# A 5G NR FR2 Beamforming System with Integrated Transceiver Module
## 2 A 28 GHz RF Beamforming System and Transceiver Module
### Development of 28 GHz RF Beamforming System  
According to antenna array theory, a linear array can achieve a minimized sidelobe level (SLL) by tuning the amplitude and phase of individual elements. The 28 GHz RF beamforming system employs a 1 \(\times\) 7 series-fed microstrip patch antenna capable of designing a phased-array antenna with low beam width using CMOS BFIC, although beamforming is only possible in the horizontal direction. Figure 2 shows the geometry of the 1 \(\times\) 7 series-fed microstrip patch antenna linear array. In the case of a series-fed patch antenna array, the amplitude is associated with the patch width, while the phase is linked to the element spacing. Consequently, achieving a low SLL involves the tapering of the patch width and introducing unequal spacing between elements. The series-fed microstrip patch antenna boasts advantages such as its compact size and enhanced directivity, making it well-suited for beamforming applications. The size of the series-fed microstrip antenna is determined using the Chebyshev weighting method and manufactured using a low-loss RF PCB substrate. The seven patch elements with the same length \(w\) are arranged symmetrically, and they are connected by a narrow microstrip line. Figure 3a shows simulated return loss results of the 1 \(\times\) 7 series-fed antenna. The return loss of the antenna obtained is over \(-\)10 dB at 28 GHz. Figure 3b shows the 2D E-plane radiation pattern of the antenna at 28 GHz center frequency. The antenna gain is 15 dBi and the 3 dB beam width is 15\({}^{\circ}\). The proposed block of the 28 GHz RF beamforming system is shown in Figure 4a. The beamforming system uses an RF low-loss PCB, and the cross-section of RF PCB with chip bonding is shown in Figure 4b. An \(8\times 7\) phased-array antenna is manufactured using a \(1\times 7\) series-fed microstrip patch antenna. The spacing of each antenna is 5 mm at 28 GHz. The planar-type phased-array antenna connects the RF and series-fed patch array antenna using a hole for signal feeding. Equations (1) and (2) show that the antenna gain and the EIRP are directly proportional to the number of elements in the array. The 28 GHz RF beamforming system incorporates an eight-channel fully differential beamforming IC. This implies that eight antennas can be connected simultaneously for either 8 Tx (transmit) or 8 Rx (receive) mode separately, as all eight channels can operate bidirectionally, resulting in a narrow beam, high EIRP, and improved SNR. This configuration allows for the versatile  
Figure 1: Block diagram of the proposed 28 GHz RF beamforming system and transceiver module. Figure 3: Simulated 1 \(\times\) 7 series-fed antenna results: (**a**) return loss, (**b**) E-plane radiation pattern. Figure 2: Layout of 1 \(\times\) 7 series-fed microstrip patch antenna. operation and efficient utilization of antenna resources for transmission and reception. The simplified block diagram of the eight-channel TRX beamforming IC is shown in Figure 5. The 28 GHz eight-channel CMOS beamforming chip was mounted on a PCB using Chip-on-Board (COB) technology. The microphotograph of the 28 GHz eight-channel fully differential CMOS BFIC is shown in Figure 6. Each channel of an eight-channel fully differential CMOS T/R IC consists of six-bit differential phase shifters, three-bit differential attenuators, differential two-stage bi-directional amplifiers (BDAs) with variable gain control, a differential two-way power divider/combiner, and an SPI. The tuning bits of 5.6\({}^{\circ}\), 1 dB are placed in the PS/ATT blocks to compensate for the phase and amplitude errors. A shift registers to control the phase shifter and attenuator including tuning bits, and the two-stage bi-directional amplifiers make phase and gain controls easy. In addition, the bias circuits including BGR and LDO are integrated to provide a stable DC bias.