Investigation of CRLH Transmission Lines for Microwave Passive Components

Abstract

For decades, engineers have been searching for ways to reduce the size of electronic circuits while maintaining the efficiency and effectiveness of the circuits. At low frequencies of the microwave band, the size of the conventional transmission line becomes larger, because the wavelength is inversely proportional to the operating frequency; thus, it is needed to reduce the size to agree with the application requirements. Metamaterials are synthetic materials engineered to have a property that is not found in nature. They gain their properties not from their composition, but from their designed structures, and it could be used to reduce sizes of the electronics components. The increasing demand for metamaterials technology to reduce sizes in electronic circuits, in conjunction with the advances in the Low Temperature Co-fired Ceramic (LTCC) technology, as well as the availability of 300 MHz of bandwidth in the C-band (4.5-5.5 GHz), have created an interest in the development of a metamaterial transmission line which can be used to produce small-size millimeter-wave systems. In this research, the idea of using metamaterial depends on replacing each section of the conventional Right Handed (RH) transmission line, by equivalent Composite Right Left Handed Transmission Line (CRLHTL) implemented using lumped elements. In this research, the CRLHTL was fabricated on ceramic substrate using 3-metal layers with dielectric constant (e_r) of 7.1 and substrate thickness of 127 µm. The measurement results were in agreement with the post-layout simulations over the bandwidth of 1-10 GHz. The on-wafer measurements of the transmission line were carried out using Agilent E8361A 10 MHz to 67.0 GHz vector network analyzer, and the EM simulation was performed by using an electromagnetic simulator (Agilent ADS). As an example of an application, the CRLHTL was implemented in the design of a Branch Line Coupler (BLC). The design of the BLC used a CRLHTL to reduce the physical size of the quadrature wavelength elements of the coupler. The design exercise resulted in a coupler dimension of 5.924mmx5.824mm that is about 22.9% smaller compared to conventional BLC (6.904mm x 6.778mm). Hence, the simulation results of the BLC achieved good performance over the bandwidth of 4.5-5.5 GHz compared to the conventional coupler. This type of coupler is widely used in microwave circuits, such as power combiners and dividers, balanced mixers, image rejection mixers, and balanced amplifiers.