The application of UAV in military reconnaissance field is mostly fixed-wing aircraft, such as global hawk and predator. But they have no fixed wing aircraft bulky, need a runway to land, the reconnaissance mission is confined to the reconnaissance range larger operations, is now considering the individual special operations to the demand of the UAV reconnaissance, is adopted to helicopter down small four rotor design, convenient carrying, used to fill a vacancy low-altitude reconnaissance a small scale. In addition, considering the clarity and planning of the purpose of the reconnaissance mission, the UAV can carry out the reconnaissance mission of aerial photography and return according to the predetermined route completely, and no excessive human intervention is needed in this process. Therefore, the small quadrotor is mainly designed for autonomous flight system. But fully autonomous flight can not be very good to adapt to the complex environment, for the sake of it, and the principle of liberation operators hands as far as possible, decided to adopt a simple electrical control of auxiliary control flight, to complete after being spotted by enemy UAV height of rise and fall, immediately return to action, such as to ensure the practicability of the reconnaissance drones.
This paper is aimed at improving the previous experiments of duffing oscillator detecting weak signals. The influence of phase transition direction, signal phase, frequency and amplitude on Duffing system is analyzed and a new method for detecting weak signal by Duffing Oscillator is proposed. This method detects weak signals by the way of reverse detection, and calculates the threshold through Poincare section, so that the detection is more accurate.
A double-layer metamaterial with epsilon-near-zero (ENZ) properties is proposed loading on the patch antenna. The double-layer metamaterial that has two layers of the same material and structure is produced on FR4 substrate. The gain and radiation directivity of the patch antenna can be greatly improved covering with the proposed ENZ metamaterial. Simulation results show that by coating the
ENZ superstrate, the gain of the patch antenna is increased from 5.99 dBi to 10 dBi, corresponding to 66.9% gain enhancement and greatly improved radiation directivity. While the performance of the
patch antenna is improved, the working frequency and bandwidth of the patch antenna are not affected.
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