# A 12-20 GHz Wideband High-Power SP2T Switch Based on Gap Waveguide Technology
## 2 WR-62 to Groove Gap Waveguide Transition  
Figure 1 shows the geometry of the periodic pins and a groove gap waveguide (GGW) structure and dimensions, as well as the simulated dispersion diagram of the periodic pin structure. To realize the PMC surface, a periodic texture of metallic pins [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28] or holes [29; 30] can be used, and by placing a metallic plate on its top, the bandgap is achieved. The periodic pin structures are more compact and have a broader bandwidth compared to the holey structures. In contrast, the manufacturing of periodic holey structures is more cost-effective. In this paper, a periodic pin structure is utilized due to its compactness and wide bandwidth. However, the proposed switch can also be designed using a periodic holey structure. By selecting the proper dimensions for the pins, the frequency range of the bandgap is determined. Full-wave simulation of the structure is performed using the eigen-mode solver of the CST Microwave Studio. Figure 1c shows the bandgap of the periodic pins. The bandgap covers from 8 GHz to 32 GHz, which includes X-, Ku- and K-bands. It is observed that the electromagnetic wave cannot propagate along the periodic pin structure within the specified frequency band. By creating a groove between the pins, the wave can propagate along it. The main part of the proposed microwave switch is a transition from standard WR62 waveguide to GGW, which is shown in Figure 2. The GGW is created using two rows of the periodic pins to achieve as high of an isolation level as often as possible. The WR62 standard waveguide is coupled to the GGW from its top layer. A metallic step is placed under the WR62 to rotate the EM waves and maximize the coupling between WR62 and GGW. To extend the bandwidth of the transition, two matching posts are introduced to the structure, i.e., a metallic matching pin and window as shown in Figure 2b. The metallic window has an inductive impedance, whereas the metallic pin acts as a capacitive impedance. Therefore, a wide impedance bandwidth can be obtained by selecting proper values for the pin and window dimensions as well as the metallic step. Briefly, the procedure of initial design of transition can be summarized as follows:  
Choose the height and width of the step as h/2 and \(\lambda 0/4\), respectively. Choose the dimensions of the matching pin (P\({}_{w}\)\(\times\) P\({}_{w}\)\(\times\) P\({}_{h}\)) as 2w \(\times\) 2w \(\times\) h/2. Figure 1: (**a**) Periodic pin structure, (**b**) groove gap waveguide structure, and (**c**) the dispersion diagram of the pins. The parameters are \(h\) = 4.5 mm, \(w\) = 1.65 mm, \(d\) = 4.1 mm, \(ag\) = 0.1 mm, and \(G_{w}\) = 15.8 mm. Figure 2: (**a**) Exploded view and (**b**) top view of the WR62 to GGW transition structure. The parameters are step height (Step\({}_{h}\) = 3 mm), step width (Step\({}_{w}\) = 4.5 mm), pin height (P\({}_{h}\) = 1.5 mm), pin width (P\({}_{w}\) = 3.5 mm), and window width (W\({}_{w}\) = 1.3 mm). Choose the width of the inductive pins (\(w_{w}\)) as w.  
The optimized parameters are mentioned in the caption of Figure 2. The simulated S-parameters (S\({}_{11}\) and S\({}_{21}\)) of the transition are shown in Figure 3. The transition structure is simulated using 3D EM simulation software (CST), and the embedded optimization tool (trust region framework) is utilized to tune the design parameters. The structure material is aluminum, in which the conductivity is \(3.56\times 10^{7}\) S/m. The reflection coefficient of the transition is less than \(-20\) dB in the desirable frequency bandwidth from 12-20 GHz, which shows that excellent impedance matching is obtained from the proposed structure. The insertion loss is less than 0.05 dB within the same frequency bandwidth, which proves the high efficiency of the transition and its excellent wave confinement inside the GGW structure. According to Figure 3a, the step height has a significant effect on the wave rotation and coupling to the GGW.