**1. Introduction**

Wireless technology and devices are fundamental components in many aspects of life including personal communications, internet activities, sensing, and imaging applications for industrial and medical purposes. Wireless technology development is always encouraged by the needs of these applications to enhance their performance in terms of service quality and cost. A fundamental issue in wireless technology is the system operating frequency which varies according to the target application. An overview of the operating standards in wireless technology reveals that most systems nowadays operate in the microwave frequency band below 3 GHz [1–7]. The current state of wireless applications reflects the demand for using higher frequency bands to enhance the performance of the wireless system. For instance, communication technology is rapidly pushed toward next-generation networks where massive data rates, very low latency, and a high level of service integration are required to enhance the performance of the wireless communication system [8, 9]. To achieve these demands, much higher bandwidths must be used to increase the capacity of the communication channel. Imaging systems are also in the demand of using higher frequencies to overcome the resolution limits at the lower microwave band. Millimeter-Wave frequency range is beyond 30 GHz, where the relative bandwidth is equivalent to multiples of frequency channels at the sub 3 GHz range. Moreover, the signal wavelength at mm-Wave is significantly small and enables high-resolution imaging. These advantages have encouraged the move to the mm-Wave band and have ignited the spark of innovating components with superior characteristics in these high frequencies [10–13].

Many challenges are addressed in the literature, where the small-signal wavelength at the mm-Wave band results in components with small physical dimensions that need high tolerance fabrication facilities with an extremely large cost. In addition, being an advantage that enables integrating large systems in a small area, this is also a limiting property for the power that can be handled by an mm-Wave communications device [14–16]. Hence, antenna arrays must be used in mm-Wave transceivers to provide a suitable amount of gain, especially to compensate for the large path loss caused by atmospheric attenuation at frequencies like 60 GHz and such [17, 18]. Furthermore, the high level of versatility in the next generation network requires running multiple services simultaneously, a property that forces the use of a diversity technique to enable various communications without the need to add bandwidth [19, 20]. Such demand can be realized using multiple-input multiple-output (MIMO) systems employing beamforming techniques to benefit from the deployed high gain array [21, 22]. Therefore, the beamforming antenna array is an essential subject in mm-Wave research in the context of next-generation networks and imaging systems. Several techniques are proposed to implement a beamforming antenna array, which required the usage of various microwave components including power dividers, crossovers, phase shifters, hybrid couplers, and antennas [23–26]. However, the realization of these components at mm-Wave frequencies using traditional printed guiding technologies is another key challenge that needs to be tackled. Although traditional guiding structures such as microstrip line and stripline support a Q-TEM mode, which is subject to minimal dispersion, it has high radiation and dielectric losses at mm-Wave frequencies [27]. On the other hand, a modern guiding structure such as substrate integrated waveguide (SIW) is developed at mm-Wave frequencies as it has low radiation losses compared to microstrip line and stripline structures [28, 29]. However, it can support only TE mode which is subject to large dispersion and causes signal distortion [30, 31]. In addition, the signal is totally propagating inside a dielectric, which leads to high losses at mm-Wave frequencies. Therefore, a novel technology of guiding structures is introduced to provide a solution for the mentioned challenges. This technology is the printed ridge gap waveguide (PRGW) technology that was introduced as a novel low loss Q-TEM guiding structure for the mm-wave frequency range [32–40].

The printed ridge gap structure is shown in **Figure 1a**, where the operating mechanism is based on the idea of wave suppression between a perfect electric conductor

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

**Figure 1.**

*Parallel Plate PEC/PMC structure. (a) PRGW with mushroom EBG cells. (b) achieving propagation with added longitudinal middle strip (c) blockage condition.*

(PEC) and a perfect magnetic conductor (PMC) parallel to each other. Such parallel plate structure does not allow wave propagation unless the separation between the plates is enough for achieving zero tangential fields at one plate and zero normal at the other. This cannot happen for separations less than a quarter wavelength. Such condition is used to prevent wave leakage through the sides of the guiding structure, where adding a middle ridge allows having a propagating mode in the longitudinal direction as shown in **Figure 1b**. Since the PMC material does not exist in practice, an emulation of such material is the artificial magnetic conductors (AMCs) that can be implemented using the mushroom-like Electromagnetic Band Gap (EBG) structure in **Figure 1a**. The design of PRGW has been well addressed in the literature, which starts by designing the EBG-cells to support the required bandgap over the operating

#### **Figure 2.**

*Design of electromagnetic band gap (EBG) structure. (a) EBG unit cell. (b) PRGW line segment and simulated dispersion diagram showing the propagating Q-TEM mode.*


**Table 1.**

*dimensions of unit cell in EBG structure designed for 26–40 GHz band.*

bandwidth. **Figure 2a** shows the EBG unit cell used to design the PRGW feeding line, where the geometrical parameters are listed in **Table 1**. As shown in **Figure 2b**, modelling the cell on CST MWS simulation software proves to achieve a bandgap covering the entire mm-Wave Ka-band of 26–40 GHz [41].

This chapter is organized in four sections as follows: Section 2 introduces two main transitions, from microstrip line and from coaxial line to PRGW that allow the integration with other technologies. Section 3 focuses on the design of PRGW hybrid couplers, crossovers, and phase shifters, which are the main building blocks of the beam switching networks. Section 4 discusses several designs of antenna elements and arrays with various polarizations and excitation techniques. The integration of the previous components to form a beam scanning antenna system will be discussed in Section 5, while the last section concludes the introduced material.
