Proposed novel imaging technique will provide all weather high-resolution imaging and recognition capability for RF/Microwave signals with good penetration through highly scattered media: fog, snow, dust, smoke, even foliage, camouflage, walls and ground. Image resolution in proposed imaging system is not limited by diffraction and will be determined by processor and sampling frequency. Proposed imaging system can simultaneously cover wide field of view, detect multiple targets and can be multi-frequency, multi-function. Directional antennas in imaging system can be close positioned and installed in cell phone size handheld device, on small aircraft or distributed around protected border or object. Non-scanning monopulse system allows dramatically decrease in transmitting power and at the same time provides increased imaging range by integrating 2-3 orders more signals than regular scanning imaging systems.
Longer radio frequency waves better penetrating through high scattered media than millimeter waves, but imaging resolution limited by diffraction at longer wavelength. Same time frequency and amplitudes of diffracted waves (frequency domain measurement) provides information of object. Phase shift of diffracted waves (phase front in time domain) consists information about shape of object and can be applied for reconstruction of object shape or even image by recording of multi-frequency digital hologram. Spectrum signature or refracted waves allows identify the object content. Application of monopulse method with overlap closely spaced antenna patterns provides high accuracy measurement of amplitude, phase, and direction to signal source. Digitizing of received signals separately in each antenna relative to processor time provides phase/frequency independence. Fly eye non-scanning multi-frequency radar system provides simultaneous continuous observation of multiple targets and wide possibilities for stepped frequency, simultaneous frequency, chaotic frequency sweeping waveform (CFS), polarization modulation for reliable object detection. Proposed c-band fly eye radar demonstrated human detection through 40 cm concrete brick wall with human and wall material spectrum signatures and can be applied for through wall human detection, landmines, improvised explosive devices detection, underground or camouflaged object imaging.
Image resolution for RF/microwave relatively long waves is limited by the diffraction limit (Abbe diffraction limit). Each point of reflecting object will work as source of diffractive waves if wavelength longer than object. But phase front of diffracted waves still will consist information about object shape. Image can be recovered from multi frequency digital hologram by combination of interferograms. In this case resolution of recovered image will be determined by receiver bandwidth, digitizing frequency and accuracy of processor time. Faster processor - better image resolution. Low frequency non-scanning wide beam in monopulse radar system can cover all object and same time provide high resolution phase measurement relative to reference beam.
The multibeam monopulse radar for Airborne Based Sense and Avoid (ABSAA) system concept is the next step in
the development of passive monopulse direction finder proposed by Stephen E. Lipsky in the 80s. In the proposed
system the multibeam monopulse radar with an array of directional antennas is positioned on a small aircaraft or
Unmanned Aircraft System (UAS). Radar signals are simultaneously transmitted and received by multiple angle
shifted directional antennas with overlapping antenna patterns and the entire sky, 360° for both horizontal and vertical
coverage. Digitizing of amplitude and phase of signals in separate directional antennas relative to reference signals
provides high-accuracy high-resolution range and azimuth measurement and allows to record real time amplitude
and phase of reflected from non-cooperative aircraft signals. High resolution range and azimuth measurement
provides minimal tracking errors in both position and velocity of non-cooperative aircraft and determined by
sampling frequency of the digitizer. High speed sampling with high-accuracy processor clock provides high
resolution phase/time domain measurement even for directional antennas with wide Field of View (FOV). Fourier
transform (frequency domain processing) of received radar signals provides signatures and dramatically increases
probability of detection for non-cooperative aircraft. Steering of transmitting power and integration, correlation
period of received reflected signals for separate antennas (directions) allows dramatically decreased ground clutter
for low altitude flights. An open architecture, modular construction allows the combination of a radar sensor with
Automatic Dependent Surveillance – Broadcast (ADS-B), electro-optic, acoustic sensors.
Proposed airborne surveillance radar system can detect, locate, track, and classify low-profile, low-altitude targets: from traditional fixed and rotary wing aircraft to non-traditional targets like unmanned aircraft systems (drones) and even small projectiles. Distributed micro-radar system is the next step in the development of passive monopulse direction finder proposed by Stephen E. Lipsky in the 80s. To extend high frequency limit and provide high sensitivity over the broadband of frequencies, multiple angularly spaced directional antennas are coupled with front end circuits and separately connected to a direction finder processor by a digital interface. Integration of antennas with front end circuits allows to exclude waveguide lines which limits system bandwidth and creates frequency dependent phase errors. Digitizing of received signals proximate to antennas allows loose distribution of antennas and dramatically decrease phase errors connected with waveguides. Accuracy of direction finding in proposed micro-radar in this case will be determined by time accuracy of digital processor and sampling frequency. Multi-band, multi-functional antennas can be distributed around the perimeter of a Unmanned Aircraft System (UAS) and connected to the processor by digital interface or can be distributed between swarm/formation of mini/micro UAS and connected wirelessly. Expendable micro-radars can be distributed by perimeter of defense object and create multi-static radar network. Low-profile, lowaltitude, high speed targets, like small projectiles, create a Doppler shift in a narrow frequency band. This signal can be effectively filtrated and detected with high probability. Proposed micro-radar can work in passive, monostatic or bistatic regime.
