Abstract: A system and method for calibrating a vehicular traffic surveillance Doppler radar are disclosed. In one embodiment, a modulation circuit portion generates double-modulated FM signals. An antenna circuit portion transmits the double-modulated FM signals to a target and receives reflected double-modulated FM signals therefrom. A calibration circuit portion responds to the reflected double-modulated FM signals by sending a calibration signal to the modulation circuit. The calibration signal is indicative of a relationship between a first range measurement derived from phase angle measurements associated with the reflected double-modulated FM signals and a second range measurement derived from speed and time measurements associated with the reflected double-modulated FM signals.

Abstract: An exemplary radar system includes a waveform generator that generates a control waveform. An in-phase and quadrature modulator receives the control waveform from the waveform generator and in turn generates a waveform output that is amplified by a power amplifier before being transmitted from an antenna.

Abstract: A time domain communications system wherein a broadband of time-spaced signals, essentially monocycle-like signals, are derived from applying stepped-in-amplitude signals to a broadband antenna, in this case, a reverse bicone antenna. When received, the thus transmitted signals are multiplied by a D.C. replica of each transmitted signal, and thereafter, they are, successively, short time and long time integrated to achieve detection.

Abstract: A millimeter wave pulsed radar system includes a radar synthesizer having a voltage controlled oscillator/phase locked loop (VCO/PLL) circuit, direct digital synthesizer (DDS) circuit and quadrature modulator circuit that are operative to generate an intermediate frequency local oscillator signal (IF/LO signal). A radar transceiver is operative with the radar synthesizer for receiving the IF/LO signal. A transmitter section has a frequency multiplier that multiplies the IF/LO signal up to a millimeter wave (MMW) radar signal and a receiver section and includes a direct conversion mixer that receives a MMW radar signal and the IF/LO signal to produce I/Q baseband signals that are later digitized and processed.

Abstract: A method, an arrangement and a radar level gauging system for preventing interference, which radar level gauging system comprises at least two radar level gauges arranged to measure a filling level of a product kept in a container. Microwave pulses are transmitted towards the surface of said product and microwave pulses reflected by said surface are received by said at least two radar level gauges. Information is provided with said microwave pulses and said information is used for controlling the measurement pulses of said at least two radar level gauges.

Abstract: A transmission-reception apparatus includes a transmission section, a reception section, a transmission control section, a signal detection section, and an operation determination section. The transmission section transmits a signal to a surrounding space. The reception section receives the signal from the surrounding space. The transmission control section controls the transmission section to transmit the signal in a pulse shape. The signal detection section detects level of the signal received by the reception section. The operation determination section determines as to whether or not a timing at which the level of the received signal exceeds a first determination level is within a first time period on the basis of detection result and a timing at which the transmission control section controls the transmission section to transmit the signal in the pulse shape, to determine as to whether or not the transmission section and the reception section operate normally.

Abstract: A short-range radar system includes short-range radar sensor means and means (41) for HF-impulse generator for the sensor means. The means for HF-impulse generation are embodied for emitting impulses with adjustable pulse duration (51, 53).

Abstract: A security inspection system uses microwave radiation to image targets on a human subject or other item. The system includes an array of antenna elements that are programmable with a respective phase delay to direct a beam of microwave illumination toward a target on the human subject or item. The antenna elements are further capable of receiving reflected microwave illumination reflected from the target. A processor is operable to measure an intensity of the reflected microwave illumination to determine a value of a pixel within an image of the human subject or item. Multiple beams can be directed towards the human subject or item to obtain corresponding pixel values for use by the processor in constructing the image.

Abstract: A method of controlling a switching element in a switching regulator power supply of a radar. The method of controlling the switching element comprises only switching the switching element during predetermined time intervals, the predetermined time intervals advantageously being sample intervals of a pulse repetition interval of the radar. Thereby by having knowledge of the time intervals the switching element is switching, being able to remove or diminish any influence the switching can have on the quality of received signals and subsequent processing of these signals.

