Randomized surface reflector
A metal plate of small, reflective cells of varying, random (within a limited rage) heights that reflect radio frequency energy such that individual reflective paths are of random length, adding neither constructively nor destructively, and thus not creating a standing wave condition between the reflective plate and the emitter or receiver is disclosed.
1. A method of calibrating a radiometer, comprising:
determining the attributes of a feed horn of the radiometer;
constructing a randomized surface reflector based on the attributes of the feed horn,
wherein the randomized surface reflector is comprised of a plurality of cells arranged on a plate, each cell having a randomly determined height above a baseline;
obtaining an actual temperature of the feed horn;
placing the randomized surface reflector adjacent to the feed horn so that the randomized surface reflector reflects the electromagnetic signals of the feed horn;
measuring the radiometric temperature of the feed horn based on a signal reflected from the calibration surface;
replacing the randomized surface reflector with an object of known temperature;
measuring the temperature of the object of known temperature based on the signal emitted from the object; and
calculating a calibration coefficient for the radiometer based on the actual temperature of the feed horn, the measured temperature of the feed horn, the actual temperature of the object, and the measured temperature of the object.
2. The method of claim 1 , wherein the step of placing the randomized surface reflector further comprises placing the randomized surface reflector so that the distance between the feed horn and the randomized surface reflector is equal to the length of the side of the randomized surface reflector divided by twice the tangent of a 25 dB taper angle of the feed horn.
3. The method of claim 1 , wherein the step of constructing a randomized surface reflector comprises constructing the sides of the randomized surface reflector so that a main lobe of the feed horn is contained within the perimeter of the randomized surface reflector to a power level greater than 25 dB below a power level at the center of the main lobe when the main lobe is centered on the randomized surface reflector.
4. The method of claim 1 , wherein each cell is of a different height above the baseline then the height of adjacent cells.
5. The method of claim 1 , wherein the random height is a random integer multiple of ¼ wavelength at a center frequency of a frequency band of interest.
6. The method of claim 5 , wherein the integer is between zero and twenty.
7. The method of claim 5 , wherein each cell is a square and the cells are arranged in a grid.
8. The method of claim 7 , wherein each cell has sides that are greater than one wavelength at a lowest frequency of a frequency band of interest.
9. The method of claim 7 , wherein each cell has a flat top and sides perpendicular to the flat top.
10. The method of claim 1 , wherein the plate is comprised of a non-ferrous, conductive material.
11. The method of claim 1 , wherein the plate is comprised of a plurality of repeating sections of cells.