Ronald RyderEnglish 202CDefinition and Description

RADAR Systems: Effective Tracking TechnologyRADAR systems, or Radio Detection and Ranging systems are systems that both the military and civilian sectors use in order to detect and locate objects at far greater distances than the human eye is able to differentiate effectively. Civilian aircraft and commercial ships use this technology continuously, and the technology is also heavily relied upon in all branches of the military. RADAR systems are able to rapidly measure range (distance between RADAR system and object being tracked), see through weather phenomena such as rain and snow, measure elevation, and measure the range rate (rate at which object being tracked is closing in on or moving away from the RADAR system). Although RADAR systems cannot provide extensive detail in regards to target identification, the information relayed to users is valuable enough to ensure safety by increasing missile protection and sounding alarms if hostile intent is recognized by the system (i.e. constant bearing, decreasing range). These systems can also provide the support necessary to make important decisions regarding the platforms travel path and speed in comparison to the object being tracked. Lack of proper RADAR use can lead to disaster, and historically has led to thousands of human deaths, such as the USS Vincennes in 1988.RADAR OverviewThe most common and basic type of RADAR used today is the pulse type system. Pulse RADAR systems use one antenna, and the components of the system serve two main functions: sending and receiving signals. Essentially, the system is turned on and then transmits electromagnetic radiation at a prescribed radio frequency for a preselected amount of time. Once the signal reaches the time limit selected by the system operator, the sending portion of the system is turned off in order to begin the receiving (listening) process. The system then stops transmitting electromagnetic radiation for a prescribed amount of time while it waits to hear the signal it just sent out return. Once the signal is returned it is deeply analyzed, gathering parametric data such as time, speed, wavelength, and frequency in order to piece together the whereabouts of the object(s) that the electromagnetic signal that was sent out hit and bounced off. The diagram to the right illustrates the situation defined above. PW, or pulse width, is the time in which the pulse RADAR system is sending out electromagnetic radiation, and consequently not listening for pulses sent out before the original pulse was transmitted. Resting time is defined as the time between electromagnetic radiation pulses, or in other words when the RADAR system is listening to the pulses it previously sent out. During resting time, the system is not sending out any electromagnetic radiation. One transmission cycle for a pulse type RADAR system includes both the Pulse Width (PW) and the Resting Time (RT). The PRT, or Pulse Repetition Time, is simply defined as the total time for one transmission cycle. Each of these parameters PW, RT, and PRT-affect the overall performance of a RADAR system and can be adjusted depending on the situation (For example, there will be different values for when the system is tracking a large, slow boat or a small, fast aircraft).Figure 1: Display of electromagnetic radiation being sent out and received by pulse type RADAR system

Individual Components of Pulse Type RADAR:Figure 2: Simplistic view of all the components of a pulse type RADAR system

The pulse type RADAR system, although technologically complex, can be broken down into seven relatively simple pieces, shown above in Figure 2. The following section will summarize the function and purpose of each of the seven main components of a pulse type RADAR.Duplexer SwitchThe duplexer switch is a simple device which electrically disconnects the receiver from the antenna when the system is transmitting pulses. It also disconnects the transmitter when it is not being used so that the system can more effectively listen to the pulses sent out without background noise. It is plausible to compare the duplexer switch to an electrical switch on a house wall. Power SupplyThe power supply portion of the system is pretty self-explanatory, it provides the system with the necessary electrical energy to function properly. This system provides the power for the display to show the user essential tracking data, for the transmitter to send out high energy pulses, and for the antenna motor to move the antenna when programmed to do so. Without the power supply, the entire system is useless and ineffective. SynchronizerThe synchronizer is typically referred to as the heart of the pulse type RADAR system because it controls the timing for entire system. The synchronizer produces trigger pulses that are sent throughout the entire RADAR system that start and stop the transmitter, change the antenna angle and flip the duplexer switch. The synchronizer also establishes the PRT (Pulse Repetition Time), and the PRF (Pulse Repetition Frequency).

TransmitterThe transmitter portion of the pulse type RADAR is the system that physically generates the electromagnetic radiation sent out by the system. The electromagnetic radiation is generated through an electron beam that is passed through a lengthy tunnel of magnets, causing an electromagnetic wave. Electromagnetic waves are essentially coupled electric and magnetic fields that constantly oscillate and travel through mediums such as air and water. Once the electromagnetic (EM) wave is generated, a modulator applies high voltage shocks to the magnets that create the pulses of radiation sent out by the transmitter. Picture the modulator as a knife that cuts the wave into small usable portions rather than a useless, never ending wave. More generically, picture the modulator as the knife that cuts a 10 foot sub (EM wave) into smaller pieces fit for human consumption at a social gathering. DisplayThe display system is the key component in any RADAR system: it allows the user to interpret the data the system has gathered and therefore make key decisions about travel path and speed. The entire point of a RADAR system is to gather information about surroundings and make decisions with justification provided by that information. Most RADAR types use a circular display (Figure 3), the center point being the location of the RADAR itself. Along the right side of the display is data including information about your own platform including speed, direction compared to true north and distance traveled. This display interface allows the user to click on a contact (yellow blips) and pull up parametric data to be further analyzed. For the military, this data can determine if a contact has hostile intent, or may just be a civilian ship or plane. For commercial/civilian uses, the data displayed on this interface will help determine if a change in path or speed needs to be made in order to avoid collision. Figure 3: Circular display of a pulse type radar system, exactly how a user would see it.

ReceiverThe receiver is the portion of the RADAR system that listens for the pulse originally sent by the system. It is tuned to the same frequency as the transmitter so that it only picks up the pulse it sent out, not pulses from other systems and noises in the external environment. The electromagnetic radiation picked up by the receiver is converted into an electrical signal that is analyzed and converted to data presented by the display. When the system is transmitting signals, the receiver cannot be electrically connected to the antenna in order to avoid damage from high power signals. The receiver is only able to interpret signals with relatively low energy (signals that have travelled a long distance and been weakened by spreading, scattering or absorption).

AntennaThe antenna portion of the pulse type RADAR system has several important functions. It radiates energy received from the transmitter in a preferred direction and not in other directions. Also, the antenna receives waves and passes this wave energy to the receiver where it is interpreted and passed along to the display. The main function of any antenna is to convert electrical energy to wave energy and vice versa. Think of the antennas involved in radio waves, the antenna at a radio station converts electrical energy into a wave form and broadcasts these waves through air, while the antenna on a car radio or household radio picks up these waves and converts the waves into electrical energy which comes out of the system as noise such as music. RADAR systems, however, use much larger and more complex antennas than those on cars or in houses (Figure 4).Figure 4: Military grade antenna used with a pulse type RADAR system.

RADAR: An Essential Tool for Safety The world we live in today relies heavily on transportation, especially in the commercial and military realms. At any given time of day there are thousands of ships at sea, planes in the sky, and submarines under water; how can we avoid disasters such as collisions that could cost hundreds of human lives? The simple answer is RADAR systems. RADAR systems allow users to effectively track and record data concerning all nearby moving and stationary objects. Airplanes use this to ensure their intended flight paths do not cross anyone elses, ships use RADAR to ensure no collisions occur and also to survey the landscape around them including underground volcanoes which could prove disastrous. Submarines rely solely on different types of RADAR when discovering the undersea. Submarines have no windows, and even if they did, the windows would prove useless after submerging below 100 feet- RADAR is a submarines eyes. The bottom line is that RADAR systems are a key technology in our daily lives, and our survival when traveling on the ocean or in the air relies heavily upon it.