| dc.description.abstract | Ice sheets in Antarctic and Arctic regions are undergoing rapid changes, causing a rise in sea level with direct impacts on society and the global system. Airborne remote sensing offers a robust way to study changes occurring in this region and the effects on climate. The Center for Remote Sensing of Ice Sheets (CReSIS) has flown many missions in polar regions to collect data on bed topography, basal conditions, and deep internal layers by using high-sensitivity radar and advanced processing algorithms. The goal of the current study is two-fold. First, a new wing-integrated antenna concept is developed for the Meridian, an Unmanned Aerial System (UAS) designed at the University of Kansas. Second, preliminary wing-sizing equations are derived from wing-integrated antenna performance analyses. The purpose of both studies is to improve both current and future UAS sensor-platforms used for remote sensing applications, such as those currently supported by CReSIS. An improved design of a wing-integrated airborne antenna array is presented by performing an antenna trade study for three low-profile antennas. This study seeks to improve not only the gain of the antenna system but the aircraft performance by developing a structurally-embedded design. Three candidate antenna designs are carried forward to the detailed design stage. These designs include a planar dipole embedded in the lower wing skin of the vehicle, a planar dipole offset a quarter-wavelength from the conductive lower wing-skin via a custom support structure, and a quarter-wave patch antenna integrated inside the wing. Considering the existing wing size limitations for antenna array integration into the Meridian wing, two different designs are recommended—the first design strictly optimizing antenna performance for the given wing size limitations and the second design improving both the electrical and vehicle performance over the original design. The planar dipole antenna offset from a ground plane offers the best results in terms of antenna performance within aircraft’s dimensional constraint. In the first design, when antenna performance is given priority, the final offset array design results in a gain improvement of about 6 dB over existing Vivaldi system. Since the ratio of received power to transmitted power is proportional to square of the gain (by Friis equation), for an antenna acting as a transmitter and receiver, the gain is actually doubled (i.e. about 12 dB improvement in gain) in decibel (dB) scale. However, this design significantly increased drag, which is expected to reduce the vehicle range by ~31% compared to the Vivaldi system. This design also adds a total additional weight of 84 lbs. due to the antenna supporting structure and modifications made to the existing Meridian wing. The second design, a dipole array embedded in the wing (bay) skin, offers advantages for both aircraft and sensor performance. The advantages, particularly from a sensor perspective, are relatively small. When compared to the existing Vivaldi system, the embedded antenna design results in ~6% increase in aircraft range, and about 2.5 dB (actually about 5 dB by Friis equation) increase in gain. This design adds an extra weight of 9.5 lbs. per wing due to composite material modifications. The results of these two systems illustrate the constant compromise that occurs between vehicle and sensor performance, and the difficulty to optimize both systems simultaneously. This study then extends toward a sensor-driven wing sizing study, in which sensor performance requirements are considered in the preliminary design process of wing sizing. The conclusions drawn based on this study are specifically applicable to dipole (half wavelength) antenna design. Considering the higher electrical performance offered by a ground plane, a single planar dipole antenna was simulated with a ground plane. The ground plane is assumed to be the lower skin of an aircraft. The ground plane length, width, and offset from the antenna were varied. For ground plane length sizing, the width and offset parameters are kept constant, while the ground plane extension outside of the antenna edge is varied. The ground plane width and offset sizing were performed in a similar manner by keeping all other variables constant. It is determined that ground plane length and width should be 50% of the wavelength extended outside the antenna edges and the ground plane-antenna offset should be kept at 15% of the wavelength for maximum dipole antenna performance. Relationships for wing ground plane span, wing chord, and thickness are derived from extensive parametric electromagnetic simulations that provide optimum antenna performance for generic planar dipole antenna. The relationships derived are for the ground plane (conductive) portion of the wing. These equations provide a useful tool that can inform the designer of expected sensor performance while determining the wing parameters. | |
