Angle of arrival estimation using hybrid rat race coupler for X-band applications
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Angle of arrival estimation using hybrid rat race coupler for X-band applications Mohammed Ismail Mohammed1,a
, Tsehaye Redae Adhena2
1 Ethiopian Institute of Technology, Mekelle University, Mekelle, Ethiopia 2 Joint Military Staff College, Mekelle, Ethiopia
Received: 9 April 2020 / Accepted: 30 July 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The conventional approaches to estimate the angle of arrival (AOA) have the limitations of hardware complexity, and where algorithms are used to optimize the estimation, there is the associated computational cost. This work presents a simplified approach in which the sum and difference of the received signals using a hybrid rat race (HRR) coupler forms the basis for the estimation of AOA. A 2 × 1 array designed to operate at 10 GHz is fed with quarter wave transformer impedance matching technique and is integrated with HRR coupler. The integrated array is evaluated for AOA estimate in both the azimuth and elevation planes. The transmit antenna foot print of 0° to ± 90° is considered. Result of the study indicates that the designed HRR coupler works optimally, exhibiting minimal reflection loss at each port, reasonable isolation between ports and acceptable phase difference at the sum () and difference () ports. The array exhibits a resolution capacity of ± 55° in the azimuth plane and ± 48° in the elevation plane, with an RMS error of less than 5° in both the planes. Beyond the estimated AOA, the array exhibits very high values of RMS error. Typically, in the transmit antenna footprint of ± 80°, the RMS error is as high as 42.5°. An important observation from the study is that the RMS error is independent of the position of the radiators in space, geometry of the array elements, and mis-orientation in the planes of the array. For a specific transmit antenna footprint of + 15° in the azimuth plane, the gain is optimal compared to that in the elevation plane. The proposed design is easy to implement, without the complexity of scanning or phased array. In addition, the absence of algorithm of any type eliminates the computation cost issue that is common in estimators based on adaptive beam forming and smart antenna.
1 Introduction The energy associated with the main lobe of the impinging electromagnetic (EM) wave is non-uniformly distributed, with a maximum at the center, and gradually tapering toward the edges. For a receiving antenna, the gain essentially depends on how best the main lobe is configured in the direction of interest, and is a measure of AOA. The AOA facilitates that the antenna captures the signal over a wider portion of the main lobe. This helps to mitigate the effects of path loss and (inter-symbol-interference) ISI, and hence provide enhanced gain with reasonable SNR. The AOA estimation is used across a wide spectrum of civilian and military
a e-mail: [email protected] (corresponding author)
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Eur. Phys. J. Plus
(2020) 135:632
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