Communications: directive radio wave systems and devices (e.g. – Testing or calibrating of radar system – By monitoring
Reexamination Certificate
2000-09-12
2001-11-13
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Testing or calibrating of radar system
By monitoring
C342S070000, C342S114000, C342S115000
Reexamination Certificate
active
06317076
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to radar systems, and more particularly to methods of range correction in radar systems.
2. Description of Related Art
Radio detecting and ranging, commonly referred to as “radar”, is used for detecting and locating an object of interest, or “target”, using the transmission, reflection, and reception of radio waves. Radar emits radio waves in a pattern emanating from the surface of the radar's antenna. Typically, radar systems are mounted to a platform such as a tower, airplane, ship, automobile or other motorized vehicle. The objective of these radar systems is to accurately locate the position of an object of interest or target relative to the radar's platform.
A number of radar techniques are well known in the art. Radar systems have been used to determine range, angular position, and range rate of objects of interest. Target range and angular position are determined by analyzing certain properties of the return radio wave signal. Target range rate is determined by taking advantage of the well-known Doppler effect. One distinguishing feature of radar systems is the type of modulation technique used to obtain range and range rate data. Examples of these different radar systems include unmodulated continuous wave (CW) radar, frequency modulated (FM) radar, pulse Doppler radar and frequency shift keying (FSK) radar. Other distinguishing features include differences in antenna types and in the approach used in extracting angular information about a target.
Radar locates a target's position by obtaining the target's “azimuth angle” and “range” relative to a reference line or a reference point of the radar antenna. A target's azimuth angle is defined as the angular distance between the antenna reference line and a line extending from the radar antenna to the target. A target's range is defined as the distance from the antenna reference point to the target. Thus defined, a target's azimuth angle and range yield a calculated target position. Many radar systems analyze frequency domain data from the return signal to calculate the azimuth angle and range of a target's position. However, the calculated range does not always correlate exactly with the actual range. Rather, due to ambient temperature variations, oscillator voltage fluctuations, and other well-known causes, errors will occur in calculated range.
Typically, the percent range error, defined as the percent difference between calculated range and actual range, is between 10% and 30%. Unless these errors are compensated for by the radar system, inaccuracies can result in the calculation of target positions relative to the radar system platform. Therefore, it is essential that range errors are accurately estimated and calibrated by the radar system to determine a target's position precisely.
Radar has been used in a wide variety of platforms to detect the position of objects. For example, radar has been mounted on “host” automobiles and other host vehicles to detect the position of objects (such as other vehicles) on a road. One such vehicular radar system is described in U.S. Pat. No. 5,302,956, issued on Apr. 12, 1994 to Asbury et al. and assigned to the owner of the present invention, which is hereby incorporated by reference for its teachings of vehicular radar systems. Another exemplary vehicular radar system using a “monopulse” azimuth radar for automotive vehicle tracking is described in U.S. Pat. No. 5,402,129, issued on Mar. 28, 1995 to Gellner et al. and assigned to the owner of the present invention, which is also hereby incorporated by reference for its teachings of vehicular radar systems. As described therein, object position data has been used in the prior art collision avoidance systems to brake or steer a host vehicle when the radar system detects a potential collision with another vehicle. Alternatively, the radar system may be used in an intelligent cruise control system to decelerate the host vehicle when the radar system detects a potential collision with another vehicle and accelerate the host vehicle when the collision danger terminates.
In both the prior art collision avoidance systems and the prior art intelligent cruise control systems, an accurate calculation of object position relative to the radar platform is critical for safe system performance. Disadvantageously, due to ambient temperature variations and oscillator voltage fluctuations, heretofore it has been difficult if not impossible to accurately estimate and calibrate the range error. Consequently, the prior art vehicular radar systems disadvantageously often introduced range errors when attempting to determine the position of targets and therefore introduced undesirable and sometimes dangerous inaccuracies into the collision avoidance process. Therefore, a need exists for a method and apparatus that can accurately estimate the range error and subsequently calibrate the calculated range.
To more fully describe the problems associated with range error, consider the exemplary collision avoidance vehicular radar system shown in
FIGS. 1 and 2
. As shown in
FIGS. 1 and 2
, a collision avoidance vehicular radar system
100
is mounted on a host vehicle
12
. The host vehicle
12
is shown in
FIGS. 1 and 2
traveling in a direction of travel
22
on a road
30
. As described in U.S. Pat. No. 5,302,956, the radar system
100
cooperates with control systems (not shown) on the host vehicle
12
in a well-known manner to prevent the collision of the host vehicle
12
with other objects on the road
30
. For example, as shown in
FIGS. 1 and 2
, the radar system
100
aids the host vehicle
12
in avoiding collision with other vehicles
40
,
50
travelling in front of the host vehicle
12
in a direction substantially parallel to the direction of travel
22
of the host vehicle
12
. As described below in more detail with reference to
FIG. 8
, and as disclosed in detail in U.S. Pat. No. 5,302,956, the radar system
100
preferably includes a radar antenna
10
and a microprocessor or micro-controller
11
(FIG.
8
). The radar antenna
10
preferably is mounted to a front bumper
13
of the host vehicle
12
such that it points in a forward direction substantially parallel to the direction of travel
22
of the host vehicle
12
. The microprocessor
11
in the radar system
100
calculates the position of objects detected by the radar antenna
10
in a well-known manner as exemplified by the monopulse azimuth radar system described in U.S. Pat. No. 5,402,129.
As shown in
FIGS. 1 and 2
, the radar antenna
10
includes an antenna reference line
20
that is defined by a line emanating from the center of antenna
10
and perpendicular to the surface of the radar antenna
10
. The radar antenna
10
locates “target” vehicles (e.g. vehicles
40
and
50
) in a well-known manner by transmitting a transmission signal (radar beam) having at least two known frequencies, F
1
and F
2
. The frequencies are separated in the frequency spectrum by some pre-defined frequency range. For example, in one typical application, the transmit frequencies are separated by 300 kHz, although other frequency deviations may be used. The radar system senses the returned transmission signal that is reflected back from the target vehicles. Azimuth angle
19
is calculated relative to the antenna reference line
20
. For example, in one exemplary radar system, wherein the radar system
100
comprises a monopulse azimuth radar system (such as that described in U.S. Pat. No. 5,402,129), the radar antenna
10
transmits a transmission signal and senses the returned transmission signal that is reflected back from the target vehicles in two physically separated locations of the radar antenna
10
. The radar antenna
10
of a monopulse radar system is split into two antennas (
10
a
,
10
b
) that are physically separated by a few centimeters. This separation of the receive antenna
10
provides a “stereo-vision” perspective to the radar system
100
. By comparin
Ameen Yashwant K.
Gingell Thomas W.
Ryan Patrick Anthony
Eaton-VORAD Technologies, L.L.C.
Jaquez & Associates
Jaquez, Esq. Martin J.
Lee, Esq. Allan Y.
Sotomayor John B.
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