Radar speedometer

The method of measuring the speed of a vehicle moving over a fixed surface comprising the steps of:

• producing an output Doppler frequency spectrum which is a function of the speed of the vehicle from a narrow beam of microwave energy transmitted toward the surface at a predetermined angle with respect to the direction of travel of the vehicle and reflected from the surface;
• processing all signals in the Doppler frequency spectrum produced by said first means to produce a normalized Doppler spectrum having a number of signals of different amplitudes and frequencies;
• and
• producing an output signal from the normalized Doppler spectrum which output signal is the weighted mean of the normalized Doppler spectrum and which output signal is a predetermined function of the speed of the vehicle with respect to the surface.

Apparatus for measuring the speed of a vehicle moving over a fixed suface comprising:

• directional antenna means adapted to be mounted on the vehicle for directing a beam, having an axis of transmitted signals of RF energy, toward the surface over which the vehicle is moving and for receiving reflected signals of the transmitted RF energy from the surface;
• first circuit means connected to the antenna means for producing the RF energy transmitted by the antenna and for producing Doppler signals, the frequencies of which are the difference between the transmitted signals and the reflected signals, said Doppler signals having a received spectrum which deviates from an idealized spectrum of said Doppler signals;
• an AGC circuit to which the Doppler signals from the first circuit means are applied for producing as its output, spectra of said Doppler signals having substantially constant maximum amplitudes;
• tracking band pass filter means to which the output of the AGC circuit is applied which passes signals substantially within the bank pass of the tracking filter means, said tracking band filter having a Q which substnatially matches the Q of the idealized spectrum of the Doppler signals and said tracking band pass filter having a center frequency;
• and
• second circuit means connected to the tracking band pass filter means to which is applied signals of the spectrum of the tracking band pass filter within the band pass of the filter for producing an output signal the frequency of which is the weighted mean of the frequencies of the Doppler signals and which output signal substantially corresponds to the center frequency of the pass band of the tracking filter means at any given time and which frequency is a function of the speed over said fixed surface.

The method of measuring the speed of a vehicle moving over a fixed surface comprising the steps of:

• directing a narrow beam of RF energy from a source mounted on the vehicle toward the surface and producing Doppler signals from the beam reflected back toward the vehicle within said beam, said Doppler signals having a spectrum;
• normalizing the amplitude of the spectrum of the Doppler signals;
• normalizing the frequency distribution of the spectrum of Doppler signals by filtering from the spectrum of the Doppler signals normalized in amplitude substantially all signals of the spectrum the frequencies of which do not lie within the pass band of a tracking band pass filter, said pass band having a Q which substantially matches the spectrum of the Doppler signals normalized in amplitude and frequency;
• and
• producing from the signals of the Doppler spectrum, normalized in amplitude and frequency, an output signal which is the weighted mean of the frequencies of the Doppler signals and which is a predetermined function of the speed of the vehicle relative to said fixed surface.

Apparatus for measuring the speed of a locomotive moving over a roadbed comprising:

• a directional antenna mounted on the underframe of the locomotive for directing a narrow beam of transmitted microwave energy toward the ground, said beam having a boresight which intersects the surface of the roadbed substantially at an angle .theta. and has a beam width of 60 ;
• a transceiver connected to the directional antenna for producing the microwave energy which is transmitted by the antenna and for producing Doppler signals by mixing transmitted signals with received signals reflected from the roadbed within the beam of the antenna, said Doppler signals having a frequency distribution which is a function of the speed of the vehicle and the position of the portions of the surface with respect to the bore sight from which the received signals are reflected, and the amplitudes of which are a function of the reflective characteristics of said portions and the Doppler frequency of the signals reflected from the portion of the roadbed intersected by the boresight frequency;
• an amplifier circuit connected to the transceiver for amplifying the Doppler signals;
• an AGC circuit connected to the amplifier circuit for varying the amplitudes of the Doppler signals amplified by the amplifier circuit so that the maximum amplitudes of the frequency distributions of the Doppler signals at its output are substantially constant;
• a plurality of tracking band pass filters;
• circuit means for applying the output of the AGC circuit to the tracking band pass filters, each tracking band pass filter having an operating frequency range, the operating frequency ranges of the filters overlapping the range of frequencies corresponding to the range of speeds of the locomotive to be measured;
• a phase locked loop;
• and
• circuit means for connecting to the phase locked loop signals from the one of said plurality of tracking filters whose operating range includes the boresight frequency for the speeds of the locomotive relative to the roadbed at any given time;
• said phase locked loop producing an output signal whose frequency is a predetermined function of the speed of the locomotive with respect to its roadbed.