www.ccsenet.org/apr Applied Physics Research Vol. 4, No. 2; May 2012 Directional Coupler Based on Metamaterial Square CSRR Shape Z. Menachem 1,2 , M. Haridim 1 , S. Tapuchi 2 , & Y. Chattah 1,2 1 Department of Electrical, Electronics, and Communication Engineering, Holon Institute of Technology, 52 Golomb St. POB 305, Israel 2 Department of Electrical Engineering, Sami Shamoon College of Engineering, Israel Correspondence: Department of Electrical Engineering, Sami Shamoon College of Engineering, Israel. E-mail: zionm@post.tau.ac.il Received: March 22, 2012 Accepted: April 6, 2012 Online Published: May 1, 2012 doi:10.5539/apr.v4n2p258 URL: http://dx.doi.org/10.5539/apr.v4n2p258 Abstract Metamaterials are artificial structures that can be designed to exhibit specific electromagnetic properties that are not in the nature. In this paper, we design a directional coupler, based on the theory of the split-ring resonators (SRRs), and the complementary SRR (CSRRs). The experiments and simulations of the directional coupler are based on the theory of the square structure (and not based on the circular structure) of the SRR and CSRR. The advantage of this circuit is that the area of the coupling is great as regards to the coupler based on the circular structure. The results of simulation and measurement with the miniature structures show the backward-wave phenomenon of the left-handed (LH) material. Keywords: directional coupler, metamaterial square CSRR shape, backward waves 1. Introduction In the recent years, artificial metamaterials have been a subject of growing interest, also in the microwave and antenna regimes. Metamaterials are artificial structures that can be designed to exhibit specific electromagnetic properties that are not in the nature. Metamaterials with negative permittivity and permeability referred to left- handed (LH) materials, have received substantial attention in scientific and engineering communities. Veselago explained the possible existence of LH materials and anticipated their unique electromagnetic properties, and showed that LH materials support electromagnetic waves with group and phase velocities that are antiparallel, known as backward wave, a phenomenon which is associated with negative index of refraction (Veselago, 1968). According to Veselago, the negative valued permeabilities enable us to realize left-handed metamaterials. Pendry et al. created in 1999 the theory of the LH metamaterial (LHM) (Pendry et al., 1999). The idea was to create materials with negative permeability. They show how to design structures made from nomagnetic thin sheets of metal, which respond to microwave radiation as if they used with an effective magnetic permeability. A wide range of permeabilties can be achieved by varying the parameters of the structures. Split ring resonator (SRR) is a metamaterial structure that is used in microwave and antenna applications. The SRR pattern is printed on a dielectric substrate in the form of conducting strip lines made of good conductors such as copper or gold. An SRR array can provide highly positive or highly negative effective permeability values over some definite frequency bands (Pendry et al., 1999). An SRR based unit cell and SRR based array structures with various sizes have been designed and fabricated in order to investigate the effects of array sizes on the transmission characteris- tics (Ekmekci et al., 2009). Transmission characteristics were obtained by both simulations and experiments. The results have shown that increasing array size increases the depth of the transmission minimum at the resonance frequency and also widens the stop-bandwidth. The resonance frequency of the array is shifted either towards the lower frequencies or towards the higher frequencies depending upon the array dimension at which the number of array elements is increased. Directional couplers have four ports. The first port is regarded as the input, the second port is regarded as through port, the third port is regarded as the coupler port, and the firth port is regarded as isolated port. One port of the directional coupler is isolated from the input port. Structures in coupled-line couplers were proposed (Liu et al., 2002), where a symmetric LH enhanced forward coupler was demonstrated. The forward coupling phenomena between artificial LH transmission lines have been explored on the basis of a transmission line approach of LH 258