# A Multi-Band Circularly Polarized-Shared Aperture Antenna for Space Applications at S and X Bands
## 2 Proposed Antenna Geometry  
The proposed shared aperture antenna comprises three square-shaped dielectric layers and two square-shaped microstrip printed elements for the S-band and X-band operation. The S-band antenna is designed for use with the uplink/downlink communication system for telemetry, tracking, and command (TT&C) data reception and transmission. The sole objective of the X-band antenna is to downlink large mission data gathered by the CubeSat to the ground station within a short ground pass. To serve the same purposes, CubeSats are normally equipped with two separate conventional antennas. This proposed antenna is compact in size, and due to its planer ground shape, it can be easily integrated with the CubeSat structure.  
Figure 1 shows the structure of the proposed antenna. The dielectric layer-1 of the antenna is h mm thick Rogers RT/duroid 5880. The square-shaped copper ground plane of the antenna has a length of g mm and thickness of 35 \(\upmu\)m and is placed at the bottom of the dielectric layer-1. The X-band patch is placed on the upper surface of the dielectric layer-1. The X-band square patch antenna has a length of L\({}_{3}\) mm with a negative perturbation of q\({}_{\rm c}\) mm. The dielectric layer-2 is stacked on top of the dielectric layer-1. This layer also has am h mm-thick Rogers RT/duroid 5880 material. Any copper cladding from the bottom of the dielectric layer-2 is removed. On top of the dielectric layer-2, a slotted square-ring patch with a crossed strip at the center is etched, which operates as the S-band antenna [23]. It has a length of L\({}_{1}\) mm and negative corner perturbation of p\({}_{\rm c}\) mm, as shown in Figure 2. Four equal-sized square-shaped slots or perforations are present inside the S-band square ring antenna. An X-band patch antenna can be placed in the middle of any of these four slots, making sure that the S-band ring patch does not block the radiation of the X-band patch antenna. A patch antenna operating in the X-band is placed in the bottom-left slot, as shown in Figure 2. Two separate 50\(\Omega\) coaxial probes are used to feed the S-band and X-band patch antennas. The dielectric layer-3 is made of h\({}_{\rm u}\) mm-thick Rogers RT/duroid 6010. It is placed on top of the second dielectric layer using nonconductive bolts. An air gap of h\({}_{\rm a}\) mm separates the dielectric layers 2 and 3. Dielectric layer-3 works as a partial reflective surface (PRS) for the X-band patch antenna. Placing the PRS at an approximate 0.5\(\chi\)\(\chi\)\(\chi\) is the wavelength at the resonance frequency of the X-band patch antenna) distance away  
from the X-band antenna means that a Fabry-Perot Resonator Cavity Antenna (FPRA) [24] is formed. FPRAs can exhibit high gain compared to normal patch antennas.  
The center of the antenna is placed at the origin of the coordinate system, as shown in Figure 2. The feed location of the S-band patch and the X-band patch is given with respect to the origin. The antenna has a total volume of 60 \(\times\) 60 \(\times\) 20 mm\({}^{3}\). Table 1 describes the parameters of Figures 1 and 2 and their optimized values for the proposed antenna.  
\begin{table}
\begin{tabular}{l l c c} \hline \hline
**Antenna Parts** & **Parameters** & **Symbol** & **Value (mm)** \\ \hline \multirow{6}{*}{Antenna Main Structure} & Dielectric Layer-1 height & h & 0.787 mm \\ \cline{2-4}  & Dielectric Layer-2 height & h & 0.787 mm \\ \cline{2-4}  & Air gap distance & h\({}_{\rm a}\) & 16.2 mm \\ \cline{2-4}  & Dielectric Layer-3 height & h\({}_{\rm u}\) & 2.5 mm \\ \cline{2-4}  & All dielectric layers and ground & g & 60 mm \\ \cline{2-4}  & Plane length & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: The design parameters of the S- and X-band-shared aperture antenna.  
Figure 1: Proposed S- and X-band shared aperture antenna (**a**) Antenna structure in isometric view; (**b**) Side view of the antenna.  
Figure 2: Geometry of the proposed S- and X-band patches.