###### Abstract  
In this study, a novel pattern shaping technique is presented and applied to the uniquely designed multiple-input multiple-output (MIMO) radio altimeter antenna, acquiring area gain. Inspired by the behavior of the perfect electric conductor, the tendency to gather a diffuse pattern is exploited to create pattern shaping. A surface with a phase response of \(0^{\circ}\) at 3.824 GHz was designed to ensure that the target radio altimeter frequency of 4.3 GHz is in the immediate vicinity of the outer phase region, where the impedance is around 166.84 \(\Omega\), transforming the diffuse pattern of the top antenna into the target conical shape. Antenna reflection values are measured as \(-20.072\) dB at 4.344 GHz (port 1) and \(-27.44\) dB at 4.32 GHz (port 2), while there is 6 mm between the top antenna and its reflector. At 4.32 GHz, the envelope correlation coefficient is 0.0043, the diversity gain is 9.999, and the transmission value between the opposing ports is \(-29.08\) dB, which indicates a low mutual coupling. A  
is the subject of this study. Therefore, in aircraft such as airplanes and unmanned aerial vehicles, the MIMO structure comes to the fore for the design of antennas to occupy the least space. However, because the antennas are placed close to each other, this situation brings about a mutual coupling problem [11] and the coupling coefficient can be high [12]. Since low insulation will lead to an increase in interference, communication quality is compromised, so this issue should also be considered in MIMO designs [13; 14]. Obtaining separate patterns through feeding from different ports can be accomplished by the beam forming method, which is used in aviation applications and satellite communications as well [15; 16; 17]. In this paper, a MIMO radio altimeter antenna is proposed with enhanced radiation properties owing to its reflective surface. The reflective surface is designed so that it organizes the diffuse pattern of the antenna while reaching radio altimeter targets at the same time. The design has been conducted with the unique top MIMO antenna, which has a pattern that will work with the reflective properties of this surface. To create such a reflective surface, the electromagnetic band gap (EBG) features were evaluated with a different interpretation. EBG, which is considered as a sub-branch of metamaterials, creates surface wave suppression by stopping the advancement of surface waves on its surface and forms stop bands in the intended frequency band. The basic logic established for the formation of these band gaps is the resonance formed by capacitance created by the gaps between the unit cells, and the inductance taking place by the connection of the upper conductor and the ground plane. Studies on photonic band gap (PBG) structures, which can be considered the pioneer of electromagnetic band gap structures, were published by [PERSON] in 1993 [18] and studies on this subject gained momentum [19; 20]. In 1999, high-impedance surfaces which created bandgaps were defined by [PERSON] et al. [21]. After these developments, studies followed, in which these surfaces were used as the ground plane along with other metamaterials for antennas, improving the antenna properties [21; 22; 23; 24; 25; 26; 27]. EBG structures are used for mutual coupling reduction [28; 29], isolation from other environments [30; 31], gain enhancement [32; 33], or unique designs [34] in the antenna engineering field. In this study, the phase response of EBG surfaces was evaluated from a different perspective, inspired by the reflective behavior of perfect electric conductor (PEC) and perfect magnetic conductor (PMC) structures. Here, it is foreseen based on the observations of the authors that being in the outside vicinity of the EBG phase region helps to regularize a scattered radiation pattern. While PEC surfaces have a tendency to gather the diffused pattern of an antenna when they are close, PMC surfaces tend to protect the pattern as it is.