Radar is an acronym for Radio Detection And Ranging.
Signal reflection is the process of bouncing a signal off a medium that does not completely absorb it. It can be presented in copper cables for electrical signals and in optical fiber for laser or optical signals. Signal reflection can also occur on external metal surfaces for electromagnetic (EM) waves. EM waves travel through most open spaces and are not visible.
Shortwave radio operators in field conditions often attempt to bounce signals off the ionosphere to increase signal range.
The study of signal reflection is used in specialized applications. The signal as sound can be reflected off a hard surface and returned to a receiver as a beep for navigation and ranging (SONAR). Ground penetrating radar uses the principle that different radio frequencies and different ground materials will produce different amounts of signal absorption and reflection. In impedance matching, the goal is to ensure that most of the signal reaches the destination or load. The source impedance should generally match the target or load impedance of a given RF subband.
In analog transmission cables, signal reflection is experienced as an echo when there is a discrepancy in the audio. Most of the problems in audio transmission have been solved by the use of digitized audio in the form of Internet Protocol data packets. Any reflections of the signal will be seen as data errors and will be removed with error correction schemes. Crosstalk, which used to be the unwanted induction of an analog signal from one cable to another, is also eliminated through the use of digital audio, such as Voice over Internet Protocol (VoIP) packets over a digital subscriber line.
The Bergeron diagram shows the resulting voltages and currents when reflected electrical energy is combined with incident energy. For best signal integrity, there should be minimal reflection, which is achieved through impedance matching. In some cases, the addition of resistive components that absorb electrical energy can eliminate reflection altogether, while in other cases complex impedances formed by series-parallel combinations of inductors and capacitors can provide the solution. The presence of distributed inductance and frequency dependent capacitance makes the design of good impedance matching circuits very challenging.
Other specialized methods of signal reflection include optical ranging, where a timed beam of light can be reflected off a target at a distance. Given the speed of light and the time it takes to receive the reflection, the distance to the target can be calculated. In radio detection and ranging (RADAR), the target reflects radio signals when the radar equipment sends out a burst of radio frequency. The equipment waits for any reflected signal and calculates the distance based on the delay between the transmission of the RF burst and the reception of the reflected signal, and the speed of the radio waves in the air.