Radar Fundamentals Flashcards
Define wavelength
Physical distance of one complete wave
Define frequency
Number of cycles that the RF energy completes per second.Hzf=c/wavelength
Define phase
A 360 degree cycle of an Em wave.The degree to which individual cycles of a wave coincide with those of a reference wave of the same frequency
Define polarization
Orientation of the electrical field in an Em wave.Vertical, Horizontal, Spiral
Define BW, Beamwidth
BW is angular measurement of the size of the mainbeam, normally expressed in degrees.
Define PW, Pulse Width
PW is the time radar is transmitting each pulse.Units Time
Define PL, Pulse Length
PL is the distance between the leading and trailing edges of a pulse. Units Distance
Define PRF, Pulse Repetition Frequency
Rate at which pulses are transmitted. Measured in pulses per second.
Lower Frequency Radar Characteristics
Long Wavelength; large antenna; components able to generate high transmit power; low atmospheric attenuation; good long range detection capability, but poor precision; best long range for EW radars
Medium Frequency Radar Characteristics
Smaller wavelengths allow smaller antennas; components cannot handle as much power, therefore less detection range; some atmospheric attenuation; used by ASR, HF, GCI, SAM, and ADA acquisition radars.
Higher Frequency Radar Characteristics
Higher frequencies have shorter wavelengths and smaller antennas; smaller components allow less power with shorter detection range; high precision; atmospheric attenuation more of a problem; fire control radars for fighters, SAM and ADA.
Linear Polarization
Horizontal, vertical, slant
Circular Polarization
Right hand, left hand waves whose polarization rotates through 360 degrees in every wavelength
Radar Power
Strength of radar signal hitting a target = 1/R^2Strength of radar signal sent/received by a radar = 1/R^4
Radar Reflection
The process of reradiating an incident radio wave.
Radar Refraction
The bending of Em energy through different materials.
Radar Ducting
The bending of radar rays due to atmospheric conditionsSubrefraction decreases radar LOS by bending the radar beam upward.Superrefraction increases radar LOS detection by bending the radar beam downward.
Radar Diffraction
Phenomenon observed when a radio wave spreads around objects whose size is comparable to its wavelength and bend around the edges of larger objects. Diffraction increases with wavelength.
Characteristics of Parabolic Antenna
Large Sidelobes (disadvantage)Easiest and cheapest to manufacture (advantage)Transmitter in front of dishBasic satellite dish
Characteristics of mechanically scanned planar array antennasMSA
Flat-faced antenna mechanically scanned in AZ and ELConsists of an array of many individual radiators of equal phase distributed over a flat surfaceSlots cut in the walls of a complex of waveguides behind the antennas faceDesigned to distribute the radiated power across the array so as to minimize sidelobes
ESA Characteristics
Mounted in fixed positionBeam is steered by individually controlling the phase of the radio waves transmitted and received by each radiating element
Passive vs Active ESA
Passive-beam is steered by an electronically controlled phase shifter placed behind radiating element, controlled by BSA or central processorActive- Instead of a phase shifter, a small T/R module is placed behind radiating element
Limitations of ESA
FOR-Apparent size of antenna decreases with off boresight; results in increased beam width and decrease in efficiency; limits maximum look angle to +-60 degrees (BW doubles, power half)Electronically complex
Advantages/Disadvantages of CW Radar(Continuous Wave)
Continuously Transmits- separate transmitter vs receiver (disadvantage), High AOP (advantage)Greater detection range (Hight AOP)- unable to determine range (disadvantage)
