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This article describes a dual-polarized end-fire antenna array for millimeter-wave frequencies. The antenna consists of a chain-slot-shaped pattern on a mobile phone metal frame. The antenna is fed using a transmission line, which would cause only a negligible capacitive loading of the sub-6 GHz antenna realized on the same metal frame and, therefore, would not significantly degrade its perfomance. This makes colocating the sub-6 GHz and mm-wave antennas in the same, shared volume possible. Measurements indicate that a 4-element array placed within a mobile phone provides a realized gain between 8 and 12.6 dBi for both polarizations across the entire band from 24.5 to 29.5 GHz. The total efficiency of a single element is better than −2 and −3 dB for the whole band for horizontal and vertical polarizations, respectively.

The smartphone, as a media device, should offer a large-size screen and fast data rates in a well-packed device. Emergent 5G technologies based on millimeter waves need efficiently radiating antennas integrated into devices whose bodies (especially glass screens) behave as waveguides in the antenna frequency bands. Using the concept of retroreflective surfaces, this work proposes a compact metasurface located below the smartphone glass screen which reduces surface-wave excitation and propagation, and significantly improves the radiation pattern and efficiency of millimeter-wave antennas integrated into mobile terminals.

This paper presents an extremely low-profile tunable antenna design for smartphones with height of only 0.75 mm. The proposed antenna is integrated into the back cover of the device to utilize the existing gap between the battery and the back cover as efficiently as possible. By utilizing both tunable components and adjustable feeding weights, the designed multiport antenna system covers 3300-4200 MHz frequency range with 100 MHz instantaneous bands. In addition to just frequency tuning, these tunable elements can be utilized to adapt the antenna for different operation environments, such as changes in the structure of the device or the user effect. We show that the proposed antenna can be extended for two-and four-element multiple-input multipleoutput (MIMO) operation. The proposed design is manufactured and measured and the results confirm good antenna performance with average total efficiencies of 35 % and 25 % in free space and with a hand phantom, respectively.

The co-existence of millimeter-wave (mm-wave) and sub-6 GHz antennas in a smartphone presents many performance-limiting aspects. When both antennas are attached to the metal frame, the feed lines of the mm-wave antennas might short-circuit the sub-6 GHz antennas, and thus, may significantly affect their performance. This paper presents a method to design feed lines that function as transmission lines at mm-wave frequencies but correspond to open circuits at sub-6 GHz. This study determines, in theory, the smallest achievable capacitive loading with different line types and experimentally validates the approach. The capacitive loading due to the feed line is small enough to maintain the sub-6 GHz performance. At the mm-wave band, the insertion loss of the line is 1 dB with a measured reflection coefficient below −10 dB. The introduced common-mode capacitive load of the feed line on the sub-6 GHz antennas corresponds to 0.19 pF capacitance.