Wide aperature radio frequency data acquisition system

• US 5,898,402 A
• Filed: 05/30/1997
• Issued: 04/27/1999
• Est. Priority Date: 05/30/1997
• Status: Expired due to Fees

• Current Assignee: Federal Communications Commission (Government of the United States of America)
• Original Assignee: Federal Communications Commission/Compliance and Information Bureau/Equipment Development Group
• Inventors: Kilpatrick, William Lloyd
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US08/865,929
• Time in Patent Office: 697 Days
• Field of Search: 342/417, 342/423, 342/424, 342/442, 342/444, 342/445
• US Class Current: 342/417
• CPC Class Codes: G01S 3/28 using amplitude comparison of signals derived simultaneously from receiving antennas or antenna systems having differently-oriented directivity characteristics

Abstract

This invention relates to a wide aperture radio frequency data acquisition system which collects coherent samples from multiple points in a defined plane at the surface of the ground. The information collected can be processed with suitable algorithms to extract the bearing, frequency, and power spectra of the arriving radio frequency wavefront.

This system consists of an antenna system; a multi-channel receiver system incorporating mixers, filters, amplifiers, analog to digital converters, digital down converters; a digital signal processor; and a computer. The electrically short, active antennas with frequency independent response are connected to the multiple channel receiving system, one channel per antenna receiving the signal. The receiver uses two frequency conversion oscillators for coarse but accurate frequency synthesis to convert the received signal'"'"'s frequency. Then, the signal is converted to a digital signal. This early conversion to a digital signal allows total intermediate frequency processing in digital mode with inherently matched filters and demodulators. The receiver is designed with low cost components to produce a very large and linear dynamic range. The digital down converter provides accurate fine tuning, bandpass filters the signal, reduces the data rate, and formats the output for extraction of amplitude and phase information from the signal.

The processing algorithm analyzes the data to determine arriving field strength, direction of arrival, elevation of arrival, frequency and power spectra of the signal. By choice of processing algorithm, the output data can be processed for either very fast information on brief signals, or thorough examination of data for fine frequency discrimination to less than one Hertz resolution.

Claims

1. A data acquisition unit for gathering data about a transmitted analog radio frequency signal having a bearing from an unknown location, comprising:

antenna array means for receiving the transmitted radio frequency signal,

said signal having a bearing, modulation, and frequency,

said array means shaped in a 60 degree triangle on a substantially flat surface with one antenna being located at the apex of the triangle, said array means having n number of antennas, wherein n=9, 11, or 13, spaced along two legs of the triangle,

said triangle having a defined apex common to both legs wherein the space between the antennas increase in a ratio of 3 to 1 from the apex on each of the two legs of the triangles,

each antenna outputting a received analog radio frequency signal having a bandwidth, frequency, and phase,

matched set of n receiver channel means for receiving said received analog radio frequency signals from each antenna of the array means and converting said received analog radio frequency signals for further processing, said receiver channel means comprising;

clock means for keeping all receiver channel means synchronized,

n sets of mixer means for translating said received analog radio frequency signals to a lower frequency, producing translated radio frequency signals,

n sets of analog to digital converter (A/D) means for converting said translated analog radio frequency signals to digital signals containing data representing said analog received radio frequency signals, and

n sets of digital down converter means for reducing the digital signals to represent a specific narrow bandwidth signals,

processor means for collecting the narrow bandwidth signals from the n sets of digital down converter means, for recording the narrow bandwidth signal, and for determining the bearing, modulation, and frequency of the radio frequency signal, and

modem means for sending the bearing, modulation, and frequency to a master control point.

2. The data acquisition unit of claim 1, further comprising:

said mixer means further comprising an up converter, a bandpass filter, and a down converter, all for removing unwanted signals from the received analog radio frequency signals,

said A/D means having a basic dynamic range, the A/D means further comprises a variable gain amplifier means for extending the dynamic range of the A/D means, and

wherein said processor means comprises means for determining the phase of said received analog radio frequency signals to calculate the bearing of the transmitted analog radio frequency signal.

