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: Conductive coating (20) is a thorough mixture of 0.03 parts per weight of carbon black together with 0.003 to 0.01 parts per weight of wetting agent and 20 parts of solvent, and further mixing in by low shearing mixing 1/2 to 1 part per weight of thermosetting resin. This is then sprayed into place on the substrate and thermoset. In this particular case, the substrate is exterior face sheet (12) of honeycomb structure (10) which may serve as part of a spacecraft, to electrically conduct away surface charges.

Abstract: An improved infrared sensor is provided which is of the type which scans across a spatial region and detects infrared energy radiating from a celestial body and in which an input electronic signal is produced in response to the detected infrared energy, wherein the improvement comprises: amplifier circuit means for providing an amplified output signal in response to the input electronic signal; threshold detection circuit means for detecting when the output electronic signal reaches a prescribed threshold level substantially below a saturation level of said amplifier circuit means said threshold detection circuit means comprising a thresholding circuit for providing a turn-on signal when the output signal reaches the prescribed threshold level; and feedback circuit means for providing a feedback signal for limiting the input electronic signal provided to said amplifier circuit means, said feedback circuit means comprising a feedback amplifier circuit responsive to the turn-on signal, such that the feedback si

Abstract: A device for coupling or dividing electromagnetic energy, especially microwaves, between two circuits includes a pair of U-shaped conductors (36, 38) of rectangular cross-section which are coaxially disposed within corresponding slots (34, 36) in an electrically conductive base (30). The conductors have opposing, closely spaced stretches (36c, 38c) at an intersecting juncture in the slots where electromagnetic energy is coupled from one conductor to the other. The conductors are suspended in coaxial relationship within the slots by a pair of coplanar, C-shaped elements (42) which are slidably supported within a second pair of slots (43) in the base and each have cutouts (42a) therein in which the conductors are closely received. A spacer (40) maintains a preselected gap between the opposing stretches of the conductors and is provided with tapered ends (40a, 40b) which cooperate with beveled surfaces (38a, 38b) on the conductors to prevent relative lateral movement between the conductors.

Abstract: An overlapping frequency sweep system (10) includes a complex multiplier (15) located between two reflective array compressors (RACs 13 and 21). The complex multiplier compensates for the distortions due to both RACs by modifying the phase and amplitude of the sweep at an intermediate point in its dispersion. This permits precise calibration of the individual sweeps between the time when they are in the form of pulses and when successive sweeps overlap.A pulse source (11) provides a series of pulse inputs to the first RAC (13), the series having a predetermined period between successive pulses. The first RAC introduces differential delays as a function of frequency, the maximum differential delay introduced in a given sweep being equal to or less than the period of the pulse series. The remainder of the desired dispersion is applied by the second RAC (21). A limiter (23) provides a constant amplitude function of frequency input to the complex multiplier.

Abstract: A direction-finding interferometer (100) includes a novel autocalibration subsystem using bi-directional transmissions at a common frequency. The interferometer determines direction using a primary phase comparator (15) to assess the phase differences in signals transmitted by signal channels (13) from multiple antennas (11). The signal channels may include RF amplifiers (17), mixers (19) coupled to a local oscillator (23), IF amplifiers (21), and transmission lines.The autocalibration subsystem employs a frequency synthesizer (25) as a calibration signal source. The calibration signal path is directed between reversing switches (40) and couplers (33) in alternating directions via transmission lines (57 and 59). In either direction, the calibration is split so that part of the signals are coupled into the signal channels, and the remaining part is directed to a secondary phase comparator (131). The outputs of the primary and secondary comparators provide the data necessary for autocalibration.

Abstract: A frequency sweep system (10) operating in the radio frequency range includes a pulse source, a reflective array compresser (RAC) (13) and a complex multiplier (15). The RAC is designed to apply a time dispersion as a monotonic function of frequency to a pulse generated by the pulse source. Since RACs are difficult to manufacture precisely, the complex multiplier is included to compensate for the imperfections in the RAC. The complex multiplier is designed to multiply its analog input by a sequence of complex digital words, including a sign bit, so that the phase and amplitude of the analog signal can be calibrated as required. The sequence of digital words is determined by comparing the desired and actual phase dispersions of the frequency sweep system. The sequence so determined is stored in a read-only memory (ROM) (17). A timing generator (19) coordinates the firing of the pulse and the introduction of the sequence of digital words into the complex multiplier.

