Isolation Enhancement Between Two Closely Packed Antennas

This paper introduces a coupling element to enhance the isolation between two closely packed antennas operating at the same frequency band. The proposed structure consists of two antenna elements and a coupling element which is located in between the two antenna elements. The idea is to use field cancellation to enhance isolation by putting a coupling element which artificially creates an additional coupling path between the antenna elements. To validate the idea, a design for a USB dongle MIMO antenna for the 2.4 GHz WLAN Band is presented. In this design, the antenna elements are etched on a compact low- cost FR4 PCB board with dimensions of 20$,times,$40 $,times,$1.6 ${rm mm}^{3}$. According to our measurement results, we can achieve more than 30 dB isolation between the antenna elements even though the two parallel individual planar inverted F antenna (PIFA) in the design share a solid ground plane with inter-antenna spacing (Center to Center) of less than $0.095lambda_{o}$ or edge to edge separations of just 3.6 mm (0.0294 $lambda_{o}$). Both simulation and measurement results are used to confirm the antenna isolation and performance. The method can also be applied to different types of antennas such as non-planar antennas. Parametric studies and current distribution for the design are also included to show how to tune the structure and control the isolation.