Communications: directive radio wave systems and devices (e.g. – Radar ew – Detection of surveilance
Reexamination Certificate
2000-12-13
2002-06-04
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Detection of surveilance
C342S193000, C342S195000, C455S228000
Reexamination Certificate
active
06400305
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to police radar detectors, and more particularly, to sensitive wide band radar detectors that alert drivers to the presence of X, K, and/or wide Ka band police radar signals without responding to interfering signals such as are generated by the local oscillator (“LO”) of other radar detectors.
BACKGROUND OF THE INVENTION
An electronic assembly for detecting the presence of police radar signals from a police radar unit is generally known, and will be referred to herein as a radar detector. In use, the radar detector is mounted in a vehicle and provides an audible and/or visual indication of the presence of a police radar signal.
Signals emitted by a police radar unit may travel a substantial distance from that unit. As is well understood, the police radar signal must travel to the vehicle under surveillance and then be returned altered by a Doppler shift representing speed of the vehicle. Microwave police radar signals lose strength as they travel over the distance between the police radar unit and the vehicle under surveillance. The greater that distance, the weaker the return police radar signal, such that at some distance and beyond, the police radar signal is too weak to return to the police radar unit and be evaluated for speed of the vehicle (detection range).
It is desirable that the radar detector capture the police radar signal while it is so weak as to be beyond the detection range of the police radar unit. However, as with the police radar unit, the greater the distance between the radar detector and the source of the police radar signal, the weaker the police radar signal. At some distance from the police radar unit, the police radar signal may be so weak that the radar detector is unable to distinguish the police radar signal from noise, meaning that a police radar signal will not be captured until the vehicle moves closer to the police radar unit. The maximum distance at which the police radar signal can still be detected and an alert given to the driver may be referred to as the capture range of the radar detector. It is clearly advantageous to design the radar detector to be sensitive and fast enough to detect police radar signals and give an alert to the driver with sufficient time to react before the vehicle is within the detection range of the police radar unit.
In order to detect very weak signals, it is necessary for the circuitry to also deal with the noise that is inherently present at low energy levels. Thus, increasing the capture range by lowering the threshold at which a signal may be considered also requires circuitry to handle the concomitant noise, otherwise the noise can be a source of unwanted and detrimental false alarms. The problems are further complicated with some of the frequencies employed for police radar signals. In particular, at higher frequencies, the police radar signal drops off or becomes weaker over ever shorter distances. Consequently, the capture range of the radar detector can become quite short, meaning that the time available to react before coming into the police radar units' detection range grows smaller, and in some cases can be non-existent unless steps are taken to maximize the detector's capture range.
Additionally, some police radar units are of the “instant-on” type meaning that they may be used in a manner to intermittently emit only short bursts of police radar signals. These instant-on police radar units tend to be higher frequency as well. Where the bursts are only given infrequently, the first burst may be given when the radar detector is too far away to detect that burst, i.e., at that distance, the signal from the police radar unit is outside the capture range of the radar detector because it is below the sensitivity threshold of the radar detector. The second burst may come after the vehicle is within the detection range of the police radar unit. Under such circumstances, the driver will have had no advance warning that the vehicle is under surveillance. Accordingly, it is desirable to extend the capture range of the radar detector so as to enhance possible early detection of such instant-on police radar signals as well.
The circuitry and techniques utilized to detect police radar signals have become quite sophisticated, and in turn, so have the police radar units. Radar detectors must be able to quickly detect very weak signals, separate them from the noise, determine whether the signal is a valid police radar signal, and if so, give an alert to the driver. All of these functions require some amount of processing time which necessarily affects the detection range of the radar detector and might thus allow the vehicle to move towards the police radar unit until at last an alert is given.
During the 1980's, police radar detectors typically covered only two microwave radio frequency (RF) bands, the so-called X band and K band. Radar detectors designed to deal with those two bands generally provided sufficient detection range for most situations. The recent addition of Ka band, and especially wide Ka band, police radar has complicated matters, as will be discussed.
In general, the X band is often defined to cover the frequency range of 8.00 GHz to 12.00 GHz, but more typically defined as the International Telecommunications Union (ITU) assigned band of 8.50 to 10.68 GHz. The Federal Communications Commission (FCC) of the United States allocated a portion of the X band of 10.50 to 10.55 GHz for police radar signals. Similarly, the K band is often defined to cover the frequency range of 18.00 GHz to 27.00 GHz, but more typically defined as the ITU assigned band of 23.00 GHz to 24.20 GHz. The FCC allocated a portion of the K band of 24.10 GHz to 24.20 GHz for police radar signals. As used hereinafter, the terms “X band” and “K band” will generally be meant to refer to the portions of the spectrum allocated to police radar signals in those bands as above described.
U.S. Pat. No. 4,313,216 (“the '216 patent”), the disclosure of which is hereby incorporated herein by reference in its entirety, sets forth an example of circuitry and techniques to detect whether a received signal is in the X band or K band, and is thus a possible police radar signal. The '216 Patent discloses a superheterodyne receiver with a first swept local oscillator (“LO”) having a fundamental frequency or first harmonic, centered at 11.5583 GHz, and in a frequency range adjacent to the police radar X band (i.e., within the broadest definition of the X band, but just outside the defined police radar X band). The second harmonic of the LO is centered at 23.1166 GHz, and is similarly in a frequency range adjacent to the police radar K band (i.e., within the broader definition of the K band, but just outside the defined police radar K band). Due to the adjacency of the LO first and second harmonics to the X and K bands, respectively, when the LO signal is mixed with signals in either of those bands, there will be produced intermediate frequency (IF) signals in the same frequency range, such as centered around 1.02 GHz. The 1.02 GHz IF signals are mixed with a second LO signal, such as a fixed frequency at about 1.03 GHz, to produce 10 MHZ IF signals, which may then be dealt with by lower frequency IF circuitry, such as bandpass filters, FM discriminators and/or quadrature detectors. Due to the adjacency of the LO frequency harmonics to the X and K bands, the IF circuitry will produce pairs of closely spaced S-curves. Each associated pair of S-curves has a time positioning relative to the beginning of the sweep and a time spacing therebetween which correlates the pair to a signal in the X band or the K band, and thus allows for identification of the band of the received signal, as well as the approximate frequency thereof in that band.
Some radar detectors leak some of the RF energy generated by their LO's. That energy could create signals that would appear to another radar detector as though they were police radar signals in the X band and/or the K band. Elimination of
Andrea Brian K
Escort Inc.
Tarcza Thomas H.
Wood Herron & Evans LLP
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