Abstract: An auto-calibration technique for optimizing the transfer function of analog-to-digital converters. The technique can be applied to analog-to-digital converter (ADC) architectures employing a cascade of n-stages to form a composite n-bit ADC transfer function. The technique utilizes evaluation of the probability density function of individual bits to determine error sign, minimize error magnitude and assure calibration convergence.

Abstract: An efficient digital wideband waveform generation and signal processing system for multi-beam electronically scanned antenna array (ESA) radar systems. The digital waveform generator (50) first produces a series of waveform phase angles corresponding to the phase angles of a common signal to be transmitted by the ESA. Then, for each antenna element, the waveform phase angles are adjusted to steer the beam by adding a time delay and a phase adjustment. A digital signal is then produced for each antenna element by applying a cosine function to the adjusted phase angles. In the illustrative embodiment, this is accomplished using a cosine look-up table (14). Each digital cosine wave is then stored in a serial memory buffer (16A to 16L) in preparation for conversion to digital. Each of digital signals is passed through a digital to analog converter (18A to 18L) and an RF filter (20A to 20L) at each antenna element.

Abstract: A clamping circuit (10) including an input/output node (12), adapted to be coupled to the protected circuit or component; a first diode (D1) having an anode connected to the input/output node (12); a second diode (D2) having a cathode connected to the input/output node (12); a third diode (D3) connected between the cathode of the first diode (D1) at a first node (14) and the anode of the second diode (D2) at a second node (16); a first arrangement for supplying a first potential at the cathode of the first diode at first node (14); a second arrangement for supplying a second potential at the anode of the second diode at second node (16); a first capacitor (C1) connected between the cathode of the first diode at first node (14) and ground; and a second capacitor connected between the anode of the second diode at second node (16) and ground.

Abstract: A communication path includes N channels or information pathways, each of which is bidirectional, i.e. each channel may be set to either send or receive. The number of send channels (S) and receive channels (R) is programmably set, such that S+R=N. The total bandwidth is N*B, where B is the bandwidth of each channel, and the send and receive bandwidths can be adjusted to any values such that N*B≧(S*B+R*B), on an as-needed basis depending on the processing algorithms being executed.

Abstract: A direct digital synthesizer (DDS) generates a sinusoidal waveform having a variable frequency within a time duration. The DDS has a memory for storing pre-computed digital values defining the sinusoidal waveform, a barrel shifter for reading the contents of the memory and for presenting the digital values from the memory to a multiplexer at a first rate determined by a first clock. The multiplexer is connected to a Digital to Analog converter. The Digital to Analog converter converts the digital values presented by the multiplexer to the analog output at a second rate determined by a second clock. The barrel shifter shifts the digital values using a plurality of pipelines and n-bit wrap-around registers. Pre-computed digital values defining the sinusoidal waveform are stored within a memory, then routed using a bus exchange switch to the barrel shifter.

Abstract: Conversion errors of the prior art are reduced by a piece wise linear analog to digital converter. The analog to digital (A/D) converter operates between a minimum voltage and a maximum voltage and uses one or more comparators to generate one or more digital bits, each of the digital bits representative of a conversion voltage. A first voltage interval is allocated for linear analog to digital conversion. This first voltage interval extends from the minimum voltage to an intermediate voltage, where the intermediate voltage is less than the maximum voltage. A second voltage interval extends from the intermediate voltage to the maximum voltage. An error correcting band is encoded in the analog signal between the first voltage interval and the second voltage interval. Each of the comparators used in the A/D has a sensing level. The error correcting band is centered with respect to one of the sensing levels, the sensing level located at the intermediate voltage.

Abstract: An Advanced Digital Antenna Module (ADAM) for receiving and exciting electromagnetic signals. The ADAM ASIC integrates a complete receiver/exciter function on a monolithic SiGe device, enabling direct digital-to-RF (Radio Frequency) and RF-to-digital transformations. The invention includes an improved analog-to-digital converter (ADC) (10) with a novel active offset method for comparators. The novel ADC architecture (10) includes a first circuit (12, 14) for receiving an input signal; a second circuit (18) for setting a predetermined number of thresholds using a predetermined number of preamplifiers (60) with weighted unit current sources (66) in each of the preamplifier outputs; and a third circuit (20) for comparing the input to the thresholds. In the preferred embodiment, the ADC (10) includes trimmable current sources (66). The ADC (10) of the present invention also includes an improved comparator circuit (62).

