Communications: directive radio wave systems and devices (e.g. – Testing or calibrating of radar system
Reexamination Certificate
2002-07-17
2004-03-02
Pihulic, Daniel T. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Testing or calibrating of radar system
Reexamination Certificate
active
06700531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for testing the performance accuracy of an automotive radar system. More particularly, the present invention relates to a downconversion of the automotive radar system signals in a radar target simulator in a manner to enable improved performance and lower cost radar components and assemblies.
2. Background
Automobile manufacturers have begun producing automotive radar systems. An automotive radar transmits a signal from an antenna typically located in the grill area of an automobile. The automotive radar then determines, from the delay of a return signal received by the antenna, the distance an object causing there turn signal. The automotive radar can also determine, from the Doppler frequency shift of the return signal, the speed an object causing the return signal is traveling. The automotive radar system can also determine the size of an object causing the return signal through the radar cross section (RCS). Automotive Radar Systems in the United States are configured to operate nominally within a 76-77 GHz frequency band allocated by the Federal Communications Commission (FCC) for automotive radar systems.
To assure proper performance of an automotive radar system, the device must be regularly tested. Testing is performed to assure the automotive radar system is operating within the required frequency range specified by the FCC. Testing is also performed to assure that the system is radiating adequate power. Test measurement is further made to assure that the automotive radar system is making proper calculations of distance to an object creating a return signal.
Test systems have been developed that utilize a single frequency conversion scheme to simulate moving targets, with a know radar cross section, at a prescribed distance. One such system is disclosed in U.S. Pat. No. 5,920,281 entitled “Radar Test System For Collision Avoidance Automotive Radar.” The system receives a 76-77 GHz signal from the automotive radar system and down-converts the signal to a fixed intermediate frequency (IF) at which the signal is analyzed to determine operating power and frequency and conditioned to simulate a target. The conditioned signal is then up-converted and re-radiated, either from a separate antenna or from the same antenna. For signal analysis, the system provides at least two IF signal outputs, one for monitoring frequency using a spectrum analyzer and another for monitoring power.
A test system can be configured to provide a signal return from a target with a known RCS, at a prescribed distance and moving at a certain velocity as described in U.S. Pat. No. 6,087,995 entitled “Universal Auto radar Antenna Alignment System.” For each target distance, the RCS level can be varied to simulate different target sizes. The delay is simulated using delay lines (coaxial or Bulk Acoustic) of various lengths, in parallel.
Simulated velocity is achieved by introducing false Doppler into the returned signal as further described in U.S. Pat. No. 6,087,995. False Doppler is achieved by offsetting the LO of the down-converter from that of the up-converter. One of the LO sources is a synthesizer referenced to a crystal resonator, while the other is a tunable synthesizer referenced to the crystal resonator. The two LO sources use the same crystal reference to ensure Doppler stability.
SUMMARY
In accordance with the present invention, a radar test system is provided for an automotive radar system, which provides multiple up-conversions and down-conversions. The multiple frequency conversion schemes provide for lower cost components and improved performance over previous radar test systems.
The radar test system in accordance with the present invention provides for conditioning an IF signal, lower in frequency than previous systems, to assure that an automotive radar system is simulating targets by providing variable parameters in the conditioned signal, including distance (using a SAW or coaxial device), and size (or RCS). Further variable speed (or Doppler shift) is provided at the first upconversion from the lower IF frequency rather than upconversion to the original RF frequency, enabling lower cost components to be used and more accuracy to be achieved. Testing to assure the automotive radar is operating within a desired frequency band can be performed by providing an external connection from the radar test system to a spectrum analyzer after the first downconversion. Similarly, power measurements can be provided using an external connection to a power meter after the first downconversion. A logarithmic detector is used after the first downconversion to detect the lower IF frequency, enabling the LO to be adjusted to assure the IF frequencies remain fixed.
REFERENCES:
patent: 5384572 (1995-01-01), Michaels et al.
patent: 5457463 (1995-10-01), Vencel et al.
patent: 5920281 (1999-07-01), Grace
patent: 6087995 (2000-07-01), Grace et al.
patent: 6384772 (2002-05-01), Bradley
Abou-Jaoude Ramzi
Bradley Donald
Geller David
Grace Martin I.
Noujeim Karam
Anritsu Company
Fliesler & Meyer LLP
Pihulic Daniel T.
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