The focusing ability of the lens antennas can significantly contribute to perform precise radio localization with low complexity in a massive antennas array (MAA) system. Thus, by combining lens antennas with an MAA, we propose an approach for radio source localization through an angle of arrival (AoA) estimation in a multipath propagation scenario. We discuss two simplified antenna selection techniques to select and process the focused subsets of antennas. Then, we implement a low-complexity time of arrival estimation scheme to detect the first arrival path (FAP) that contains the actual AoA information. Finally, the FAP signal is processed to estimate the AoA very efficiently, by applying one of the traditional subspace-based methods. To further simplify the system architecture with only slight degradation in performance, we also propose a mixed analog-digital AoA estimation structure based on the application of the sum-difference signal patterns technique. The simulated root mean squared error performance curves as a function of the signal-to-noise-ratio demonstrate that the proposed approach is capable of providing good AoA estimation results while considerably reducing the overall system complexity compared with the MAA system without the lens.

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This work proposes the direction finding antenna system in two axis (θ1, θ2) in X band using sum (Σ) and difference (Δ) patterns of received signal. Direction finding system is constructed by implementing the microstrip patch antenna array and 180° hybrid rat race ring coupler which generates Σ and Δ patterns of received RF signal. Initially, direction of arrival (DOA) is obtained in one axis, (θ1), vertical direction, using the Σ–Δ patterns of antenna array of two elements. Using the equations of Σ and Δ of two input signals, radiation patterns at different θ values have been observed in simulation and compared with measured pattern values of constructed circuit. By taking the ratio of Δ to Σ patterns, DOA has been estimated of designed circuit. Another circuit similar to first circuit, oriented at 90° (horizontal direction) has been implemented to estimate the DOA (θ2) in other axis. By taking the 3D radiation patterns of each circuit in anechoic chamber, both circuits are measured for performance; and from 0 to ±40°, DOA has been observed with rms error of less than 5° in both axis. At 10 GHz operating frequency, experimental results, using material RT Duroid 5880, show that satisfactory performance can be achieved with proposed setup. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2085–2092, 2015

In recent times, massive antenna array technology has captured significant attention among wireless communication researchers. This is a field with strong potential to increase rates of data transfer; mitigate interference and serve a large number of users simultaneously. To contribute further to this emerging technology, this paper presents an approach for the line-of-sight (LoS) based direction of arrival (DoA) estimation using the electromagnetic (EM) lens-focusing antenna concept. The EM lens focuses the received signal energy as a function of the angle of arrival (AoA) to a small subset/area of the antenna array. This is advantageous, as it helps to reduce both hardware implementation (RF chains) and the complexity of signal processing in the large number of antennas system. Furthermore, this focusing capability of the EM lens provides additional interference rejection gain which leads to estimate the DoA of user terminals precisely. Hence, in this work, subsets based antenna selection approach and subspace-based high resolution DoA estimation algorithms have been considered in combination with the EM lens assisted massive antenna system. In simulations where the DoA is estimated with the EM lens, the results are comparable with conventional methods of DoA estimation without an EM lens, despite the significantly reduced overall system complexity.

Abstract-This paper presents a performance analysis of a !"# ! hybrid rat race (HRR) coupler, widely used in radio frequency (RF)/wireless communication systems to couple the power in the desired way. The !"# ! HRR ring coupler consists of 4 ports, two for the input signals and two for the output signals. In this work, the couplers have been designed and simulated at central frequencies (! ! ) of 2.4 and 10 GHz using different types of substrates. Furthermore, the coupler has been analyzed in the context of direction finding, where we combine the designed !"# ! HRR coupler with a simple two antenna elements array and we have fabricated the circuit in order to validate the performance of the coupler by estimating the direction of arrival (DoA) using the difference (!) and sum (!) ports. The measured scattering parameters and DoAs are in good agreement to the simulated results. The experimental results show that the DoA can be estimated in the range 0 to ±50 degrees with errors less than ! ! .