Radar frequencies and the electromagnetic spectrum
Standard radar-frequency letter-band nomenclature
Basic Principle of Radar
A Simplified Pulsed Radar Block Diagram
Fig. a) Train of transmitted and received pulses Fig. b) Illustrating range ambiguity
Plot of Max. unambiguous range as a function of PRF
Radar Waveforms - Example
Resolving targets in range and cross range
Fig. a) Two unresolved targets Fig. b) Two resolved targets
Radar Block Diagram and Operation
Fig. a) PPI presentation displaying range Vs angle (intensity modulation)Fig. b) A-Scope presentation displaying amplitude Vs range (deflection modulation)
Typical envelope of the radar receiver output as a function of time
Examples of Probability Density Functions: a) Uniform b) Gaussian c) Rayleigh (Voltage) d) Rayleigh (Power)
Simplified block diagram of threshold receiver and envelope detector
Envelope of receiver output illustrating false alarms due to noise
Average time between false alarms as a function of threshold level VT and the receiver bandwidth B; ψo is the mean square noise voltage
Probability density function for noise alone and signal plus noise, illustrating the process of threshold detection
Probability of detection for a sine wave in noise as a function of signal to noise (power) ratio and the probability of false alarm
Table: Single Pulse SNR, dB
Integration Improvement Factor
Integration Loss as a function of ‘n’
Radar Cross Section of the sphere. a = radius; λ = wavelength
RCS of a cone sphere with 150 half angle as the function of diameter in wavelengths
Measured RCS (σ/λ2 given in dB) of a large cone sphere with 12.50 half angle and radius of base=10.4λ (a) Horizontal (perpendicular polarization), (b) Vertical (parallel polarization)
Multiple time around echoes that give rise to ambiguities in range
Fig. a) Radar-Centered PPI Fig. b) Radar A-Scope
Geometry of radar and target in deriving Doppler frequency shift.
Target 1 generates zero Doppler; Target 2 generates maximum Doppler; Target 3 is in between
Doppler frequency shift from a moving target as a function of target’s radial velocity and radar frequency band
Example: Compute the Doppler frequency measured by the radar shown in fig. below
Fig. a) Simple CW radar block diagram Fig. b) Response characteristic of beat frequency amplifier
Block diagram of CW Doppler radar with non-zero IF receiver
Frequency spectrum of CW oscillation of (a) infinite duration and (b) finite duration
Fig. a) Block diagram of IF Doppler filter bankFig. b) Frequency response characteristic of Doppler filter bank
Spectra of received signals: Fig. a) No Doppler shift, no relative target motion; Fig. b) Approaching target; Fig. C) Receding target
Measurement of Doppler direction using synchronous, two-phase motor
Fig. a) Linear FM; Fig. b) Triangular LFM signals Fig. c) Beat frequency for stationary target
Block diagram of FM-CW radar
Transmitted and received LFM signals and beat frequency, for moving targets
Block diagram of FM-CW radar using sideband superheterodyne receiver
Unwanted signals in FM altimeter
Fig. a) Simple CW radarFig. b) Pulse radar using Doppler information
Fig. a) RF echo pulse trainFig. b) Video pulse train after the phase detector for fd > 1/τFig. c) Video pulse train for fd < 1/τ
Typical radar return PSD when clutter and target are present
Fig. a) Typical radar return PSD when clutter and target are presentFig. b) MTI filter frequency responseFig. c) Output from an MTI filter
Fig’s (a) & (b) : Two successive sweeps of an MTI radar A-scope displayFig. c) : When (b) is subtracted from (a) echoes from stationary targets are cancelled, leaving only moving targets
MTI receiver with delay - line canceler
Block diagram of MTI radar with power-amplifier transmitter
Block diagram of MTI radar with power-oscillator transmitter
Fig. a) Single delay line canceler Fig. b) Magnitude of Frequency response ; T = delay time = 1/fp = Tp
Plot of the first blind speed as a function of prf for the various radar frequency bands
Configuration for a double delay line canceler
Relative frequency response of the single delay line canceler (solid curve) and the double delay line canceler (dashed curve). Shaded area represents clutter spectrum
Fig. a) Frequency response of a single delay line canceler for fp = 1/T1
Fig. b) Same for fp = 1/T2
Fig. c) Composite response with T1/T2 = 4/5
Fig. a) Staggered pulse train with four different pulse periodsFig. b) Frequency response of a five-pulse (four-period) stagger
Block diagram of MTI radar using range gates and filters
Frequency-response characteristic of MTI using range gates and filters
Block diagram of a Noncoherent MTI Radar
Basic Principle of Continuous angle tracking
Sequential Lobing: Fig. a) Target is located on track axis Fig. b) Target is off track axis
Conical scan tracking
Block diagram of conical scan tracking radar
Monopulse antenna pattern
Fig. 1) Illustration of Monopulse conceptFig. 2) Monopulse Comparator
Monopulse antenna patterns and error signal in one coordinate. Left hand diagrams in (a-c) are in polar coordinates; right hand diagrams in rectangular coordinates.Fig. a) Overlapping antenna patterns Fig. b) Sum patternFig. c) Difference pattern Fig. d) Product (error) signal
Block diagram of amplitude-comparison monopulse radar (one angular coordinate)
Wavefront phase relationships in phase-comparison monopulse radar
Single coordinate phase-comparison monopulse antenna, with sum and difference channels
Split-range-gate tracking
Examples of acquisition search patterns: (a) Trace of helical scanning beam; (b) Palmer scan; (c) Spiral scan; (d) Raster, or TV, scan; (e) Nodding scan
Efficiency, relative to a matched filter, of a single-tuned resonant filter and rectangular shaped filter, when the input signal is a rectangular pulse
Efficiency of nonmatched filters compared with the matched filter
Principle of branch-type duplexer
Balanced duplexer using dual TR tubes and two short-slot hybrid junctions. Fig. a) Transmit condition Fig. b) Receive condition
Circulator and receiver protector
Fig. a) N-element linear arrayFig. b) Steering of an antenna beam with variable phase shifters
Series arrangements for applying phase relationships in an array.Fig. a) Fed from one end Fig. b) Center-fed