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Here at Global Marine Electronics, S.A., we acknowledge that the pure physics behind our products is just as important as the applications of our products. That being said, we consider ourselves to be well versed in the radar industry. We know how the importance of radar has increased over the last 4 decades because we have been around the industry that long. Radar is a contraction of the phrase "Radio Detection And Ranging." Radar works when microwave energy from a transmitter is reflected back to the sending station by objects in the path of the emitted wave. The time required for the return of the reflected wave is then measured to determine the distance to the reflecting object. Three systems in common use for the transmission of Radar include frequency modulation, which is widely used in aircraft altimeters, frequency shift, which is commonly used in police speed traps, and pulse, which is frequently used on ships, aircraft, and search equipment. The pulse method is by no means new. Did you know that the reflection of radio waves was observed as early as 1922, and in 1926 the height of the ionosphere was measured by this method. (Source: University Physics, 6th ed. Miller, Franklin, et al., Harcourt Brace Jovanovich, Publishers. 1987.) In pulse radar, short, powerful bursts of electromagnetic energy are emitted by a transmitter and narrowly beamed in the direction of an object to be detected. A small amount of the radiated energy is reflected from the target back to a sensitive receiver located at the same position as the transmitter. The distance is determined by measuring the length of time required for the reflected signal to return. The echo is then amplified and displayed visually on a screen. For persistence and continuity of display, the emitted pulses are repeated periodically at a fixed rate with sufficient intervening time to allow the return of any echo. The visual display is then interpreted by an operator to obtain the required information. Continuous transmission can not be used in the pulse radar system since it would be difficult to determine which part of the transmission caused returning echoes. The measurement of echo time and target range would consequently be impossible. The following is a diagram of a typical pulse radar system:
Now, what do all of these components do? The timer synchronizes the indicator and transmitter circuits. Due to this synchronized action, a pulse of r-f energy is emitted by the transmitter at the same instant as the indicator sweep begins. The modulator applies triggering pulses of specified duration to the transmitter at regular intervals. These pulses cause the the transmitter to oscillate and produce the necessary bursts of high r-f energy. The transmitter is the generator of the r-f energy at microwave frequencies, or around 10 [GHz]. This component produces a constant frequency and amplitude which are delivered to the antenna for radiation. A magnetron such as the one commonly found in microwave ovens is an important component of the pulse system since it is the apparatus that produces the radio waves. A magnetron is a vacuum tube that controls the flow of electrons using a magnetic field external to the tube. It is the excited state of these electrons resulting from flow confinement that the magnetron utilizes to fire off r-f energy. Magnetrons that have lived their lifespan may be described as being "gassy", and this is determined by its amperage. The t-r switch acts an electric switching device that allows for a single antenna system to be used for both the transmission and reception of microwaves. A stereoheterodyne receiver is designed to have very high sensitivity, wide band pass, and a low noise figure. Echoes are routed to the receiver from the antenna and amplified sufficiently for visual display on the screen. The indicator visually displays the time required for a transmitted pulse to reach a target and return. Using a calibrated screen, time is interpreted in terms of miles, yards, and/or meters, thereby indicating a distance or "range" to a target. The power supply supplies the required high and low voltage to the various components employed throughout the system. |
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