## 2 Antenna Design and Configurations
They can be accurately represented by composite right-/left-handed (CRLH) transmission lines, integrating the properties of capacitors and inductors, and additional modifications are required to achieve a broadside radiation pattern. The proposed MIMO LWA integrates uneven components, such as lengthwise slots designed to enhance OSB performance and crosswise slots intended to address OSB-related challenges. As a result, these features adjust the radiation pattern to optimize it for broadside emission rather than end-fire or back-fire directions. Additionally, the slots  
Figure 1: The proposed antenna: (**a**) perspective view and (**b**) side view. enhance the separation between antennas in the array and reduce surface waves generated by LWAs. The characteristic mode approach is utilized to study and develop these slots, assessing their influence on the radiation pattern throughout the design process--from start to finish--while accounting for the concepts of asymmetrical radiation, as shown in Figure 2.  
Figure 2: A simulated prototype of the proposed antenna: (**a**) layer 1 (Interface 2/6 is air), (**b**,**c**) layer 3, (**d**) layer 4, (**e**) layer 5, and (**f**) layer 6. The waveguide port in the proposed antenna uses the TE\({}_{10}\) mode, unlike the TE\({}_{01}\) mode in the dielectric inset. As shown in this figure, the antenna's radiation relies on an asymmetrical structure to improve the OSB. The symmetrical slots with the TE\({}_{10}\) mode produce no horizontal field at the aperture. In contrast, asymmetrical T- and L-shaped slots induce a horizontal TEM wave for broadside radiation. Adjusting slot asymmetries controls the TE\({}_{10}\) leakage rate, and the new design mitigates leakage through slot spacing and asymmetries, maintaining fixed inset spacing [34]. The antenna initially utilizes basic microstrip lines (Interface 3/6) on a dielectric base and the ground coplanar waveguide technique, where waves travel through the rectangular patch and escape whenever they encounter a slot in the design. The currents originating from the source flow through the microstrip, scattering due to impedance variations on the surface to form the intended radiation. The antenna achieves two resonances at 3.2 GHz and near 7.6 GHz. Moving to the second phase, a rectangular patch is modified by carving out a long longitudinal U-shaped slot, introducing a disturbance and leakage. This disruption in the patch's current flow boosts the array's beamwidth and impedance range while generating an additional resonance around 5.6 GHz and expanding the upper 7.6 GHz band. However, this adjustment pushes the operational frequencies--3.2 GHz, 5.6 GHz, and 7.6 GHz--upward, needing a shorter transverse section in the U-slot to counteract the shift. The transverse slot acts as a left-handed capacitive series, altering the radiation direction away from both end-fire and back-fire patterns. In the third stage, three smaller U-shaped slots of varying widths were placed in a nesting configuration, taking into account the surface current distribution (SCD) figures presented later in the text. These slots offer a multi-band feature that introduces an approximate extension at a lower band, from 3.8 GHz, and a resonance around 8.65 GHz. It also widens the lowest resonance and slightly lowers the third one. In the fourth stage (Figure 3), two strips were added at the back of the substrate as the ground section of the ground co-planar waveguide (GCPW) technique to broaden the operational bandwidths at these bands, along with another resonance around 15 GHz. In addition to these ground strips, two elliptical split ring resonators (ESRRs) forming a complementary ESRR (CESRR) are added at the back, covering the substrate radially to reduce the negative fringing fields and improve the antenna's performance around 8.5 GHz.