Method and system for calibration of a phase-based sensing system

A phase-based radar system useful for obtaining a distance to a target comprising:

• a signal source operative to generate a plurality of transmit signals and a plurality of corresponding reference signals in response to sweeping in selected frequency increments a frequency band of the signal source;
• an antenna, functionally coupled to the signal source, for transmitting the transmit signals and receiving a plurality of received signals, wherein each received signal represents a reflection of one of the transmit signals off of the target;
• at least a pair of detectors, functionally coupled to the antenna and to the signal source, for detecting the received signals and the reference signals;
• and
• a processor operative to identify a rate of change of phase between the reference signals and the received signals as detected by the at least pair of detectors,
• the processor further operative to calculate the distance to the target based on the rate of change of phase as a function of frequency between the reference signals and the received signals,
• wherein a propagation medium connects the signal source to the antenna, the frequency band comprises the stopband of the antenna, the target comprises the antenna, and the distance to the target comprises the length of the propagation medium.

A computer-implemented method for calibrating a phase-based radar system useful for obtaining a distance to a target, the phase-based radar system comprising a signal source, an antenna and at least a pair of detectors, comprising the steps of:

• (a) identifying a length of a propagation medium to the antenna by:
• transmitting a plurality of transmit signal to the antenna via the propagation medium and a plurality of corresponding reference signals for detection by the at least pair of detectors in response to sweeping in selected frequency increments the signal source within a stopband of the antenna,
• receiving a plurality of received signals from the antenna via the propagation medium, each of the received signals representing a reflection of one of the transmit signals off of the antenna,
• determining a rate of change of phase between the reference signals and the received signals as detected by the at least pair of detectors, and
• calculating a distance from the signal source to the antenna based on the rate of change of phase as a function of frequency between the reference signals and the received signals;
• (b) identifying the distance to the target by:
• transmitting a plurality of transmit signals to the antenna via the propagation medium and a plurality of corresponding reference signals for detection by the at least pair of detectors in response to sweeping in selected frequency increments the signal source within a passband of the antenna,
• receiving a plurality of received signals from the antenna via the propagation medium, each of the received signals representing a reflection of one of the transmit signals off of the target,
• determining a rate of change of phase between the reference signals and the received signals as detected by the at least pair of detectors, and
• calculating the distance to the target based on the rate of change of phase as a function of frequency between the reference signals and the received signals;
• and
• (c) completing a calibration of the phase-based radar system by subtracting the length of the propagation medium from the distance to the target to obtain a distance between the antenna and the target.

A computer-implemented method for obtaining a distance to a target by use of a phase-based radar system comprising a signal source, at least a pair of detectors offset in phase, and an antenna, comprising the steps of:

• (a) transmitting a transmit signal for transmission via the antenna and a corresponding reference signal at a transmit frequency within a predetermined frequency band of the signal source;
• (b) receiving a received signal via the antenna, the received signal representing a reflection of the transmit signal from the target;
• (c) measuring an amplitude level for the received signal and the reference signal at each of the least pair of detectors, each amplitude level representing a phase difference between the reference signal and the received signal, and storing each amplitude level in a memory storage device to maintain a record of stored amplitude data;
• (d) changing the transmit frequency to another transmit frequency within the predetermined frequency band and repeating steps (a), (b) and (c), the other transmit frequency representing an incremental change in the transmit frequency;
• (e) repeating step (d) until the predetermined frequency band of the signal source is swept;
• (f) calculating a complex Fast Fourier Transform (FET) for the stored amplitude data;
• and (g) calculating the distance to the target by identifying a peak frequency, normalized by the Nyquist rate, for the complex FFT, multiplying the peak frequency by the incremental change in the transmit frequency to derive a target result, and dividing the target result by a constant value.

A computer-implemented method for obtaining a distance to a target by use of a phase-based radar system comprising a signal source, a pair of detectors offset in phase, and an antenna, comprising the steps of:

• (a) transmitting a transmit signal for transmission via the antenna and a corresponding reference signal at a transmit frequency within a predetermined frequency band of the signal source;
• (b) receiving a received signal via the antenna, the received signal representing a reflection of the transmit signal from the target;
• (c) measuring an amplitude level for the received signal and the reference signal at each of the detectors, each amplitude level representing a phase difference between the reference signal and the received signal, deriving a phase value by calculating the arctangent of a ratio of the amplitude level measured at each of the detectors, and storing the phase value in a memory storage device to maintain a record of stored phase measurements;
• (d) changing the transmit frequency to another transmit frequency within the predetermined frequency band and repeating steps (a), (b) and (c), the other transmit frequency representing an incremental change in the transmit frequency;
• (e) repeating step (d) until the predetermined frequency band of the signal source is swept;
• (f) determining unwrapped phase values by completing phase unwrapping of the stored phase measurements;
• (g) calculating a slope of a line derived from a comparison of the unwrapped phase values to the wavelength for each transmit frequency in step (d);
• and
• (h) calculating the distance to the target by multiplying the slope by a ratio of the longest wavelength in step (g) to the shortest wavelength in step (g) to derive a target result and dividing the target result by a constant value.