A quad-band branch line coupler with high frequency ratio

Abstract

In this paper, a novel quad-band branch line coupler with high ratio (from 6.27 to 14.96) of the largest operating frequency to the smallest operating frequency is presented. To realize quad-band operations, a combination of coupled lines and open stubs is proposed which can make the design flexible. By using analysis of even and odd modes, the equivalent equations for the quad-band operation are obtained. Compared to the existing quad-band branch line coupler, the proposed quad-band coupler has the highest ratio of the largest operating frequency to the smallest operating frequency, which is valuable for wideband and ultra wideband application. For practical applications, a quad-band coupler operating at 0.7, 1.64, 4.09, and 5.03 GHz which can be used for the long term evolution (LTE) and Wi-Fi is designed, fabricated, and measured. The simulated and measured results agree well with the design theory.