Design of high directivity microstrip coupler with single floating conductor on coupled edges

This paper presents a design of new quarter-wavelength microstrip coupler with high directivity, which consists of a single floating conductor in the slot on the inner edges. 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. Using this new design, a 15-dB coupler is designed and a high directivity of 25 dB or more is obtained over a considerably wide bandwidth. The validity of the design concept is confirmed by EM-simulations.