Abstract: A method and corresponding devices for monitoring the performance of a radar system (2, 4) which is equipped with a shield 2 (radome) to protect it against weather influences are described. For this purpose, a part of the radiated radar signal is modified and fed as a monitor signal to the reception system after interacting with a coating (5) which is possibly present on the radom (2). Influences of a damping or reflecting coating (5) on the radom (2) change the monitor signal. By analyzing these changes it is possible to draw conclusions about the coating of the damping or reflection of the radar signals which is caused by the coating (5).

Abstract: A digital polarimeteric system employs a signal time stretching technique and digital signal processing of the time-stretched signal to accurately measure the polarization of a received RF signal with commercially available digital hardware. A superheterodyne receiver down converts received RF signal components to IF, and analog-to-digital converters sample the signal components at much lower sampling rates than would normally be required to accurately measure the signal polarization. Each signal sample is “time stretched” by storing each sample in M locations in a memory, such that N samples occupy M×N memory locations. A digital signal processor applies incremental phase shifts to the digital samples until a phase-shifted combination of the digital samples yields a minimum null output. The phase shifts producing the minimum null identify the polarization of the received signal.

Abstract: To provide a radar system for controlling a gate power supply and drain power supply of a MMIC (microwave monolithic IC), protecting the MMIC at the time of start and shut-off, and simultaneously avoiding an occurrence of a failure in the MMIC due to a residual charge and an abnormal supply potential at the time of shut-off. A power supply control means controls the gate and drain power supplies at the rise time so that an output voltage of the gate power supply rises earlier than that of the drain power supply. Another power supply control means controls the gate and drain power supplies at the fall time so that an output voltage of the gate power supply falls later than that of the drain power supply. Another power supply control means turns off the drain power supply of the FET among power supplies when it is detected by a voltage monitoring means that even either of output voltages of the power supplies is not within said specified range.

Abstract: To provide a radar system mounted on a vehicle that reliably detects the reception of the interference wave with high-performance and inexpensively. There is provided a radar system mounted on a vehicle for detecting a target object, including a transmitter for transmitting an electromagnetic wave, a receiver for receiving the electromagnetic wave reflected by the target object, a signal processor for measuring a distance between a vehicle of his/her own and the target object and a relative velocity on the basis of the transmitting electromagnetic wave and the receiving electromagnetic wave, and an interference detector for suspending a transmit operation of the transmitter under a control of the signal processor to detect an interference signal from another external device.

Abstract: In a pulse-radar method, in particular for motor vehicles, different time slots of a time frame are predefined. During one time slot, a radar sensor emits at least one radar pulse and receives the echo signal(s). During the remaining time slots the radar sensor monitors whether interference signals occur. On the basis of the interference signals occurring per time slot, a decision is made whether the radar sensor should continue its transmitting and receiving operation in the predefined time slot or should switch to one of the remaining time slots of the time frame. The method is suited for the concurrent operation of a plurality of radar sensors, without this causing interference.

Abstract: To provide a filter cover which has little electromagnetic effect on a dielectric resonator and is able to lengthen the life of a press mold without impairing isolation between transmission and reception. A VCO comprising a dielectric resonator, a high-frequency oscillator, a base, a cover, in which the distance between the surface of the cover facing the dielectric resonator and the surface of the base facing the dielectric resonator is half or below of the effective wave length of the oscillator frequency, and the cover has periodic projections facing the dielectric resonator which are a quarter of effective wave length of the oscillator frequency, wherein the nearest distance between the surface of the dielectric resonator facing the cover and the surface of the cover facing the dielectric resonator is a quarter or over of the effective wave length of the oscillator frequency.

Abstract: A system-of-systems avionics architecture that is compatible with futuristic multi-function multi-platform sensor applications. The method and device of the invention is based on localized “adaptive” waveform and spectrum allocation for ultra-wideband radio frequency and microwave signals. The invention includes a plurality of system platforms with each platform comprising a common radio frequency front end for receiving ultra-wideband signals, a common radio frequency back end for transmitting ultra-wideband signals and a plurality of sensors for exchanging data between platforms.

