At this time has been much research on the next-generation 5G in millimetter wave which more than five billion devices capable of voice communications, data and other applications. Due to the high propagation losses at millimetter wave, it will be difficult to use either omnidirectional antenna or fixed beam antenna. The high path loss caused by atmospheric absorption also demands the use of array antennas for getting a high gain on the mobile communication side. Several studies have recently been conducted using butler matrix which is part of the switchable antennas to overcome these problems. Previous studies also have designed vivaldi array antennas in 28 GHz frequency, but the it provides a directional radiation pattern that requires real phase setting that can not reach the wide area.
In this research, the antenna used is vivaldi while the butler matrix used is 4x4 by using phase shift of 45 degree. Both of them will be divided into 3 sub arrays-buttler matrix then arranged on the left, right and top side using Rogers RT5880 with 0.254 mm thickness and relative permittivity of 2.2. It is works at a frequency of 28 GHz and placed on the mobile handset then integrated with mobile phone modeling using the software. Further adjustment of the antenna has been confirmed with the expected antenna specification such as return loss, radiation pattern, gain, mutual coupling, esc. As well as with the butler matrix, it is expected to be able shifts the phase on the output port of +45, -135, +135, -45. Eventually, it is also performed the evaluation
and validation of overall performance in terms of devices and systems that have been integrated with each other involves human's body using four scenarios from CTIA such as (i)free space, (ii)talking position, (iii)talking position with hand and (iv)browsing mode. It is also expected to have a small SAR (Specific Absorption Rate) value in accordance with IEEE C95.1-2005 standards on SAR Limit <= 2 W/Kg.
Best results of the simulation were picked for an overall system at 28 GHz, and the results of antenna array were as follows: the return loss was below -10 dB, the realized antennas gain was 10.2 dB with unidirectional radiation pattern. The butler matrix dimension is 20.52 mm x 26.4 with average phase different between output port is - 44.106, 137.38, -137.66, 43.95 with phase error of 0.894, 2.38, 2.66, 1.06. While sub array antenna-butler matrix dimension is 20.52 mm x 29.52 mm is able to shift radiation pattern on the input port successively -141.1, -29, 32, 42 with the range of beam that can be achieved equal to 185 degrees. Eventually, laying down the subarray-butler matrix on the left, top and right side of the mobile phone that has been designed using the software is capable to cover the wide area which is almost 360 degree. SAR values measured using four positions of CTIA is <= 2 W/kg with return loss <=-10