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. 2020 Sep 19;11(9):871.
doi: 10.3390/mi11090871.

Full-Azimuth Beam Steering MIMO Antenna Arranged in a Daisy Chain Array Structure

Kazuhiro Honda  1 , Taiki Fukushima  2 , Koichi Ogawa  1
Affiliations

Full-Azimuth Beam Steering MIMO Antenna Arranged in a Daisy Chain Array Structure

Kazuhiro Honda et al. Micromachines (Basel). .

Abstract

This paper presents a multiple-input, multiple-output (MIMO) antenna system with the ability to perform full-azimuth beam steering, and with the aim of realizing greater than 20 Gbps vehicular communications. The MIMO antenna described in this paper comprises 64 elements arranged in a daisy chain array structure, where 32 subarrays are formed by pairing elements in each subarray; the antenna yields 32 independent subchannels for MIMO transmission, and covers all communication targets regardless of their position relative to the array. Analytical results reveal that the proposed antenna system can provide a channel capacity of more than 200 bits/s/Hz at a signal-to-noise power ratio (SNR) of 30 dB over the whole azimuth, which is equivalent to 20 Gbps for a bandwidth of 100 MHz. This remarkably high channel capacity is shown to be due to two significant factors; the improved directivity created by the optimum in-phase excitation and the low correlation between the subarrays due to the orthogonal alignment of the array with respect to the incident waves. Over-the-air (OTA) experiments confirm the increase in channel capacity; the proposed antenna can maintain a constant transmission rate over all azimuth angles.

Keywords: Monte Carlo simulation; beam steering array; connected car; daisy chain multiple-input multiple-output (MIMO) antenna; large-scale MIMO; over-the-air (OTA) testing.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Conceptual illustration of a massive MIMO system.
Figure 2
Figure 2
A big challenge toward 100 Gbps channel capacity. (A) A family of daisy chain MIMO antennas. (B) History of the development.
Figure 3
Figure 3
Beam steering MIMO antenna arranged in a daisy chain array structure. (a) The whole structure of a 32 × 32 MIMO system. (b) 4 × 4 MIMO system.
Figure 4
Figure 4
Combinations of the subarrays. (a) Combination1. (b) Combination2. (c) Combination3. (d) Combination4.
Figure 5
Figure 5
Beam forming network for full-azimuth steering.
Figure 6
Figure 6
Channel model used for performing the Monte Carlo simulation. (a) Cluster channel model of M × N MIMO. (b) Coordinates of the k-th scatterer.
Figure 7
Figure 7
Incident wave model for the Monte Carlo simulation. (a) Gaussian incident wave in azimuth. (b) Two polarization components.
Figure 8
Figure 8
Principle of the cardioid radiation pattern created by two isotropic point sources. (a) Configuration of the array. (b) Cardioid radiation pattern.
Figure 9
Figure 9
Radiation gain of each element.
Figure 10
Figure 10
Radiation pattern of Subarray2 when the 4 × 4 MIMO antenna is used. (a) ϕ = 0 deg (Combination1). (b) ϕ = 45 deg (Combination2). (c) ϕ = 90 deg (Combination3). (d) ϕ = 135 deg (Combination4).
Figure 11
Figure 11
Radiation patterns of Subarray2 and Subarray18 when the 32 × 32 MIMO antenna is used. (a) Subarray2. (b) Subarray18.
Figure 12
Figure 12
Channel capacity as a function of the radius of the array.
Figure 13
Figure 13
Channel gain as a function of the number of each subarray.
Figure 14
Figure 14
Channel capacity as a function of the angle of the incident wave.
Figure 15
Figure 15
Channel capacity vs. the angular power spread.
Figure 16
Figure 16
Channel gain and correlation characteristics of each subarray. (a) Channel gain. (b) Correlation.
Figure 17
Figure 17
CDF characteristics of eigenvalues. (a) σ = 60°. (b) σ = 10°.
Figure 18
Figure 18
Radiation pattern measurement setup of a 4 × 4 MIMO array in an anechoic chamber. (a) Fabricated microwave circuit. (b) Prototype of a 4 × 4 MIMO array.
Figure 19
Figure 19
Measured impedance of Subarray2.
Figure 20
Figure 20
Measured and calculated results of radiation patterns. (a) Subarray1. (b) Subarray2.
Figure 21
Figure 21
OTA testing of a 32 × 32 daisy chain MIMO antenna. (a) Two-dimensional fading emulator. (b) External view.
Figure 22
Figure 22
Channel capacity of a 4 × 4 MIMO array antenna measured by OTA testing.
Figure 23
Figure 23
Channel capacity of a 32 × 32 MIMO array antenna measured by OTA testing.
Figure 24
Figure 24
Channel gain and correlation of a 32 × 32 MIMO array measured by OTA testing. (a) Channel gain. (b) Correlation.
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