# CubeSat-Based Observations of Lunar Ice Water Using a 183 GHz Horn Antenna: Design and Optimization
## 1 Introduction
Over the past 50 years, corrugated horn antennas have been well collected as feeds for reflector antennas [21]. The diverse capabilities of corrugated horn antennas make them a valuable tool in remote sensing applications, particularly in space [22]. Their ability to operate over a wide frequency range and their superior performance characteristics make them highly desirable for the development of remote sensing instruments [23; 24]. At these frequencies, the size of the antenna becomes very small and fabrication tolerances become very tight. As a result, even minor variations in the fabrication process can cause significant malfunctioning in the antenna [25]. Hence, simpler horn antennas are preferred in CubeSat remote sensing applications due to their enhanced gain, directivity, and ease of manufacturability. Such antennas have been used in planetary water detection missions, including the 183 GHz smooth-walled corrugated horn antenna designed for a CubeSat THz spectrometer payload [26; 27]. Horn antennas play a key role in reflectometry systems. There are several horn antenna options available for quasi-optic systems, but among them, the corrugated horn antenna fulfills the requirements for reflectometry systems [28]. Establishing high-frequency antennas presents unique challenges [29]. To overcome these, we initiate our process by creating a model of the corrugated horn antenna in MATLAB, followed by a simulation of the antenna using CST software, from which we obtain initial simulation results. These results then undergo a smoothing process, as we input the corrugated horn antenna's (x, y) data into MATLAB's smooth spline curve fitting tool, thereby transforming the corrugated data into a smooth-walled format. This approach provides the data necessary to transition from a corrugated to a smooth-walled horn antenna design. Simulation results of the smooth-walled horn antenna demonstrate that applying the smooth spline algorithm enhances antenna gain and directivity, improves side lobe bands, and expands bandwidth. In the end, we successfully manufactured a smooth-walled horn antenna using a 3D printer and ABS plastic material. We thoroughly evaluated the functionality of the fabricated antenna, including \(S_{11}\) and VSWR results. This cost-effective method offers viable options for employing the antenna on CubeSat engineering models or primary models, effectively demonstrating the functionality of the mission and payload. Moreover, this approach proves invaluable for university student projects, enabling them to assess their designs at an affordable price and explore concepts related to magnetic fields. Our plan is to integrate this antenna into a 3-Unit CubeSat platform, which will also include a THz subharmonic mixer-spectrometer. The mission will orbit the moon to determine the presence of ice water. The integrated system is designed to capture the moon's surface spectrum in the 160 GHz-200 GHz frequency range, thus enabling the detection of water spectral signatures and the identification of ice water locations on the moon's surface [29]. This paper introduces our methodology and theoretical concept, beginning with an explanation of the corrugated horn antenna formula. Subsequently, we demonstrate the transformation of this corrugated design into a smooth-walled antenna using MATLAB's spline curve fitting algorithm. The simulation of both antennas is presented, comparing the results and revealing that, within an equivalent waveguide, aperture, and horn length, we achieve nearly identical magnetic behavior. Next, we proceed with the fabrication of the antenna, highlighting the utility of our proposed design in CubeSat remote sensing applications. By showcasing the successful implementation of our antenna in this field, we emphasize its practicality and effectiveness. This research lays the groundwork for using the smooth-walled antenna in CubeSat missions, particularly in the context of remote sensing, thereby contributing to advancements in space exploration and satellite technology experimental works.