High directivity microstrip coupler with single slot of unequal length for GSM dual band

In this paper a simple design procedure is used with accurate formulation. It comprises a complete design of symmetrical two-line Microstrip directional coupler including physical length at the desired operational frequency. The design procedure doesn´t require the prior knowledge of the physical geometry of the coupler and requires only the information of the port impedances, coupling and operational frequency. To improve the directivity, the microstrip coupler was designed by a new approach for phase velocities compensation, which utilizes a coupled-Microstrip with a single slot of unequal length on its inner edges. Using this new design, a 15-dB coupler is designed and a high directivity of 34 dB or more is obtained over a considerably wide bandwidth for GSM dual band applications. The validity of the design concept is confirmed by em-simulations.