High-Gain Dual-Loop Antennas for MIMO Access Points in the 2.4/5.2/5.8 GHz Bands

A high-gain, three-antenna system suitable to be concealed inside wireless access points for multiple-input multiple-output (MIMO) applications in the WLAN 2.4/5.2/5.8 GHz bands is presented. The MIMO antenna system is composed of three dual-loop antennas occupying a moderate size of 10 × 20 × 40 mm³. Each dual-loop antenna further comprises a large outer loop and a small inner loop, both operating at 1.0-wavelength resonant mode and sharing common antenna feeding and grounding portions. In addition, the antennas are placed in a sequential, rotating arrangement on a ground plane with an equal inclination angle of 120° to form a symmetrical multiple-antenna structure. Good impedance matching for outer and inner loops over the 2.4 and 5.2/5.8 GHz bands can easily be achieved by tuning the widths of feeding and grounding portions and a small gap therein between. The results show that well port isolation can be obtained together with high-gain, directional radiation characteristics. Calculated envelope correlation is less than 0.007 within the bands of interest. Details of a design prototype are described and discussed in the paper.