Compact Switched-Beam Array Antenna with a Butler Matrix and a Folded Ground Structure

Abstract

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 2.16λo × 0.54λo × 0.07λo. 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 28-GHz Switched-Beam Antenna with Integrated Butler Matrix and Switch for 5G Applications

“…Meanwhile, in contrast to the reflective switches used in [ 21 , 24 ], the absorptive switch in this work as well as in [ 22 , 23 ] alleviate the possible impedance mismatch issue and thus improve the RF performances. The sidelobe level of this work is much better than [ 19 , 20 , 21 , 22 ] and comparable to [ 24 ]. However, it is found to be worse than [ 10 , 11 , 12 ] having no integrated switch.…”

“…Since this work is focused on the full integration of all the key building blocks such as the antenna elements, Butler matrix, switch, and metal enclosure, the previous works [ 19 , 20 , 21 , 22 , 23 , 24 ] that also have demonstrated the similar integration level are chosen for comparison. However, their operating frequencies are not 28 GHz, but 24 GHz [ 21 ], 60 GHz [ 22 , 23 , 24 ], and 1.9–2.4 GHz [ 19 , 20 ]. Many 28-GHz switched-beam antennas can be found in the literature [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ].…”

“…However, it is found to be worse than [ 10 , 11 , 12 ] having no integrated switch. This work only utilizes a single SP4T switch like [ 21 , 22 ], whereas others utilize multiple SPDT switches [ 19 , 20 , 23 , 24 ].…”

“…The very low normalized form factor of [ 23 ] is achieved by employing an expensive multi-layer low temperature co-fired ceramic (LTCC) process rather than the low-cost conventional PCB process. In addition, the very small normalized form factors of [ 19 , 20 ] are accounted for by relaxed design allowances that can be depended on in the non-mm-wave low-GHz frequency range.…”

“…For integrating a switch in a planar printed circuit board (PCB), interfaces and transitions between the switch and Butler matrix after chip-mounting on PCB must be carefully designed. From the switch-integration viewpoint, previous reports by Fang et al [ 19 ] and Kim et al [ 20 ] were interesting because they successfully demonstrated a complete integration of switch, Butler matrix, and antenna array, but only in 1–2 GHz non-mm-wave band. In contrast, fully integrated switched-beam antenna systems in mm-wave band are not found much in literature.…”