Novel Composite Right/Left-Handed Metamaterial-Based Leaky-Wave Transmission-Lines

The focus of this dissertation is on the design procedure as well as analysis of a very interesting category of metamaterial-based structures namely composite right/left-handed (CRLH) Leaky-wave (LW) transmission-lines (TL). As a result several unique CRLH-TLs are designed and presented. Each of the discussed CRLH LW-TLs has exceptional and beneficial characteristics, which is only realizable due to their composite right/left-handed nature and dispersion characteristics. The operation mechanism of CRLH-TL is explained in the first chapter by the overview of the theory behind the CRLH concept. The dispersion diagram of a CRLH unit-cell shows that the phase constant (beta) is a non-linear function of frequency with a beta = 0 point at a non-zero frequency. Furthermore, a CRLH-TL supports left-handed slow-wave (guided-wave) and fast-wave (leaky-wave) modes, where the phase velocity and the group velocity are anti-parallel and phase advanced is achievable, as well as right-handed slow-wave and fast-wave modes, where the two velocities are parallel and phase delay can be observed.;The subject of the second chapter is conformal CRLH LW-TLs. The effect of conformation of a planar uniform CRLH LW-TL on a convex and a concave surface are investigated. It is shown when the CRLH LW-TL is operating in the fast-wave region the conformation affects its radiation characteristics and the radiation pattern becomes wider in both convex and concave cases. A dispersion engineering method is introduced to modify the conformal structure such that it provides comparable performance to that of the planar version in terms of radiation characteristics. Then taking advantage of the proposed modification method a multifunctional electronically controlled conformal CRLH LW-TL is introduced in a later part of this chapter. Varactor diodes are introduced in the unit-cells to electronically control its guided and radiation characteristics. This CRLH-TL has the ability to operate partially in the slow-wave mode and partially in the fast-wave mode by applying proper biasing voltages to the different sections of the TL. Therefore, it has a unique radiation aperture selectivity function which results in controlling the radiation angle and beamwidth at a fixed frequency. In addition this electronically controlled conformal CRLH LW-TL has the capability to compensate for the conformation effect and refocus the radiation beam by adjusting the biasing voltages properly.;The subject of the third chapter is CRLH LW-TLs with different polarization states and properties. First, a via-free coupled CRLH LW-TL that behaves as a conventional CRLH LW-TL under differential-mode excitation but with radiation polarization orthogonal to that of the conventional CRLH LW-TL. But when common-mode excitation is applied, the TL only supports right-handed guided- and leaky-waves and the left-handed waves are cutoff. Next, a dual polarized coupled CRLH LW-TL is a discussed which is a modification of the first type by inserting vias at the center of the left-handed stub of each unit-cell along the symmetry plane to provide a physical short-circuit to the ground. This structure behaves as a conventional CRLH LW-TL under both common- and differential-mode excitations but with orthogonal polarizations when operating in the fast-wave mode. The following section of this chapter is on a two port CRLH LW-TL that has the capability of switching between two orthogonal polarizations while operating in the fast-wave region. This switchable functionality is achievable based on the configuration of the unit-cells in use for the proposed structure. Each unit-cell consists of two orthogonal CRLH portions and two orthogonal microstrip sections. Each microstrip section is in parallel to one of the CRLH portions. The active propagation path of the unit-cell includes only one CRLH and one microstrip portion. Depending on the chosen propagation path of the CRLH portion followed by the microstrip section or vice versa, two orthogonal radiating field polarizations can be obtained. At last a circularly polarized (CP) CRLH LW-TL is presented in this chapter. This CRLH LW-TL consists of two conventional CRLH LW-TL oriented orthogonal to each other which are connected to a quadrature hybrid coupler for a 90° phase difference feeding purpose. This structure maintains its CP characteristic while performing continuous frequency beam scanning from backward direction to forward direction including broadside radiation in the fast-wave mode.;The subject of the fourth chapter is a dual-band (DB) CRLH-TL. In this chapter the concept of a simple DB-CRLH-TL which is based on combination of a conventional CRLH unit-cell with two microstrip sections is discussed. The equations required for analysis/synthesis of such structure is derived and presented. Using the DB-CRLH concept, two types of DB-CRLH LW-TLs are demonstrated. First is a straight DB-CRLH LW-TL and it has a dual-band radiation beam steering feature when operating in the fast-wave mode. For this case the polarization of the radiated waves are the same for both frequency bands. The second type is a zigzag-shaped DB-CRLH LW-TL. This structure also has the capability of backfire to endfire beam steering including broadside radiation in two different frequency bands. But interestingly in this case during the fast-wave mode operation the radiated waves from the first frequency band have orthogonal polarizations in compare to those from the second frequency band.