Abstract: A system and method for monitoring a cargo container. The novel system (100) includes a sensor module (10) mounted in each target area (20) and a central monitoring system (40). Each sensor module (10) includes one or more sensors (22) and a transceiver (28) for transmitting data from the sensors to the central monitoring system (40). The central monitoring system (40) includes a transceiver (44) for receiving the data from all sensor modules (10) and a local master processor (46) for processing and analyzing the data. In the preferred embodiment, each transceiver (28) is capable of receiving and retransmitting signals of other sensor modules to relay signals of a particular sensor module (10) in a daisy chain fashion to and from the central monitoring system (40).

Abstract: An optically transparent dielectric reflector (200) that reflects an incident millimeter-wave beam at a design frequency. The reflector (200) includes layers of different optically transparent dielectric materials. The thickness of the individual layers is chosen so that the transmitted waves cancel almost completely in the forward direction, yielding a high degree of transmission loss and substantial reflection. In the preferred embodiment, the invention is comprised of alternating layers of optical sapphire and air. In the best mode, there are seven sapphire layers, with outer sapphire layers (50) having a nominal thickness of 70.8 mils, inner sapphire layers (52) with a nominal thickness of 30.4 mils, and air layers have a nominal thickness of 32.0 mils Vented metal spacers (54) are used to maintain optimal thickness of air layers.

Abstract: A system and method for monitoring a cargo container. The novel system (100) includes a sensor module (10) mounted in each target area (20) and a central monitoring system (40). Each sensor module (10) includes one or more sensors (22) and a transceiver (28) for transmitting data from the sensors to the central monitoring system (40). The central monitoring system (40) includes a transceiver (44) for receiving the data from all sensor modules (10) and a local master processor (46) for processing and analyzing the data. In the preferred embodiment, each transceiver (28) is capable of receiving and retransmitting signals of other sensor modules to relay signals of a particular sensor module (10) in a daisy chain fashion to and from the central monitoring system (40).

Abstract: A flat metal plate (20) has a plurality of holes (50) that have a property that changes across the surface of the plate so that the flat plate (20) mimics the behavior of a curved wavefront transformer. The changing property can include a dimension, such as radius or depth, such that the holes (50) near the center of the plate (20) are smaller, for example, than the holes (50) further away from the center of the plate (20). The size of each hole (50) is a function of the local phase change imparted on an electromagnetic wave of a particular wavelength or frequency that hits the hole (50), plus the propagation phase change that occurs in the reflected wave exiting the hole (50) as it travels the distance between the hole (50) and the focal point.

Abstract: A wave plate (10) formed of a perforated metallic plate of a particular thickness (L) has circular holes (12) that induce a change in the polarization of an electromagnetic wave passing through the holes in the plate. By choosing the proper hole diameter, the hole spacing in orthogonal directions, and the plate thickness, the desired relative phase shift is achieved with maximum transmission and minimal reflection. Two or more axially-aligned wave plates form a variable wave plate system. By changing the relative rotational positions of the wave plates, the polarization of the electromagnetic wave passing through the system can be selectively varied.

Abstract: An optically transparent dielectric reflector (200) that reflects an incident millimeter-wave beam at a design frequency. The reflector (200) includes layers of different optically transparent dielectric materials. The thickness of the individual layers is chosen so that the transmitted wavbes cancel almost completely in the forward direction, yielding a high degree of transmission loss and substantial reflection. In the preferred embodiment, the invention is comprised of alternating layers of optical sapphire and air. In the best mode, there are seven sapphire layers, with outer sapphire layers (50) having a nominal thickness of 70.8 mils, inner sapphire layers (52) with a nominal thickness of 30.4 mils, and air layers have a nominal thickness of 32.0 mils Vented metal spacers (54) are used to maintain optimal thickness of air layers.

Abstract: A variable beamsplitter (10) for use with quasi-optical millimeter-wave beams. The beamsplitter (10) consists of a circular metal plate (20) into which a periodic array (30) of rectangular slots is cut. The plate (20) is arranged so that the incident millimeter-wave beam is incident at an angle of 45° relative to the surface of the plate (20). The polarization of the incident beam is parallel to the surface of the plate (20). When the orientation of the plate (20) is such that the electric field is perpendicular to the slots (i.e., the electric field is directed across the narrow dimension of the slots), the plate (20) transmits nearly 100% of the incident power. If the plate is rotated about its axis by 90° (while maintaining a 45° angle between the incident beam and the plate) so that the incident electric field is parallel to the slots, then the plate (20) transmits 0% and reflects nearly 100% of the incident power at an angle of 90° relative to the incident beam.

