## 1 Introduction  
Microstrip patch antennas (MPAs) are broadly used in various types of applications. These antennas have many advantages like low profile, low cost, and easy integration with other devices [1, 2, 3, 4, 5, 6, 7]. However, traditional MPAs usually suffer from some drawbacks like narrow operating bandwidth, low efficiency, and robust cross-polarized fields [8]. The operating bandwidth of single-feed MPAs could be increased by using thick dielectric materials with low dielectric relative permittivity [9], creating resonance slots [10], parasitic patches [11], or advanced electromagnetic structures [12, 13, 14, 15, 16]. However, these approaches could increase the surface currents of MPAs, which could have a negative impact on the antenna's radiation characteristics and efficiency. Microstrip lines and coplanar waveguides (CPWs) are often used to feed conventional microstrip patch antenna arrays. The operating bandwidth of conventional MPAs with these planar feeding networks is usually less than 5%. By increasing operating frequency,these planar antennas often face many serious problems and challenges. In particular, in higher frequencies, unwanted radiations have suddenly appeared from the feeding network, and the antenna's efficiency has increasingly dropped [17; 18; 19; 20; 21; 22]. The radiation efficiency of wireless communication systems is one of the most important parameters that can increase their reliability. The antenna radiation efficiency in satellite and remote-sensing applications is essential due to the inherent losses in long-distance communications. Limiting the antenna's efficiency can have a direct impact on bandwidth [23; 24; 25] and gain [26; 27]. MPA arrays are commonly fed by microstrip lines. Microstrip lines are typically preferred because they facilitate the routing of low-profile feeding networks. They do, however, introduce unwanted radiation losses, which could have a significant impact on the antenna's radiation performance and reduce its radiation efficiency. Substrate integrated waveguide (SIW) technology is one of the best alternatives for microstrip lines and CPWs at higher frequencies. Despite the fact that SIWs require more space than microstrip networks, they provide reliable performance at a higher frequency. In recent years, SIW technology has been used for a wide variety of applications due to its advantages, such as low cost, low loss, and ease of integration. Compared to hollow rectangular waveguide structures, SIW structures have many of the same features and similar radiation characteristics, but they are much less expensive. SIW technology, therefore, could be an effective replacement for RWG. Various types of microwave and millimeter-wave components, such as antennas, feeding networks, filters, etc., have been implemented using SIWs [28; 29; 30; 31; 32]. Different strategies have been used to feed MPA with SIW feeding networks. Vertical integration between MPA and an SIW cavity is one of the most effective methods [33; 34]. This method leads structures to be compact. These architectures are well known cavity-backed patch antennas. In cavity-backed patch antennas, two different strategies can be used to excite radiating elements; 1. probe feeding (PF) and 2. aperture coupling (AC). Although, by using the PF method, the impedance characters can be significantly improved, these structures still suffer from high cross-polarization levels [35; 36]. Surface currents and higher mode excitation produce robust cross-polarization fields in these antennas. More detailed investigations on conventional MPAs confirm that there are serious concerns about the cross-polarization radiations in these antennas. In rectangular microstrip patch antennas, the cross-polarization level at the H-plane is usually higher than at the E-plane. The cross-polarization level in these antennas and in a range of beamwidth \(\pm\)25 degrees is usually between \(-\)10 and \(-\)18 dB.