# CubeSat-Based Observations of Lunar Ice Water Using a 183 GHz Horn Antenna: Design and Optimization
## 4 Smooth-Walled Horn Antenna Fabrication and Practical Results
### Fabrication Process  
The fabrication of the horn antenna was conducted using 3D printing technology, with ABS as the material of choice. The ABS allowed for a precise yet cost-effective production of the smooth-walled antenna. Subsequent to the 3D printing process, a copper conductive thin layer was brushed on the antenna surface. This step involved brushing the antenna with the paint to provide a conductive layer, thereby enabling it to function as an antenna. In Figure 9, we show a fabricated antenna with a copper conductive surface. Utilizing the facilities at the Beijing Institute of Technology, we tested the functionality of our smooth-walled antenna design. In our experimental setup, we utilize a 220 GHz multiplier and a 220 GHz mixer to down-convert signals into the frequency range of DC to 3 GHz. This enables us to evaluate the functionality of the antennas in sending and receiving data. In this configuration, one antenna functions as the transmitter, while the other acts as the receiver. As depicted in Figure 10, the transmitter antenna is connected to a receiver, which, in this case, is a 220 GHz multiplier. The multiplier multiplies the 61 GHz input signal with a 12 dB power to generate a 183 GHz signal, which is then transmitted by our smooth-walled antenna. On the receiver side, another smooth-walled antenna is connected to a 22 GHz mixer, with a 6 dB Local Oscillator signal as the entry. This setup down-converts the received signal to a 1 GHz baseband. At this stage of our experiment, our primary objective is to verify the capability of the copper-coated antenna in signal transmission. Figure 10 illustrates the presence of signals on the oscilloscope, confirming the successful transition capability of our antennas. This step serves to demonstrate that the antennas are indeed capable of transmitting and receiving signals. In the subsequent paragraph, we will present practical measurements of the antennas' VSWR and \(S_{11}\) parameters, further validating the performance of our smooth-walled antennas. Our primary goal is to streamline the fabrication of high-frequency corrugated horn antennas and to verify that the functionality remains consistent between the smooth-walled and corrugated horn designs. To achieve this, we utilized the advanced Keysight E5080A ENA analyzer, capable of measuring \(S_{11}\) and VSWR parameters of our smooth-walled antenna with precision. During the practical measurements, we connected the smooth-walled antenna to the Keysight E5080A ENA using suitable coaxial cables and connectors for the 183 GHz  
Figure 9: Fabricated smooth-walled horn antenna. frequency range. We performed accurate calibration using a well-defined calibration kit to remove any systematic errors from the measurement setup. Subsequently, we initiated the \(S_{11}\) measurement, wherein the ENA sent a signal to the smooth-walled antenna and precisely measured the reflected signal. The obtained \(S_{11}\) data represented the reflection coefficient of the antenna at various frequencies. The practical results for \(S_{11}\) were presented in Figure 11, depicting the antenna's performance in terms of impedance matching. Figure 11: \(S_{11}\) Measurement results for smooth-walled antenna. Figure 10: Experimental setup demonstrating the transmission and reception of signals between two smooth-walled antennas. Furthermore, we conducted VSWR measurements on the same setup to assess the magnitude of impedance mismatch between the smooth-walled antenna and the transmission line. The Keysight E5080A ENA precisely calculated VSWR based on the measured \(S_{11}\) data. The practical VSWR results were illustrated in Figure 12, showcasing the antenna's impedance-matching capabilities across the operating frequency range. By leveraging the Keysight E5080A ENA analyzer for \(S_{11}\) and VSWR measurements, we validated the smooth-walled antenna's functionality in effectively transmitting and receiving signals at 183 GHz.