## 3 Antenna Design and Parameters Study  
### Design and Simulation of the EBG MPAs  
As suggested in [23], the band-gap performance is improved as the number of EBG rings increases. However, when applying the mushroom-like EBG ring structure to the CubeSat platform, we will face the challenge of surface area limitation. It will be difficult to design two or more EBG rings with reasonable spacing around the MPA for the EBG structure to be effective. Therefore, practically for CubeSat MPA designs in the X-band and below, the number of EBG rings should only be one when applying to the 10 cm \(\times\) 10 cm surface area. However, not all of that area can be used for antenna mounting, because the four outer corners of the surface are the protruding terminals of the four main rails, where the satellite's deployment switches can be mounted for CubeSats to use the Poly Picosatellite Orbital Deployer (P-POD) launcher tube [31; 32]. Furthermore, according to the CDS of Cal Poly, the total height of the antenna structure must not exceed 6.5 mm in the direction normal to the surface from the plane of the rails [6]. This constraint  
Figure 2: Examples of the deployment of a mushroom-like EBG structure: (**a**) the single-element MPA and (**b**) the MPA array. ensures compatibility with the P-POD deployment system and prevents interference with adjacent payloads during the launch. However, this is a stringent condition that limits many attractive high-gain antenna designs, such as multiple EBG layers, metamaterial superstrates, or the Frequency Selective Surface (FSS), being applied to CubeSat. Our single-layer EBG antenna design offers a viable solution that can compromise between these CubeSat requirements and the antenna performance. Figure 3 illustrates the primary structure of a 1U CubeSat with protruding rails and the available surface area (colored in blue) on which the antenna can be mounted on the \(\pm\)Z side. This figure also shows the unavailable areas in which the rails are located (colored in red). The metallic and non-metallic parts of the antenna are indicated in yellow and white, respectively. Our proposed X-band EBG MPAs for circular polarization (CP) are designed as shown in Figure 4. The antenna includes an outer ring of 16 mushroom-like EBG elements, which surround the main patch radiator at the center; these components are located on the top layer of the antenna and are all made of copper. Each EBG element has a connecting via at the center that connects them through the dielectric substrate to a normal copper ground layer. The dielectric substrate is Rogers RT5880 which has the thickness h = 1.6 mm and the permittivity \(\varepsilon\) = 2.2. The gaps between the EBG elements and the presence of these connecting via form the L and C components of the mushroom EBG structure, as explained above. When the EBG elements are arranged periodically in a ring around the center patch radiator, a composite surface with a frequency-selective bandgap behavior is created. Furthermore, the EBG ring modifies the local effective permittivity and permeability in the areas where it is present, resulting in the suppression of the surface wave propagation. Therefore, the metamaterial characteristics of the antenna structure have been created. Each EBG element has the dimensions of 10 mm \(\times\) 10 mm, which is the same as that of the center patch radiator, and the spacing between two adjacent EBG elements is 2 mm. The four outer corners of the antenna are cut off to allow it to be mounted on the CubeSat surface without touching the rails, and each cut-out square is 15 mm \(\times\) 15 mm in size. Though the EBG ring is the main factor in increasing the antenna gain, these truncated corners also contribute to this increment, as will be discussed later. The input impedance of the antennas is 50 Ohms, and the center square patch is fed by a single-probe feed using an SMA connector from the antenna ground plane. Figure 3: (a) The 1U CubeSat primary structure; (b) the available zone for antenna mounting.