**2. Transitions**

To ensure the full integrability of the PRGW technology with other TEM guiding structures such as microstrip and coaxial lines, several types of PRGW transitions have been proposed in the literature correspondingly [42, 43]. The microstrip line to PRGW is considered the most simple and straightforward transition that can be used to excite the PRGW with a deep matching level over a broad bandwidth. **Figure 3** shows the geometrical configuration of microstrip line to PRGW transition, where the PRGW is directly connected with the 50 Ω microstrip line through a taper transformer with length *Lt* and width *Wt* [44, 45]. These two parameters are then optimized to adjust the matching level over the operating bandwidth, where the optimum dimensions are listed in **Table 2**. The operation of the transition is assessed using a PRGW bend junction as shown in **Figure 3a**. Comparison between the simulated and measured S-parameter results are shown in **Figure 3c**, where a matching level below 15 dB over the operating frequency bandwidth is achieved. It can be noticed that the measured insertion loss of this type of transition reaches 1 dB, where a large part of these losses results from the microstrip line radiation losses. This results in an inaccurate assessment of the PRGW devices through using this type of transition [44, 45].

Therefore, another type of transition, from coaxial to PRGW, is proposed to reduce the radiation losses, with the configuration illustrated in **Figure 4**. Such transition is useful in many circumstances where the PRGW device is the first component in the system taking the feed from the output coaxial terminal of the source. Like the previous design, mushroom shape periodic patch cells are used for emulating the artificial magnetic conductor. Two substrate materials are used in this multilayer configuration with an empty region in one substrate to provide the air gap [46]. Additionally, a group of metal vias is drilled around the transition to the ground plane to enhance the device performance [46]. The design dimensions are optimized to cover the whole band of 24–42 GHz and are listed in **Table 3**, while the simulation and measurement results in **Figure 4c** assess that operation.

*Ridge Gap Waveguide Beamforming Components and Antennas for Millimeter-Wave Applications DOI: http://dx.doi.org/10.5772/intechopen.105653*

#### **Figure 3.**

*Microstrip to printed ridge gap waveguide transition. (a) Front and side views of the model. (b) Fabricated transition. (c) simulated and measured S-parameter responses.*


#### **Table 2.**

*Dimensions of the microstrip\PRGW transition illustrated in Figure 3.*