There is a need for small Sense and Avoid (SAA) systems for small and micro Unmanned Aerial Systems (UAS) to
avoid collisions with obstacles and other aircraft. The proposed SAA systems will give drones the ability to “see” close
up and give them the agility to maneuver through tight areas. Doppler radar is proposed for use in this sense and avoid
system because in contrast to optical or infrared (IR) systems Doppler can work in more harsh conditions such as at
dusk, and in rain and snow. And in contrast to ultrasound based systems, Doppler can better sense small sized obstacles
such as wires and it can provide a sensing range from a few inches to several miles. An SAA systems comprised of
Doppler radar modules and an array of directional antennas that are distributed around the perimeter of the drone can
cover the entire sky. These modules are designed so that they can provide the direction to the obstacle and
simultaneously generate an alarm signal if the obstacle enters within the SAA system’s adjustable “Protection Border”.
The alarm signal alerts the drone’s autopilot to automatically initiate an avoidance maneuver. A series of Doppler radar
modules with different ranges, angles of view and transmitting power have been designed for drones of different sizes
and applications. The proposed Doppler radar micro SAA system has simple circuitry, works from a 5 volt source and
has low power consumption. It is light weight, inexpensive and it can be used for a variety of small unmanned aircraft.
All digital radar architecture requires exclude mechanical scan system. The phase antenna array is necessarily large because the array elements must be co-located with very precise dimensions and will need high accuracy phase processing system for aggregate and distribute T/R modules data to/from antenna elements. Even phase array cannot provide wide field of view. New nature inspired all digital radar architecture proposed. The fly’s eye consists of multiple angularly spaced sensors giving the fly simultaneously thee wide-area visual coverage it needs to detect and avoid the threats around him. Fly eye radar antenna array consist multiple directional antennas loose distributed along perimeter of ground vehicle or aircraft and coupled with receiving/transmitting front end modules connected by digital interface to central processor. Non-steering antenna array allows creating all-digital radar with extreme flexible architecture. Fly eye radar architecture provides wide possibility of digital modulation and different waveform generation. Simultaneous correlation and integration of thousands signals per second from each point of surveillance area allows not only detecting of low level signals ((low profile targets), but help to recognize and classify signals (targets) by using diversity signals, polarization modulation and intelligent processing. Proposed all digital radar architecture with distributed directional antenna array can provide a 3D space vector to the jammer by verification direction of arrival for signals sources and as result jam/spoof protection not only for radar systems, but for communication systems and any navigation constellation system, for both encrypted or unencrypted signals, for not limited number or close positioned jammers.
Revolutionary new fly eye radar sensor technologies based on an array of directional antennas is eliminating the
need for a mechanical scanning antenna or complicated phase processor. Proposed sense and avoid radar based on
fly eye radar technology can be very small, provides continuous surveillance of entire sky (360 degree by azimuth
and elevation) and can be applied for separate or swarm of micro/nano UAS or UGS. Monopulse technology
increases bearing accuracy several folds and radar can be multi-functional, multi-frequency. Fly eye micro-radars
are inexpensive, can be expendable. Prototype of sense and avoid radar with two directional antennas has been
designed and bench tested.
To compensate for its eye’s inability to point its eye at a target, the fly’s eye consists of multiple angularly spaced sensors giving the fly the wide-area visual coverage it needs to detect and avoid the threats around him. Based on a similar concept a revolutionary new micro-radar sensor technology is proposed for detecting and tracking ground and/or airborne low profile low altitude targets in harsh urban environments. Distributed along a border or around a protected object (military facility and buildings, camp, stadium) small size, low power unattended radar sensors can be used for target detection and tracking, threat warning, pre-shot sniper protection and provides effective support for homeland security. In addition it can provide 3D recognition and targets classification due to its use of five orders more pulses than any scanning radar to each space point, by using few points of view, diversity signals and intelligent processing. The application of an array of directional antennas eliminates the need for a mechanical scanning antenna or phase processor. It radically decreases radar size and increases bearing accuracy several folds. The proposed micro-radar sensors can be easy connected to one or several operators by point-to-point invisible protected communication. The directional antennas have higher gain, can be multi-frequency and connected to a multi-functional network. Fly eye micro-radars are inexpensive, can be expendable and will reduce cost of defense.
A next generation of Smart antennas with point-to-point communication and jam, spoof protection capability by verification of spatial position is offered. A directional antenna array (DAA) with narrow irradiation beam provides counter terrorism protection for communications, data link, control and GPS. Communications are “invisible” to guided missiles because of 20 dB smaller irradiation outside the beam and spatial separation. This solution can be implemented with current technology. Directional antennas have higher gain and can be multi-frequency or have wide frequency band in contrast to phase antenna arrays. This multi-directional antenna array provides a multi-functional communication network and simultaneously can be used for command control, data link and GPS.
