**4. Co-design of the mm-wave array in the mobile phone with lower frequency band antenna**

The broadside mm-wave arrays in Section 2 and the endfire mm-wave arrays in Section 3 have achieved superior performance which can cover the desired beam directions 1–6 in **Figure 1**. The commercial mm-wave array module has been adopted in Samsung Galaxy S20 in 2020 [10]. However, because the full-display, curveddisplay, metal-bezel, glass back cover, metal back cover requirement of the mobile phone, the mm-wave array in mobile phone should fit the ID of mobile phones. Also, because most of the spaces are reserved for the displays, cameras, battery, PCB, motor, speaker, and so on for better user experience, the antenna in mobile phones should only occupy a very small space. So, the co-design of the mm-wave array in the mobile phone with a lower frequency band antenna is also widely studied. In this section, we first analyze the design of integrating the mm-wave array with metal-bezel in mobile phones. Then, the shared-aperture design of the mm-wave array with the lower frequency band antenna is summarized.

#### **4.1 Integrating the mm-wave array with metal-bezel in the mobile phone**

As the mm-wave array is deployed in the mobile phone, the modules of the mobile phone might have a significant effect on the performance of the mm-wave array. In [67], the effect of different kinds of mobile phone housing on the performance of four canonical types of mm-wave antennas is studied. The effective beam-scanning efficiency is proposed to evaluate the coverage performance. In [68], the effect of the metal-bezel of the mobile phone on the radiation pattern of the mm-wave array is studied. The blockage of the metal-bezel to the horizontal-polarized antenna is more severe than for the vertical-polarized antenna. And the coupling metal strips [68, 69] can be applied to reduce the blockage from metal-bezel. Also, the slots on the metal-bezel [70, 71] can be also used to reduce the blockage from the metal-bezel. In [72], a rectangle window in the metal-bezel was used to install the mm-wave array so that the mm-wave array could radiate the power through the rectangle window directly as shown in **Figure 11(a)**. This practical solution has been adopted in some commercial 5G mobile terminals such as Apple iPhone 12 with a wee mm-wave window [73]. Apart from reducing the effect from the metal-bezel, in [74], the metal-bezel can be applied to design the mm-wave leakywave array as shown in **Figure 11(b)**. In addition, the mm-wave array antenna could be directly implemented via the slot on the metallic bezel of the mobile terminals [75, 76]. Thus, the blockage effect from the metal-bezel is solved.
