Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 131

The velocity of EM‐wave propagation in a dispersive medium has been discussed in the previous section. The transmission line is a 1D wave‐supporting medium. The lossy line is a dispersive medium, whereas a lossless line, modeled through the line constants L and C, is a nondispersive medium. It acts as a low‐pass filter (LPF). This section shows that a reactively loaded lossless line could be a dispersive medium. A variety of transmission line structures with interesting properties can be developed by using several additional combinations of C and L. Such line structures can be realized with the lumped elements and also by the modification of planar transmission lines. The transmission medium with negative relative permittivity and negative relative permeability has been synthesized with the help of the modified, i.e. reactively loaded line structures. These wave supporting media form a new class of materials known as the metamaterials. They do not exist in nature. However, these novel media have been developed with the defects in the transmission line and using the embedded resonators in the transmission line [B.19, J.8]. The present section considers only an infinitesimal section of the transmission line, modeled as a lumped circuit elements network. The modeled network is reactively loaded to get the loaded line. However, in practice, a finite length of the line is periodically loaded with reactance. Such reactively loaded lines offer novel and improved designs of microwave components and circuits. The periodically loaded line, creating the 1D – EBG and metalines are discussed in the chapters 19 and 22.