Abstract: An optical system comprises a three-mirror anastigmat including a primary mirror, a secondary mirror, and a tertiary mirror positioned to reflect a beam path. An intermediate image is formed on the beam path at an intermediate-image location between the secondary mirror and the tertiary mirror. A negative-optical-power field mirror is positioned in the beam path at a field-mirror location subsequent to the intermediate-image location along the beam path. The field mirror reflects the intermediate image to the tertiary mirror.

Abstract: A small,compact optical scanning system with small aperture size requirements, wide field-of-regard and minimal color dispersion characteristics. The inventive scanning system and method provides for optical beam steering over a broad spectral band and over a wide field-of-regard. The inventive system includes a novel device for receiving an input wavefront of electromagnetic energy along a first axis and refracting the wavefront as an output wavefront along a second axis. The device is a unique form of a liquid crystal array which can be electrically manipulated to change the effective refractive index of each pixel. The index of refraction of the device varies in response to an applied voltage. The voltage is supplied by a microprocessor and/or a servo-control system. By changing the index, the incident phase front can be steered at an angle with respect to the first axis and otherwise manipulated according to the index variant pattern induced in the array.

Abstract: A band pass filter circuit for microwave frequencies, including a plurality of parallel-coupled resonators formed in a planar transmission line medium, including coupling between alternate resonators in the form of transmission line gaps.

Abstract: An interferometer array system for processing pulse signals from a target emitter includes an n element interferometer array of radiator elements for producing radiator signals in response to the pulse signals from the target emitter. M processing channels process radiator signal elements, where m<n. A switch matrix is connected between the array and the processing channels, switching different combinations of the radiator elements to the channels within a single pulse to achieve processing of all radiator signals within a single pulse of said pulse signals from the target emitter.

Abstract: Targets imaged by radar systems typically have shadows associated with them. Target detection and identification is enhanced by analyzing the shadow characteristics of a suspected target. Features of the shadow cast by the suspected target enhance the identification process. Authenticating the suspected target shadow as being indeed cast by the target comprises a) Generating a radar image using radar returns, the radar image containing both the target and its suspected target shadow; b) Forming a pentagonal perimeter adjacent to the target (within the radar image), the pentagonal perimeter chosen to contain the suspected target shadow, the pentagonal perimeter separating the target from its suspected target shadow; c) Testing the suspected target shadow within said pentagonal perimeter to authenticate that the suspected target shadow is cast by the target. One aspect of the testing performed on the suspect target shadow uses a 2 by 2 dilation and majority filter.

Abstract: A system and method for detecting a target. The inventive method includes the steps of receiving a complex return signal of an electromagnetic pulse having a real and an imaginary component; extracting from the imaginary component information representative of the phase component of the return signal; and utilizing the phase component to detect the target. Specifically, the phase components are those found from the complex range-Doppler map. More specific embodiments further include the steps of determining a power spectral density of the phase component of the return signal; performing a cross-correlation of power spectral density of the phase component of the return signal between different antenna-subarray (quadrant channels); and averaging the cross-correlated power spectral density of the low frequency components. In an alternative embodiment, the cross-correlation is performed on the phase component of the range-Doppler map directly.

Abstract: A radar system has improved range resolution from linear frequency modulated (LFM) first sub-pulse and second sub-pulse, both having linear frequency modulation about different center frequencies. The first transmitted sub-pulse and the second transmitted sub-pulse have chirp slope &ggr;. Sample shifting and phase adjusting is performed for the first radar returns with respect to second radar returns to form a line of frequency modulated chirp slope &ggr; with respect to time, the line connecting the center frequencies of the center frequencies. The first sub-pulse and second-sub pulse can have equal time duration, where the first and second center frequency are equidistant from a reference frequency. The returns are reflected by a target located at a location near a reference point s.

