MEASUREMENTS

Figure 7

Figure 7 AMC-backed dipole array antenna and Butler matrix layout (a), fabricated board (b) and measured return loss (c).

Figure 8

Figure 8 AMC-backed dipole array antenna measurement set-up (a) and simulated (b) and measured (c) far-field patterns.

Figure 8 shows the integrated antenna array far-field radiation patterns along with simulated and measured array patterns in a benign (normal) environment. There is good agreement in the number and shapes of the beams. Differences stem from losses and irregularities in the FR-4 substrate.

As shown in Figure 9a, a metal plane is placed in close proximity to the AMC backed dipole antenna array. Figure 9b shows four distinct beams similar to those in Figure 8c, which were measured in a benign environment. Measurements of a dipole array without the AMC (see Figure 9c), however, show a strong impact, compromising beam directionality. This pattern degradation is accompanied by an impedance mismatch (|S11| > -4 dB) over a broad bandwidth.

CONCLUSION

A new flat beamforming antenna element, employing a thin AMC-backing dipole and a new balun, has low susceptibility to harsh boundary conditions. Four of these elements are arrayed with a Butler matrix to produce four directional beams with little effect from the introduction of a closely located metal plane.

ACKNOWLEDGMENT

This work was supported by Incheon National University Research Grant 2015. Prof. Qun Wu’s collaborative advice on the work with equivalence to co-authorship is appreciated.

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Figure 9

Figure 9 Configuration for determining array sensitivity to a nearby metal plane (a) and patterns with four distinct beams (b) and an array without AMC (c).