Abstract: A millimeter wave imaging system is disclosed which has wide applicability throughout transportation and related industries. For example, the system may be used to provide an aircraft pilot with an image of a landing field which is essentially unaffected by fog, rain, snow, blowing sand, etc. The system comprises an array of imaging elements as its fundamental component. Each of the imaging elements of the basic array comprises an antenna consisting of a pair of conductive elements and a non-linear circuit element connected thereacross. A image can then be formed responsive to millimeter-wave radiation without complex processing steps or any form of mechanical or electronic scanning.To increase the sensitivity of the imaging array system, a local oscillator signal may be mixed with the energy received from the field of view in each of the imaging elements by the non-linear circuit element. The oscillator used to provide the local oscillator signal can also be used to illuminate the field of view.

Abstract: A MICrowave RADiometric (MICRAD) guidance system is disclosed which utilizes an antenna having four beams, designated right, left, up and down. Information from the four beams is monitored essentially 100% of the time by passing through appropriate ferrite cross-switching means to four separate receivers. Information from two of the receivers passes through a first multiplexer and feedback gain balancer to provide a target azimuth output, and information from the remaining two receivers passes through a second multiplexer and feedback gain balancer to provide a target elevation output. A local oscillator heterodynes each of the four receivers in common, and a switch driver couples each of the multiplexers to the ferrite cross-switching means and gain balancers for appropriate selection.

Abstract: A technique for near-field tomographic imaging using a multiple-receiver correlating interferometer. A target object or scene to be imaged is located in a near-field or Fresnel region of a receiver system. The target object radiates or reflects a signal that is sensed by a plurality of antennas. The received signals are correlated using conventional correlation algorithms. An image pixel for a focal point is then computed by correcting a differential time delay between a signal emitted at the focal point and received at first and second antennas. The system is focused on the target object by correcting a phase term of the correlation algorithms. The phase term is corrected by multiplying the correlation algorithms by a phase factor. A peak correlated value is developed when the focal point is at the target object location. A series of snapshots is generated from data produced by the focussing process, as the focal point is moved through the scene.

Abstract: A switchable local oscillator for use in a shared mixer radiometer is capable of providing at least two separate frequencies. The local oscillator contains at least two cavity resonators, a voltage controlled oscillator controlling a microwave generator, a microprocessor to intermittently control the voltage controlled oscillator and an output voltage detection circuit to provide output voltage levels to the microprocessor. The microprocessor controls the voltage controlled oscillator to tune the microwave generator through a frequency range. Output voltage level of the local oscillator is detected, and a resonant frequency is determined. In response, the microprocessor fixes the voltage of the voltage controlled oscillator at a voltage corresponding to the resonant frequency of one of the cavity resonators. Microprocessor control of the voltage controlled oscillator is then relinquished. The local oscillator generates a resonant frequency while measurements are made by the radiometer.

Abstract: A camera system in which microwave radiation from objects in a field-of-view is collected by an antenna having a beam direction which is a function of the beam frequency. The collected radiation is analyzed to produce an image of the objects in the field-of-view. In a simple embodiment of the invention a one dimensional image is produced. This one dimensional image can be converted to a two dimensional image by rotating the camera system or mounting the camera on a moving platform. In a preferred embodiment of the present invention the microwave radiation collected by the antenna is converted into electronic acoustic signals which sets up a diffraction pattern in a Bragg cell to diffract a laser beam which is focused on a television camera to produce one dimensional image of the field-of-view. The antenna can be scanned to produce a two dimensional image. In another preferred embodiment an array of antennas and a multi-channel Bragg cell is used to produce a two dimensional real time image.

Abstract: The apparatus of the invention detects, characterizes and evaluates electromagnetic radiation, primarily in the radio frequency range, which is emitted by the fusing portion of the explosive train found in certain destructive devices. The apparatus includes a chamber for containing items to be tested, such as airline luggage, in a sealed or confined environment shielded from outside radiation and subjecting any fusing devices, which may be located in such items, to the condition or conditions under which such devices are activated. The invention further includes equipment for receiving, detecting, and evaluating any electrical signals emitted by such fusing devices. The invention is primarily for use in determining the presence of hazards in aircraft cargo but can easily be adapted for other uses.

Abstract: In visualizing an unknown object possessed by a person to be checked, a narrow pulsating radio wave beam is scanned over the whole surface of the person to observe the intensity of a reflected radio wave at each scan point. The frequency of the radio wave beam is set at a frequency easy to be transmitted by the human body to suppress the reflection from the human body and emphasize the unknown object to thereby discriminate between them. An image of the person to be checked is displayed and the portion having a strong reflection is color-displayed on the image to allow the check of the unknown object possessed by the person without contacting the person.

