This paper presents a new technique to improve the port isolation between two closely spaced dual band patch antenna elements using shunt frequency dependent reactive impedances. A compact two element dual band microstrip antenna array is designed to operate for Bluetooth at 2.45 GHz and WIMAX at 3.5 GHz applications. The proposed approach utilizes two edge coupled transmission lines after inserting a transmission line adjusted to convert trans-admittance between input ports to a pure positive and negative imaginary values at the lower and higher frequencies respectively. Measurement results show an isolation enhanced by 29 dB and 24 dB at 2.45 GHz and 3.5 GHz respectively. The proposed technique shrinks the space between the two elements to be λ0 /10 at 3.5 GHz. The design has been simulated and validated experimentally.