Radar detectors warn drivers of the use of police radar, and the potential for traffic citations if the driver exceeds the speed limit. A speed detecting system is a device that measures the velocity of a moving object by sending out a continuous radio wave and measuring the frequency of reflected wave. A speed detection system which utilizes radar may generally be referred to as a so-called radar gun. Radar guns typically include a microwave signal source which emits a signal having a frequency in either the X, K or Ka frequency regions of the electromagnetic spectrum. The X and K bands are relatively narrow frequency ranges, whereas the Ka band is a relatively wide range of frequencies. Radar guns may emit signals in either a continuous or a pulsed mode. A police radar gun is an apparatus which transmits a radar wave of a frequency ranging from microwave to millimeter wave frequencies toward a moving car and detects the frequency shift of the reflected wave. The speed of the car is determined via doppler effect. A radar detector, which is placed in an automobile to detect the existence of such police radar gun operating in the vicinity, is designed to capture those radar waves belonging to the frequency bands for the police radar gun. 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. A typical superheterodyne radio receiver includes a mixer for receiving electromagnetic signals and a local oscillator (LO) signal to convert the frequency of the received signals to the frequency of an intermediate (IF) amplifier 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. Signals emitted by a police radar unit may travel a substantial distance from that unit. 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. Recent developments in radar detectors have focused on the sensitivity of the detectors and the various bandwidths within which radar signals are detected.

Typical radar detectors are self-contained single units containing receiver circuitry and alert circuitry. There are a variety of types of radar detectors. Radar detectors typically comprise a microwave receiver and detection circuitry that is typically realized with a microprocessor or digital signal processor (DSP). Systems including a digital signal processor have been shown to provide superior performance over solutions based on conventional microprocessors due to the DSP's ability to find and distinguish signals that are buried in noise. Microwave receivers are generally capable of detecting microwave components in the X, K, and very broad Ka band. Radar detectors often include a fixed frequency oscillator which generates a signal in the X-band frequency range. The DSP or microprocessor in a modem radar detector is programmable. They can be instructed to manage all of the user interface features such as input switches, lights, sounds, as well as generate control and timing signals for the microwave receiver. A radar detector typically includes an antenna which receives radiated radio-frequency electromagnetic waves and converts them into electrical signals. The antenna and receiver component may be packaged with the control/indicator component in a single module mounted on the dashboard of a vehicle. The two components also may be separated, with the antenna and receiver component located under the hood of the automobile, the antenna facing forward through the grille, for example, while the control/ indicator component is mounted on the dashboard or at some other location convenient to the operator of the vehicle. The radar detector is powered via a corded plug that can be inserted into a powered receptacle of the motor vehicle or may be powered by batteries. Recent improvements in microelectronic circuitry have enabled many of the known radar detectors to undergo a considerable size reduction, often with a corresponding lowering of the energy consumed by the circuitry. Methods for conditioning detector response are gaining importance, because there is an increasing number of signals present in the X, K, and Ka bands from products that are completely unrelated to police radar. The growing number of such signals is rapidly undermining the credibility of radar detector performance. False detections by a radar detector are often caused by signals of radio-frequency energy transmitted by other nearby radar detectors which run on the same signal-receiving principle.

Radar detector units have become a popular accessory for vehicles in recent years and units of various convenient sizes are available in the marketplace. The radar detector is typically mounted within the passenger compartment of the motor vehicle in a location within the view and reach of the driver. To optimize the reception of the antenna, these detectors should be installed within the windshield area, preferably high on the windshield and in a horizontal plane with the front end of the receiver which houses the antenna oriented toward the front of the vehicle. Most commonly, these devices are held in position through means of some form of bracket or attachment device secured to the dashboard, windshield or visor of the vehicle. As the vehicle approaches the source of the radar signal, signal strength normally indicated by the typical detector increases. As the vehicle passes the source of the radar signal, the indicated signal strength drops since a forwardly aimed directional antenna of the detector is no longer pointed in the general direction of the signal source. Remote radar detectors have been developed in which the receiver aspect of the detector is in a unit situated outside the vehicle passenger compartment, while the alert aspect of the detector is in a unit that continues to be mounted inside the vehicle passenger compartment. Such remote radar detectors allow for more optimal placement of the units so as to increase sensitivity of the receiver aspects of the detector and allow for more discreet positioning of the alert unit, such as along the dashboard or steering wheel column, instead of in the middle of the windshield.