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.