**5. References**


274 Trends in Electromagnetism – From Fundamentals to Applications

Moreover, a new type of backward CLC composed of two different coupled lines, i.e. interdigital and conventional microstrip TLs has been proposed, fabricated, and investigated theoretically and experimentally. In this structure, an interdigital capacitor with only one finger is used as interdigital TL. This interdigital TL is coupled with a conventional microstrip TL and achieves an asymmetrical backward CLC. The proposed backward-wave coupler with 0.2 mm spacing between two coupled lines exhibits the amplitude balance of *±*2 dB from 2.2 GHz to 4.2 GHz and the phase balance of 90º*±*10º from 2.2 GHz to 3.5 GHz. Finally, a forward CLC composed of two identical microstrip TLs and periodic shunt stubs between them has been proposed and investigated experimentally and theoretically. Using loaded stubs between two microstrip coupled-lines forms the proposed 0-dB forward CLC which exhibits the amplitude balance of *±*2 dB around center frequency of 3 GHz from 2 GHz to 4 GHz (66% bandwidth). A matching (| <sup>11</sup> S |<15-dB) bandwidth of over 4 GHz (1-5 GHz) bandwidth and at least 15 dB isolation between adjacent ports have been seen in measurement results. In this forward-wave CLC, by increasing the length of the stubs, the

Abdelaziz, A. F., Abuelfadl, T. M., & Elsayed, O. L. (2009). Realization of composite

Caloz, C. & Itoh, T. (2002). Application of the transmission line theory of left-handed (LH)

Caloz, C. & Itoh, T. (2004). A novel mixed conventional microstrip and composite right/left

Caloz, C., & Itoh, T. (2005). *Electromagnetic Metamaterials: Transmission Line Theory and* 

Caloz, C., Sanada, A., & Itoh, T. (2004). A novel composite right/lefthanded coupled-line

Chang, C., Qian, Y. & Itoh, T. (2001). Enhanced Forward Coupling Phenomena Between

Cristal, E.G. (1966). Coupled-Transmission-Line Directional Couplers with Coupled Lines of

Bahl, I. (2003). *Lumped Elements for RF and Microwave Circuits*, ArtechHouse, Boston.

*USNC/URSI National Radio Science Meeting,* vol. 2, pp. 412–415.

right/left-handed transmission line using coupled lines. *Progress In Electromagnetics* 

materials to the realization of a microstrip LH transmission line. I*n Proc. IEEE-AP-S* 

handed backward-wave directional coupler with broadband and tight coupling characteristics. *IEEE Microwave Wireless Component Letter,* vol. 14, no. 1, pp. 31-33. Caloz, C. & Itoh, T. (2004). Transmission line approach of left-handed (LH) structuresand

microstrip realization of a low-loss broadband LH filter. *IEEE Trans. Antennas* 

directional coupler with arbitrary coupling level and broad bandwidth. *IEEE Trans.* 

Microstrip Lines on Periodically Patterned Ground Plane. *IEEE MTT-S International* 

Unequal Characteristic Impedances. *G-MTT International Symposium Digest,* vol. 66 ,

*<sup>g</sup>* , respectively. Also, this coupler exhibits

structure are approximately*¸* 4

coupler length decreases, proportionally.

*Research*, Vol. 92, pp. 299–315.

*Propagation*, vol. 52, no. 5, pp. 1159–1166.

*Microwave Applications*, Wiley, New York.

*Microwave Theory Technique*, vol. 52, pp. 980–992.

*Microwave Symposium Digest*, pp. 2039–2042.

no. 1, pp. 114 – 119.

**5. References** 

λ

higher design simplicity than the existing CRLH CLCs.

*<sup>g</sup>* and 36 λ


**12** 

*Iran* 

**Theory and Applications of Metamaterial Covers** 

Metamaterial covers exhibit inimitable electromagnetic properties which make them popular in antenna engineering. Two important features of metamaterial covers are: (1) increasing of the transmission rate and (2) control of the direction of the transmission which enable one to design directive antennas. In this chapter, the possibility of increasing both bandwidth and directivity of the printed patch antenna using metamaterial covers is examined. The printed patch antennas are a class of low-profile antennas, which are conformable to planar surfaces, simple and inexpensive to manufacture using printed-

Furthermore, novel polarization-dependent metamaterial (PDMTM) covers, whose transmission phases for two principal polarizations are different, are presented (Veysi et al., 2011). A full-wave Finite Difference Time Domain (FDTD) numerical technique is adopted for the simulations. A schematic of the metamaterial cover with square holes is shown in Fig. 1. It consists of two planar layers with similar square lattices. It was demonstrated in (Pendry et al., 1996; Tsao & Chern, 2006) that in the frequency range, where the wavelength is very large compared to the period of the metamaterial cover, this structure acts as a homogenous medium. The equivalent refractive index of this medium, in the microwave

1 *<sup>P</sup>*

where *fP* denotes the plasma frequency and *f* denotes the operating frequency. If the operating frequency is selected slightly larger than the natural plasma frequency of the metamaterial cover, the equivalent refractive index will be extremely low. Consequently, the

The ultra refraction phenomena, in which the transmitted rays are parallel to each other, can be expected where the transmission coefficient reaches its maximum value. In other words, the zero transmission phase occurs at the same frequencies where the magnitude of the transmission coefficient becomes maximum. Hence, it acts similar to an equally phase surface at its plasma frequency. It is evident from Eq.1, that the equivalent refractive index

As a starting point, we consider a two-layer metallic grid placed on top of the patch antenna backed by a ground plane. The simulations have been carried out to examine the

*<sup>f</sup> <sup>n</sup> <sup>f</sup>*

*eff*

transmission phase at the plasma frequency is extremely low.

and thus the antenna directivity are very sensitive to the frequency.

2

= − (1)

**1. Introduction** 

circuit technology.

domain, is given by:

Mehdi Veysi, Amir Jafargholi and Manouchehr Kamyab

*E.E. Dept. K. N. Toosi University of Technology, Tehran,* 

