Miniaturised broadband branch line coupler for WiMAX and LTE applications

Abstract

This paper presents the bandwidth enhancement and miniaturisation of the branch line coupler for LTE/WiMAX applications (2.45-2.7 GHz). The broadband nature of conventional branch line coupler is attained by using three-section branch line coupler. The circuit area of the broadband coupler is reduced with the aid of von Koch fractal method of miniaturisation. An FR4 (Flame Retardant type 4 Epoxy) substrate having a thickness of 1.6 mm is selected to construct the microstrip circuit of broadband and miniaturised broadband branch line couplers. S-parameter simulation is carried out to compare the performance of proposed miniaturised broadband coupler with broadband and conventional branch line couplers. The simulation result shows that the proposed coupler achieves a bandwidth of 610 MHz with an area reduction of around 34%. The printed circuit board fabrication of the conventional, broadband and miniaturised broadband coupler was done to evaluate the measurement results using vector network analyser.