Abstract: A contraband detection system especially suited for detecting concealed non-metallic contraband such as ceramic or plastic weapons or illegal drugs carried by a person is disclosed. Plural sources of quasi-coherent millimeter wave radiation are disposed so as to uniformly illuminate a field of view. In the preferred embodiment, the radiation emitted by the sources is linearly polarized in a single plane such that the polarization of the radiation with respect to the plane in which linearly polarized radiation is preferentially received by the detectors can be controlled. For detection of dielectric objects, such as ceramic weapons or narcotics, these planes of polarization should be orthogonal to one another. The detector is a staring array which does not require scanning to generate an image of the entire field of view; the signal provided by each element of the detector array corresponds to the illumination reflected from objects in a single portion of the field of view.

Abstract: A radiometer system is disclosed, the system incorporating a cylindrical parabolic reflector and a plurality of radiation sensors disposed along the focal line of the reflector in a minimum redundancy array. Digital processing circuitry is connected to the output of the sensors for digitally processing signals using a cross-correlation signal processing and fast Fourier transform circuitry to generate image signals, the system providing reduced weight and increased signal integration time. Several embodiments of the system are disclosed including analog and digital versions having a multiplicity of antenna configurations.

Abstract: The present invention is a microwave radiometer for passive microwave remote sensing of the earth's surface. This microwave radiometer is formed as a cross array including a vertical linear array pointed toward nadir and a perpendicular horizontal linear array. A beamformer is coupled to each array for forming a plurality of adjacent fan beams. A plurality of cross correlators produce overlap beams from the overlap of each pair of vertical and horizontal-array fan beams. This arrangement receives microwave energy from the earth at a constant incidence angle, a feature useful in passive microwave sensing. This microwave radiometer provides acceptable radiometric sensitivity and a spatial resolution while requiring less collecting area and thus much less mass than a dish antenna with the equivalent spatial resolution and needing no moving parts.

Abstract: An improved millimeter imaging system is disclosed which generates high quality images from the field of view. Such system can be employed in a variety of application ranging from providing an aircraft pilot with an image of the landing field in fog, rain, snow, blowing sand, etc. to detection of concealed non-metallic contraband. The system elements, in which different elements detect signals from different portions of the field of view, so that images of the entire field of view are generated in real time, without using electrical or mechanical scanning. The outputs of the array elements are mapped to display pixels. The resolution of such images has previously been limited by the response characteristics of array elements to energy from only a portion of the corresponding field of view. One aspect of the invention is a significant improvement in image resolution.

Abstract: A digital aperture synthesized radiometer for synthesizing the imaging an image scene. A plurality of antenna arrays receive radiation emitted or reflected from an scene, and an analog to digital coverter converts received radiation into digitized signals. A digital beamformer synthesizes the digitized signals to provide an image corresponding to the scene. The digital beamformer comprises individual digital beamformers which generate a set of fanbeam signals for each array. The beamformers provide for cross track imaging of the scene. A digital interferometer correlates corresponding pairs of fanbeam signals from the two sets of fanbeam signals to produce a chirp signal for each pair. A matched filter processes the chirp signals to transform each chirp signal into a corresponding image point of the scene. This provides for along track imaging of the scene.

Abstract: An electrically scanning microwave radiometer for measuring the brightness temperature of an object by performing a conical scan of the object. The microwave radiometer comprises a torus-type reflector and an array of radiators. The radiators are grouped to form a plurality of subarrays. The beams formed by the respective subarrays are correspondingly switched to perform the conical scan on the surface of the object. The signals received by the radiators during the conical scan are arithmetically operated to obtain the brightness temperature value of the object located within the width of the antenna beam.

Abstract: A signal detector for receiving a wide band (W) of frequency-hopped signals which channelizes the incoming signals, via filter banks into a plurality (L) of channels. Magnitude squaring circuits in each channel generate a "power" estimate which is compared to a preset threshold value by threshold-quantizer units that produce a positive voltage (=1) if the threshold is exceeded. After summation of all the channels, the direct sequence (DS) signal component and noise component are processed so that a DC voltage is produced if a frequency-hop signal (FH) is present which is greater in value than when the signal is not present. Thus the DC signal indicates whether the FH signal is present or absent.

Abstract: A millimeter wave sensing device is disclosed comprising a local oscillator source generating a millimeter wave signal which is mixed with millimeter wave radiation reflected from or emitted by objects in a field of view. The mixing is performed in a staring array of mixer/detector elements which need not be mechanically or electronically scanned to generate signals responsive to the entire field of view. In a first embodiment of the invention, the device detects millimeter wave radiation emitted by or reflected from the object to be imaged. In a second embodiment of the invention, the oscillator used to provide the local oscillator signal is also used to illuminate the field of view. In the second embodiment of the invention, the oscillator signal is preferably linearly polarized, and a polarizing grid is used to separate the local oscillator signal and illumination beam and direct them in a simple and efficient manner.

