Communications: directive radio wave systems and devices (e.g. – Radar ew – Detection of surveilance
Reexamination Certificate
1999-10-22
2001-01-16
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Detection of surveilance
C342S089000, C455S227000, C455S313000, C455S314000, C455S315000, C455S344000, C455S345000
Reexamination Certificate
active
06175324
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to police radar detectors and, more particularly, to police radar detectors and methods of operating police radar detectors wherein an improved frequency scheme enables improved sweeping of the X, K, K
u
, and K
a
radar bands, and also selective sideband suppression during sweeps of the X, K and K
a
radar bands.
Police have used radar waves to monitor the speed of motor vehicles for many years. The frequencies currently used throughout the world include: the X band—10.50 gigahertz (Ghz) to 10.55 Ghz; the K
u
band—13.40 to 13.50 Ghz; the K band—24.05 Ghz to 24.25 Ghz; and the K
a
band—33.40 Ghz to 36.00 Ghz. To alert motorists of the presence of police radar, electromagnetic signals within these radar bands are monitored using a police radar detector which issues an audible and/or visual alert upon detection of a radar signal within one of the bands.
Police radar detectors are basically superheterodyne radio receivers in which the tuning of the receivers is repeatedly swept through the frequencies which are to be received or detected, i.e., the frequencies of the radar bands. A typical superheterodyne radio receiver includes an antenna for receiving electromagnetic signals and a circuit for mixing signals from the antenna and local oscillator (LO) signals to convert the frequency of received electromagnetic signals to the frequency of an intermediate frequency (IF) with the LO being swept in frequency to tune the required frequencies. Incoming electromagnetic signals can then be received at the LO frequency plus or minus the IF frequency, known as upper and lower sidebands, respectively.
Generally, signal reception occurs in only one of these two sidebands and the other sideband or image frequency is suppressed by filtering or phasing to thereby perform single sideband (SSB) reception. SSB operation is usually preferable because it generally delivers improved noise figure relative to double sideband (DSB) operation and also reduces sensitivity in the alternate sideband, thus reducing susceptibility to undesired signals. Sometimes DSB operation is intentionally adopted in the interest of economy or because in some circumstances it can facilitate expanded frequency coverage.
The frequencies used within the police radar detector, including frequencies or swept frequency bands of local oscillators and frequencies of intermediate amplifiers, and the tuning methods, are referred to in the art as frequency schemes and a variety of frequency schemes are known and utilized in police radar detectors. For example, see U.S. Pat. No. 5,068,663; 5,268,689; 5,305,007; and, 5,917,441.
While known frequency schemes are satisfactory for operation of police radar detectors, there is an ongoing need for new and advantageous frequency schemes which improve operation of police radar detectors, reduce costs of manufacturing police radar detectors and/or simplify circuitry or operation of police radar detectors.
SUMMARY OF THE INVENTION
This need is currently met by the invention of the present application wherein a novel frequency scheme for a police radar detector enables improved sweeping of the X, K, K
u
and K
a
radar bands. The novel frequency scheme requires two initial frequency conversions for detection of the X, K and K
a
radar bands and a single initial frequency conversion for the K
u
radar band with single initial frequency conversion being enabled by disabling the second mixer of the police radar detector. During sweeping of the X, K and K
a
radar bands, selectable sideband suppression, i.e., either upper sideband suppression or lower sideband suppression, is employed to reduce undesired image sidebands and noise prior to the second frequency conversion. In addition, noise at the second intermediate frequency, for example about 725 megahertz (Mhz), is reduced to prevent this noise from feeding through the second mixer into the second IF amplifier. During the K
u
radar band sweep, the second mixer is bypassed and shunting of signals at the second IF frequency is disabled so that these signals enter the second IF amplifier.
In accordance with one aspect of the present invention, a police radar detector comprises an antenna for receiving incoming electromagnetic signals. A first local oscillator generates a first local oscillator signal which is swept through a first range of frequencies to sweep the X, K and K
a
radar bands and a second range of frequencies to sweep the K
u
radar band. A first mixer is coupled to the antenna and the first local oscillator for mixing the incoming electromagnetic signals with the first local oscillator signal to generate first intermediate frequency signals. A second local oscillator generates a second local oscillator signal. A second mixer is coupled to the first mixer for mixing first intermediate frequency signals with the second local oscillator signal to generate second intermediate frequency signals at a second intermediate frequency. Detector circuitry is coupled to the second mixer for detecting received electromagnetic signals within the X, K
u
, K and K
a
radar bands. Signal conditioning and control circuitry selectively enables the second local oscillator when the X, K and K
a
radar bands are swept and disables the second local oscillator and bypasses the second mixer when the K
u
radar band is swept.
The police radar detector may further comprise a first intermediate frequency amplifier passing signals encompassing the second intermediate frequency and amplifying the first intermediate frequency signals. For this embodiment, the first intermediate frequency amplifier couples the first mixer to the second mixer which then mixes amplified first intermediate frequency signals with the second local oscillator signal. When the second intermediate frequency is about 725 megahertz, the first range of frequencies comprises about 14.310 gigahertz to about 15.160 gigahertz. However, the first range of frequencies may comprise about 14.310 gigahertz to about 15.160 gigahertz for the K and K
a
radar bands and a subrange of frequencies comprising about 15.090 gigahertz to about 15.160 gigahertz for the X radar band. The second range of frequencies comprises about 14.125 gigahertz to about 14.225 gigahertz. The second mixer may comprise a 90° hybrid circuit and first and second diodes. For this embodiment, one of the first and second diodes is forward biased by the signal conditioning and control circuitry to bypass the second mixer when the K
u
radar band is swept.
The police radar detector preferably further comprises sideband suppression circuitry for selecting an upper sideband signal or a lower sideband signal from the first intermediate frequency signal when the detector is sweeping the X, K and K
a
radar bands. For example, when the second intermediate frequency is about 725 megahertz, the upper sideband signal is around 6.050 gigahertz and the lower sideband signal is around 4.600 gigahertz. The sideband suppression circuitry may comprise a varactor controlled by the signal conditioning and control circuitry to select the upper sideband or the lower sideband.
The police radar detector may further comprise a noise suppression circuit which suppresses noise around the second intermediate frequency, for example around 725 megahertz, when the X, K and K
a
radar bands are swept. When a noise suppression circuit is provided, it may comprise a diode coupled between the signal conditioning and control circuitry and an input of the second mixer stage, the diode being forward biased when the X, K and K
a
radar bands are swept and being reversed biased when the K
a
radar band is swept.
In accordance with another aspect of the present invention, a police radar detector comprises an antenna for receiving incoming electromagnetic signals. A first local oscillator generates a first local oscillator signal which is swept through a range of frequencies to sweep the X, K and K
a
radar bands. A first mixer is coupled to the antenna and the first local oscillator for mixing the inc
Gould Harry Joe
Scholl Stephen Ray
Valentine Michael David
Gregory Bernarr E.
King & Schickli PLLC
Valentine Research, Inc.
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