Multipolarized vector sensor array antenna system for search and rescue applications
The present disclosure is directed towards direction finding (DF) systems that can detect and locals a radio frequency (RF) signal (e.g. an emergency beacon) is two dimensions (i.e., azimuth and elevation). In one embodiment, a DF system comprises an array of multipolarized loop antennas coupled to a beamformer which provides monopole, dipole, and loop antenna element modal signals. The DF system may also comprise a multi-channel digital receiver system coupled to the beamformer. The multi-channel digital receiver system is configured to receive modal signals provided thereto from the beamformer which can be used for accurate two-dimensional geolocation of RF signals including, but not limited to, location of RF emergency beacon sources.
1. A direction finding system comprising:
a ground plane;
an array antenna comprising four multipolarized loop antenna elements disposed above the ground plane, the four loop antenna elements arranged in three perpendicular planes with two of the antenna elements crossed and the remaining two antenna elements in a plane that is perpendicular to the planes of the crossed elements;
a beamformer coupled to each of the loop antenna elements and configured to provide at outputs thereof, six orthogonal monopole, dipole, and loop antenna element modes in response to signals provided thereto from at least some of said loop antenna elements; and
a multi-channel digital receiver system coupled to the beamformer, wherein the multi-channel digital receiver system is configured to receive the beamformer outputs and to determine a two-dimensional geolocation of at least one radio frequency source.
2. The system of claim 1 , wherein the beamformer comprises seven hybrid magic tee components that output the monopole, dipole, and loop antenna element modes in response to signals from the loop antenna elements.
3. The system of claim 1 , wherein said loop antenna elements are provided as wire loop antenna elements.
4. The system of claim 3 , wherein a height of each of the wire loop antenna elements over the ground plane is one-quarter wavelength at a highest operating frequency of the direction finding system.
5. The system of claim 4 , wherein each of the wire loop antenna elements has a circular cross section diameter 0.003 wavelengths at a highest operating frequency of the direction finding system.
6. The system of claim 3 , wherein each of the wire loop antennas comprise at least one of: a metallic electrical conducting wire, or a rod, or a strip comprising aluminum, or brass, or copper.
7. The system of claim 1 , wherein the loop antenna elements are disposed to provide a collocated array of antenna elements having common phase centers.
8. The system of claim 1 , wherein the beamformer comprises a printed circuit board, and wherein each of the loop antenna elements is coupled to the printed circuit board using a retainer comprising a conical threaded split ferrule and a compression nut, wherein the compression nut squeezes the split ferrule closed to make both mechanical and electrical contacts to each of the loop antenna elements.
9. The system of claim 1 , wherein said digital receiver system is configured to operate over two or more switchable frequency bands.
10. The system of claim 1 , wherein the digital receiver system is configured to determine a two-dimensional geolocation of: a 457 kHz avalanche beacon, or a 406 MHz personal locator beacon for land applications, or a 406 MHz Emergency Position Indicating Radio Beacon for marine applications.
11. The system of claim 1 , wherein the direction finding system is mounted on: an aircraft fuselage, or a satellite, or a tower, or a building, or a stationary ground vehicle, or a moving ground vehicle, or a ship, or a person's apparel, or a person's accessory.
12. The system of claim 1 , wherein the direction finding system is operated to calibrate against scattering from surrounding structures including one or more of: an aircraft, satellite, tower, building, ground vehicle, ship, or backpack.
13. The system of claim 12 , wherein the direction finding system is operated to calibrate against scattering by receiving, in each of the loop antenna elements, a signal transmitted by a known radio frequency source and measuring amplitude and phase of the received signal at the loop antenna elements.
14. The system of claim 12 , wherein the direction finding system is operated to calibrate against scattering by calculating, using electromagnetic simulations, a signal amplitude and phase of a signal received by each of the loop antenna elements from a known radio frequency source.