A wide-coverage unmanned aerial vehicle (UAV) antenna system for air-to-ground communications is proposed in this paper. The proposed antenna system has reconfigurable beam patterns based on five sets of dual-polarization and high gain antennas. Each antenna set is configured by a dual-polarization crossed inverted-V radiator and switched feed network to drive switched beamforming operations. Depending on the switch modes of the proposed antenna, main beam direction and circular polarization types can be independently selected. Further, each antenna set is faced toward the ground level at different angles from the center of UAV to provide wide beam coverage. To verify the antenna performance, each antenna set is designed at the center frequency of 5.7 GHz and total five sets are integrated with a switched feed network and a microcontroller. To implement the wide angle switched beamforming with 2-D angle-shifted main beams, a 3-D printed conformal fixture is used to connect both the antenna module and a drone body. The maximum measured bandwidth was more than 22% and the measured peak gain with the de-embedded switch feed network loss was about 10.2 dBic.

This article presents a switched beamforming antenna array with reconfigurable quad-polarization and switched feed network. The proposed beamforming architecture is configured by a crossed inverted-V antenna array and a dual Butler matrix-based feed network to drive polarization diversity as well as beam steering. The crossed inverted-V array adopts a planar director to enhance antenna gain, while the outputs of the dual Butler matrix network are connected to each pair of the gain-enhanced inverted-V antenna elements. Furthermore, the dual Butler matrix is integrated with a polarization mode selection switch matrix. Based on the switching operations with the dual Butler matrix, both the beamforming and switchable polarizations among vertical, horizontal, right-hand circular, and left-hand circular polarizations (CPs) can be achieved. To verify the switched beam and quad-polarization performance, the proposed architecture with a $1\times $ 4 array configuration was implemented at 5.8 GHz. The measured 1 $\times $ 4 antenna gain excluding the dual Butler matrix showed the average gain of 12.8 dBi(c) for all polarizations. Furthermore, the switched main beams driven by the dual Butler network and the polarization mode selection matrix showed four different angles in a $1\times $ 4 array.

Electrically conformal antenna arrays (ECAA) for 2-dimensional (2-D) beamforming configured by wide beamwidth multipole radiation elements are proposed. Unlike the conventional conformal antenna array with physically curved shape, the proposed arrays are planar structures with wide-angle beam steering. The wide range of beam steering with a low gain variation allows the planar array structure to achieve the electrically conformal phased array patterns. In order to verify the ECAA concept, two different types of ECAA in a 1x8 configuration using planar multipole antenna elements were fabricated at 5.8 GHz and compared to the conventional patch array. Each multipole element had half-power-beamwidth (HPBW) wider than 110° at both E- and H-planes with the maximum HPBW of 175°. The first type of ECAA showed a measured peak gain of 10.8 dBi with a measured half power steering angle of 155° while maintaining a side lobe level (SLL) less than -10 dB. Further, the second ECAA showed a measured peak gain of 12.8 dBi with a measured half power steering angle of 144° while keeping the SLL less than -10 dB. These scan angles of the first and second types were extended about 66.7% and 54.8%, respectively from the conventional patch array with the same size. Lastly, two types of 8x8 array modules for 2-D beam steering were verified at 5.8 GHz and the first type showed a maximum peak gain of 21.0 dBi. Further, the 2-D half power steering angles in E- and H-planes of the second type were about 145° and 137°, respectively.

A high gain stacked antenna based on a planar magneto-electric dipole structure is proposed. The main radiator is configured by a probe-fed patch with a symmetrically arranged pair of dipole radiation elements. Further, an additional air-gapped radiator with multiple patch elements is integrated for gain enhancement. Since both the main and stacked radiators are planar structures, the overall volume can remain low-profile regardless of the airgap. To verify the performance of the proposed structure, a single magneto-electric dipole antenna and three different types of stacked radiators were implemented at 5.8 GHz. The magneto-electric dipole antenna showed measured 10-dB impedance bandwidth and gain of 5.2% and 8.0 dBi, respectively with the overall size of 0.96 λ0 x 0.96 λ0 including a ground plane. With the additional stacked radiator having the airgap of 0.1 λ0, the maximum measured gain was increased to 9.6 dBi. Further, to verify the beamforming performances, three types of 1x8 phased array stacked structures were fabricated with a volume of 0.96 λ0 x 6.38 λ0 x 0.14 λ0 at 5.8 GHz. The measurements showed a maximum peak gain of 18.1 dBi and a half-power-beamwidth scan angle of 49˚ with a side-lobe level less than -8 dB.

A compact switched-beam array antenna, based on a switched Butler matrix with four folded ground antennas, is presented for unmanned aerial vehicle (UAV) applications. The folded ground structure, including a slotted patch radiator surrounded by multiple air-gapped ground layers, is adopted to maximize compactness. The extra ground layers provide extra capacitive coupling around the patch antenna, resulting in a down-shift of resonant frequency and a reduction in the antenna size. Also, to optimize aerial operation with a wider beam coverage, the 1 × 4 array is integrated with a switched Butler matrix controlled by a microcontroller unit (MCU). The choice of the Butler matrix reduces the complexity of beamforming circuitry and avoids the use of high-cost phase shifters requiring extra control-bit signals. Further, the array antenna is optimized for high isolation among the antenna ports and a minimal UAV body effect. Then, the proposed structure was verified at 1.96 GHz for test purposes only, and the array size, excluding the antenna case, was 2.16λ_o × 0.54λ_o × 0.07λ_o. The measured 10 dB impedance bandwidth for all antenna elements in the array was always better than 3.4%, and the isolation among the antenna ports was also better than 19 dB. The measured peak gain, excluding the loss of the switched Butler module, was about 9.98 dBi, on average. Lastly, the measured peak scan angles were observed at −39°, −17°, 9° and 31° according to switching modes.

A new design approach for a mmWave high gain planar antenna is presented. The proposed method can increase antenna directivity with a minimally enlarged radiation patch while the operation frequency is still matched at a higher target frequency. The fundamental structure of the proposed antenna is configured by a H-shaped and slot-loaded patch with a shorting pin symmetrically located across a signal excitation port. Further, to match the operation frequency with the frequency for the highest achievable gain, a vertically stacked matching conductor was inserted along the signal feed path between the radiation patch and the ground layer. The proposed single antenna showed the simulated directivity of 9.46 dBi while the conventional patch with a same dielectric had 8.07 dBi. To verify practical performance, a 2 × 2 array antenna was fabricated at 28 GHz and showed the measured gain of 12.5 dBi including the array feed loss.