Communications: directive radio wave systems and devices (e.g. – Determining velocity
Patent
1988-12-01
1990-05-01
Tarcza, Thomas H.
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
342117, G01S 1358
Patent
active
049222554
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement for measuring speeds with the aid of microwave signals.
The use of microwave signals for measuring the relative speeds, or velocities, of two objects is known, inter alia, from Swedish Patent Specification No. 7307800-8. It is also known from this patent specification to use a microwave transmitter and two microwave receivers and to effect a correlation between the received signals such as to determine velocity on the basis of a time displacement between the signals.
The use of microwave signals affords several important advantages. One advantage is that such systems function well in dirty environments, while another advantage resides in the relatively long range or reach of such systems in comparison with systems which utilize, e.g., light.
Microwave systems, however, are also encumbered with a number of drawbacks.
One serious problem is that the system is dependent on differences in distances between the two receivers and the object against which the microwaves are reflected, due to the fact that the signals received in the receivers are phase dependent, these phase-dependent signals being correlated in accordance with known systems.
Such systems may be used to measure the speed of an automotive vehicle in relation to the ground. When the vehicle in question is a tractor or some other type of vehicle moving across uneven ground, the distance between respective receivers and the ground will vary. When the speed of an aircraft is measured from the aircraft, a change in attitude of the aircraft relative to the horizontal will result in a change in the distance between respective receivers and the ground.
The distance dependency consisting of such changes in distances between respective receiver antennae and the ground either gives rise to an erroneous correlating result or simply prevents correlation of the signals. The use of phase-dependent signals and their correlation is thus highly disadvantageous.
Furthermore, the correlators used to correlate phase dependent signals of microwave frequency are relatively expensive.
Another problem is that constant, relatively powerful reflexions are obtained from the immediate surroundings of the arrangement on a vehicle, such as permanent vehicle fixtures for example. The reflexes are often powerful in relation to the signals reflected against the object, e.g. against the ground.
The present invention solves the aforesaid problems, and is particularly beneficial in that the aforesaid distance dependency is eliminated.
The present invention thus relates to an arrangement which is intended for measuring speeds between a first and a second object with the aid of microwave signals and which comprises a microwave generator connected to a transmitter antenna, and two receiver antenna which are preferably placed on respective sides of the transmitter antenna and which are intended to receive microwave signals reflected against an object, and in which arrangement each receiver antenna is connected to a respective receiver channel and said channels are connected to a correlator for correlating the signals received on the receiver antennae, the mutual time difference of said Signals corresponding to the speed of said objects in relation to one another, the arrangement being characterized in that said microwave generator is also connected to a respective mixer in each of the receiver channels, respective receiver antennae being connected to respective mixers; and in that the outputs of respective mixers are connected to an envelope detector which detects the envelope of respective signals, there being formed two phase-independent signals which are compared in the correlator.
The invention will now be described in more detail with reference to exemplifying embodiments thereof illustrated in the accompanying drawings, in which
FIG. 1 is a schematic view of an arrangement which includes a transmitter and two receivers;
FIG. 2 is a block schematic of an arrangement in which homodyne envelope detection is employed;
FIG. 3 is a block sc
REFERENCES:
patent: 3147477 (1964-09-01), Dickey, Jr.
patent: 4106017 (1978-08-01), Roeder et al.
patent: 4107680 (1978-08-01), Kaplan
patent: 4176352 (1979-11-01), Tyler
patent: 4426647 (1984-01-01), Tomasi
Hellner Mark
Stiftelsen Institutet for Mikrov.ang.gsteknik vid Tekniska Hogsk
Tarcza Thomas H.
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