Compact and closely spaced tunable printed F-slot multiple-input–multiple-output antenna system for portable wireless applications with efficient diversity

In this work, miniaturised tunable two-antenna multiple-input-multiple-output (MIMO) systems composed of printed F-slot shaped are developed to operate in the global positioning system (GPS), personal communication system (PCS), distributed control system and Universal Mobile Telecommunications System bands. The two-element MIMO antenna occupies a volume of 50 × 37.5 × 1.6 mm³, and is printed on an FR4 substrate. Initially, the frequency tunability of the MIMO antennas was verified by lumped capacitors with values between 0.75 to 2.75 pF to achieve a tuning range from 1.55 to 2.07 GHz while the low mutual coupling between the radiators was accomplished by adding an I-shaped branch to a cut-away ground plane. The two antennas are then loaded with varactors to simultaneously achieve miniaturisation and tunability. Simulation and measurement results demonstrate the successful implementation of a tunable MIMO with coupling reduction mechanism for a portable handheld wireless transceiver. The channel capacity of the proposed antenna is investigated and found to be close to that of a un-correlated system with efficient diversity in which the mutual coupling across the full bandwidth was better than -13 dB. Owing to the compact size and ease of manufacture, the proposed antennas can be a promising solution for adaptive MIMO systems in handheld devices.