Digital antenna positioning system and method

• US 3,924,235 A
• Filed: 10/23/1973
• Issued: 12/02/1975
• Est. Priority Date: 07/31/1972
• Status: Expired due to Term

• Current Assignee: Francis T. Annulis, Robert I. Heller, Walter Jachimski
• Original Assignee: Francis T. Annulis, Robert I. Heller, Walter Jachimski
• Inventors: Heller, Robert I., Annulis, Francis T., Jachimski, Walter
• Primary Examiner(s): Farley, Richard A.
• Assistant Examiner(s): Montone, G. E.
• Application Number:
  US05/408,963
• Time in Patent Office: 770 Days
• Field of Search: 343/5DP,7.4,7.3,7.7,17.1R,16M
• US Class Current: 342/75
• CPC Class Codes: G01S 13/68 for angle tracking only

Abstract

A digital system for positioning an antenna of a tracking radar system, particularly of the type employing a driven beam reflector of the type utilized in a cassegrain antenna system, without the use of rate gyros. Signals representing various angular quantities are simultaneously sampled periodically and all preliminary functions such as normalizing are performed before the data is stored. The handling of the data as a block of data eliminates undesirable time skewing and the digital data may be used as a block of data in positioning the radar antenna. A digital target line-of-sight error signal representing the error between the radar beam line-of-sight and the target lineof-sight in a line-of-sight coordinate system is generated and then referenced to a fixed coordinate system. In a radar system employing an antenna having an axis system corresponding to the beam line-of-sight axis system, the line-of-sight error signal is referenced to the fixed coordinate system by first referencing the error signal to an aircraft axis system and then to the fixed coordinate system to obtain a fixed coordinate referenced error signal. The fixed coordinate referenced line-of-sight error signal may then be employed to generate fixed coordinate referenced line-of-sight error rate and position signals through the use of a predetermined transfer function and an integrator having a predetermined, fixed coordinate system referenced constant of integration. The line-of-sight position signals referenced to the fixed coordinate system may then be used to generate antenna angular pointing error signals which may be used to drive the antenna in a direction tending to null the line-ofsight error signal. In a system employing a driven beam reflecting element such as in a cassegrain system, the rotation affect of the reflector on the beam is taken into account in referencing the line-of-sight error signals to the fixed coordinate system. Moreover, the complex relationship between beam position and reflector position is accounted for in transforming to and from the fixed coordinate system. A method and system for generating line-of-sight angular rate signals for use in fire control systems is also disclosed.

Claims

1. In a radar antenna positioning system, a method for normalizing data signals comprising the steps of:

a. Initially sampling electrical data signals representative of a constant multiplied by the sines and cosines of twice the azimuth and the elevation angles of the reflector;

b. simultaneously sampling electrical data signals representaTive of a constant multiplied by the sines and cosines of the angular deviation of the aircraft axes from the axes of a predetermined coordinate system;

c. simultaneously sampling the AC line voltage;

d. calculating a reference constant in response to the data signals representative of each angle;

e. generating, in response to the calculated constants, normalized signals representing the data signals with all constants removed;

f. updating, at a predetermined sampling rate, the sampling of the data signals and the AC line voltage;

g. comparing the initial AC line voltage sample with the updated sample;

h. modifying the reference constant in response to the comparison of the initial and updated AC line voltage samples;

i. calculating updated normalized signals in response to the updated samples of the data signals and the modified reference constant; and

, j. recalculating, at a regular rate lower than the sampling rate, updated reference constants and reference AC line voltage samples for each data signal.

2. A method of positioning an antenna of a radar system mounted on a movable platform having a platform axis system comprising the steps of:

a. generating signals representing platform attitude relative to a fixed coordinate system and antenna position relative to the platform axis system, the signals being related in amplitude to a reference voltage;

b. simultaneously sampling all of the generated signals and the reference voltage as a first block of data signals and temporarily storing the block of data signals at a first time;

c. generating a first reference normalization constant for the first block of data signals by calculating the square root of the sum of the squares of each of the data signals in the first block of data signals;

d. normalizing each of the data signals in the first block of data signals in response to the first generated reference normalization constant;

e. temporarily storing each of the normalized data signals in a buffer memory until all normalized data signals of the block of data signals are stored;

f. transferring all of the normalized data signals as a block of normalized data signals from the buffer memory into an operational memory; and

, g. generating antenna positioning signals responsively to the block of normalized data signals in the operational memory.

3. The method of claim 2 including the steps of:

generating a normalization constant for subsequent blocks of data signals subsequent to the first block in response to the value of the first generated normalization constant and the ratio of the values of the reference voltage in the subsequent blocks of data signals and the first sampled reference voltage; and

, generating a second reference normalization constant for each data signal in a subsequent block of data after sampling a predetermined number of blocks of data signals.

4. The method of claim 3 wherein the reference normalization constant is calculated for each data signal of the sampled blocks of signals at a different sampling time.

5. In a radar antenna positioning system, apparatus for normalizing data signals comprising:

means for sampling electrical data signals representative of a constant multiplied by the sines and cosines of twice the azimuth and the elevation angles of the reflector;

means for simultaneously sampling electrical data signals representative of a constant multiplied by the sines and cosines of the angular deviation of the aircraft axes from the axes in a predetermined coordinate system;

means for simultaneously sampling the AC line voltage;

means for calculating and subsequently re-calculating on a relatively low frequency basis a reference constant in response to the data signals representative of each of the angles;

means responsive to said calculating means for generating normalized data signals representing the data signals with all constants removed;

means for updaTing the sampling of the data signals and the AC line voltage;

means for comparing the initial AC line voltage sample with the updated sample and for modifying the reference constant in response thereto; and

, means responsive to said sample updating means and to said reference constant modifying means for calculating updated normalized signals.

6. The apparatus of claim 5 including:

means for generating digital radar tracking error signals; and

, means for positioning the radar antenna to track a target in response to the normalized data signals and the tracking error signals.