Phase II Final Report - NASA's Institute for Advanced Concepts

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Planetary Exploration Using Biomimetics An Entomopter for Flight on Mars tivity, the number of emitters must increase in order to get adequate angular coverage. In the limit, this will approach the number of emitters found in the phased array, the difference being that one is a conformal array while the other is a more planar array. 4.3.4.2 Requirements Driving the Antenna Design The goal is to accomplish the described requirements with as much overlap in functionality as possible for power conservation. For this application, the obstacle detection poses the most stringent requirements, so the focus will be on this aspect of the project first. It would be beneficial to use the same antenna to provide front hemispherical coverage for communications as well as obstacle detection. Phased array antennas are commonly used for searching and tracking applications where the 2D or 3D location of an object must be provided. A hemispherical domeshaped phased array as described in [129] would fulfill all these requirements. However, a large number of antenna elements would be necessary, each requiring a carefully designed signal path to eliminate phase differences between different paths. In addition, each signal path requires a phase shifter and gain-controlled low noise amplifier. The phase and gain are controlled to provide the desired antenna pattern. The complexity of this design may prohibit its use for this application where low power and reliability are critical. Switched arrays, on the other hand, offer more simplicity, because pattern diversity can be achieved by controlling the state of a number of RF switches but produce a limited number of beam patterns. In this way, beam coverage and resolution can be controlled selectively on a “need only” basis. In this way, power is conserved by illuminating only the required coverage area for the functionality needed at a certain time (obstacle detection, communications, etc.). The linearly tapered slot antenna (LTSA) circular array (sunflower antenna) shown in Figure 4-8 and described in [240 and 154] is one such switched array that could fulfill the Entomopter's multifunctional needs. A photo of an operational K-band sunflower antenna is shown in Figure 4-8. This antenna, proposed for mobile communications, is fed by a 1:16 microstrip line power splitter composed of T junctions and right angle bends. A conventional microstrip-toslotline transition is used to electromagnetically couple the output ports of the splitter to the slotline of the LTSA. The measured radiation pattern of this endfire antenna is shown in Figure 4-9 at 19.8 GHz when the antenna is placed over a reflecting ground plane. From the figure it is obvious that the antenna beam is omnidirectional in the azimuthal plane and is displaced about 28 degrees above the horizon in the elevation plane. The displacement in the elevation plane is proportional to the distance between the antenna and the ground plane. As shown in Figure 4-10, by removing the ground plane, this displacement above the horizon can be removed and the antenna beam centered about the elevation angle φ = 0 o . The shape of the sunflower elements can be varied to achieve the desired frequency, bandwidth, gain and 3 dB antenna beam bandwidth. This antenna has advantages of wide bandwidth operation and compact configuration, making it an attractive antenna for this mission where onboard space is limited and very wide band signals are being considered. It resembles a hockey puck that can be mounted easily on the Entomopter body. The diameter of the K-band design shown in Figure 4-8 is approximately 16 cm (6.3"). A potential mounting scenario is shown in Figure 4-11, where half of the LTSA is mounted on the front and half on the back of the Entomopter. In this way, when all elements are illuminated, 360 o of azimuthal coverage can be obtained by slightly widening the first and last sunflower pet- 244 Phase II Final Report
Chapter 4.0 Entomopter Flight Operations 4.3 Entomopter-borne Active Emitters for Navigation and Communication als to provide just over 180 o of azimuthal radiation at the front and back antennas. The overlapping patterns would provide full azimuthal coverage for communication as shown in Figure 4- 12, where an illustration of the top view of the Entomopter and antenna patterns are shown. The inherent gain variation of this antenna in elevation can be used to provide only the needed gain above and below the Entomopter (where the range is considerably less), and maximum gain in front, back, and to the sides (where range is considerably larger) as shown in Figure 4-13, where a side view of the Entomopter and antenna patterns are shown. The elements can be switched on and off to achieve narrower beams in azimuth for obstacle detection. The shape and number of elements can be varied to provide adequate gain and horizontal/vertical resolutions. If additional resolution or coverage is needed for obstacle detection in elevation, additional hockey puck halves can be configured above/below the mounting scenario shown in Figure 4-11. A single element, or sunflower petal, could be configured on the bottom of the Entomopter so that its narrow tip is pointing down for altimetry. This would provide the needed coverage as shown in Figure 4-13. The antenna would be designed so that its beam width is wide enough to maintain ground contact when the vehicle is banking, with maximum expected pitch and roll angles. The distance below would be calculated based on an inertial knowledge of the bank angle and an assumed flat surface beneath. This will require less complexity than steering the beam over small angles to keep it vertical. Altimetry accuracy is not critical at large altitudes, and when the Entomopter is close to the ground, it will probably not be doing high-angle pitch and roll maneuvers (except possibly during flare-out for landing). The full antenna as shown in Figure 4-8 could be mounted on the refueling rover to provide coverage needed for communications. Monopulse techniques could also be performed using the elements, or sunflower petals, to determine the azimuthal position of the Entomopter relative to the rover. The rover antenna would be mounted on a ground plane to achieve an antenna pattern displaced from the horizon. Figure 4-8: Linearly Tapered Slot Antenna (LTSA) Circular Array (Sunflower Antenna) 245
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Planetary Exploration Using Biomime
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Table of Contents Table of Contents
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List of Tables List of Tables Table
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List of Figures List of Figures Fig
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List of Figures Figure 3-54: Pressu
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List of Figures Figure 3-138: Stere
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List of Figures Figure 4-24: Averag
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List of Contributors List of Contri
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Executive Summary Executive Summary
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Chapter 1.0 Introduction Chapter 1.
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Chapter 1.0 Introduction Figure 1-2
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Chapter 1.0 Introduction 1.1 Histor
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Chapter 1.0 Introduction 1.2 Origin
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Chapter 1.0 Introduction 1.3 Missio
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1.3.3.1 Surface Imaging The Entomop
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Chapter 2.0 Entomopter Configuratio
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Chapter 3.0 Vehicle Design 3.1 Wing
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3. Density: 1.40E-2 kg/m 3 4. Press
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Chapter 3.0 Vehicle Design 3.4 Reci
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Chapter 3.0 Vehicle Design 3.5 Fuel
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Appendix B: Sizing Results Length 0
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Appendix B: Sizing Results Lenght 0
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Appendix C: List of References Appe
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Appendix C: List of References 41.
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Phase II Final Report - NASA's Institute for Advanced Concepts

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