Abstract: A system and method provide for the collection of interferometric synthetic aperture radar (IFSAR) data. In the system, a first space vehicle configured for emitting electro-magnetic energy and collecting the reflection from a region of interest (ROI), may be directed along a first orbital track. The collected image data may be stored and later provided to a ground station for image and interferometric processing. A second space vehicle may also be configured for emission and collection of electro-magnetic energy reflected from the plurality of ROI's. The second space vehicle is positioned in an aligned orbit with respect to the first space vehicle where the separation between the vehicles is known. In order to minimize decorrelation of the ROI during image processing, the lead and trail satellite are configured to substantially simultaneously emit electromagnetic pulses image data collection.

Abstract: In an underground object locating system in which a modulated RF signal is applied to the underground object and an emitted signal is detected by a receiver, ambiguity in the direction of current flow in the underground object is resolved by modulating the RF signal with a modulation signal such that the modulated signal, f(t) has an average value of zero and is not equal to ?f(t+K) where K is any practical value. In specific embodiments, the modulation can be amplitude modulation where the modulating signal is lower in frequency than the RF signal and is related thereto by a rational number, such as one-half (½).

Abstract: Systems and methods are described for HF radar frequency sharing with GPS time modulation multiplexing. A method is provided that includes generating clock signals from the time information contained in a GPS signal. Radio frequency signals are transmitted and received in a sequence whose start times are dictated by the clock signals. The clock signals also control the modulation of the radio frequency signals. The radio frequency signals are modulated by using a sweep modulation. An apparatus to implement the method includes a GPS receiver, a state machine, a clock generator, a microprocessor, a memory chip, a signal synthesizer, and a digital data output device. The GPS receiver extracts time information from GPS signals. The state machine controls radar functions versus time. The microprocessor performs modulation multiplexing on radar signals.

Abstract: A power system for a phased-array radar system powers an antenna array with a single multiphase transformer. A plurality of AC/DC converters are connected in parallel between the single multiphase transformer and a common bus. The common bus is balanced with respect to chassis ground reducing noise and improving operating safety of the antenna. The AC/DC converters each has a multi-sloped characteristic which enables the converters to share power by modifying output impedance as a function of load without external control signals. The system also has several layers of fault detection.

Abstract: A radar system is operated by controlling and thereby limiting the mean power of the transmitted signal in response to the mean power of the received signal thereby limiting the power to a predetermined power range. Preferably the power control or regulation is performed by varying the pulse repetition frequency and/or the pulse duration of the transmitter pulses. This method is well suited for operating a motor vehicle range warning system.

Abstract: A guided wave radar measurement instrument comprises a probe defining a guided wave radar transmission line. A pulse circuit is connected to the probe for generating a very fast stream of pulses on the transmission line and receiving reflected pulses returned on the transmission line. The reflected pulses represent a characteristic of a material being measured. An equivalent time sampling circuit is connected to the pulse circuit operable to sample reflected pulses to build a time multiplied picture of the reflected pulses and comprises a ramp generator circuit generating a saw tooth ramp signal used to selectively delay sampling reflected pulses to build the time multiplied picture. In one aspect of the instrument, the saw tooth ramp signal has a controlled ramp start for each cycle and retrace at an end of the cycle.

Abstract: An HF radar system comprises a transmitting system, a receiving system, a signal processing system and a frequency management/ionospheric sounding system. The transmitting system comprises a transmitting antenna array configured to transmit a beam in a near vertical direction and a transmitting device arranged to drive the transmitting antenna array at frequencies suitable for downward refraction by the ionosphere. The receiving system comprises a receiving antenna array configured to receive returning signals from a target area returning to the receiving antenna array via refraction at the ionosphere. The signal processing system comprises a digital data processing system. The frequency management/sounding system comprises cooperating transmitting and receiving systems sending HF signals to the ionosphere and analysing the returning signals. Alternatively, the system may have a duplexed antenna array.

