# T-Type Vertical Wall for Decoupling and Pattern Correction of Patch Antenna
## 1 Introduction
Two modes were simultaneously excited to generate the specific null-field region to locate the feeding probe at the null field, enabling the designer to achieve extremely low mutual coupling [22]. While excellent isolations have been achieved by using so many techniques, one common problem exists, namely radiation pattern beam tilt after decoupling. This often happens for edge-to-edge spacings larger than 0.1 \(\lambda_{0}\)[4; 6; 12; 17; 19; 21; 22], and this always involves a distance of approximately 0.05 \(\lambda_{0}\)[3; 9; 10; 11; 13; 14; 15; 16; 18; 20]. This tilt affects the antenna gain in the broadside direction and the whole performance of the corresponding array. Thus, correcting the tilt towards the broadside direction for a closely spaced antenna array is necessary, and this is also the present focus for the miniaturized antenna array design. A method to correct the pattern for the single frequency was proposed using the vertical wall. However, the realized gain was very low and reduced significantly in the proposed structure [23]. In this paper, the substrate was replaced by a lower loss tangent material F4 BTM440 for the patch antenna to obtain a higher realized gain, and a single substrate vertical wall for simplifying the decoupling structure was used to realize the pattern correction at a single frequency. At the same time, the method to improve the antenna gain is also discussed in the following. The vertical wall for decoupling consists of a rectangular substrate inserted into the antenna substrate, and two symmetrical T-type metal strips are etched on the wall. In addition, a long rectangular slot is cut on the antenna substrate to hold the wall where the T-type metal is connected to the ground plane. The structure simultaneously affects the surface current, surface wave, and radiated power to reduce the mutual coupling. Proper T-type metal size is used to adjust the resonator to the desired frequency, and radiation pattern correction is realized at this frequency. The general step for the proposed technique is considered to be: (1) Conventional patch antenna design with a given close spacing, which is taken as the benchmark for the decoupling structure; (2) lossy-wall substrate determination, this determines the realized gain and the corresponding pattern correction; and (3) resonator design on the wall, the proper dimension of the resonant structure associated with the final decoupling and correction. Depending on these steps, we can migrate this technique into the specific frequency of the 5G/6G application. The rest of this paper is organized as follows. In Section 2, we introduce the whole configuration of the antenna and the corresponding decoupling vertical wall and discuss the influence factors on the antenna performance by using parametric analyses, including the dimension effect of the vertical wall and the wall substrate losses. The antenna prototype is subsequently fabricated, as shown in Section 3, and then the corresponding simulated and measured results are compared to validate the design, while the comparisons with other designs are provided later. Finally, the current distribution comparison is also shown. After these, the decoupling mechanism and equivalent circuit analysis are indicated in Section 4. The conclusion is provided in Section 5.