11. A data acquisition unit as set forth in claim 1 further comprising:

said antenna comprising;

an active element comprising a hollow cylinder 1 meter long, having a top end, a bottom end, and a diameter of 11 cm,

a weather proof cap covering the top end of the active element,

a base comprising a hollow cylinder having a top end, a bottom end, and the diameter, said top end of the base connected to the bottom end of the active element, the bottom end of the base connected to the flat plate in a perpendicular relationship, said flat plate having multiple holes,

multiple ground rods placed through the multiple holes,

a feed wire connected to the active element, said feed wire connected to the top end of the active element,

an impedance matching amplifier connected to the feed wire, said amplifier comprising a capacitive signal splitter network to produce frequency independent response, and

coaxial cable connected to the amplifier for receiving power and carrying the signal to the receiver means.

12. A data acquisition unit as set forth in claim 2 further comprising:

said antenna comprising;

an active element comprising a hollow cylinder 1 meter long, having a top end, a bottom end, and a diameter of 11 cm,

a weather proof cap covering the top end of the active element,

a base comprising a hollow cylinder having a top end, a bottom end, and the diameter, said top end of the base connected to the bottom end of the active element, the bottom end of the base connected to the flat plate in a perpendicular relationship, said flat plate having multiple holes,

multiple ground rods placed through the multiple holes,

a feed wire connected to the active element, said feed wire connected to the top end of the active element,

an impedance matching amplifier connected to the feed wire, said amplifier comprising a capacitive signal splitter network to produce frequency independent response, and

coaxial cable connected to the amplifier for receiving power and carrying the signal to the receiver means.

3. A process of data gathering to determine desired characteristics of a transmitted analog radio frequency signal from an unknown location:

detecting the transmitted analog radio frequency signal at a specific time via a linearly dispersed antenna array and outputting n analog radio frequency signals,

wherein the transmitted analog radio frequency signal has a bearing, and the n analog radio frequency signals have a phase,

wherein the antenna array is shaped in a 60 degree triangle on a substantially flat surface,

said array having n number of antennas, wherein n=9, 11, or 13, spaced along two legs of the triangle, and

said triangle having a defined apex between two legs wherein the space between the antennas increase in a ratio of 3 to 1 from the apex on each of the two legs,

receiving said n analog radio frequency signals with a multi-channel receiver using a clock to synchronize the channels and outputting n converted radio frequency signals,

converting the n converted radio frequency signals to n digital signals, said n digital signals containing data representing the n analog radio frequency signals, via an analog to digital converter (A/D),

reducing the n digital signals to a corresponding narrow bandwidth signal by digital down conversion,

determining the phase of the n analog radio frequency signals, and

calculating the bearing of the transmitted analog radio frequency signal.

4. A process of data gathering according to claim 3 further comprising:

wherein said determining the phase comprises;

defining multiple points in time beginning at a specified time and extending over a specified time span, and

at each point in time, determining the average phase over a specified bandwidth utilizing a sample by sample method, wherein the sample by sample method comprises;

gathering the real and imaginary components of the signal at each antenna at each instant in time, and

calculating the magnitude and phase of the composite received radio frequency signal at each antenna at each instant in time, and

wherein calculating the bearing comprises;

solving for a reference wavefront plane consistent with the n multiple points.

5. A process of data gathering according to claim 4 further comprising:

using a linear regression technique to derive a best straight line phase fit along each leg according to the wavelength of the radio frequency signal and the antenna spacing, and

calculating the final bearing utilizing values determined by the best straight line fit for both legs of the antenna array.

6. A process of data gathering according to claim 3 further comprising:

wherein said determining the phase comprises;

defining multiple points equally spaced in time beginning at a specified time and extending over a specified time span,

isolating the spectral components of the radio frequency signal using fast Fourier transform techniques to reduce the interfering components from undesired signals,

calculating the phase of the selected spectral components of interest, and

wherein calculating the bearing comprises;

solving for a reference plane consisting of n multiple points.

7. A process of data gathering according to claim 4 further comprising:

wherein said calculating the bearing further comprises

averaging similar bearing calculations to yield one or more time averaged bearings over a time span.

