Microstrip Line Impedance Matching Using ENZ Metamaterials, Design, and Application

The idea of this paper is to extend the tunneling effect of epsilon-near-zero (ENZ) narrow channel for matching two microstrip lines with different impedance characteristics. The main advantage of this method is the possibility to design a channel with subwavelength electrical size and obtain similar matching condition when compared with a conventional \lambda /4-transformer. The bandwidth of the structure is directly related to the bandwidth of the ENZ metamaterials. The suggested matching circuit is comprised of a metallic wall and an ENZ narrow channel. To realize the ENZ channel, a rectangular waveguide which operates in TE 10 mode is designed and implemented using a substrate integrated waveguide (SIW) technology. A set of vias are also needed for emulating the metallic wall to reduce the ENZ channel cross section. The proposed structure for different impedance values of 50, 100, and 150~\Omega was designed, simulated, fabricated, and tested. Moreover, as an important application of a matching network, a microstrip patch antenna has been matched over the desired frequency band. The simulation results based on CST microwave studio have a good agreement with measurements. It is shown that the bandwidth of the circuit is 8%-15%.