# Low Cost AIP Design in 5G Flexible Antenna Phase Array System Application
## 5 Conclusions  
The design and simulation of a \(2\times 2\) low cost phase array antenna module for 5G applications operating at 28 GHz with 14.4 dBi antenna gain was proposed in this paper. The air-filled cavity used for patch antenna structure was with a FR4 PCB material for cost reduction instead of using a Roger or M6 material PCB. Moreover, it improved the antenna radiation efficiency by reducing the loss of the material. Furthermore, the designed array unit could be used and combined for a higher order array along two dimensions with a suitable surface mount technology (SMT) gap. It helps to easily and reliably implement a high order array. Therefore, the proposed array antenna is a promising candidate for the mm-wave 5G small cell applications. Table 2 summarizes the performance of this work and compares it with state-of-the-art mm-wave phased-array antennas [27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38]. The proposed patch shows around an 8.5 dBi antenna gain, which is better than [31; 35; 37; 38], at a similar frequency. It describes that the air-filled cavity as a patch gap between the ground increased the antenna efficiency effectively instead of a lossy FR4 PCB material. The measured results of the single array unit show that the maximum radiation direction can be steered from -34 to +34\({}^{\circ}\) continuously in the X-cut and -26 to +26\({}^{\circ}\) continuously in the Y-cut at 28 GHz. The total dimension of the resulting design package was 18 mm \(\times\) 14 mm \(\times\) 0.71 mm. The gain of the array antenna achieved 14.4 dBi and the reflection coefficient of the array antenna was less than -10 dB from 26.5 to 29.5 GHz. Figure 21: Array antenna (\(2\times 2\)) gain measurement results (phase 0/180/180/0, Y-cut). Figure 22: 3D radiation pattern of the array antenna at 28 GHz: (**a**) simulation result and (**b**) measurement result (normalized). **Author Contributions:** Conceptualization, W.-Y.C. and S.-L.C. ; Data curation, W.-S.T., C.-K.L., P.-Z.R., and W.-M.C. ; Formal analysis, C.-K.L., P.-Z.R., and W.-M.C. ; Funding acquisition, W.-Y.C. ; Investigation, W.-S.T. and W.-Y.C. ; Methodology, W.-Y.C. and C.-K.L. ; Project administration, P.-Z.R. ; Resources, W.-Y.C., C.-A.C., P.A.R.A., and S.-L.C. ; Supervision, C.-A.C., P.A.R.A., and S.-L.C. ; Writing--original draft, W.-S.T., W.-Y.C., C.-A.C., and F.A. ; Writing--review and editing C.-A.C., P.A.R.A., F.A., and S.-L.C. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was supported by the Ministry of Science and Technology (MOST), Taiwan, under grant numbers of MOST-108-2628-E-033 -001-MY3, MOST-108-2622-E-033 -012-CC2, MOST-109-2622-E-131-001-CC3, MOST-109-2221-E-131-025, MOST-106-2119-M-033-001, MOST 107-2112-M-131-001, and MOST 108-2112-M-131-001 and the National Chip Implementation Center, Taiwan. **Acknowledgments:** This work was supported by the Ministry of Science and Technology (MOST), Taiwan, under grant numbers of MOST-108-2628-E-033-001-MY3, MOST-108-2622-E-033-012-CC2, MOST-109-2622-E-131-001-CC3, and MOST-109-2221-E-131-025, the National Center for High Performance Computing (NCHC), which supports the EM wave simulators (ANSYS HFSS), and the National Chip Implementation Center, Taiwan. The technology information and resource supported by Shenzhen Science and Technology Program. **Conflicts of Interest:** The authors declare no conflict of interest.