Analysis of Beamforming Antenna for Practical Indoor Location-Tracking Application

Abstract

The single antenna used in conventional ultra-wideband radar has difficulty tracking targets over a wide range because of a relatively narrow beamwidth. Herein, we propose a beamforming antenna that can track targets over a wide range by electronically controlling the main beam of the antenna. The proposed beamforming antenna was fabricated by connecting a 1 × 4 linear array antenna and a 4 × 4 Butler matrix. The Butler matrix was fabricated in a laminated substrate using two TRF-45 substrates. Furthermore, the input Ports 1–4 generate a phase difference at regular intervals in each output port, and the output phase is fed to the array antenna. The proposed tapered-slot antenna was fabricated on a Taconic TLY substrate, and the impedance bandwidth of the antenna was achieved within a wide bandwidth of 4.32 GHz by satisfying a VSWR (Voltage Standing Wave Ratio) ≤2 within the 1.45–5.78 GHz band. Furthermore, the fabricated antenna has directional radiation patterns, which was found to be a suitable characsteristic for location tracking in a certain direction. Finally, the beamforming antenna has four beamforming angles, and to verify the performance for an indoor location tracking application of impulse-radio ultra-wideband radar, it was connected to an NVA-R661 module.

A Miniaturized Butler Matrix Based Switched Beamforming Antenna System in a Two-Layer Hybrid Stackup Substrate for 5G Applications

“…However, even though the block-level designs are well carried out, in this 28-GHz mm-Wave band, the overall system performances are very likely to be affected and degraded by interfacing and interconnecting the Butler matrix and antenna elements. From this point of view, some of the previous works were rather incomplete because they only presented Butler matrix miniaturization designs without realizing full integration with antenna array [8][9][10][11], or only connectorized interconnection [12]. In this work, we have carefully carried out intensive co-optimization of the total system including the Butler matrix, antenna elements, and the interfacing structures in between.…”

“…Thus, the switched beamforming antenna system is more preferred when precise and continuous beam steering function is not necessarily required, whereas implementation cost and producibility are of 2 of 11 more importance. Passive beamforming matrices such as Blass matrix [3], Nolen matrix [4], and Butler matrix [5][6][7][8][9][10][11][12][13][14] are generally adopted for the switched beamforming antenna system. Among them, the Butler matrix is more widely used due to its wideband characteristic and simple structure.…”

“…Many previous works have been reported focusing on the miniaturization of the Butler matrix. The previous techniques can be categorized into a single-layer substrate based design [5][6][7] and a multi-layer substrate based design [8][9][10][11][12][13][14]. For the single-layer substrate designs, several techniques, such as a higher characteristic impedance transmission line based design [5], a directional coupler employing lumped components [6], and an artificial transmission line employing quasi-lumped elements and discontinuities structure [7], were effective for the miniaturization.…”

“…The multi-layer substrate design approach can alleviate the spurious radiation issue more effectively because the Butler matrix and the antenna elements are placed in different layers. In addition, such previous multi-layer designs have employed further miniaturization techniques, such as the suspended stripline [8], dual transmission line structure in a multi-layer structure [9], forward-wave directional coupler [10], modularized multi-folded structure [11], slot-directional hybrid coupler [12], and dual-layer substrate integrated waveguide (SIW) based crossover elimination structure [13,14]. Yet, it should be noted that those miniaturization techniques inevitably lead to higher implementation cost and less producibility.…”

“…Yet, it should be noted that those miniaturization techniques inevitably lead to higher implementation cost and less producibility. It is also interesting to note, that those previous works [8][9][10][11][12][13][14] have utilized only the same-property homogenous substrates for the multiple layers.…”