Doppler complex FFT police radar with direction sensing capability

• US 7,068,212 B2
• Filed: 11/10/2003
• Issued: 06/27/2006
• Est. Priority Date: 07/21/1998
• Status: Expired due to Term

• Current Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Original Assignee: Applied Concepts Incorporated (Emerson Electric Company)
• Inventors: Gammenthaler, Robert S., Aker, John L.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/705,056
• Publication Number:
  US 20040257268A1
• Time in Patent Office: 960 Days
• Field of Search: 342/104, 342/105, 342/107, 342/109, 342113-115, 342/118, 342/127, 342/133, 342/146, 342/147, 342/175, 342192-197, 375/222, 340/939
• US Class Current: 342/114
• CPC Class Codes: G01S 13/589 measuring the velocity vector
• CPC Class Codes: G01S 7/04 Display arrangements
• CPC Class Codes: G01S 7/2883 using FFT processing

Abstract

A series of police Doppler single mode radars and a multimode police Doppler radar, all with direction sensing capability are disclosed. A quadrature front end which mixes received RF with a local oscillator to generate two channels of Doppler signals, one channel being shifted by an integer multiple of 90 degrees in phase relative to the other by shifting either the RF or the local oscillator signal being fed to one mixer but not the other. The two Doppler signals are digitized and the samples are processed by a digital signal processor programmed to find one or more selected target speeds. Single modes disclosed are: stationary strongest target; stationary, fastest target; stationary, strongest and fastest targets; moving, strongest, opposite lane; moving, strongest, same lane; moving, fastest, opposite lane; moving, fastest and strongest, opposite lane; moving, fastest, same lane; moving fastest and strongest, same lane.

Claims

1. Traffic surveillance radar apparatus having directional sensing and indication capability, comprising:

an antenna assembly for (a) transmitting radar waves of given oscillator frequency toward moving traffic targets that are both approaching and receding from said radar apparatus, (b) receiving radar waves reflected from said moving traffic targets, and (c) generating Doppler shifted RF signals representative of said received radar waves;

a mixer assembly, comprising first and second mixers with phase shift means coupled between said first and second mixers, for mixing signals having the said oscillator frequency with said Doppler shifted RF signals to respectively produce first and second sets of signals at the outputs of said first and second mixers, said first and second sets of signals including Doppler signals having a frequency equal to the difference between said oscillator frequency and said Doppler shifted RF signals;

means for converting said first and second sets of Doppler signals into digital samples; and

a digital signal processor programmed to (a) perform a fast Fourier transform on said digital samples, to determine therefrom the speed of selected ones of said moving targets and the direction of travel whether said selected ones of said moving targets are approaching or receding from said radar apparatus, and (b) display the speed of at least one of the selected ones of said moving targets and an indication of the direction of travel of the target having the displayed speed.

2. The apparatus of claim 1 wherein said digital signal processor is further programmed to display, in response to operator command, selected ones of the moving targets only approaching said radar or only receding from said radar, or both approaching and receding from said radar.

3. The apparatus of claim 1 wherein said digital signal processor is programmed to simultaneously display the speed of the strongest target along with the display of the speed of one of the targets traveling faster than the strongest target.

4. A process carried out by traffic surveillance radar apparatus capable of determining the speed of moving traffic targets and the relative direction of said moving traffic targets relative to said radar apparatus, comprising:

(a) transmitting radar waves of a given frequency toward at least moving targets approaching and receding from the radar apparatus;

(b) receiving radar waves reflected from said moving traffic targets and generating Doppler shifted RF signals representative of said received radar waves;

(c) mixing a signal of said given frequency with said Doppler shifted RF signals in a first mixer to generate, in a first channel, a first set of signals at the output of said first mixer, the output signals from said first mixer including Doppler signals having a frequency equal to the difference between said given frequency and said Doppler shifted RF signals;

(d) mixing a signal of said frequency with said Doppler shifted RF signals in a second mixer to generate, in a second channel, a second set of signals at the outputs of said second mixer, the output signals from said second mixer including Doppler signals having a frequency equal to the difference between said given frequency and said Doppler shifted RF signals, in which either the signal of given frequency or the Doppler shifted RF signals supplied to the second mixer are shifted in phase relative to the phase of the signal of given frequency or the Doppler shifted RF signal, respectively, that are supplied to said first mixer;

(e) converting said first and second sets of Doppler signals in to digital samples;

(f) performing a fast Fourier transform on said digital samples to determine therefrom the speed of selected ones of said moving targets as well as the direction of travel of said moving targets with respect to said radar apparatus; and

(g) displaying the speed of at least one of the selected ones of said moving target as well as and indication of the direction of travel of the target having the displayed speed.

