Abstract: In a log-periodic monopole antenna array of the type described in U.S. Pat. No. 3,286,268, each antenna of the array having active elements spaced over the top surface of a ground structure and grounded parasitic elements interspersed between the active elements, the improvement of means for mechanically and electrically connecting the parasitic elements to a non-solderable ground structure comprising an elongated block compressed into a correspondingly shaped groove in the structure. Screw means threadedly engage the ground structure in a direction transversely of the top surface thereof and abut against the block. The lower strip portion of the parasitic elements is disposed in the groove between the block and a groove side wall and is compressed therebetween when the screw means is tightened into the structure and against the block.

Abstract: The foreshortened dipoles of the antenna described in U.S. Pat. No. 3,732,572 are further substantially shortened without performance impairment with a new construction in which each radiating element comprises a planar rectangular body electrically connected to the feed line by a stem attached to the body remotely from the feed line and spaced slightly from the plane of the body.

Abstract: The output of a laser oscillator is doubly passed through a birefringement medium, a quarter-wave plate and a laser amplifier by reflection from a phase conjugate mirror, the birefringent medium being between the oscillator and the plate in the path of the initial and reflected oscillator output. The birefringent medium divides the oscillator output into a first set of orthogonal polarization components (rays) and refracts one of them at a first angle successively through the plate and amplifier for reflection from the mirror through the amplifier, plate and medium. The reflected ray is amplified and then divided by the medium into a second set of orthogonal ray components which exit the medium at different angles away from the oscillator. In another embodiment, a second quarter-wave plate is added between the amplifier and mirror, and in a third embodiment the amplifier is positioned between the oscillator and the birefringent medium.

Abstract: Drift of the standing wave pattern in an acoustic doppler intrusion detection system in a confined space is compensated by adjusting the relative radiating and receiving positions of the radiator and receiver transducers, respectively, either mechanically or electrically until the signal level of the carrier wave at the receiver transducer is optimized. In the mechanical adjustment mode, either the receiver transducer or the radiating transducer is supported for movement relative to the other and is moved by a motor energized under the control of a signal level sensor circuit connected to the output of the receiver transducer. In another mode, a plurality of receiver (or alternatively radiator) transducers are connected through a switch to the signal level sensor circuit which in response to a drop in received signal level below a predetermined threshold, selectively switches the active transducer to optimize the received signal level.

Abstract: A multilayer antenna aperture polarizer comprises a single continuous electrically conductive trace on a flexible thin dielectric strip, the trace being formed into a plurality of arrays of grid lines with adjacent arrays interconnected by shorting leads and with a ground lead connected to the last or end array. The strip and shorting leads are folded at the locations of the shorting leads to form a stack of plane parallel polarizer panels, each comprising an array on the strip, adjacent panels in the stack being spaced apart in a direction transversely of the planes of the panels by insulator spacers, respectively. The polarizer is inserted in front of the aperture of the antenna and the ground lead is electrically connected to the antenna frame for grounding the several arrays. The shorting and ground leads are located at the corners of the stack in the neutral or minimum field zone of the antenna.

Abstract: A log-periodic antenna comprises two arrays of dimensionally tapered radiating elements disposed in the E-plane and each fed by a balanced line consisting of the inner conductors of two coaxial cables. In one embodiment the elements of each array are dipoles and in another embodiment are formed of continuous conductive strips in zig-zag patterns on non-conductive support members. Each array preferably has two sets of elements disposed in planes, respectively, which converge toward the smaller end of the array with vertically aligned radiating elements of each set projecting in opposite directions from the array axis. Periodic gain dropout anomalies across the antenna operating band are eliminated by use of a shielded feed line.

Abstract: A multimode perimeter intrusion detection system comprises at least one elongated electret tape mounted on a barrier, such as a fence or wall, along the perimeter of an area to be protected and operated simultaneously in both active and passive modes to detect intruders in proximity to, as well as in contact with, the barrier. The tape is directly mechanically coupled to the barrier above and parallel to the ground or floor and is electrically connected to a sound wave generator and to signal processing apparatus which detects signals produced on the tape by intruders and activates an alarm. In the active mode, the tape radiates sound waves, preferably in the ultrasonic range, outwardly from the barrier and receives doppler-shifted reflections from a person moving in the sound field for transmission to the signal processing apparatus.

