Improved bandwidth via-free lumped-element quadrature hybrid couplers

Two via-free lumped-element compact quadrature hybrid couplers are presented, which enables low loss and ease of fabrication. The present approach uses lumped LC elements in ring form without short-circuit connections and the number of elements used is less than that required for the conventional designs. Furthermore, the present approach exhibits wider coupler bandwidth than that of the conventional coupler. Design equations are derived explicitly and graphs are provided. A prototype coupler, using three inductors and four capacitors, is fabricated at 375 MHz for validation along with the conventional coupler. The designs are suitable for low frequency and ultra-miniature high frequency couplers applications.