5. Traffic surveillance radar apparatus having directional sensing and indication capability, comprising:

an antenna assembly for (a) transmitting radar waves of given oscillator frequency toward moving traffic targets that are both approaching and receding from said radar apparatus, (b) receiving radar waves reflected from said moving targets, and (c) generating Doppler shifted RF signals representative of said received radar waves;

a mixer assembly, comprising a phase shifter, for mixing signals having the said oscillator frequency with said Doppler shifted RF signals to respectively produce first and second sets of signals respectively including first and second sets of Doppler signals having a frequency equal to the difference between said oscillator frequency and said Doppler shifted RF signals, the first and second sets of Doppler signals being phase shifted by the phase shifter with respect to one another;

analog-to-digital converter for converting said first and second sets of Doppler signals into digital samples; and

a digital signal processor programmed to (a) perform a fast Fourier transform on said digital samples to develop an approaching target Fourier spectrum and a receding target Fourier spectrum and determine therefrom the speed of selected ones of said moving targets and whether said moving targets are approaching or receding from said radar apparatus, and (b) indicate to the user of the radar apparatus the speed of at least one of the selected ones of said moving targets and direction of travel of the target having such speed.

6. A process carried out by traffic surveillance radar apparatus capable of determining the speed of moving traffic targets and the relative direction of travel of said moving traffic targets as approaching or receding from said radar apparatus, comprising:

(a) transmitting radar waves of a given frequency in a direction to engage moving traffic targets to be respectively approaching and receding from said radar apparatus;

(b) receiving radar waves reflected from said moving traffic targets and generating Doppler shifted RF signals representative of said received radar waves;

(c) generating a first set of signals which include Doppler signals having a frequency equal to the difference between said given frequency and said Doppler shifted RF signals;

(d) generating a second set of signals which include Doppler signals having a frequency equal to the difference between said given frequency and said Doppler shifted RF signals, but which are shifted in phase relative to the phase of the first set of signals;

(e) converting said first and second sets of signals into digital samples;

(f) performing a Fourier transform on said digital samples to develop an approaching target Fourier spectrum and a receding target Fourier spectrum to determine therefrom the speed of selected ones of said moving targets as well as the approaching or receding direction of travel of said moving targets with respect to said radar apparatus; and

(g) indicating to the user of the radar apparatus the speed of at least one of the selected ones of said moving targets as well as whether the direction of travel of the target having such speed is approaching or receding from said radar apparatus.

7. A radar subsystem comprising:

an antenna;

a local oscillator having an output;

a duplexer coupled to said antenna, said local oscillator output and to a quadrature mixer input, to guide outgoing radar signals from the local oscillator to said antenna and guide reflected radar signals received by said antenna to a quadrature mixer input;

a quadrature mixer having received signal input coupled to said quadrature mixer input and having a local oscillator input, and having channel A and channel B outputs, said quadrature mixer functioning to mix local oscillator energy received at said local oscillator input with reflected radar signals received at said quadrature mixer input in first and second mixers, said first mixer having an output coupled to said channel output and said second mixer having an output coupled to said channel B output, each mixer having an input coupled to said local oscillator input and having a second input coupled to said quadrature mixer input, said first and second mixers generating quadrature output signals at said channel A and channel B outputs by either shifting the phase in any way of the local oscillator signal applied to one mixer by some integer multiple of 90 degrees relative to the local oscillator signal applied to the other mixer, or shifting the phase in any way of the reflected radar signals applied to one mixer relative to the other mixer and coupling to resulting outputs of said channel A and channel B outputs; and

at least one probe coupled to said local oscillator output and coupled to said local oscillator input of said quadrature mixer so as to supply local oscillator energy thereto;

first and second analog-to-digital converters coupled to digitize the output signals appearing at said channel A and channel B outputs; and

a digital signal processor programmed to perform a fast Fourier transform on said digital samples to generate a Fourier spectrum.

8. The apparatus of claim 7 further comprising matched amplifiers amplifying the signals at said channel A and channel B outputs and coupling the amplified signals to analog signal inputs of said first and second analog-to-digital converters, and wherein said first and second analog-to-digital converters are matched.

9. The apparatus of claim 8 further comprising matched gain control circuitry coupled to each of said channel A and channel B inputs.

10. The apparatus of claim 9 further comprising matched gain control circuitry coupled to each of said channel A and channel B inputs, and wherein the gain of said automatic gain control circuits is controlled by one or more signals from said digital signal processor.

11. The apparatus of claim 7 further comprising a display and switches coupled to said digital signal processor, and wherein said digital signal processor is programmed to receive user inputs from said switches governing which search mode to use and is programmed to perform searching in a predetermined number of different modes including the ability to search for targets selected only from the class of targets which have relative velocities approaching the radar or targets selected only from the class of targets having relative velocity receding from the radar.

12. The apparatus of claim 11 wherein said digital signal processor is programmed to have search modes in which fastest targets can be found in either the class of targets with approaching relative velocities or receding relative velocities and their speed displayed.