Pulse-Doppler radar

Dopplerpulse-Dopplerpulse doppler
Pulse-Doppler techniques also find widespread use in meteorological radars, allowing the radar to determine wind speed from the velocity of any precipitation in the air. Pulse-Doppler radar is also the basis of synthetic aperture radar used in radar astronomy, remote sensing and mapping. In air traffic control, they are used for discriminating aircraft from clutter. Besides the above conventional surveillance applications, pulse-Doppler radar has been successfully applied in healthcare, such as fall risk assessment and fall detection, for nursing or clinical purposes. The earliest radar systems failed to operate as expected.

Aperture synthesis

aperture synthesis imagingsynthetic apertureinterferometric imaging
Interferometric synthetic aperture radar (IfSAR or InSAR). Synthetic aperture radar (SAR) and Inverse synthetic aperture radar (ISAR). Synthetic aperture sonar. Beamforming. Synthetic aperture magnetometry. Light field. Development of radio interferometry, from Astronomical Optical Interferometry, A Literature Review by Bob Tubbs, Cambridge, 2002. Cambridge Optical Aperture Synthesis Telescope. APerture SYNthesis SIMulator (an interactive tool to learn the concepts of Aperture Synthesis).

Phased array

phased array radarphased-arrayphased-array radar
Interferometric synthetic-aperture radar. Inverse synthetic-aperture radar. Multi-user MIMO. Optical heterodyne detection. Phased array ultrasonics. Phased-array optics. Radar MASINT. Side-scan sonar. Single-frequency network. Smart antenna. Synthetic-aperture radar. Synthetic aperture sonar. Synthetically thinned aperture radar. Thinned-array curse. Wave field synthesis. History of smart antennas. Radar Research and Development - Phased Array Radar—National Severe Storms Laboratory. Shipboard Phased Array Radars. NASA Report: MMICs For Multiple Scanning Beam Antennas for Space Applications. Principle of Phased Array @ www.radartutorial.eu. 'Phased Array' microphone system of Tony Faulkner.

Pulse repetition frequency

PRFpulse repetition frequenciesmedium pulse repetition frequency
Unlike lower radio signal frequencies, light does not bend around the curve of the earth or reflect off the ionosphere like C-band search radar signals, and so lidar is useful only in line of sight applications like higher frequency radar systems. Radar. Laser range finder. Sonar. Radar. Pulse-Doppler radar. Weather radar.

Polarization (waves)

polarizationpolarizedpolarized light
Polarization is also important in the transmission of radar pulses and reception of radar reflections by the same or a different antenna. For instance, back scattering of radar pulses by rain drops can be avoided by using circular polarization. Just as specular reflection of circularly polarized light reverses the handedness of the polarization, as discussed above, the same principle applies to scattering by objects much smaller than a wavelength such as rain drops. On the other hand, reflection of that wave by an irregular metal object (such as an airplane) will typically introduce a change in polarization and (partial) reception of the return wave by the same antenna.

Matched filter

matched filteringmatched-filteringNorth filters
Matched filters are commonly used in radar, in which a known signal is sent out, and the reflected signal is examined for common elements of the out-going signal. Pulse compression is an example of matched filtering. It is so called because impulse response is matched to input pulse signals. Two-dimensional matched filters are commonly used in image processing, e.g., to improve SNR for X-ray. Matched filtering is a demodulation technique with LTI (linear time invariant) filters to maximize SNR. It was originally also known as a North filter. The following section derives the matched filter for a discrete-time system.

Doppler radar

DopplerDoppler navigationDoppler navigation radar
. * Description of Doppler shift used in Continuous wave Doppler radar Coherent pulsed (CP). Pulse-Doppler radar. Continuous wave (CW), or. Frequency modulation (FM). Radar gun. Continuous-wave radar. Semi-active radar homing.

Doppler effect

Dopplerdoppler shiftDoppler shifts
The Doppler effect is used in some types of radar, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each wave increases, increasing the wavelength. In some situations, the radar beam is fired at the moving car as it approaches, in which case each successive wave travels a lesser distance, decreasing the wavelength.

Radio astronomy

radio astronomerradioradioastronomy
Surprisingly the first use of a radio interferometer for an astronomical observation was carried out by Payne-Scott, Pawsey and Lindsay McCready on 26 January 1946 using a SINGLE converted radar antenna (broadside array) at 200 MHz near Sydney, Australia. This group used the principle of a sea-cliff interferometer in which the antenna (formerly a World War II radar) observed the sun at sunrise with interference arising from the direct radiation from the sun and the reflected radiation from the sea.

Ground-penetrating radar

ground penetrating radargeoradarGPR
Wall-penetrating radar can read through non-metallic structures as demonstrated to ASIO and Australian Police in 1984 while surveying an ex Russian Embassy in Canberra. Showed police how to watch people up to two rooms away laterally and through floors vertically, could see metal lumps that might be weapons; GPR can even act as a motion sensor for military guards and police, Project carried out first in 1984 Canberra Australia.(Also used for detecting "Ghosts" on TV show.{air disturbance in a locked room}) The "Mineseeker Project" seeks to design a system to determine whether landmines are present in areas using ultra wideband synthetic aperture radar units mounted on blimps.

Interferometric synthetic-aperture radar

interferometric synthetic aperture radarInSARSAR interferometry
Interferometric synthetic aperture radar, abbreviated InSAR (or deprecated IfSAR), is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation, using differences in the phase of the waves returning to the satellite or aircraft. The technique can potentially measure millimetre-scale changes in deformation over spans of days to years. It has applications for geophysical monitoring of natural hazards, for example earthquakes, volcanoes and landslides, and in structural engineering, in particular monitoring of subsidence and structural stability.