Abstract: A radiometer circuit for determining the character of the modulation of a signal received from a radio frequency transmitter. The circuit will determine if the transmission is one of the following classes: continuous wave (CW) frequency modulated CW (FMCW), noise modulated FMCW and noise; or pulse modulated, burt pulse modulated, random pulse modulated, or any pulse modulated noise. A single radio frequency amplifier is used to detect and discriminate between pulsed and CW transmissions.

Abstract: A system for continuously establishing and indicating the location of a movable object comprises a first transmitter secured to the object for periodically transmitting, at a first predetermined frequency, first radio frequency signals representative of an identification code uniquely associated with the object. A plurality of receiver/repeater stations are positioned at spaced locations within a predetermined geographic area, each receiver/repeater station including a plurality of spaced receivers for receiving and demodulating the first radio frequency signals to provide an object identification code signal and a device associated with each first receiver for determining the strength of the received first radio frequency signal and for generating a strength signal for each receiver.

Abstract: The totally passive object identification system and method involves the use of a radiometer to produce a signal corresponding to the radiation pattern generated by an object of interest in the frequency band to which the radiometer is sensitive, and involves comparing the produced signal with a signal corresponding to a given class of objects. The comparator produces a signal indicative of correspondence or a lack of correspondence between the object of interest and the given class of objects.

Abstract: A microwave radiometer is formed of a set of frequency scanning antennas disposed parallel to each other and connected by a common microwave feeder. Signals of individual ones of the antennas are translated to different intermediate frequencies such that differences between the intermediate frequencies are proportional to baseline spacings between pairs of antennas of nested interferometers. A correlator containing parallel delay lines and a set of multiplier channels coupled to paired taps of the delay lines receives signals at the intermediate frequencies to produce a set of correlation signals. A two-dimensional Fourier transformation is applied to the correlation output signals to provide the power spectral density of microwave radiation incident upon the array of antennas.

Abstract: An electronically scanned radiometer has a dispersive serpentine antenna with one or two ports. A mixer is connected to each port with each mixer being fed by a variable frequency local oscillator. Each oscillator provides the mixer to which it is connected with a drive signal that varies in frequency. The antenna most efficiently receives one or more beams through radiators at an angle that varies with the frequency of the drive signal at the mixer. An output is received at each port and is appropriately displayed. When the serpentine has two ports the radiometer can be operated at two orthogonal polarizations. The frequency being fed to each mixer can be varied in various predetermined patterns. Scanning of the beam can be effected by changing the frequency of observation without physically rotating the antenna. Also two simultaneous beams rotating in opposite directions with independent motions can be achieved.

Abstract: A threat field sensor has a hollow metal enclosure with imperforate side walls except for a single aperture that is small as compared with the wavelength of interfering electromagnetic energy. A coaxial conductor is located in the enclosure cavity and has separate sets of leads interconnected to each conductor end. Electric signals induced in the coaxial conductor and present at the conductor ends by the external electromagnetic fields passing through the enclosure aperture are converted to two corresponding light signals. The light signals are transmitted to remotely located processing apparatus by an optical fiber link where the light signals are converted once again to electric signal counterparts. Summing and differencing these electric signals provides two final signals representative of the electric and magnetic field, respectively.

Abstract: A radiometric imager for providing a series of registered images of a scene, each image corresponding to the radiation pattern for a unique, narrow frequency band. One embodiment includes a single frequency-dispersive linear antenna providing an output signal based on a series of conical fanbeams, with the antenna being controllably rocked about one axis and rotated about a perpendicular axis such that each fanbeam intersects each segment of the scene a plurality of times. In alternative embodiments, the imager includes a second frequency-dispersive linear antenna arranged in parallel with the first antenna to produce a fanbeam interferometer. Rocking movement of the two antennas coupled with either translation of the two antennas, rotation of the two antennas about an axis parallel with the antenna axes, or movement of the two antennas toward and away from each other, provides sufficient data to permit creation of the registered images.

Abstract: A method and apparatus for precisely determining the relative velocity of an interferometer and a scene being scanned. The apparatus uses a matched filter technique in which reference signals based on high and low relative velocity estimates are correlated with an incoming interferometer signal and controllably adjusted until the correlation is maximized. The controllably adjusted reference signals are then used to produce an extremely accurate and precise measurement of relative velocity.