Abstract: A system and method for controlling clutter Doppler spread in a bistatic radar system is developed resulting in enhanced detection of low-Doppler targets or improved SAR mode performance. In an illustrative embodiment, a bistatic radar system (10) includes a transmitter (12) for transmitting electromagnetic energy (106) towards a target (16), a receiver (14) adapted to receive the electromagnetic energy (116) reflected from the target (16), and a processor (122) for optimizing a parameter or parameters of the system such that the directional derivative of the bistatic Doppler field along the isorange contour is near a desired value. The parameters to be optimized may include the transmitter velocity vector, the receiver velocity vector, or the receiver azimuth flight direction. The desired value is the minimal absolute value of the directional derivative in order to minimize the clutter Doppler spread, or the maximum absolute value of the directional derivative in order to maximize the clutter Doppler spread.

Abstract: The height of a radar target above a horizontal plane at a location within the horizontal plane is measured using a synthetic aperture radar (SAR). The synthetic aperture radar is mounted on a moving platform. The moving platform moves along a continuous climbing path with respect to the horizontal plane acquiring a plurality of SAR arrays of radar return information. Monopulse , Interferometric SAR (IF-SAR), and shadow length height measurements are fused to refine the target height measurement. Monopulse and IFSAR are combined to resolve target height ambiguities. The SAR arrays are separated vertically, at separate heights with respect to the target, and acquired sequentially in time, as a single pass.

Abstract: An RF phase shifter circuit includes first and second RF ports, and a switch circuit comprising a plurality of micro-electro-mechanical (“MEM”) switches responsive to control signals. The switch circuit is arranged to select one of a plurality of discrete phase shift values introduced by the phase shifter circuit to RF signals passed between the first and second RF ports. The circuits can be connected to provide a single-pole-multiple-throw (SPMT) or multiple-pole-multiple-throw (MPMT) switch function. The phase shifter circuits can be used in an electronically scanned array including a linear array of radiating elements, with an array of phase shifters coupled to the radiating elements. An RF manifold including a plurality of phase shifter ports is respectively coupled to a corresponding phase shifter RF port and an RF port. A beam steering controller provides phase shift control signals to the phase shifters to control the phase shift setting of the array of the phase shifters.

Abstract: A method and system for maintaining uniformity in a FLIR display. During a one-time initialization procedure, a plurality of dynamic ranges are defined by covering a specific range of bucket fill levels when in a certain gain. To cover all dynamic ranges possible, a plurality of pairs of responsivity equalization (RE) calibrations (each pair producing a RE set of pixel gain corrections) are also accomplished in the same one time initialization period. A plurality of corresponding level equalization (LE) calibrations (each using the appropriate calibrated RE set and producing a LE set of pixel level corrections) for each anticipated dynamic range are made at every power-up initialization. Each of the calibrations is done with respect to a thermal reference source to produce a uniform scene at the desired bucket fill level.

Abstract: A holographic telescope (40). The novel invention is comprised of an eyepiece (44) and a first holographic optical element (42) positioned to receive incident electromagnetic energy and focus the energy on the eyepiece (44). In the preferred embodiment, the eyepiece (44) is a second holographic optical element, and both holographic optical elements are volume holograms. Each holographic optical element can be transmissive or reflective depending on packaging needs. The holographic telescope (40) can be multi-spectral by including multiple independent holograms in each holographic optical element, each hologram responding only to a particular wavelength.

Abstract: An optical alignment system for controlling the position of a laser beam through an optical train. The optical alignment system includes a semiconductor laser source for the generation of an alignment beam, and a beam steering device to manipulate the position of the alignment beam on a multi-element detector. The semiconductor laser is driven to mode hop at a frequency greater than the upper frequency limit of the multi-element detector. Driving the semiconductor laser to mode hop at a frequency greater than the upper frequency limit of the multi-element detector results in a more uniform alignment beam as seen by the detector, as the alignment beam becomes an average of all the operational modes of the semiconductor laser. A more uniform alignment beam results in improved accuracy of the alignment system.