###### Abstract  
A novel patch phased array antenna with improved scanning performance is presented in this paper. The active element pattern is changed as desired through a modified SIW cavity, resulting in an extension of the phased array's 3 dB scanning range. Furthermore, sequential rotation is used to reduce the cross-polarization level of the array, which also improves the scanning gain at \(\pm\)45\({}^{\circ}\). Without altering the element size or profile, the array has the merits of low cost, low complexity, and a simple feed structure. The presented phased array antenna (PAA) exhibits a gain fluctuation of less than 2.2 dB when steering to 45\({}^{\circ}\). Furthermore, the cross-polarization levels are below \(-\)68.1 dB when scanning to 45\({}^{\circ}\) in a E-/H-plane over the whole working band. To validate the proposed design, a prototype of a 24 \(\times\) 16 active PAA is designed, fabricated, and measured. A good agreement between the simulated and measured results is achieved, Thus, this paper offers a viable solution to enhance the scanning performance of a PAA with fixed interelement spacing. phased array antenna; low gain fluctuation; low cross-polarization levels; sequential rotation 2024202 In general, we use a simple ideal \(\cos(\theta)\) pattern as the element factor. As the scanning angle moves away from broadside, gain decreases as a cosine function. This is due to the roll-off of the element pattern impacting the array pattern. Typically, conventional PAAs can scan its main beam from \(-45^{\circ}\) to \(+45^{\circ}\) with a gain fluctuation of \(4\)-\(5\) dB [4]. Therefore, it cannot satisfy the requirements of most practical applications. Moreover, it is very challenging for MPA PAAs to be designed with high performances and wide-angle scanning abilities due to the appearance of scanning blind spots. Generally, scan spots are a phenomenon that can be explained as the phase matching of the forced resonance of surface waves in the dielectric substrate with the Floquet modes [5]. PAAs will fail to radiate or receive electromagnetic energy to the free-space when near scan blindness angles because the mutual coupling between surface waves and substrate waves leads a strong impedance mismatch that allows the magnitude of the active reflection coefficient to reach the channel. Therefore, most of the power transmitted by the PAA is reflected back to its sources. Consequently, achieving good impedance matching and eliminating the possibility of scan blindness occurrences are critical aspects in designing high-performance PAAs. Some methods have been developed to compensate the mutual coupling among elements and obtain high-performance PAAs [6; 7]. Tightly coupled dipole arrays use mutual coupling to enhance wide-angle scanning [8]. However, this approach requires small interelement spacing (generally less than \(0.3\lambda\)), which increases the number of cells for a given aperture array; consequently, the number of transmit/receive (T/R) channels increases, leading to heightened system costs, particularly for larger arrays. In general, for a given scan range and desired PAA gain, we use large spacing to reduce the number of elements in general. A more common approach is to suppress mutual coupling. Strong mutual coupling between elements can significantly reduce an antenna's realized gain, increase side lobes, and decrease efficiency during array steering with large elevation angles. While increasing the distance between elements can mitigate these effects, it must be noted that beyond a certain distance, undesired grating lobes may appear, particularly for thick substrates. To address this challenge, various techniques have been proposed, including wide-angle impedance matching (WAIM) surfaces [9], metasurfaces [10; 11; 12], modes [13], metal walls [14], SIW cavities [15; 16], reconfigurable technology [17], decoupling networks [18], cavity backing [19], and shorting posts [20].