# Radiator Enablers for Wireless Communication Evolution
## 3 Radiators' Novel Technologies, Design, and Implementation Issues
### Advanced Antenna Designs in the mmWave Frequencies
#### 3.5.4 Example Designs of mmWave and FR2 Antennas
For fixed installations such as 5G BSs, where directional broadcasting is necessary, an antenna similar to the traditional Yagi-Uda antenna can be designed. The proposed construction (ref. [104]) has dimensions of 12 mm \(\times\) 72.72 mm and is assembled of rhombus-shaped printed patches. The distinguishing feature is that it is flexible and thus changes the angle of the beam. The maximum gain (12 dBi) is at 32 degrees from the broadside. An antenna model for compact 5G applications with highly acceptable matching (S11 = \(-\)22.5 dB) is proposed in [105]. It is recommended for devices with very limited space; indicatively, the dimensions are (6.2 \(\times\) 8.4 \(\times\) 1.57) mm. The antenna operating frequency is at 28 GHz, with a satisfactory bandwidth of 5.57 GHz. Another solution for small antenna construction, such as the sensors in 5G and specifically in 28 GHz, is presented in ref. [106]. The array, assembled of two such single antennas, intended for MIMO, exhibits overall dimensions of (30 \(\times\) 15 \(\times\) 0.203) mm. The antenna achieves a large bandwidth (6.4 GHz) with minimum isolation at 35 dB and gain at 5.42 dBi. A low-cost antenna is presented in ref. [107]. It is characterized as mmWave aperture-coupled antenna with operating frequencies of 24-44 GHz. The simple construction supports dual polarization. It exhibits a satisfactory bandwidth (60%) and high gain (7 dBi). New mobile phone antenna designs that support mmWaves communications, are studied in ref. [108]. The antenna works at 24 to 40 GHz and is very thin (0.76 mm). When the structure becomes so thin, it is difficult to match; thus, a special structure is proposed to address the issue. Another antenna for mobile phones at the frequency of 28 GHz is proposed in ref. [109]. The authors chose a special name, \"Quasi-Yagi\", and constructed the radiator as a parameterized folded dipole. The antenna is fabricated on a multilayer PCB and utilizes vias for layer connection to make the antenna smaller (the dimensions of the antenna are 5 \(\times\) 5 \(\times\) 0.75 mm). The element operates at 26.3 to 29.75 GHz, with a gain of approximately 5.52 dBi. One more solution for smartphones in mmWaves (5G and 6G) is provided in ref. [110]. It is a differential-fed patch antenna with dual-polarization capability with (4.5 \(\times\) 4.5 \(\times\) 1) mm dimensions. It is also inexpensive since it utilizes a single dielectric substrate. For various mmWave applications that require operation over a very wide frequency range, a patch antenna was constructed in a \"cornetto\" shape, ref. [111]. Its dimensions are (51.6 \(\times\) 40.4 \(\times\) 0.8) mm, and it requires CPW feeding. The construction is slightly bulkier, but it operates over a quite wide range from 2 to 60 GHz. For beam reconfiguration, an antenna is proposed in ref. [112]. The overall antenna is \"integrated with linear tapered slot radiators\", and with the help of SPDT switches and p-i-n diodes, the beam is electronically steered (from \(-\)45\({}^{\circ}\) to \(+\)45\({}^{\circ}\)). The dimensions of the construction are W = 11.9 mm and L = 14.7 mm, and it is built on a CuClad 217 substrate. A transparent antenna is proposed in ref. [113]. More specifically, an initial antenna design utilizing Cu and Roger RT/duroid 5880 substrate is repeated on AgHT8 and PET substrate to make the construction transparent. The dimensions of the radiator in both cases appear to be the same (Ws = 8 mm and Ls = 5.5 mm). Subsequently, some designs that aim at higher frequencies will be presented. An 8 \(\times\) 8 antenna array for operating frequencies from 97.8 to 107 GHz, which consists of a composition of smaller 2 \(\times\) 2 arrays, is presented in ref. [114]. For feeding, an RGW is used to properly distribute the power, and then a SIW is used for the \(2\times 2\) arrays. The entire construction is implemented inside a metal box, and its dimensions are (26.0 \(\times\) 34.0 \(\times\) 11.4) mm. It has relatively high aperture efficiency of 75% and satisfactory gain of 26.5 dBi at 105 GHz.