Co-Existing Antennas in Modern Handsets

Abstract

Fifth generation (5G) mobile networks significantly increase the data transfer rates of wireless communications. This increase is achieved by utilizing multiple-input multiple-output (MIMO) systems at sub-6 GHz frequencies. Furthermore, 5G introduces new millimeter-wave (mm-wave) frequencies in which more bandwidth is available for high-capacity communications. A common factor for both frequency ranges is that handsets should be equipped with more antennas than before. Another challenge for antenna designers is the limitations set by the phone industry. Current smartphones are already densely packed, with a maximized screen-to-body ratio. Due to the limited volume, antennas must be integrated into the handset body. However, phone manufacturers are strict about the visual appearance of the device, which further restricts the placement of the antennas. The first part of this thesis presents methods to integrate antennas into the handset body at both the sub-6 GHz and the mm-wave frequencies. The sub-6 GHz antennas are implemented in the metal frame of a handset with a fully metallic back cover according to industry requirements. The antenna performance is confirmed with antenna measurements. 5G mm-wave antennas are desired to be dual-polarized and to operate at two frequency bands. The effect of the handset chassis on the antenna performance is investigated. The second part of the thesis considers the co-existence of mm-wave and sub-6 GHz antennas with a focus on effective volume utilization. To fit all the required antennas into a handset, antennas must be able to perform in a shared volume. A mm-wave antenna is designed and located within the same space as the traditional LTE antenna, and the mm-wave antenna is enclosed with plastic and radiates through an opening in the metal frame of the phone. The plastic isolates the two antennas and allows adequate performance for both. The presented co-design method is verified, and the beam-steering capability of the mm-wave antenna is demonstrated experimentally. Integrating mm-wave antennas into the metal frame of a phone might short-circuit the sub-6 GHz antennas and thus destroy the LTE performance. To prevent the short-circuiting, a design method for a capacitively-loaded feed line is developed. The loaded feed line behaves like a transmission line at mm-waves frequencies but presents as a small common-mode capacitance at the sub-6 GHz range. This behavior allows sub-6 GHz antennas to operate normally. The presented method enables improved integration of mm-wave antennas into the metal frame of a phone.