This paper presents an innovative circularlypolarized compact cavity antenna based on metasurfaces; the proposed design is explained starting from a linearly-polarized antenna based on similar concepts. The main objective is to cover three different GNSS systems, namely Galileo E1, GLONASS G1 and GPS L1, with a single antenna embedded in a metallic cavity. The aperture dimension is set to 0.26λ0×0.26λ0, with a central frequency of 1578 MHz. Loading the aperture with a metasurface allows an efficient radiation within such a small aperture size. Our experimental results are in very good agreement with the simulations, with an axial ratio lower than 2 dB between 1540 MHz and 1655 MHz.
The knowledge of the roll angle of a projectile is decisive to apply guidance and control law. For example, the goal of ISL's project GSP (Guided Supersonic Projectile) is to change the flight path of an air-defence projectile in order to correct the aim error due to the target manoeuvres. The originality of the concept is based on pyrotechnical actuators and onboard sensors which control the angular motion of the projectile. First of all, the control of the actuators requires the precise control of the roll angle of the projectile. To estimate the roll angle of the projectile, two magnetometers are embedded in the projectile to measure the projection of the earth magnetic field along radials axes of the projectiles. Then, an extended Kalman nIter is used to compute the roll angle estimation. As the rolling frequency of the GSP is about 22 Hz, it is easy to test the navigation algorithm in laboratory. So in previous papers ([1),[5)) the in-lab demonstration of this concept shows that the roll angle estimation was possible with an accuracy of about 1° at 22 Hz. In this paper, the demonstration is extended to in-flight test, with a roll rate about 35 Hz. Thus, two magnetometers, a DSP and a LED (to simulate a thruster) are embedded inside the projectile; the DSP runs an extended Kalman nIter and a guidance algorithm to compute the trigger times of the LED. By using a high speed camera (a trajectory tracker), we can observe that the LED is switch on at the target angle.
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