Stealth aircraft

stealthstealth fighterstealth bomber
Later stealth approaches do not rely on controlling the specular reflections of radar energy and so the geometrical benefits are unlikely to be significant. Researchers at the University of Illinois at Urbana–Champaign with support of DARPA, have shown that it is possible to build a synthetic aperture radar image of an aircraft target using passive multistatic radar, possibly detailed enough to enable automatic target recognition.

Beamforming

beam formingbeamformerAntenna beamforming
Inverse synthetic aperture radar (ISAR). Synthetic aperture radar. Synthetic aperture sonar. Thinned array curse. Window function. Synthetic-aperture magnetometry (SAM). Microphone array. Zero-forcing precoding. Multibeam echosounder. Pencil (optics). Periodogram. MUSIC. SAMV. Spatial multiplexing. Antenna diversity. Channel state information. Space–time code. Space–time block code. Dirty paper coding (DPC). Smart antenna. WSDMA (Wideband Space Division Multiple Access). Golomb ruler. Audio Surveillance. Reconfigurable antenna. Sensor array. Louay M. A. Jalloul and Sam. P.

Radar altimeter

radio altimeterradar altimetryelectronic altimeter
The primary difference between delay-doppler (or Synthetic Aperture Radar) and pulse-limited altimetry is that delay-doppler altimetry looks at a smaller section of the pulse-limited radar footprint, but emits far more pulse signals to give the effect of covering the same footprint as pulse-limited but with better resolution. The top-down view in the figure below shows the decreased footprint size of the delay-doppler signal. In order to determine the power signal of the delay-doppler radar as a function of time, we'll need to assume that the footprint of the pulsed radar is small enough to be considered two rectangles of width W.

SAMV (algorithm)

SAMViterative Sparse Asymptotic Minimum Variance
Applications include synthetic-aperture radar, computed tomography scan, and magnetic resonance imaging (MRI). The formulation of the SAMV algorithm is given as an inverse problem in the context of DOA estimation. Suppose an M-element uniform linear array (ULA) receive K narrow band signals emitted from sources located at locations, respectively. The sensors in the ULA accumulates N snapshots over a specific time. The M \times 1 dimensional snapshot vectors are where is the steering matrix, contains the source waveforms, and {\bf e}(n) is the noise term. Assume that, where is the Dirac delta and it equals to 1 only if n=\bar{n} and 0 otherwise.

X band

XX-bandX-
In radar engineering, the frequency range is specified by the IEEE at 8.0 to 12.0 GHz. The X band is used for radar, satellite communication, and wireless computer networks. X band is used in radar applications including continuous-wave, pulsed, single-polarization, dual-polarization, synthetic aperture radar, and phased arrays. X band radar frequency sub-bands are used in civil, military, and government institutions for weather monitoring, air traffic control, maritime vessel traffic control, defense tracking, and vehicle speed detection for law enforcement. X band is often used in modern radars.

Cassini–Huygens

CassiniCassini spacecraftCassini'' spacecraft
The Italian Space Agency (ASI) provided the Cassini orbiter's high-gain radio antenna, with the incorporation of a low-gain antenna (to ensure telecommunications with the Earth for the entire duration of the mission), a compact and lightweight radar, which also uses the high-gain antenna and serves as a synthetic-aperture radar, a radar altimeter, a radiometer, the radio science subsystem (RSS), the visible channel portion VIMS-V of VIMS spectrometer. The VIMS infrared counterpart was provided by NASA, as well as Main Electronic Assembly, which includes electronic subassemblies provided by CNES of France.

Space-time adaptive processing

In comparison with SIMO radar systems, which will have M transmit degrees of freedom, and NL receive degrees of freedom, for a total of M+NL, MIMO radar systems have MNL degrees of freedom, allowing for much greater adaptive spatial resolution for clutter mitigation. Array processing. Beamforming. MIMO. Multistatic radar. Phased array. Synthetic aperture radar. Brennan, L.E. and I.S. Reed, Theory of Adaptive Radar, IEEE AES-9, pp. 237–252, 1973. Guerci, J.R., Space-Time Adaptive Processing for Radar, Artech House Publishers, 2003. ISBN: 1-58053-377-9. Klemm, Richard, Principles of Space-Time Adaptive Processing, IEE Publishing, 2002. ISBN: 0-85296-172-3.

Radar engineering details

radar sensorradar antennaradar sensors
Synthetic aperture radar (SAR) allow for an angular resolution beyond real beamwidth by moving the aperture over the target, and adding the echoes coherently. Architecture: The field of view is scanned with a highly directive frequency-orthogonal (slotted waveguide), spatially orthogonal (switched beamforming networks), or time-orthogonal beams. In case of time-orthogonal scanning, the beam of an ESA is scanned preferably by applying a progressive time delay, \Delta \tau, constant over frequency, instead of by applying a progressive phase shift, constant over frequency. Usage of true-time-delay (TTD) phase shifters avoids beam squinting with frequency.

Rockwell B-1 Lancer

B-1B-1BB-1B Lancer
The Lancer's offensive avionics include the Westinghouse (now Northrop Grumman) AN/APQ-164 forward-looking offensive passive electronically scanned array radar set with electronic beam steering (and a fixed antenna pointed downward for reduced radar observability), synthetic aperture radar, ground moving target indication (GMTI), and terrain-following radar modes, Doppler navigation, radar altimeter, and an inertial navigation suite. The B-1B Block D upgrade added a Global Positioning System (GPS) receiver beginning in 1995.