Correct Answer : Situation awareness
Explanation : The fundamental limitation in military radars is situation awareness. This limitation is overcome by the electronically scanned array which has a very high rate of scanning.
Correct Answer : Phase shift
Explanation : In ESA, the antenna’s beam is moved electronically by setting the phase angles of phase shifters located at each radiating element to provide a linear phase taper across the array surface.
Correct Answer : Slope of the phase taper
Explanation : The ESA controls the beam by phase shifters. The slope of the phase taper determines the direction in which the antenna beam will be pointed.
Correct Answer : Microseconds
Explanation : Since the antenna’s phase shifter settings can be changed in a few microseconds, an ESA’s beam can be repositioned almost instantly.
Correct Answer : Computer
Explanation : The beam shape and direction is controlled by an on-board computer which gives the necessary phase shift to the phase shifters to change the beam direction and shape.
Correct Answer : Interleaving radar modes
Explanation : Beam agility makes it possible for one phased array radar to act as multiple radars each with its own beam shape and scan pattern! This is referred to as interleaving radar modes. The same radar can be tracking for airborne threats using one beam shape and scan pattern while searching for ground targets using another beam shape and scan pattern.
Correct Answer : AESA
Explanation : AESA radars can produce multiple radar frequencies with multiple beams. This allows the radar to have faster scan rates and can track multiple targets with ease.
Correct Answer : Electronic scanning capability
Explanation : One of the basic common features between the AESA and PESA is that both provide electronic scanning. This allows the use of narrow beams since the rate of scanning is very high.
Correct Answer : Because it uses a, multiple frequencies, it is less susceptible to enemy jammers
Explanation : In a PESA only one transmitter drives the whole antenna and hence only one frequency can be achieved at a time. This allows it to be more susceptible to jammers.
Correct Answer : Reliable
Explanation : The antenna reliability is dramatically improved in an ESA since there is no moving parts present. The antennas face one direction but the radar beam can be steered electronically to a very wide angle.
Correct Answer : Phase shifter
Explanation : The ESA has no mechanical moving parts, such as antenna gimbals, potentiometers, rotary joints, or hydraulic/electronic motors. It uses phase shifters to electronically steer the beam.
Correct Answer : Pulse
Explanation : Both AESA and PESA that are currently in use are pulse radars. Its basic principle is that shorts bursts of radio pulse are emitted which reflect off a target and the reflected pulse gives the information about the object.
Correct Answer : Height of the aircraft
Explanation : One of the major disadvantages of the primary radar is that it cannot provide a three dimensional fix, that is position and altitude. They are radars that can find the height of the aircraft but can only be used for short distances.
Correct Answer : Friend or foe identification is possible
Explanation : Friend or foe identification is not possible in primary radar and hence it is hard to determine if the aircraft is an enemy or friend. It has a wide range and requires high transmitting power due to the two way travel of the radar signal.
Explanation : The primary radar uses pulse techniques. It sends out short bursts of pulse and the aircraft surface reflects the radio energy back to the radar antenna. It is possible to measure the elapsed time and determine the range or distance of the aircraft.
Correct Answer : Clutter
Explanation : The primary radar pulse is reflected by buildings and clouds and cause undesirable effects in the actual identification. These are called as clutter and can be eliminated by combing primary radar with secondary radar.
Correct Answer : Mode A
Explanation : There are two types of interrogations in the ATCRBS: mode A and mode C. Mode A provides identity only and mode C provides identity and altitude of the aircraft.
Correct Answer : Second
Explanation : In the secondary radar, the strength of the communication system varies inversely with distance to the second power, compared with primary radar which reduced with the fourth power.
Correct Answer : Low RCS
Explanation : Military aircraft usually wish to have a very low RCS or radar cross section so that they are stealthy and undetectable on the enemy’s primary radar. RCS can be reduced by various methods like using radar energy absorbing materials on the surface of the aircraft and not having sharp corners on the aircraft which are more likely to reflect radio energy back to the radar antenna.
Correct Answer : The objects RCS
Explanation : When radar pulse strikes the aircraft some radio pass through the object whereas some get reflected back. The amount of radio energy that gets reflected back depends upon the Radar cross section of the aircraft. RCS depends on size, material on the surface of the aircraft and many more parameters.
Correct Answer : Radio Detection and Ranging
Explanation : The term Radar was coined by the U.S. navy for as the acronym for Radio Detection and Ranging. The term has entered several languages and is used so extensively that it lost capitalization and is used as a common noun.
Correct Answer : More data can be transferred
Explanation : The mode S system works similar to that of mode A and mode C system and causes a transponder to reply when its identity is not known. In a mode S system, additional data other than just altitude and identity can be provided in the MTI.
Correct Answer : 1030 MHz
Explanation : The interrogation pulse is transmitted at 1030 MHz and the reply pulse by the aircraft transponder is given at 1090 MHz. Since the reply is coded information, it does not interfere with other transponders that are using the same frequency.
Correct Answer : Mode S
Explanation : Different modes have its own unique features; mode A gives only identity, mode c gives identity and altitude, mode B is used in European operations and mode S is used for selective calling of transponders.
Correct Answer : 6
Explanation : Mode S interrogations are divided into two types: selective and non-selective. The non-selective are the simplest and include familiar techniques. There is a total of 6 non-selective interrogations.
Correct Answer : Squitter
Explanation : An important transponder characteristic that aids TCAS is the transmission of a mode S reply at quasi-random intervals of about 1 sec, which is called squitter.
Correct Answer : Garble
Explanation : If several aircraft are within the range of the secondary radar and reply to the same interrogation pulse there is a chance that two reply pulses can overlap each other and cause an error in the values of interfere with different aircraft.
Correct Answer : Unique code for each transponder
Explanation : Unlike the ATCRBS where a squawk code is dialed into the transponder, a mode S transponder has a unique identity permanently assigned to it. The mode S radar system can have more than 16 million different identities, enough for each airplane in the world to have a unique identity.
Correct Answer : Tau
Explanation : Tau is the range of the other aircraft with respect to an aircraft divided by range rate. Range divided by range rate is time-essentially the time that would elapse before a collision.
Correct Answer : Maneuverability of the aircraft
Explanation : The threshold number for Tau, whether it is 10 sec or 100 sec depends on the ability of the aircraft to maneuver and avoid a collision.
Correct Answer : 4 min
Explanation : The range of a general TCAS system is around 4 minutes before collision. At 45 seconds before collision TCAS gives traffic advisory and at 25 seconds before collision provides resolution advisory.
Correct Answer : 4ft
Explanation : With radar system operating in excess of 5kW output, the minimum safe approach distance to weather radar is about 4ft.
Correct Answer : 25 dB
Explanation : The signal strength of echoes from storms located at a distance from the aircraft is very low, which requires the transmitter to operate at very high power levels and that the antenna have a gain of more than 25 dB.
Correct Answer : 9375 MHz
Explanation : The weather radar operates at a frequency of 9375 MHz, corresponding to a wavelength of 3 cm. This small wavelength gets easily reflected from clouds containing high water concentrations.
Correct Answer : 200 nmi
Explanation : The use of airborne weather radar is one method of storm avoidance. A weather radar system can show centers at a distance of up to 200 nmi.
