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At what speed do EM waves travel at?

3x10^8 m/s

Explain how a CW radar works.

A Continuous Wave radar does not send pulses, but rather a steady amplitude signal. The CW system cannot detect range. However is is excellent at detecting closing speed of a target using Doppler shift. With a CW system, the transmitted RF energy is radiated, strike the target and returns to the receiver. The frequency of the returning RF is compared with the frequency of the transmitted energy. If the target is moving relative to the radar, the returning energy is at a different frequency (a Doppler shift). The difference is amplified, processed and sent to the indicator as a target velocity.

Name three types of radar display and describe each.

A-SCOPE Target signal amplitude vs. range or velocity. Displays all targets along pencil beam for selected range limits. Displays tracking gate. Usually raw video. Some modern radars have raw video a-scopes as an adjunct to synthetic video displays. Must be used with a separate azimuth and elevation display of some sort. Also called a range scope (R-Scope). B-SCOPE Range vs. azimuth or elevation. Displays targets within selected limits. Displays tracking gate. May be raw or synthetic video. Surface radars usually have two. One azimuth/one elevation which can result in confusion with multiple targets. PPI PPI scope (plan position indicator). Polar plot of direction and distance. Displays all targets for 360 degrees. Sector PPI scope. Polar plot of direction and distance. Displays all targets within a specific sector. Origin may be offset so that "your" radar position may be off the scope.

What is absorption and at what frequency does it start to become a problem for radars?

Absorption reduces the power or strength of the wave. There is no absorption of EM in free space. In the atmosphere however, EM waves ca be absorbed, as energy from the EM wave is transferred to the atoms and molecules of the atmosphere. Atmospheric absorption of EM waves below about 10GHz is insignificant.

Why is a target RCS not constant in reference to illuminating radars?

An object reflects a limited amount of radar energy back to the source. The factors that influence this include: the material of which the target is made; the absolute size of the target; the relative size of the target (in relation to the wavelength of the illuminating radar); the incident angle (angle at which the radar beam hits a particular portion of target which depends upon shape of target and its orientation to the radar source); the reflected angle (angle at which the reflected beam leaves the part of the target hit, it depends upon incident angle); the polarization of transmitted and the received radiation in respect to the orientation of the target

Name a common tracking technique used to determine the direction of the target from a radar.

Conical scan: If the target is on the scan axis, the strength of the reflected signals remains constant (or changes gradually as the range changes). But if the target is slightly off the axis, the amplitude of the reflected signals will change at the scan rate.

What is the difference between instantaneous FOV and FOV?

FOV, or Field of View, is the largest area that your imager can see at a set distance. It is typically described in horizontal degrees by vertical degrees—for example, 23º X 17º. (These "degrees" are units of angular measurement, not to be confused with the degrees of temperature measurement.) Essentially, it is like a rectangle extending out from the center of your camera's lens extending outward. The farther away you look, the larger the rectangle becomes. IFOV, or Instantaneous Field of View (otherwise known as Spatial Resolution), is the smallest detail within the FOV that can be detected or seen at a set distance. What does this mean? It means that at certain distance, you may not be able to see certain small details if your Spatial Resolution is not good enoug

At what point on the main beam is the beamwidth measured?

Half the maximum (3dB beam width)

Name two air-to-ground modes and describe each.

Laser-guided bomb - A guided bomb that uses semi-active laser guidance to strike a designated target with greater accuracy than an unguided bomb. These weapons use on-board electronics to track targets that are designated by laser, typically in the infrared spectrum, and adjust their glide path to precisely strike the target. Since the weapon is tracking a light signature, not the object itself, the target must be illuminated from a separate source, either by ground forces, by a pod on the attacking aircraft, or by a separate support aircraft.Paveway II 500-pound LGBs (such as GBU-12) are a cheaper lightweight PGM suitable for use against vehicles and other small targets, while a Paveway III 2000-pound penetrator (such as GBU-24) is a more expensive weapon suitable for use against high-value targets. GPS guided - Poor visibility does not affect satellite-guided weapons such as Joint Direct Attack Munition (JDAM) and Joint Stand-Off Weapon (JSOW), which make use of the United States' GPS system for guidance. This weapon can be employed in all weather conditions, without any need for ground support. Because it is possible to jam GPS, the guidance package reverts to inertial navigation in the event of GPS signal loss. Inertial navigation is significantly less accurate;

What is the formula for power density (inverse square law)?