Abstract: In a radar apparatus for automobiles for transmitting a radio wave, receiving a radio wave reflected from an object and measuring a rate of the object, a digital signal processor has at least two operation modes, a normal operation mode and a low energy consumption mode, and has a function of switching between the operation modes of the digital signal processor in accordance with a signal supplied from a counter (judgement unit) for judging whether a received signal satisfies predetermined conditions. The radar apparatus can reduce consumption power when necessary.

Abstract: A pulse radar device includes a rectangular signal generating section for generating a rectangular signal that is a reference signal; a transmit timing voltage setting section for setting a voltage value for determining a transmit timing; a transmit pulse generating section for generating a transmit pulse based on the rectangular signal and the voltage value; a receive section for receiving a reflection wave obtained by reflecting the electric wave transmitted by the transmit section by a plurality of objects; a receive saw-tooth wave generating section for generating a saw-tooth wave in synchronism with the transmit pulse; a receive signal sample hold section for sample-holding the receive signal based on the outputs from the saw-tooth wave and the rectangular signal; and a detecting and distance measuring section for detecting the objects and measuring a distance to the objects based on the sample/hold output.

Abstract: Disclosed is a transmit-receive FM-CW radar apparatus which switches between transmission and reception by time division control, wherein amplifiers capable of controlling gain are provided in a transmitter signal path and a receiver signal path, respectively, and wherein the gain in the leading edge portion of a receive timing interval or the gain in the trailing edge portion of a transmit timing interval is suppressed by controlling the gain of the amplifier provided in the receiver signal path or the gain of the amplifier provided in the transmitter signal path, respectively.

Abstract: A transmit-receive FM-CW radar apparatus according to one mode of the invention comprises: a mixer for downconverting an IF signal; a switch provided on the input side of the mixer; and a switch controller for controlling the switch on and off in different modes and selecting the IF signal in the different modes for supply to said mixer. A transmit-receive FM-CW radar apparatus according to another mode of the invention comprises: a mixer for downconverting an IF signal; a switch for turning on and off a local signal to be supplied to the mixer; and a switch controller for controlling the switch on and off in different modes and selecting the local signal in the different modes for supply to the mixer.

Abstract: A current source modulator (202; 302, 502) provides power to radar transmitters. The modulator comprises a power supply (210, 310, 510) providing, when enabled, a known current to a storage capacitor (145). A comparator circuit (220) provides a signal (V220) when voltage (VC) across the storage capacitor (145) falls a reference voltage, and an enable circuit (225) responds to the comparator signal (V220) and an ON command signal to enable the power supply (210, 310, 510). The modulator (202, 302, 502) further includes a network (220N) associated with the comparator circuit (220) to retain the value of the signal (provide hysteresis) when the voltage across the storage capacitor is above the reference voltage. The modulator (202, 302, 502) may include a second network (320N) associated with a second comparator circuit, operable to retain a second signal when capacitor (145) voltage VC is above a reference voltage. In this aspect, there is a rapid charge and a trickle charge that reduces any charging overshoot.

Abstract: An RFID system using encoded digital information utilizing pulsed linear frequency modulation (LFM). The LFM waveform is sent from an24 aircraft or satellite and is received by a transponder. The LFM waveform is demodulated using both, an AM and an FM receiver. The demodulated data is compared to preprogrammed criteria tables, and after validation is decoded and utilized. Algorithms in the transponder are used to determine the frequency deviation and for calculating the direction of the slope of the LFM input signal. The valid RF signal is stored in a delay element, encoded with the transponder data using phase modulation (PM), and frequency modulation (FM). The tag transmission is synchronized to the input LFM waveform. The transmit/receive chopping signal prevents unwanted oscillations and is capable of randomization.

