Signal processing and radio ranging system

• US 4,887,088 A
• Filed: 11/23/1988
• Issued: 12/12/1989
• Est. Priority Date: 10/12/1984
• Status: Expired due to Term

• Current Assignee: MBDA UK Ltd. (MBDA SAS)
• Original Assignee: British Aerospace, Inc.
• Inventors: Beckett, Andrew R.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US07/275,596
• Time in Patent Office: 384 Days
• Field of Search: 342/128, 342/145, 342/61, 342/134, 342/129-132, 342/192, 342/194-196
• US Class Current: 342/128
• CPC Class Codes: G01S 13/341 wherein the rate of change of the transmitted frequency is adjusted to give a beat of predetermined constant frequency, e.g. by adjusting the amplitude or frequency of the frequency-modulating signal
• CPC Class Codes: G01S 13/584 adapted for simultaneous range and velocity measurements
• CPC Class Codes: G01S 13/64 Velocity measuring systems using range gates

Abstract

A radio slant ranging system having a bank of range gates producing outputs X_I to X_N which comprise ground clutter components on a thermal noise pedestal. The clutter components are regarded as defining a single sinusoidal ripple envelope on the noise pedestal and a clutter centroid tracking signal is derived by using a digital filter to calculate the real and imaginary components A_1R and A_1I of the transform: ##EQU1## and then forming the arctangent of A_1I /-A_1R. The signal processing method used in the system may have general application.

Claims

1. A method of radio ranging comprising the steps of:

receiving a radar return signal;

discriminating the radar return signal to form a plurality N of range channel signals X₁ to X_N representative of return signal components associated with respective ones of N consecutive range cells; and

determining the location of the centroid of a peak in the ripple envelope defined by the range channel signals by filtering those signals to form the real and imaginary components A_1R and A_1I, respectively, of the A₁ transform of a discrete Fourier transform;

##EQU7## and then calculating a range error signal from the arctangent of A_1I /-A_1R.

2. A radio ranging system comprising;

receiver means for receiving a radar return signal;

discriminating means connected to the receiver means for discriminating the radar return signal to form a plurality N of range channel signals X₁ to X_N representative of components of said return signal associated with respective ones of N consecutive range cells;

filter means connected to the discriminating means for forming respective signals representative of the real and imaginary components A_1R and A_1I, respectively, of the A₁ transform of a discrete Fourier transform;

##EQU8## and calculating means connected to the filter means for calculating a range error signal from the arctangent of A_1I /-A_1R so as to determine the location of the centroid of a peak in the envelope defined by the range channel signals.

3. A radio ranging system for use on board an airborne weapon to determine the slant range from the weapon to the ground, the system comprising:

radar means for illuminating the ground and for receiving clutter returns from the ground;

range gate means connected to the radar means for discriminating the clutter returns to form a plurality N of range channel signals X₁ to X_N representative of clutter returns received from within respective ones of N range cells; and

centroid locating means connected to the range gate means for determining the location of the centroid of a peak in the ripple envelope defined by the range channel signals, said centroid locating means comprising filter means for forming respective signals A_1R and A_1I, respectively, of the A₁ transform of a discrete Fourier transform;

##EQU9## and calculating means connected to the filter means for determining a range error signal from the arctangent of A_1I /-A_1R.