Abstract: A flat metal plate (20) has a plurality of holes (50) that have a property that changes across the surface of the plate so that the flat plate (20) mimics the behavior of a curved wavefront transformer. The changing property can include a dimension, such as radius or depth, such that the holes (50) near the center of the plate (20) are smaller, for example, than the holes (50) further away from the center of the plate (20). The size of each hole (50) is a function of the local phase change imparted on an electromagnetic wave of a particular wavelength or frequency that hits the hole (50), plus the propagation phase change that occurs in the reflected wave exiting the hole (50) as it travels the distance between the hole (50) and the focal point.

Abstract: A variable beamsplitter (10) for use with quasi-optical millimeter-wave beams. The beamsplitter (10) consists of a circular metal plate (20) into which a periodic array (30) of rectangular slots is cut. The plate (20) is arranged so that the incident millimeter-wave beam is incident at an angle of 45° relative to the surface of the plate (20). The polarization of the incident beam is parallel to the surface of the plate (20). When the orientation of the plate (20) is such that the electric field is perpendicular to the slots (i.e., the electric field is directed across the narrow dimension of the slots), the plate (20) transmits nearly 100% of the incident power. If the plate is rotated about its axis by 90° (while maintaining a 45° angle between the incident beam and the plate) so that the incident electric field is parallel to the slots, then the plate (20) transmits 0% and reflects nearly 100% of the incident power at an angle of 90° relative to the incident beam.

Abstract: A millimeter-wave window is constructed from a high conductivity metal plate. The metallic plate is made transparent over a range of frequencies by perforating it with a periodic array of slots. In one embodiment, the millimeter-wave window is used in a gyrotron as the output window. In such a case, one suitable periodic array of slots comprises an equilateral triangular array of slots for operation at 95 GHz. By proper choice of the hole spacing and diameter, the window can be made transparent at any desired frequency. In addition to being transparent, however, the window must also be vacuum tight, as the pressure inside a gyrotron is on the order of 10−9 torr. The present invention solves this problem by covering the surface of the window with a thin layer of a suitable dielectric material, such as fused quartz.

Abstract: A millimeter-wave window is constructed from a high conductivity metal plate. The metallic plate is made transparent over a range of frequencies by perforating it with a periodic array of slots. In one embodiment, the millimeter-wave window is used in a gyrotron as the output window. In such a case, one suitable periodic array of slots comprises an equilateral triangular array of slots for operation at 95 GHz. By proper choice of the hole spacing and diameter, the window can be made transparent at any desired frequency. In addition to being transparent, however, the window must also be vacuum tight, as the pressure inside a gyrotron is on the order of 10−9 torr. The present invention solves this problem by covering the surface of the window with a thin layer of a suitable dielectric material, such as fused quartz.

Abstract: A compact four-way waveguide power divider (10). The inventive power divider (10) includes an input waveguide (11) that terminates at a junction with two adjacent waveguides on opposite sides of the input waveguide. On the opposite side of the junction is a conducting wall into which is built an inductive septum (20). The inductive septum (20) serves to partially match the input impedance of the structure. Second and third inductive septums (22 and 24) are also built into the output arms of the power divider (10). The purpose of the second and third septums (22 and 24) is twofold. In addition to partially matching the power divider's input impedance, the positions of the second and third septums (22 and 24) can be adjusted to equalize the power division between the output arms. Hence, the waves exiting the four output arms of the power divider have highly equalized amplitudes and phases. Further, the phases at the output ports are equalized by adjusting the lengths of the output arms.

Abstract: An explosively-driven magneto-cumulative generator that employs a Bitter coil with configurable electromagnet windings and insulation in its stator. An armature with a conducting metal liner filled with high explosive is initiated by an initiator and a switchable seed capacitor. The stator is coaxially aligned with and surrounds the armature and comprises the Bitter coil. A load is coupled between the armature and the Bitter coil. The Bitter coil comprises a series of conducting annular disks with an azimuthal sector of conductor removed. The disks are stacked with interleaved insulation, and are connected turn-by-turn. The windings of the Bitter coil can be modified, turn-by-turn, to change the inner and outer radii, and thickness, of each winding, and the material, size, and spacing of the interleaving insulation. This design variability solves many performance problems of conventional magneto-cumulative generators.

