Аннотация
Realizing beam-steerable antennas to compensate for path losses at the mmWave band in a compact design is challenging. To address this, a series-fed antenna array integrated with a $4\times 4$ Butler matrix (BM) is presented. In contrast to standard planar implementations, the proposed design adopts a multilayer structure in which the BM is vertically embedded beneath the antenna array and interconnected via metallic vias, resulting in a 39.76% reduction in size. A controlled comparison against a conventional planar counterpart employing the same BM and radiating elements shows that this compactness is obtained as a quantified trade-off. The vertical integration reduces the total efficiency by approximately six percentage points, and the peak realized gain by 0.4 dB, while improving the sidelobe level by more than 2 dB owing to the intermediate ground planes that isolate the feed network from the radiating aperture. The proposed design achieves an impedance bandwidth spanning 27–30 GHz with a peak realized gain of 13.9–15.2 dBi and a beam-steering range of approximately 70°, with a beam-pointing error below 3.7° across all four ports. An isolation level of better than −20 dB between input ports is achieved in compact dimensions of $40.29 \times 56.48 \times 0.762$ mm3. The proposed design is fabricated and measured, showing good agreement with the simulated results. A potential application in autonomous aerial vehicles is also presented, together with a received-power analysis confirming that the antenna sustains a usable link to ground users across its full steering range. Owing to its compact size, high gain, and beam-steering capability, the proposed design is well-suited for 5G mmWave UAV-based IoT applications.