Electromagnetic detection apparatus

• US 4,305,074 A
• Filed: 05/12/1980
• Issued: 12/08/1981
• Est. Priority Date: 05/12/1980
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Wakeman, David R., Green, Dennis A., Barzana, Luis C.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US06/148,890
• Time in Patent Office: 575 Days
• Field of Search: 343/7 A, 343/10, 343/16 R, 343/113 R
• US Class Current: 342/100
• CPC Class Codes: G01S 13/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S13/46
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured

Abstract

An electromagnetic detection apparatus for sensing an object, has a transter for radiating electromagnetic energy toward the object. The apparatus also has an array of at least three spaced receiving antennas and one parasitic antenna. The parasitic antenna is spaced from and mounted alongside the array. Also included is a phase detection circuit for measuring the phase difference between signals received by one of the receiving antennas with respect to the other two. This apparatus can sense phase difference and correlate it to the azimuthal position of the object.

Claims

1. Electromagnetic detection apparatus for sensing an object, comprising:

transmission means for radiating electromagnetic energy toward said object around a given transmission frequency and with a swept frequency;

an array of at least three spaced receiving antennas wherein each of the antennas of said array is spaced from the nearest other one of said antennas by a distance corresponding to about one-quarter of the wavelength of said transmision frequencey;

a parasitic antenna spaced from and mounted alongside said array, wherein said receiving and parasitic antennas are arranged as the four corners of a square;

mixing means responsive to said array for reducing its recieved signals in frequency by an amount corresponding to the frequency being radiated by said transmission means, whereby swept returns from an object are converted to a constant frequency that is a function of the range of said object;

phase detection means for measuring the phase difference between signals received by a given one of said receiving antennas and the other ones of said receiving antennas, whereby said phase difference varies with the angular position of said object;

a controlled oscillator having a control input for producing a local signal at a frequency bearing a predetermined relation to the signal applied to said control input; and

frequency conversion means for changing the frequency of the output of said mixing means by an amount corresponding to the frequency of said local signal.

2. Electromagnetic detection apparatus according to claim 1 further comprising:

a frequency sensing means driven by said conversion means for producing a signal indicative of whether the output frequency of said conversion means exceeds a predetermined magnitude, said sensing means driving said control input.

3. Electromagnetic detection apparatus according to claim 2 wherein said sensing means comprises:

a pair of filters having contiguous passbands; and

differential means for producing a differential signal that is a function of the difference in magnitude of the outputs of said pair of filters, said differential signal being applied to said control input of said conrolled oscillator.

4. Electromagnetic detection apparatus according to claim 1 further comprising:

an upper conductive plate, said receiving and parasitic antennas comprising four parallel monopoles perpendicularly mounted on said upper plate; and

a lower conductive plate, said transmission means comprising a monopolar transmission antenna perpendicularly mounted on said lower plate.

5. Electromagnetic detection apparatus according to claim 4 wherein said upper conductive plate is sized and positioned to shield said array from said transmission antenna.

6. Electromagnetic detection apparatus according to claim 5 further comprising:

an upstanding strut mounted on said lower plate, said upper plate being mounted on said strut.

7. Electromagnetic detection apparatus according to claim 6 wherein said strut comprises:

four rods, each aligned with a corresponding one of said receiving and parasitic antennas.

8. Electromagnetic detection apparatus according to claim 7 further comprising:

an upper plurality of spaced, coplanar, conductive arms projecting outwardly from the edge of said upper plate; and

a lower plurality of spaced, coplanar, conductive arms projecting outwardly from the edge of said lower plate.

9. Electromagnetic detection apparatus according to claim 1 further comprising:

high pass filter means driven by said mixing means for supplying to said phase detection means a signal that is substantially invariant in magnitude with respect to the range of the object.