Abstract: An optically tuned magnetron oscillator employs materials whose electrodynamic properties are altered by the absorption of light. A probe constructed from a leaky dielectric light guide coated with a photoconductive material is inserted into each of the magnetron's cavities. When light is injected into the light guide, it leaks into the coating where it is absorbed, creating free charge carriers whose presence alters the dielectric properties of the material, thereby perturbing the resonant frequency of the cavity. The frequency can be controlled by varying the amount of light injected into each of the optical probes. When no light is present, the resonant frequency of the magnetron cavity will be at one extreme of its operating band; when the light is at full intensity, the change in the properties of the probe will be maximum as will be the change in the resonant frequency.

Abstract: A high power TM01 mode radio frequency antenna. The inventive antenna comprises a conical horn for receiving an electromagnetic input signal and radiating an output signal in response thereto. An inner window is disposed within the conical horn. An outer window is mounted at an output aperture of the conical horn in alignment with the inner window. The antenna has a gradual taper from a waveguide input to the aperture over a cone angle of 45 degrees. The outer window is mounted at the aperture in concentric alignment with the inner window. For an optimal compact design, the inner and outer windows are of polycarbonate construction.

Abstract: A microwave source system includes a magnetron source having an antenna, and an output dome covering the antenna. The output dome is formed as a ceramic substrate having an inner surface and an outer surface, and a conductive layer of a high thermal conductivity material overlying and contacting the inner surface and/or the outer surface. The ceramic substrate is preferably fused quartz, and the conductive layer is preferably polycrystalline synthetic diamond.

Abstract: A high average-power microwave window is provided whose thermal conductivity has been enhanced to enable it to transmit higher average RF power levels than conventional windows of the same size. Such a window is suitable for use with high-average power RF sources such as klystrons and magnetrons. The window comprises a ceramic substrate, typically a low-loss ceramic such as alumina or quartz, to which narrow strips of a high thermal conductivity material have been bonded. One such high thermal conductivity material is synthetic polycrystalline diamond, which can be bonded to the surface of a dielectric substrate using a high-temperature cement or can be directly deposited on the surface by a process such as chemical vapor deposition (CVD). High-purity alumina, a commonly-used material for high-power RF windows, has a thermal conductivity of 26.4 W/m.multidot..degree. C., while synthetic diamond has a thermal conductivity of 1000 W/m.multidot..degree. C., 2.6 times that of copper and 38 times that of alumina.

Abstract: An apparatus for propagating electromagnetic waves at a predetermined reduced guide wavelength. A waveguide (27b) is provided for receiving and guiding the electromagnetic waves. A dielectric (28) is disposed in the waveguide (27b) to decrease the guide wavelength of the received electromagnetic waves. The dielectric (28) allows the width of the waveguide (27b) to be reduced without significantly compromising its power-carrying capability.

Abstract: Improved magnetron oscillators that controllably form a plasma within each of its resonant cavities to rapidly change the resonant frequency of each cavity. The present invention also provides for frequency tuning methods for use with magnetron oscillators. The plasma is controllably formed in one or more subcells of each resonant cavity in a manner that alters the electromagnetic field within each cavity. Preferably, a magnetized collisional plasma is controlled to rapidly change the resonant frequency of each cavity. However, many types of plasmas may be used to implement the present invention. Controlling formation of the plasma within each cavity tunes the magnetron oscillator on a submillisecond time scale.

Abstract: A light-activated reflector having a plurality of coplanar arrays of parallel optical fibers that are each covered with a thin coating of a semiconductor material. Silicon, germanium, and indium antimonide, for example, along with other suitable materials, may be used as the coating of semiconductor material. The number and spacing of the coplanar arrays are determined by the shortest wavelength at which the reflector is to be operated. Electron-hole pairs are created in the coating of semiconductor material when it is illuminated by photons having energy greater than the band-gap energy of the semiconductor material. Light is injected into the optical fibers of a selected array. The injected light is absorbed and creates electron-hole pairs in the coating of semiconductor material, which modifies the permittivity of the coating. The absorbed light causes the coating to become reflective at millimeter wave frequencies.