Using radar targets of opportunity to build a monopulse calibration table

In a radar system, a method of determining off-bore sight angles of a target using a plurality of signals received from the target at sum and difference antenna channels of a rotating radar antenna at each azimuth angle of a plurality of azimuth angles, the method comprising the steps of:

• a) at each azimuth angle θi of a plurality of i azimuth angles, calculating a normalized received signal ΔVi for signals that are received at the antenna from a target from a Vsum signal and a Vdiff signal;
• b) calculating the target's actual azimuth angle θboresight as the sum of the product of all θi−ΔVi, divided by the sum of all ΔVi;
• c) for each of the i azimuth angles θ, of step a), calculating an off bore sight angle 74 off bore sight i for each corresponding ΔVi by calculating the difference between each azimuth angle θi, of step a) and the azimuth angle θboresight determined in step b) to obtain i, off-bore sight angles, θoff bore sight i, whereat a corresponding ΔVi of step a) was determined;
• d) correlating each of the normalized received signals ΔVi obtained at step a) to a corresponding off-bore sight angle θoff bore sight angle i determined in step c).

A radar system comprised of:

• a rotating antenna that receives signals at sum and difference antenna channels from targets at different elevations, within an angular-shaped beam, the center of which is the antenna's bore-sight, the angle formed between a reference direction and the bore-sight being an azimuth angle;
• a receiver coupled to the antenna and receiving signals from the sum and difference channels of the antenna in an elevation angle range;
• a computer coupled to the receiver and receiving data that represents signals received at the sum and difference channels of the antenna;
• and
• memory, coupled to the computer, said memory storing program instructions, which when executed cause the computer to:
• a) calculate a normalized received signal from a target of opportunity in an elevation angle range at each of a plurality of i different azimuth angles θ, using a signal received from the target at the antenna's sum channel and using a signal received from the target at the antenna's difference channel;
• b) identify an azimuth angle θboresight of where the target of opportunity is actually located, as the azimuth angle whereat the magnitude of the normalized received signal obtained in step a) is greatest;
• c) for each of the other i azimuth angles of step a), calculate the difference between each of the i azimuth angles of step a) and the azimuth angle determined in step b) to obtain i, off-bore sight angles where each of the normalized received signals of step a) was determined;
• d) correlate each of the normalized received signal obtained at step a) to a corresponding off-bore sight angle determined in step c).

A radar system comprised of:

• a rotating antenna that receives signals at sum and difference antenna channels within an angular-shaped beam, the center of which is the antenna's bore-sight, the angle formed between a reference direction and the bore-sight being an azimuth angle;
• a receiver coupled to the antenna and receiving signals from the sum and difference channels of the antenna;
• a computer coupled to the receiver and receiving data that represents signals received at the sum and difference channels of the antenna;
• and
• memory, coupled to the computer, said memory storing program instructions, which when executed cause the computer to:
• a) determine at each azimuth angle θi of a plurality of i azimuth angles in an elevation angle range, a normalized received signal ΔVi for signals that are received at the antenna from a target in said elevation angle range;
• b) calculate a target's actual azimuth angle θboresight in the elevation angle range as the sum of the product of all θi·ΔVi, divided by the sum of all ΔVi;
• c) for each of the i azimuth angles θ in the elevation angle range of step a), calculate the off bore sight angle θoff bore sight of each ΔVi by calculating the angle difference between each azimuth angle θi, of step a) and the azimuth angle θboresight determined in step b) to obtain i, off-bore sight angles, θoff bore sight i, whereat each of the normalized signals ΔVi of step a) was determined;
• d) correlate each of the normalized received signals ΔVi obtained at step a) to a corresponding off-bore sight angle θoff bore sight i determined in step c).

In a monopulse radar receiver, a method of building a plurality of monopulse calibration tables from signals received from a plurality of live radar targets at a plurality of different elevation ranges, each of the plurality of monopulse calibration tables determining the off bore sight angle location of targets within a corresponding elevation range, each of the tables having N entries, each of the N entries comprising a monopulse discriminant and comprising a corresponding azimuth angle whereat signals from the live targets are obtained, the method comprising the steps of:

• receiving a first signal that identifies a first live radar target as being within a first elevation range;
• determining a first azimuth angle θ that corresponds to a first monopulse discriminant, for the first live target;
• receiving a second signal that identifies a second live radar target as being within said first elevation range;
• determining a second azimuth angle θ that corresponds to the first monopulse discriminant, for the second live target;
• calculating a running average of the first and second azimuth angles θ for the first monopulse discriminant obtained from the first and second live targets within said first elevation range;
• assigning the running average of the first and second azimuth angles θ for the first monopulse discriminant to a first monopulse calibration table for live targets within said first elevation range.