are discarded. A sequence of target returns can be monitored through a device known as a plot extractor. The non-relevant real time returns can be removed from the displayed information and a single plot displayed. In some radar systems, or alternatively in the command and control system to which the radar is connected, a radar tracker is used to associate the sequence of plots belonging to individual targets and estimate the targets' headings and speeds. Engineering A radar's components are: A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator. A waveguide that links the transmitter and the antenna. A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations. A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter. A display processor to produce signals for human readable output devices. An electronic section that controls all those devices and the antenna to perform the radar scan ordered by software. A link to end user devices and displays. Antenna design Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions. This leaves the radar with the problem of deciding where the target object is located. Early systems tended to use omnidirectional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance, the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other showed a minimum. One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the "target", the transmitting aerial should also be directional. Parabolic reflector More modern systems use a steerable parabolic "dish" to create