Wireless technology now employs 5G (generation) communication, while 6G is the subject of increased research. Various G's have evolved due to the need to achieve high data transfer for reliable communication. A tremendous data transfer rate expressed in terabits per second (Tbps) is facilitated by the terahertz (THz) spectrum. The photonic crystal (PhC) patch antenna has been proposed in this chapter, and the consequences of a line defect were examined. The defect has been embedded in the perpendicular and parallel directions of the antenna substrates. The antenna's performance regarding return loss (RL), directivity, and voltage standing wave ratio (VSWR) is evaluated. The structure is simulated using CST, and the PhC structure results show excellent characteristics such as -48.02 dB RL, 1.007 VSWR, and 5.23 dB directivity at THz frequency.
TopI. Introduction
A PhC’s (Danasegaran et al., 2024; Povinelli et al., 2021) dielectric constant varies periodically in any direction. When the PhCs dielectric constant varies in just a single direction, it is referred to as one-dimensional (1D) PhC. Two-dimensional (2D) PhC structures are those in which the material arrangement is periodic in two directions. The identical is exact for (3D) PhC, whose dielectric constant values contrast in 3D and the categorization of various PhC is shown in figure 1.
2D PhC is the most commonly used in antenna design. The 2D PhC is available in two topologies: hole form and rod form. The hole form PhC is composed primarily of semiconductor material by a filling aspect greater than 50%. It has a structure of less indexed air-filled holes set on a back of highly indexed material. The highly indexed rods in rod type PhC are enclosed by less index surface material, and the filling factor is < 50%. Figures 2 (a) and (b) show the rod and hole category PhC structures.
Figure 2. (a) Rod type PhC, (b) hole type PhC
In optics, the defect is a change in the PhC structure's periodical dielectric material. The PhC defect comes in two different forms: point and line defect. The optical cavity in the point defect supports the capture of light. A line defect benefits to direct light from one to another location, providing a waveguiding effect. The EM waves are powerful in the defect area and evanescent in the surrounding regions. Figures 3 (a) and (b) depict a point and line defected structure sample.
Figure 3. PhC structure (a) point defect, (b) line defect
A “line defect” is a form of structural variability or alteration underneath a PhC topological structure. PhCs are materials with constant changes in refractive index on the wavelength scale. These PhC structures can be designed in various ways to regulate the light flow. In PhC, a line defect corresponds to a linear area where the periodicity of the structure is disrupted or altered. It can be achieved by creating a directed path for light inside the PhC by introducing a line defect. The idea is similar to the employing of waveguides in conventional optics, however, in this case, it takes benefit of the PhC lattice's unique properties.
The topology of the PhC defect is critical for controlling light flow and enabling various optical functionalities. Photonic crystals are periodic dielectric structures that, through their bandgap properties, may influence the propagation of electromagnetic waves including light. Defects in these structures provide localized states inside the bandgap, allowing optical devices to be created. The lattice of the PhC slab (Johnson et al., 1999) falls into two categories such as square and triangular as shown in figures 4 (a) and (b). In the PhC slab, the total internal reflections control the light localization caused by the high index contrast between the high and the low index surface. Conversely, the distributed Bragg reflector emerges from the 2D PhC structure and controls the confinement in a longitudinal direction.
Figure 4. PhC structure (a) square lattice, (b) triangular lattice