Plannar Photonic Bandgap Structures

Planar PBGSs are a classes of periodic, which are photogenic analogs of the semiconductors. Electromagnetic (EM) waves behave in photonic substrates as electrons behave in semiconductors. Due to these characteristic PBGSs are known as EM bandgap structures (EBGSs). PBGSs exhibit wide band-pass and band-rejection properties at microwave and millimeter-wave frequencies and have offered tremendous applications in active and passive devices [1]-[12].
Introducing periodic perturbation such as dielectric rods, holes and patterns in waveguides and microstrip substrates forms PBG materials.

While various configurations have been proposed in literature, only the planar etched PBG configurations are attracted much interest due to their ease of fabrication and integration with other circuits with photolithographic processes. The passband of PBGSs is used as slow wave medium that is useful for compact design. On the other hand the stopband is used to suppress the surface wave, leakage and spurious transmission [13] - [17]. Due to these unique properties of PBG structures, they find potential application in filter, antennas, waveguides, phased arrays and many other microwave devices and components.   

 

In the conventional phased array antenna, solid-state phase shifters are used. They are expensive and the volume of the circuit increases with the number of switches. For beam steering [18] purpose PBGSs can play an important role. Thus PBG engineered structures are useful structures in microwave engineering. Inclusion of PBGSs provides many advantageous features at a time such as compactness, surface wave suppression and beam steering capabilities in the design of a PBG assisted reconfigurable phased array antenna. Therefore attention will be paid to PBG designs in significant portions of this thesis. Which can be implemented in antennas, filters, phased arrays and reconfigurable phased arrays.

Besides PBG structures, defected ground structures (DGSs) [19] will be focused. DGS differs from the PBG structures both in configuration and in principle of operations. DGSs are formed from 2-D regular square patterned PBGSs with narrow vertical slot connections. They are known as dumbbell shaped DGSs. In principle, PBGSs follow Bragg’s condition [20] to generate the stopband. On the other hand the behavior of DGSs is controlled by current path around the DGS element. Both DGSs and PBGSs are termed as EBGSs. DGSs will be applied in second and third harmonics suppression of bandpass filter (BPF). Finally regular PBGSs and DGSs are applied in phased arrays. Additionally to these, reconfigurable phased array antennas are investigated and PBGSs in phase steering are implemented. Following sections describe the importance of reconfigurable microstrip antennas.