Metamaterial-Based Broadband Branch-Line Coupler and its Application in a Balanced Amplifier

This paper presents a design of a compact broadband two-section branch-line coupler (BLC) based on Dual Composed Right Left Hand (D-CRLH) Metamaterial at a center frequency of 1.8 GHz. To realize a good miniaturization, a V-shape coupled-line sections unit cell has been suggested and analyzed. It achieves very good characteristics without using lumped elements, via holes or defected ground structures. The designed coupler has been implemented using microstrip technique and simulated using the CST software. It has been fabricated and measured. The comparison between the simulated and measured results shows good agreement. It has a fractional bandwidth of 51.6% and a size reduction of 44.6 % comparing to the conventional coupler. As an application, the proposed coupler has been used to build a balanced amplifier. For this purpose, a microwave transistor amplifier has been designed and simulated at the center frequency, 1.8 GHz. The simulated results of the balanced amplifier show a good flat gain over a 1 GHz bandwidth with 13.7 dB gain at the central frequency, 1.8 GHz.