Abstract: An RFID system using encoded digital information utilizing pulsed linear frequency modulation (LFM). The LFM waveform is sent from an aircraft or satellite and is received by a transponder. The LFM waveform is demodulated using both, an AM and an FM receiver. The demodulated data is compared to preprogrammed criteria tables, and after validation is decoded and utilized. Algorithms in the transponder are used to determine the frequency deviation and for calculating the direction of the slope of the LFM input signal. The valid RF signal is stored in a delay element, encoded with the transponder data using phase modulation (PM), and frequency modulation (FM). The tag transmission is synchronized to the input LFM waveform. The transmit/receive chopping signal prevents unwanted oscillations and is capable of randomization.

Abstract: To provide a radar system for controlling a gate power supply and drain power supply of a MMIC (micro wave monolithic IC), protecting the MMIC at the time of start and shut-off, and simultaneously avoiding an occurrence of a failure in the MMIC due to a residual charge and an abnormal supply potential at the time of shut-off.

Abstract: This invention relates to a frequency modulation of continuous wave (“FMCW”) radar altimeter capable of controlled linear sweep modes. The FMCW radar altimeter is characterized by the following functions: (1) adopts sweep up frequency and sweep down frequency to solve problems of distance and doppler signal mixture; (2) injects a random generated variable time delay in between sweep intervals to overcome interferences among different altimeters; and (3) switches different sweep frequency bands in accordance with different altitudes.

Abstract: A method for radar-based gauging of the level of a substance in a tank (13) having at least one interfering structure (16a-c), comprises the steps of: (i) transmitting a microwave signal in a plurality of radiation lobes (15a-b; 15a-d), each of which being individually directed towards the substance and at least one of which being directed towards the interfering structure; (ii) for each of the radiation lobes detecting temporally resolved the microwave signal as reflected against the substance, and for at least one of the lobes detecting the microwave signal as reflected against the interfering structure; (iii) based on signal strengths of the detected microwave signals, distinguishing the detected microwave signals, which have been reflected against the substance; and (iv) based on a propagation time of at least one of the microwave signals distinguished as those, which have been reflected against the substance, calculating the level of the substance.

Abstract: In an automotive radio wave radar, a center frequency of a transmitted wave is shifted at a certain cycle, and position information of an obstacle detected at three or more center frequencies is subjected to decision by majority to determine whether detection results of the obstacle are erroneous with the occurrence of jamming. If any of the detection results is determined to be abnormal, the abnormal result is discarded. An automotive radio wave radar is realized which can correctly perform the obstacle detection even in the event of jamming without causing erroneous obstacle detection or omission of the detection.

Abstract: A radar transmitter includes a digital ramp generator circuit for generating a VCO control signal. The ramp generator includes a digital signal processor and a digital-to-analog converter. In one embodiment, the VCO output signal is up-converted to provide the transmit signal and in another embodiment, the VCO operates over the transmit frequency. Also described is a VCO comprising a DR and a phase shifter. A temperature compensation feature includes detecting the transmit frequency and comparing the DSP output generating the detected frequency to a DSP output stored in association with the detected frequency. Also described is a technique for compensating for non-linear VCO operation in which the DSP output words are adjusted to provide a waveform complementary in shape to the non-linear VCO characteristic. Susceptibility of the radar to interference is reduced by randomly varying at least one parameter of the ramp signal, such as offset interval or voltage range, in at least one ramp signal cycle.

Abstract: A radar system having a tactical mode and a calibration mode includes a transmitter section for providing high-power amplification of an RF pulsed waveform from an exciter during the tactical mode and the calibration mode. A circulator system has an input port connected to an output of the transmitter section and including first, second and third switchable junctions, and a high-power attenuator. The circulator system provides a transmit tactical mode signal path and a transmit calibration mode signal path of virtually identical electrical path lengths for a transmitter output signal, the tactical path passing through the first, second and third junctions in a first direction to an antenna I/O port, the calibration path passing through the first, second and third junctions in a second direction and through the high-power attenuator to an output port.

