Much like the previous ASR-9, known to the military as AN/GPN-27, the ASR-11 has been deployed to airports across the United States to meet the requirements of a digital, automated air traffic monitoring system. The main purpose of the ASR-11's development was to replace aging radar systems at airfields that did not receive the ASR-9, as well as use across the world by the US military. Many of the advanced parameters such as weather and digital pinpoint monitoring found in the ASR-9 are also found in the ASR-11.
Transmitted electromagnetic signals reflect off the surface of more than 1,000 aircraft within sixty nautical miles of the radar location.[2] The reflected signals received are sent to the processing equipment which measures the echo delay, or the amount of time it takes for the electromagnetic signals to return, and the direction from which they came.[5] The processed information is relayed to an air traffic control (ATC) tower, or a terminal radar approach control (TRACON). That information contains digital tags describing location, heading, and speed at which the aircraft is moving. The overall operation of the ASR-11 is similar to that of the ASR-9, with relatively few differences between the two radar systems.[1] There are only two main areas where the ASR-11 has an advantage over the ASR-9, with it also having some disadvantages due to its weather capability.
Advantages
The first advantage the ASR-11 offers over the ASR-9 is the use of a low peak power (25 kW),[3]solid-state transmitter with pulse compression technology, replacing the ASR-9's high peak-power, short pulse power system. This gives the radar the ability to deliver the same amount of RF energy to a target at long range while making the radar less sensitive at shorter ranges. Any aircraft that comes closer than six nautical miles from the radar cannot be located with the long range pulse system built into the ASR-11. Installing additional radar equipment to the same antenna is required for close range location and weather detection.
The second advantage of using an ASR-11 is the radar's utilization of pulse sequence diversity resulting in the capability to limit processing dwells to a small number of pulses.[jargon] This feature becomes most important when monitoring of air traffic is the primary use of the radar. Reducing the number of pulses transmitted by the radar has a direct adverse affect on Doppler resolution resulting in decreased ability to process live weather conditions.[1]
Disadvantages
The main disadvantage of using an ASR-11 radar system is the aforementioned reduction of Doppler radar resolution. Like the ASR-9, the ASR-11 has an on-site, dedicated weather reflectivity processor, with six separate measured levels of precipitation reflectivity. The limited number of pulses sent out by the radar system has a direct effect on its ability to measure weather conditions. Unlike the ASR-9, the ASR-11 is less suited for wind shear detection, Doppler wind measurement, and precipitation reflectivity. The ASR-11 radar system will remain as is, with no further plans to upgrade the current detection system with a Weather Systems Processor (WSP.)[1]
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