The Doppler spectrum from an extended object illuminated by a finite beam is analyzed theoretically. The long-time spectrum is the product of an antenna spectrum and an object spectrum, which may lead to significant systematic errors in determination of velocity. The error probability is larger for short-time spectra. Experimental results on automobiles also indicate the existence of a very wide spectrum, which may be multipeaked with incorrect dominating peaks for short periods of time. Physically the errors may be interpreted as a result of moving phase centers.

Doppler spectrum of single automobiles

This paper surveys the field of automotive radar and represents an expansion of a previous paper, "Automotive Radar-Problems and Promises" [1]. Both the roadside environment in which the car and driver operate and on-board physical environments in which the electronics must function are treated. Applications involving speed sensing, predictive crash sensing, obstacle detection, braking, and station keeping are addressed. Current radar system state of the art is reviewed. Considerations relating to target discrimination, weather penetration, and basic radar system parameters are covered. Modulation techniques for range determination are examined, and radar system configurations are discussed in an effort to identify the advantages and disadvantages of each. It is concluded that although considerable development work remains before radar becomes a practical automotive system, significant progress has been made.

Automotive radar: A brief review

Vehicular Radar Speedometer

The operation of radar speed-measuring devices is explained; it is based on the Doppler principle, which relates the frequency shifts in reflected radiation to the relative velocity between the reflecting object and observer. These devices (either stationary or moving mode) should be used only in moderately heavy or light traffic. More obvious sources of error in the stationary mode (e.g. patrol car fan, citizen's band transmissions) are identified, as well as more subtle sources ("cosine effect," radar oscillator frequency outside Federal Communication Commission specifications, and equipment "convenience" options). Sources of error in the moving mode are described, including the possibilities for erroneous target speed readings in the presence of multiple moving targets. Improved calibration test procedures and electronic speedometers to measure patrol car speeds are cited as the most important ways to improve existing equipment. Other possibilities include display improvements, range controls, beam-width optimization, and frequency standardization. Efforts to develop radar equipment performance standards are described. Separate notes describe the four classes of electronic speed-measuring devices used in traffic law enforcement (electronic speedometer, Vascar, Orbis, and radar) and explain the moving mode cosine effect.

Doppler spectrum of single automobiles

References

Automotive radar: A brief review

Vehicular Radar Speedometer

Shortcomings of radar speed measurement

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