Abstract: The present invention relates to a circuit and method for generation of trigger signals for a radar level gauging systems. A pulse-width modulator, has an input connected to a pulse-repetition-frequency generating oscillator. A monostable multivibrator, has an input connected to an output of the pulse-width modulator. First and second integrators are connected to an output of the pulse-width modulator and the monostable multivibrator respectively. A voltage summation element, is connected to an output of the first and second integrators respectively and at least one control signal input. A servo regulator provides a control loop between an output of the voltage summation element and a control port of the pulse-width modulator. A reference clock output is provided at the output of the monostable multivibrator and a second clock output is provided at the output of the pulse-width modulator.

Abstract: A doppler radar device having comparing means 142 for comparing the level of pulse signal to be transmitted, sampled through a burst gate, with a predetermined threshold value and search means 143 for changing a set position of the gate, wherein a timing of oscillating the pulse signal is monitored and tracked to fix “range 0” by shifting a timing for triggering transmission of the pulse signal in consideration of a deviation of the timing of oscillating the pulse signal and a jitter value.

Abstract: A coherent radar detection system (2) comprises a radar signal transmitter (4) and a correlation receiver (6). The transmitter (4) comprises a waveform generator which generates a signal at an intermediate frequency. The signal is divided into two divided signals by a coupler, and then the divided signals are mixed together in a mixer to generate an output signal which has a wider bandwidth than the intermediate frequency. The bandwidth can be increased further by repeating the coupler/mixer stage. The system generates very wide bandwidth signals coherently, allowing coherent processing in high resolution range gates.

Abstract: A calibration module and methods for a time-of-flight ranging system. The calibration module may be built into the circuitry of the time-of-flight ranging system and allows various operating parameters to be measured and evaluated. The calibration modes include amplitude calibration, frequency calibration, and time delay calibration. The calibration mode also includes an electronic noise measurement mode. The calibration modes may be initiated on power-up or reset, or in response to user input or time-based trigger.

Abstract: A method for exciting an antenna with a waveform having a burst width and pulse width scaled proportionately with a selected range scale and a temporal filter to address any ambiguities in range resulting from the transmission of a signal in accordance with the novel waveform. The inventive filtering method includes the step of scanning a beam including a plurality of pulses of electromagnetic energy. The step of scanning the beam includes the step of outputting a beam excited by a waveform having a burst width and pulse width scaled proportionately with a selected range scale. Reflections of these pulses are received as return signals. The returns are processed to extract range in range rate measurements. The range and range rate measurements are compressed to form a plurality of range bins. The pulses are selectively weighted to reduce sidelobes resulting from a subsequent Fast Fourier transform (FFT) operation.

Abstract: A road antenna apparatus includes a road antenna 104 which is mounted on a post 103 and at an elevated position on a road R and establishes radio communication with an on-vehicle radio device 102 mounted in a vehicle 101 which is traveling over the road. A receiving rate of the established radio communication is detected. A transmission output is set based on detecting a suitable receiving rate for a desired communications area established between the transmitter and the receiver.

Abstract: A mixer used in a millimeter-wave band and a microwave band capable of achieving loss reduction, a radar module, and a communication apparatus incorporating the mixer and having high efficiency. The mixer includes two electrodes formed on one main surface of a dielectric substrate and another electrode formed on another main surface thereof such that non-electrode portions on both main surfaces are opposed to each other via the dielectric substrate. Additionally, a diode is connected bridging a slit between the two electrodes on one main surface to constitute a circuit board. The circuit board and a dielectric strip are arranged between upper and lower conductive plates.

Abstract: A radar based sensor detection system comprises a microwave source operative to provide a continuous wave signal at an output. A pulse-former is coupled to the output of the source and is operative to provide at an output a variable length pulse that increases the transmitted energy of the radar system according to the range of object detection. A modulator is coupled to the output of the pulse-former for providing a modulated pulse signal. A transmit receive switch coupled to the output of the modulator is selectively operative between a first transmit position and a second receive position. A transmit channel coupled to the transmit receive switch transmits the pulse signal when the switch is operated in the transmit position. A receiving channel coupled to the transmit receive switch receives the modulator signal when the switch is operated in the receive position.

