Capacitively-Loaded Feed Line to Improve mm-Wave and Sub-6 GHz Antenna Co-Existence

Abstract

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.

Development of Low Profile M-Shaped Monopole Antenna for Sub 6 GHz Bluetooth, LTE, ISM, Wi-Fi and WLAN Applications

“…Kulkarni designed triple folded monopole antenna for laptop devices and ultrathin antenna model for communication applications [11,12]. Kurvinen and Li H proposed antenna models for mmwave communication and Sub 6 GHz communication applications [13,14]. Ren [15] designed dual band multiple input multiple output self-decoupled antenna for 5G communication applications which fall under Sub 6 GHz bands.…”

Co‐design of Sub‐6 GHz and mm‐wave array antennas with metal frame for 5G mobile terminals

“…However, the total antenna size is large. To reduce the size, there are designs that use one radiator and two feed networks 26–27 . However, the independent frequency tuning of the two bands is difficult.…”