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.