Abstract: The exterior surfaces of a laser rod and pump lamp are covered with a highly reflective metal foil to prevent light leakage from the rod and lamp. The laser rod and pump lamp operate within a cavity inside a heat sink. Between the metal foil and the housing is a thermally conductive fluidic material selected to provide a tailored thermal impedance between the heat sink and the rod and pump to optimize the steady state temperatures of these components. The conductive fluid is not circulated but is contained to act as a simple heat conductor. The optically reflective and the heat transfer functions of the laser pumping operation are essentially separate from each other, enabling selection of materials for these respective functions to enhance performance of the laser and substantially simplify its construction.

Abstract: Laser apparatus with an electro-optic Q-switch assembly comprises a lasing medium which produces an unpolarized light beam when pumped, a polarizing beam splitter dividing the unpolarized beam into two orthogonally polarized parallel sub-beams, and a totally reflecting turning element which returns each sub-beam to the beam splitter along the path of the other sub-beam. A Q-switch is located in the path of one of the sub-beams. When the Q-switch is energized, the reflected polarization-shifted sub-beams are recombined at the splitter and pass through the lasing medium and adjacent partially-reflecting element as the output. When the Q-switch is deenergized, the sub-beams are dumped at the splitter which prevents the laser from oscillating.

Abstract: The exterior surfaces of a laser rod and pump lamp are covered with a highly reflective metal foil to prevent light leakage from the rod and lamp. The laser rod and pump lamp operate within a cavity inside a heat sink. Between the metal foil and the housing is a thermally conductive fluidic material selected to provide a tailored thermal impedance between the heat sink and the rod and pump to optimize the steady state temperatures of these components. The conductive fluid is not circulated but is contained to act as a simple heat conductor. The optically reflective and the heat transfer functions of the laser pumping operation are essentially separate from each other, enabling selection of materials for these respective functions to enhance performance of the laser and substantially simplify its construction.

Abstract: Drift of the standing wave pattern in an acoustic doppler intrusion detection system with radiating and receiving transducers in a confined space is compensated by changing the operating frequency of the carrier wave generator when the magnitude of the received carrier wave is less than a predetermined threshold level. The magnitude of the received carrier wave is continuously monitored and compared to the threshold level. The generator frequency is incrementally increased until the carrier wave magnitude is optimum. This invention comprehends the apparatus for and method of optimizing signal strength at the receiving transducer by this technique.

Abstract: Laser apparatus having a very narrow (<1A) spectral output comprises a laser cavity having a metal vapor cell as one of the reflecting elements. This cell reflects the laser beam over a narrow wavelength region in the vicinity of one of the metal vapor's resonant absorption lines and achieves frequency locking to an atomic resonance line without any external frequency sensors or feedback loops.

Abstract: The annular energy distribution in the output beam of a laser having an unstable resonator is evenly distributed across the entire beam profile by a synthesizer comprising a pair of mirrors adjacent to the output end of the resonator and operative on the output beam to redirect part of the beam from the annular outer portion to the energy-vacant central portion. One of the pair of mirrors is partially optically transmissive and concavely shaped and is disposed to reflect and converge part of the outer beam portion toward the other mirror and to transmit the balance. The other mirror is highly reflective and convexly shaped and is disposed to redirect and collimate the reflected beam part within the central portion toward the concave mirror parallel to the outer beam portion.

Abstract: A log-periodic antenna comprises two arrays of dimensionally tapered radiating elements disposed in the E-plane and each fed by a balanced line consisting of the inner conductors of two coaxial cables. In one embodiment the elements of each array are dipoles and in another embodiment are formed of continuous conductive strips in zig-zag patterns on non-conductive support members. Each array preferably have two sets of elements disposed in planes, respectively, which converge toward the smaller end of the array with vertically aligned radiating elements of each set projecting in opposite directions from the array axis. Periodic gain dropout anomalies across the antenna operating band are eliminated by use of a shielded feed line.