Power density=transmitted power/area Pr=Pt / (4 x π x r^2) Where Pr is power density at a distance r from an isotropic source (radiates in all directions equally and Pt is transmitted power.

Aside from a CW radar, name and describe two common types of radar.

Pulsed radar: In a pulsed radar system, the transmitter is turned on and off by the modulator at a fixed repetition rate and for a fixed duration. The antennae transmits the pulse, then listens for echoes until the next pulse is to be transmitted. By measuring the time delay between sending a pulse and receiving the echo, the target range can be detected.

Name three air-to-air modes and give a brief description of each.

Semi-active radar homing (SARH) They function by detecting radar energy reflected from the target. The radar energy is emitted from the launching aircraft's own radar system. However, this means that the launch aircraft has to maintain a "lock" on the target (keep illuminating the target aircraft with its own radar) until the missile makes the interception. This limits the attacking aircraft's ability to maneuver, which may be necessary should threats to the attacking aircraft appear. Infrared guided (IR) IR missiles home on the heat produced by an aircraft. Early infra-red detectors had poor sensitivity, so could only track the hot exhaust pipes of an aircraft. This meant an attacking aircraft had to maneuver to a position behind its target before it could fire an infra-red guided missile. This also limited the range of the missile as the infra-red signature soon become too small to detect with increasing distance and after launch the missile was playing "catch-up" with its target. Early infrared seekers were unusable in clouds or rain (which is still a limitation to some degree) and could be distracted by the sun, a reflection of the sun off of a cloud or ground object, or any other "hot" object within its view. More modern infra-red guided missiles can detect the heat of an aircraft's skin, warmed by the friction of airflow, in addition to the fainter heat signature of the engine when the aircraft is seen from the side or head-on. This, combined with greater maneuverability, gives them an "all-aspect" capability, and an attacking aircraft no longer had to be behind its target to fire. Active radar (AR)-guided missiles carry their own radar system to detect and track their target. However, the size of the radar antenna is limited by the small diameter of missiles, limiting its range which typically means such missiles are launched at a predicted future location of the target, often relying on separate guidance systems such as Global Positioning System, inertial guidance, or a mid-course update from either the launching aircraft or other system that can communicate with the missile to get the missile close to the target. At a predetermined point (frequently based on time since launch or arrival near the predicted target location) the missile's radar system is activated (the missile is said to "go active") and the missile then homes in on the target.

Name another common tracking technique used to determine the direction of the target from a radar.

Sequential lobing: Tracking is achieved (in one coordinate) by continuously switching the pencil beam between two pre-determined symmetrical positions around the antenna's Line of Sight (LOS) axis. Hence, the name sequential lobing is adopted. As the beam is switched between the two positions, the radar measures the returned signal levels. The difference between the two measured signal levels is used to compute the angular error signal.

Why are sidelobes undesirable (2 reasons)?

Sidelobes can permit energy from undesired returns to enter the system (i.e. ground returns and jamming).

What electromagnetic effect allows radars to measure the velocity of a moving target?

The Doppler effect is used to measure the velocity of detected objects.

What is Pulse Repetition Frequency?

The number of pulses radiated per second is termed the PRF and is measured in Hz. The higher the PRF the more data returned and the greater the accuracy of the system. However higher PRFs give worse Maximum ambiguous Ranges.

Define polarisation and list three different types of polarisation.

The term polarisation refers to the physical orientation of radiated energy in space. Types of polarisation are linear (vertical and horizontal), random and circular (right hard, left hand and elliptical).

What is the relationship between frequency and wavelength?

Wavelength = speed of light / frequency The higher the frequency, the shorter the wavelength.