Abstract: A vehicle sensing apparatus and method for detecting the size and speed of a vehicle travelling on a roadway. The apparatus comprises a directional microwave non-emitting antenna for collecting reflected microwave signals from above a roadway. An electronic vehicle sensing circuit is connected to the antenna for processing detected signals to identify a vehicle's physical parameter. The sensing circuit has an ambient temperature detector and a peak detector, the latter detecting a reflected temperature signal at said antenna and generating a detected temperature signal. A physical parameter calculating circuit is provided for determining the true amplitude of the detected signal and interpreted by the maximum ratio of the solid angles of the antenna beam filled by the vehicle to be detected and a roadway in the beam of the antenna. A processing circuit (ROM) is provided to identify the vehicle's physical parameter.

Abstract: The proposed surveillance system for surveilling a given scenario in azimuth and in elevation comprises an infrared surveillance detection device passively operating in the infrared region and a radar search and/or tracking device operating in the active mode for range determination. The targets or target information data are obtained as video signals from the infrared surveillance detection device during each search cycle and are processed in an infrared data processor. The video signals are discriminated and stored in an infrared signal processor with respect to their elevation angle values (.lambda.) and azimuth angle values (.alpha.). The values of the azimuth angle (.alpha.) are simultaneously fed to a radar activation and contol unit for triggering a momentary or short-time emission by the radar search and/or tracking device.

Abstract: A radiometric countermeasures system installable on a military tank to det a passive millimeter wave sensor in a guidance system on an enemy missile. The system comprises an oscillator source of mm waves; a variable attenuator connected to the oscillator to adjust the power level of the oscillator output signal; a circular polarizer connected to the attenuator; an antenna connected to the polarizer to broadcast mm wave radiation to the ambient atmosphere in which the military tank is located; and means for adjusting the attenuation of the attenuator such that total mm wave emission from the tank and from the antenna is substantially equal to the naturally-occurring mm wave radiation emitted by the background scenery in the vicinity of the tank.

Abstract: A microwave radiometer reconstructs images by fanbeam inversion. True time delay (100), frequency (600, 700) and mechanical scanning systems (200) are disclosed. The mechanically scanning radiometer includes a fanbeam antenna (210) to scan a scene so that the antenna output is a projection of the scene taken along the direction of scan. The mechanical scanning motion is provided by a rocking motor (254) controlled by a computer (214). Projections are obtained for successive orientations as the antenna is rotated by another motor (212). By application of an inverse Radon transform, the scene scanned is reconstructed by the computer.In one frequency scanning system (600), a filter bank spectrometer is implemented to obtain the projections, and in the other frequency scanning system (700), a transform spectrometer implemented. In the delay scanning system (100), a beam forming computer is used in the reconstruction process.

Abstract: To measure the figure of merit (G/T) and beam radial pointing error of a satellite earth station multiple Y-factor measurement are taken using a "drift cut" procedure and then these measurements are processed using a maximum likelihood estimate (MLE) algorithm. For carrying out the "drift cut" measurement process, the earth terminal's antenna is positioned such that the antenna beam intersects the path of the apparent star motion with a predetermined declination offset and ahead of the current star position. As the star position approaches the stationary antenna beam position, power measurements uniformly spaced in time are recorded. These power measurement "samples" are then divided by the "cold sky" power measurement to obtain corresponding Y-factor measurements. To eliminate the problem of antenna pointing error and star ephemeris error, multiple drift cuts are carried out, each offset in declination by a different amount from the estimate star declination, to produce a matrix of Y-factor values.

Abstract: Method and equipment are disclosed for picking up the radiation pattern of an antenna to be tested from measurements in near-field. The antenna to be tested is illuminated by a transmit antenna having wavefronts in the shape of circular cylinders. The radiation pattern of the antenna to be tested then is expressed by an integral transform of a unidimensional function which is solved by computing means.

Abstract: A passive imaging system (400) includes a frequency scanning array (412) for receiving radiation emissions from a scene with a flat or known spectrum of emissions over the operating frequency of the array. Different beam directions are addressed by a spectrum analyzer (404). An image coordinate generator (410) may be used where necessary to normalize the image which may be stored or displayed by an appropriate device (406).In one embodiment, the array is planar so as to generate pencil beams. The planar array comprises parallel line-source antenna elements (402), with a common feed (414). The feed has a large "wrap-up" so that frequency-frequency scanning is employed.Alternatively, one-dimensional images can be effected with a single line-source frequency scanning antenna element. Also, one-dimensional frequency scanning may be supplemented by a different scanning approach for resolution orthogonal to that provided by the frequency scanning. In one embodiment, phase gradient scanning is employed.

Abstract: A horizon reference system has a plurality of microwave radiation sensors which are selectively connected by a controller to a superheterodyne receiver. The output signals of the receiver are processed in conjunction with antenna selection data to provide roll angle with reference to the horizon and roll angle rate data about any particular axis of the platform on which the sensors are mounted.