Stabilizing method of synthetic aperture radar and position determining method thereof

A position determining system for determining a position of a radar platform, comprising:

• a radar mounted on the radar platform;
• and
• at least three signal answer back means arranged in predetermined mutually different positions;
• the radar including means for transmitting at least three first signals having mutually different predetermined frequencies to the at least three signal answer back means;
• each signal answer back means including:
• means for receiving one of the first signals transmitted from the radar;
• and
• means for transmitting a second signal, having a predetermined frequency, to the radar platform in response to receiving the one of the first signals,
• the radar further including:
• means for receiving the second signals transmitted from the signal answer back means;
• first detecting means for detecting times from the transmitting of the first signals to the receiving of each of the second signals;
• second detecting means for detecting phases of each of the second signals received;
• first calculating means for calculating distances between the radar platform and the signal answer back means on the basis of the times detected and the phases detected;
• and
• second calculating means for calculating a position of the radar platform on the basis of known positions of the signal answer back means and the distances calculated.

A motion compensation method of a synthetic aperture radar mounted on a radar platform, comprising the steps of:

• a first step for transmitting a first signal having a predetermined frequency from the radar to at least three signal answer back means arranged in predetermined mutually different positions;
• a second step for receiving the first signal transmitted in the first step by each signal answer back means;
• a third step for generating in each of the signal answer back means a second signal by frequency modulating the first signal with a predetermined modulation frequency;
• a fourth step for transmitting the second signal from each signal answer back means toward the radar platform;
• a fifth step for receiving the second signals transmitted from the signal answer back means by the radar;
• a sixth step for detecting times from the transmitting of the first signal to the receiving of each of the second signals, by the radar;
• a seventh step for detecting phases of each of the second signals received in the fifth step by the radar;
• an eighth step for calculating distances between the radar platform and the signal answer back means on the basis of the times detected in the sixth step and the phases detected in the seventh step;
• a ninth step for calculating a position of the radar platform on the basis of known positions of the signal answer back means and the distances calculated in the eighth step;
• a tenth step for generating a reference signal for motion compensation on the basis of the position of the radar platform, calculated in the ninth step;
• an eleventh step for transmitting a signal from the radar to an object to be acquired and receiving a reflected signal from the object;
• and
• a twelfth step for multiplying the reference signal for motion compensation by the reflected signal received in the tenth step,
• the position calculated in the ninth step varying depending on an inclination of the radar platform, the reference signal for phase compensation generated in the tenth step varying depending on the inclination of the radar platform, a phase variation of the reflected signal received in the eleventh step being compensated by the multiplying in the twelfth step.

A system for determining a position of a radar platform, comprising:

• a radar mounted on the radar platform;
• and
• at least three signal answer back means arranged in predetermined mutually different positions, each of the signal answer back means including:
• means for receiving a first signal transmitted from the radar;
• means for generating a second signal by frequency modulating the first signal with a predetermined frequency, and
• means for transmitting the second signal to the radar platform;
• the radar further including:
• means for transmitting the first signal;
• means for receiving each second signal transmitted from each of the signal answer back means;
• first detecting means for detecting time periods from the transmitting of the first signal to the receiving of each of the second signals;
• second detecting means for detecting phases of each of the second signals received;
• first calculating means for calculating distances between the radar platform and each signal answer back means on the basis of the time periods detected and the phases detected;
• and
• second calculating means for calculating a position of the radar platform on the basis of known positions of the signal answer back means and the distances calculated.

A synthetic aperture radar system including motion compensation comprising:

• a radar mounted on a radar platform;
• and
• at least three transponders, each transponder including:
• a receiver that receives a first signal from the radar;
• a frequency modulator that frequency modulates the first signal at a predetermined modulation frequency to create a second signal;
• a transmitter that transmits the second signal to the radar;
• and the radar further including:
• a transmitter that transmits the first signal;
• a receiver that receives each second signal from each of the transponders;
• a relative distance calculator that calculates distances from the transponders and the radar based on time and phase differences between the first signal and the second signals;
• a platform position calculator that determines the position of the radar platform based on known positions of the transponders and the distances from the transponders to the radar;
• a reference signal phase compensation generator that generates a reference compensation signal based upon the position of the radar platform;
• a radar transmitter that transmits a signal from the radar to an object to be acquired by the radar;
• a radar receiver that receives a reflected signal from the object to be acquired;
• and
• a multiplier that combines the received reflected signal with the reference compensation signal.