Miniaturized branch-line hybrid coupler with broadband impedance matching network

This paper presents a compact broadband branch-line hybrid coupler. It is composed of a miniaturized branch-line hybrid coupler and broadband impedance matching networks. A coupled-line structure is used for the broadband impedance matching network. The branch-line hybrid coupler is realized by using high-impedance transmission lines and distributed capacitors. In order to further reduce the circuit size, the distributed capacitors are placed in the center space of the hybrid coupler and the coupled lines are effectively meandered. For validation, a prototype of the compact hybrid coupler was designed and fabricated at the center frequency of 1 GHz. For given conditions, the proposed hybrid has 29.4% bandwidth which is from 870 to 1170 MHz. Compared to the conventional 3-dB branch-line hybrid coupler, it exhibited a size reduction of 50.8% and an extended operating bandwidth of 66.7%.