Two-Way Power Divider With Wide Tunable Power Ratio Range for Weighted-Polarization MIMO Antenna in BAN Radios at 2.45 GHz

Abstract

This study presented an implementation of weighted-polarization multiple-input–multiple-output (MIMO) antenna for wireless body area networks at 2.45 GHz. The weight function determined by considering the variation in the cross-polarization power ratio <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(XPR)</i> and the antenna tilt angle was realized by a two-way power divider (PD), where tunable power ratio range of proposed PD could not only cross the boundary of equal power ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1), but also maintain a wide tunable range at the same time. The patch array antenna fed by the proposed PD consists of microstrip lines, capacitors, resistors, and varactor diodes can overcome the polarization mismatch in dynamic off-body channel due to the variation in radio-propagation environment and human movement by adjusting the bias voltages. The experiment of 2 × 2 MIMO channel capacity was conducted using a three-dimensional spatial fading emulator. The measured and simulated results are in good agreement. Under the considered condition of arm-swinging angle and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">XPR</i> , the tunable power ratio range of proposed PD can be realized from −1.25 dB to 20 dB; therefore, it is suitable for radio-frequency control antenna to obtaining high data transmission in future wearable MIMO applications.