Abstract: A pulsed or CW laser is rapidly switched to operate at one or more selectable wavelengths by means of intracavity insertion of beam dispersion and focussing elements and an apertured focal plane mask and shutter assembly. The laser beam has an axis and is dispersed into components or sub-beams having different axes and representing different wavelengths, the sub-beams being focussed to substantially reduced diameters on the focal plane mask at points, respectively, at which apertures are formed. Movable shutters adjacent to the respective apertures control alternate opening of and closing of the apertures and selectively permit the laser to resonate at at least one of a plurality of wavelengths corresponding to that of the sub-beam passing through an open aperture. Mask apertures having very small diameters (<50 microns) and separations are achieved enabling switching between different operating wavelengths in milliseconds.

Abstract: A log-periodic antenna comprises two arrays of dimensionally tapered radiating elements disposed in the E-plane and each fed by a balanced line consisting of the inner conductors of two coaxial cables. In one embodiment the elements of each array are dipoles and in an other embodiment are formed of continuous conductive strips in zig-zag patterns on non-conductive support members. Each array preferably has two sets of elements disposed in planes, respectively, which converge toward the smaller end of the array with vertically aligned radiating elements of each set projecting in opposite directions from the array axis. Periodic gain dropout anomalies across the antenna operating band are at least substantially reduced by use of shielded feed lines. In another embodiment which has particular advantage at HF frequencies, a single array is operated over a ground plane which provides a mirror image thereof.

Abstract: A log-periodic antenna comprises two arrays of dimensionally tapered radiating elements disposed in the E-plane and each fed by a balanced line consisting of the inner conductors of two coaxial cables. In one embodiment the elements of each array are dipoles and in another embodiment are formed of continuous conductive strips in zig-zag patterns on non-conductive support members. Each array preferably has two sets of elements disposed in planes, respectively, which converge toward the smaller end of the array with vertically aligned radiating elements of each set projecting in opposite directions from the array axis. Periodic gain dropout anomalies across the antenna operating band are eliminated by use of a shielded feed line. In another embodiment having advantage in direction finding, the sets of elements of each array are located on associated opposite sides of a right rectangular pyramid. These pyramidal arrays are used in pairs for direction finding.

Abstract: A fiber optic sensor useful, for example, in intrusion detection systems for sensing seismic or pressure disturbances produced by an intruder, comprises a cable having an optical fiber core for transmitting the output of a laser, a hard preferably electrically nonconductive strand wound helically on and coextensive with the fiber, and a compliant tubular sleeve over the fiber and strand. The coils of the strand are axially spaced apart and circumferentially engage the fiber. The sleeve fits snugly over the strand and fiber and transmits through the strand coils to the fiber forces resulting from disturbances to be detected, subjecting the fiber to bending stresses. With cable connected at one end to the laser output, the polarization of light transmitted by the fiber is changed by the induced stresses and is detected at the other end of the cable to indicate the occurrence of the disturbance.

Abstract: A bi-loop antenna system comprises an array of four bi-loop antennas equally spaced from the array axis and fed in phase and with equal power. Each antenna comprises an electrical conductor configured as two substantially identical open-ended coplanar loops, preferably square in shape, having colinear axes parallel to the array axis and electrically connected together, the open ends defining two closely spaced feed points at the middle of the array. The array is fed by a four-way coaxial power divider with output ports connected to the antennas, respectively, remote from the feed points thereof by coaxial lines of equal length. A balun comprising a portion of one of the loops of each antenna and a closely spaced coextensive conductive strip connects the inner and outer conductors of the coaxial cable to the two feed points, respectively, of the antenna. In a preferred embodiment, the conductors of each antenna are formed on a dielectric sheet or board by printed circuit techniques.

Abstract: The width of the output pulse of a Q-switched cavity dump laser is substantially reduced by rapidly discharging a high voltage across the cavity dump crystal with an electro-optical switch which is closed by regenerative feedback from the optical output of the laser. The switch comprises a semiconductor body in intimate contact with the cavity dump crystal and has electrodes spaced by a small gap which control discharge of the high voltage across the crystal. A small fraction of the laser output is fed back to the switch and regeneratively creates a d-c current in the semiconductor body across the gap to accelerate closure of the switch and discharge of the voltage across the crystal to produce an extremely narrow output pulse.