coupling between the transmitter and receiver elements for the oppositely polarized QHA antennas with other commonly used through-wall radar antennas such as the Vivaldi and horn antennas. The system is tested in through-wall conditions.

Orthogonal Circular Polarized Transmitter and Receiver Antennas for Mitigation of Mutual Coupling in Monostatic Radars

TL;DR

The paper tackles the mutual coupling challenge in through-wall monostatic radars by proposing orthogonal circular polarization using quadrifilar helix antennas (QHA). The authors design and compare QHA variants (printed and wire) to broadband Vivaldi and horn antennas, showing that orthogonal polarization can reduce direct Tx–Rx coupling while preserving first-bounce target reflections, with an emphasis on a resonant region near GHz and bandwidths exceeding GHz. Experimental measurements demonstrate an approximate reduction in mutual coupling at GHz for OP configurations, enabling higher transmit power () and improved target detection behind walls, validated through measurements and a trihedral target behind an -inch wall. The work concludes that the QHA, owing to its compact size, high gain, wide bandwidth, and low axial ratio, is well-suited for practical, portable TWR systems, with polarization reversal on odd reflections aiding target visibility.

Abstract

Through-wall radar systems require compact, wideband and high gain antennas for detecting targets. Building walls introduce considerable attenuation on the radar signals. When the transmitted power is raised to compensate the through-wall attenuation, the direct coupling between the transmitter and receiver can saturate the receiver because of which weaker reflections off the target may remain undetected. In this paper, we propose using transmitter and receiver antennas of orthogonal circular polarization to reduce the direct coupling between the transmitter and receiver while retaining the first bounce off the target. In our paper, we demonstrate that the quadrafilar helical antenna (QHA) is a good candidate for this operation since it is characterized by a small size, wide frequency band of operation, high gain and low axial ratio over a wide field of view. We compare the reduced mutual coupling between the transmitter and receiver elements for the oppositely polarized QHA antennas with other commonly used through-wall radar antennas such as the Vivaldi and horn antennas. The system is tested in through-wall conditions.
Paper Structure (7 sections, 5 figures, 3 tables)

This paper contains 7 sections, 5 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Proposed Method for Mitigating Mutual Coupling
  3. Choice of antennas for through-wall radars
  4. Quadrifilar helix antenna
  5. Comparison of Antennas for TWR Purposes
  6. Experimental Results
  7. Conclusion

Figures (5)

  • Figure 1: Reduced mutual coupling due to orthogonal circular polarized antennas in through-wall radar
  • Figure 2: (a) Printed quadrafilar helical antenna (b) Wire wound quadrafilar helical antenna (c) Quadrature feed network
  • Figure 3: Commonly used through-wall radar antennas (a) Linear polarized Vivaldi (b) Linearly polarized antipodal Vivaldi (c) Linearly polarized broadband horn
  • Figure 4: Wideband monostatic radar using two orthogonal circular polarized quadrafilar helical antennas and a vector network analyzer (b) Trihedral corner reflector used as radar target
  • Figure 5: $S_{21}$ measurements with VNA when transmitter and receiver have (1) the same sense of polarization (SP) (2) opposite senses of polarization (OP)