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 phase shifter for microwave electromagnetic energy propagating through a waveguide has a composite structure of a series of capacitive phase shifting posts positioned within the waveguide diametrically across from a symmetrically tapered ridge. The series of posts introduce a nominal value of phase shift with an incremental value which increases with increasing frequency of the electromagnetic energy. The tapered ridge introduces a nominal value of phase shift plus an incremental value which decreases with increasing frequency of the electromagnetic energy. The rates of increase and decrease of the incremental values of phase shift cancel so as to provide a resultant phase shift which is substantially invariant with frequency.

Abstract: An analog radio frequency spectrum analyzer (10) includes a calibration section (30) for compensating distortions. The spectrum analyzer includes a first reflective array compressor or "RAC" (12), a frequency sweep section (20), and a second RAC (14). Frequency domain compensations introduced at the signal input by the calibration section compensate distortions in the time domain at the output of the spectrum analyzer. This system corrects, for example, nonlinearities in the second RAC. The calibration function is determined by a network analysis of the spectrum analyzer and is specific to the RAC included. The function is stored in a ROM or other memory as a sequence of complex digital words. An address generator (36) directs the words to a complex multiplier (32) so that each input symbol period is multiplied by the sequence. Each complex digital word corresponds to an amplitude and phase modulation of the incoming signal over a fraction of a symbol period.

Abstract: An adaptive antenna 10 embodying the present invention includes an array of sensors 12. Each sensor 12 has associated therewith a main channel 14, a feedthrough path 16 and a feedback path 18. Correlators 20 coprocess signals in the feedthrough path 16 and the feedback path 18; the result is transformed according to an algorithm by a computer 22 which controls a weighting circuit 24. The weighting circuit 24 thus progressively modifies the signal in the main channel 14 to minimize interference with a desired signal. Placement of a limiter 26 along the feedback path 18 simplifies correlator design relative to adaptive antennas without such limiters and improves performance relative to adaptive antennas with limiters in the feedthrough path.

Abstract: A receiver is disclosed for acquiring and tracking a data signal in a highly stressed environment. The receiver comprises first and second I.F. sections, a mixer for translation from the first I.F. frequency to the second I.F. frequency, a 2 KHz bandpass filter at the second I.F. frequency, signal translator for synchronous translation of the signal at the second I.F. frequency to baseband, a digitizer for complex sampling operation on the baseband signal, a microprocessor for processing the digital samples, and a numerically controlled oscillator coupled to the mixer and controlled by the microprocessor. The microprocessor formulates matched digital discrete Fourier Transform filters which drive frequency, phase and symbol lock loops at the symbol rate. Each of the loop filters is formed by symbol-rate recursive, first-order equations.

Abstract: Conductive coating (20) is a thorough mixture of 0.03 parts per weight of carbon black together with 0.003 to 0.01 parts per weight of wetting agent and 20 parts of solvent, and further mixing in by low shearing mixing 1/2 to 1 part per weight of thermosetting resin. This is then sprayed into place on the substrate and thermoset. In this particular case, the substrate is exterior face sheet (12) of honeycomb structure (10) which may serve as part of a spacecraft, to electrically conduct away surface charges.

Abstract: A switch (10) of the type comprising a rectangular arrangement of ports (21, 22, 23 and 24) includes a diagonally extending connector bar (35) disposed on one side of the rectangular arrangement opposite four laterally extending connector bars (31, 32, 33 and 34). The diagonally disposed connector bar is actuatable independently of the other bars. Electromagnetically driven rockers (79) or other means are provided to actuate the rods. In one realization of the switch, the ports are coaxial connectors for a microwave network. Each connector bar resides within a corresponding groove (51, 61) in a conductive housing and is independently actuatable. When actuated, a bar contacts the center conductors of two ports. The actuated bar cooperates with the walls of the containing groove to form an air-line microwave connection between the contacted ports. When the contained bar is unactuated, the groove becomes a waveguide-beyond-cutoff to isolate the respective ports.

Abstract: A coaxial phase shifter for shifting the phase of a signal being transmitted along a transverse electromagnetic transmission line. The phase shifter is in line with the transmission line's inner conductor, such that it is very compact and such that the transmission line's outer conductor need not be modified. The phase shifter includes electrically-conductive fingers arranged in spaced, confronting relationship with each other, to capacitively couple the signal from one segment of the transmission line's inner conductor to another. In addition, the phase shifter is configured to provide an input impedance at both of its ends that matches the characteristic impedance of the transmission line.