Abstract: A radar device is described having means (12) for generating a first code, means (18) for modulating a transmission signal in a transmitting branch using the first code, means (32) for delaying the first code, means (20) for modulating a signal in a receiving branch using the delayed first code, and means for mixing a reference signal with a reception signal, multiple receiving channels (111, 112, . . . 11k) being provided, the receiving channels (111, 112, . . . 11k) having means (1201, 1202, . . . 120k) for generating additional codes (C1, C2, . . . Ck), the receiving channels (111, 112, . . . 11k) having means (131, 132, . . . 13k) for demodulating using the respective additional codes (C1, C2, . . . Ck), and means (15) being provided for modulating the transmission signal using at least one of the additional codes (C1, C2, . . . Ck). A method which may be implemented advantageously using the radar device described is also described.

Abstract: A doppler radar device having comparing means 142 for comparing the level of pulse signal to be transmitted, sampled through a burst gate, with a predetermined threshold value and search means 143 for changing a set position of the gate, wherein a timing of oscillating the pulse signal is monitored and tracked to fix “range 0” by shifting a timing for triggering transmission of the pulse signal in consideration of a deviation of the timing of oscillating the pulse signal and a jitter value.

Abstract: A method for selecting a pulse repetition frequency to detect, track or search for a target that includes identifying a first feature representative interval of each pulse repetition frequency within a set of pulse repetition frequencies, choosing a selected pulse repetition frequency from the set of pulse repetition frequencies based on cost assigned to each pulse repetition frequency, wherein the cost assigned to a first pulse repetition frequency is at least based on a first cost function of a first position of a first target feature in relation to a first feature assessment interval of the first pulse repetition frequency, and emitting pulsed energy from the emitter using the selected pulse repetition frequency.

Abstract: A bistatic radar system and method. In the illustrative embodiment, a receiver is positioned in a horizontal plane. A transmitter is then positioned in Middle Earth Orbit at a position that is nearly vertical to the plane of the receiver. This configuration provides significant flexibility for the radar system. As such, the radar system may engage in flight patterns, in which the transmitter and receiver have velocity vectors in opposite directions (GMTI mode), the same direction (SAR mode) and variations in between (mixed mode). Lastly, a broad beam is generated from the transmitter and illuminates an area enabling several receivers to simultaneously observe the illuminated area.

Abstract: An HF radar system comprises a transmitting system, a receiving system, a signal processing system and a frequency management/ionospheric sounding system. The transmitting system comprises a transmitting antenna array configured to transmit a beam in a near vertical direction and a transmitting device arranged to drive the transmitting antenna array at frequencies suitable for downward refraction by the ionosphere. The receiving system comprises a receiving antenna array configured to receive returning signals from a target area returning to the receiving antenna array via refraction at the ionosphere. The signal processing system comprises a digital data processing system. The frequency management/sounding system comprises cooperating transmitting and receiving systems sending H-F signals to the ionosphere and analysing the returning signals. Alternatively, the system may have a duplexed antenna array.

Abstract: A digital polarimeter employs a signal time stretching technique to apply polarization phase shift characteristics to digitally generated polarization agile signal components. An RF signal to be transmitted is down-converted to an intermediate frequency and digitally sampled at a rate feasible with currently-available analog-to-digital converters. Horizontal and vertical signal components of the sampled IF signal are generated by processing the digital signal samples. Each digital signal sample is “time stretched” by storing each sample in M memory locations, such that N samples occupy M×N memory locations. Because each sample is stored in M memory locations, each incremental phase shift from one memory location to the next corresponds to 1/Mth of the actual sampling interval. The stretching process effectively increases the digital sampling frequency, yielding sufficient phase resolution.