8. A process of data gathering according to claim 6 further comprises:

wherein said calculating the bearing further comprises;

averaging similar bearing calculations to yield one or more time averaged bearings over a time span.

9. A data acquisition unit for gathering data about a transmitted analog radio frequency signal having a bearing from an unknown location, comprising:

an antenna array means for receiving the transmitted radio frequency signal,

said signal having a bearing, modulation, and frequency,

said array means comprising multiple antennas, and

each antenna outputting a received analog radio frequency signal having a phase

matched set of n receiver channel means for receiving said received analog radio frequency signals from each antenna of the array means and converting said received analog radio frequency signals for further processing, said receiver channel means comprising;

clock means for keeping all receiver channel means synchronized,

n sets of mixer means for translating said received analog radio frequency signals to a lower frequency, producing a translated radio frequency signals,

n sets of analog to digital converter (A/D) means for converting said translated radio frequency signals to digital signals containing data representing said analog received radio frequency signals, and

n sets of digital down converter means for reducing the digital signals to narrow band width signals,

processor means for collecting the narrow bandwidth signals from the n sets of digital down converter means, for recording the narrow bandwidth signal, and for determining the bearing, modulation, and frequency of the radio frequency signal, and

modem means for sending the bearing, modulation, and frequency to a master control point.

10. The data acquisition unit of claim 9, further comprising:

said mixer means further comprising an up converter, a bandpass filter, and a down converter, all for removing unwanted signals from the received analog radio frequency signals,

said A/D means having a basic dynamic range, the A/D means further comprises a variable gain amplifier means for extending the dynamic range of the A/D means, and

wherein said processor means comprises means for determining the phase of said received analog radio frequency signals to calculate the bearing of the transmitted analog radio frequency signal.

13. A data acquisition unit as set forth in claim 9 further comprising:

said antenna comprising;

an active element comprising a hollow cylinder 1 meter long, having a top end, a bottom end, and a diameter of 11 cm,

a weather proof cap covering the top end of the active element,

a base comprising a hollow cylinder having a top end, a bottom end, and the diameter, said top end of the base connected to the bottom end of the active element, the bottom end of the base connected to the flat plate in a perpendicular relationship, said flat plate having multiple holes,

multiple ground rods placed through the multiple holes,

a feed wire connected to the active element, said feed wire connected to the top end of the active element,

an impedance matching amplifier connected to the feed wire, said amplifier comprising a capacitive signal splitter network to produce frequency independent response, and

coaxial cable connected to the amplifier for receiving power and carrying the signal to the receiver means.

14. A data acquisition unit as set forth in claim 9 further comprising:

said antenna comprising;

an active element comprising a hollow cylinder 1 meter long, having a top end, a bottom end, and a diameter of 11 cm,

a weather proof cap covering the top end of the active element,

a base comprising a hollow cylinder having a top end, a bottom end, and the diameter, said top end of the base connected to the bottom end of the active element, the bottom end of the base connected to the flat plate in a perpendicular relationship, said flat plate having multiple holes,

multiple ground rods placed through the multiple holes,

a feed wire connected to the active element, said feed wire connected to the top end of the active element,

an impedance matching amplifier connected to the feed wire, said amplifier comprising a capacitive signal splatter network to produce frequency independent response, and

coaxial cable connected to the amplifier for receiving power and carrying the signal to the receiver means.

15. A data acquisition unit as set forth in claim 10 further comprising:

said antenna comprising;

an active element comprising a hollow cylinder 1 meter long, having a top end, a bottom end, and a diameter of 11 cm,

a weather proof cap covering the top end of the active element,

a base comprising a hollow cylinder having a top end, a bottom end, and the diameter, said top end of the base connected to the bottom end of the active element, the bottom end of the base connected to the flat plate in a perpendicular relationship, said flat plate having multiple holes,

multiple ground rods placed through the multiple holes,

a feed wire connected to the active element, said feed wire connected to the top end of the active element,

an impedance matching amplifier connected to the feed wire, said amplifier comprising a capacitive signal splitter network to produce frequency independent response, and

coaxial cable connected to the amplifier for receiving power and carrying the signal to the receiver means.