Regular micro and nano radars cannot provide reliable tracking of low altitude low profile aerial targets in urban and
mountain areas because of reflection and re-reflections from buildings and terrain. They become visible and vulnerable
to guided missiles if positioned on a tower or blimp. Doppler radar cannot distinguish moving cars and small low
altitude aerial targets in an urban area. A new concept of pocket size distributed radar technology based on the
application of UAV (Unmanned Air Vehicles), UGV (Unmanned Ground Vehicles) is proposed for tracking of low
altitude low profile aerial targets at short and medium distances for protection of stadium, camp, military facility in
urban or mountain areas.
There are two switching processes where observe in polymer-dispersed liquid crystals (PDLC) when pulse electric field applied: - Slow switching process with rise time hundreds microseconds; - Fast switching process with nanoseconds rise time. The result of research, design and testing ultra-fast PDLC optical gate is presented. The feasibility of 100 nsec rise time optical gate with 1 square inch crystal clear transmission (better than 1.54 dB) and attenuation in OFF state more than 26 dB (30.4 dB for two serial layers) for non-polarized light has been shown.
Proc. SPIE. 8045, Unmanned Systems Technology XIII
KEYWORDS: Defense and security, Safety, Detection and tracking algorithms, Receivers, Geographic information systems, Signal processing, Sensing systems, Algorithm development, Collision avoidance, Global Positioning System
Military and other national security agencies have been denied unfettered access to the National Air Space (NAS)
because their unmanned aircraft lack a reliable and effective collision avoidance capability. To overcome the constraints
imposed on UASs use of the NAS, a new, conformable collision avoidance system has been developed - one that will be
effective in all flyable weather conditions, overcoming the shortfalls of other sensing systems. Upon implementation this
system will achieve collision avoidance capability for UASs deployed for national security purposes and will allow
expansion of UAS usage for commercial or other civil purposes.
Wide dynamic range gating photosensor modules has been design for LIDAR-RADAR applications on base R7400U
(active area 8 mm. diameter) R7600U (active area 18x18 mm.) Hamamatsu photomultiplier tubes. The photomultiplier
tubes R7400U, series have two kinds of photocathode: low resistance semitransparent multialkali photocathodes and
semitransparent bialkali photocathodes with large resistance. Different kinds of photocathodes require different approach
to gating circuits design. High-speed pulse gating (gating rise time 10 nsec, setting time 40 nsec for 99%) has been used
for enhancing of target contrast at ocean optic application for both kinds: semitransparent bialkali and semitransparent
multialkali photocathodes. Wide dynamic range (50 dB of optical power) has been achieved by optimizing of applied to
dynodes voltages. Compression up to 30 dB has been used for following output signal digital processing. Hamamatsu
photosensitive modules were used in the two system receivers in pulsed LIDAR system. The system was mounted on
the bow of the R/V New Horizon and collected data from August 25 thru September 8, 2005 as part of the LOCO field
test in Monterey Bay. Approximately 4 million LIDAR profiles were collected during this period. During the field test
the profiles were processed to show relative changes in water optical properties and to reveal water column structure in
New approach to high-speed detection and modulation based on application of capacitance modulation is offered. Application of capacitance modulation allows to increase sensitivity and noise immunity of high-speed photodetectors in microwave range.
Subject: INTEVAC hybrid photomultiplier vacuum tube IPD-280 with 18 mm GaAsP photocathode, imaging electron optics, ion trap and 0.5, 1.0 diameter Schottky barrier anode.
Problem: Large area intensified photodiodes (IPDs) have parameters (high sensitivity, gain, speed of operation, bandwidth, low noises), which are ideal for Ocean optic applications. However, these IPDs have not enough dynamic range and lifetime.
Target of objective investigation: Identify the cause for small dynamic range and short lifetime of IPDs and optimize them for Ocean Optic applications.
The voltages applied to photocathode and focusing electrodes have been experimentally optimized for maximal IPD sensitivity,dynamic range, pulse rise, and transit time. The photoelectrons trajectories and ions have been simulated using SIMION 3D 7,0 software for various voltages applied to the focusing electrodes. The uniformity of the photocathode has been tested to determine the impact of ions on the photocathode. Electron and ion currents investigations have been made for both negative and positive voltages applied to the ion trap electrode. Optimizing the regime for electron focusing and minimizing the ion current impact to photocathode was determines as result of the investigation. Reducing the voltages applied to photocathode and focusing the electrodes from 8 KV to 4-6 KV decreased the ion current. In this regime, the gain of IPD does not decrease significantly and the rise time and transit time of IPD remined practically the same.
The transformation of an optical signal in a microwave range allows increasing a processing speed of an optical signal. But the problem of a highly sensitive reception of a signal remains actual. The use of photo-diodes and field effect transistors with a Schottky barrier is accompanied by significant losses of an optical signal. Optical controlled microwave circuits with a negative resistance -- negatrons allows to increase sensitivity of transformation and to reduce losses of an optical signal. The purpose of the article is the analysis of a possibility of application of various types of microwave circuits with a negative resistance for transformation of an optical signal.