Design of Miniaturized 10 dB Wideband Branch Line Coupler Using Dual Feed and T-Shape Transmission Lines

This paper presents a design mechanism of miniaturized wideband branch line coupler (BLC) with loose coupling of 10 dB. Dual transmission lines are used as a feed network which provides a size reduction of 32% with a fractional bandwidth (FBW) of 60% for 10 +/- 0.5 dB coupling but return loss performance is found to be poor in the operating band. For further improvement of return loss performance as well as for size reduction of the BLC, a T-shape transmission lines are used instead of series quarter wavelength transmission lines, and hence the overall size reduction of around 44% with FBW of 50.4% is achieved. The return loss and isolation performance is found to be < 15 dB in the entire operating band (2.5-4.1 GHz) with respect to design frequency 3G Hz. The proposed BLC is analyzed, fabricated and tested.