Abstract: An antenna includes a first dipole arm and a second dipole arm. The first dipole arm is connected to a first conductor and is formed of a first conducting material. The first dipole arm extends in an axial direction from the first conductor. The second dipole arm is connected to a second conductor that is distinct from the first conductor and is formed of a second conducting material. The second dipole arm extends in the axial direction from the second conductor and is wound around the first dipole arm to form a number of loops. The second dipole arm does not contact the first dipole arm. An axial length of the second dipole arm in the axial direction is less than 90% of an axial length of the first dipole arm in the axial direction.

Abstract: A system and method for an electron paramagnetic resonance imaging (EPRI) system includes a magnet configured to apply a static magnetic field to a subject to be imaged and a gradient coil configured to apply a magnetic field gradient to the static magnetic field. The system also includes a parallel plate waveguide (PPWG) configured to use a traveling wave to generate a radio frequency (RF) magnetic field over a volume of interest (VOI) in the subject to elicit EPRI data from the VOI and a processor configured to reconstruct the EPRI data into an image of the VOI.

Abstract: A lens is provided. The lens includes a first two-dimensional (2-D) grid of capacitive patches and a first sheet layer. The first sheet layer includes a dielectric sheet and a second 2-D grid of capacitive patches. The dielectric sheet has a front surface and a back surface. The first 2-D grid of capacitive patches is mounted directly on the back surface of the dielectric sheet, and the second 2-D grid of capacitive patches is mounted directly on the front surface of the dielectric sheet. The first 2-D grid of capacitive patches is aligned with the second 2-D grid of capacitive patches to form a time delay circuit at each grid position of the aligned 2-D grids.

Abstract: An antenna system is provided that includes a coaxial cable, an antenna, a reflector wall, and a slot wall. The reflector wall is formed of a conductive material connected to a conductive shield to extend in an axial direction, is separated from an antenna conductor by a second dielectric material in a radial direction relative to the antenna conductor, and partially surrounds the antenna conductor in the radial direction from a first angle to a second angle when projected into a radial plane. The slot wall is formed through a portion of the conductive shield to expose a dielectric material from a third angle to a fourth angle when projected into the radial plane, is formed on a first side relative to a base. The first angle, the second angle, the third angle, and the fourth angle are defined relative to a common axis parallel to the radial plane.

Abstract: A balun includes a center conductor, a dielectric material, a tapered wall, a ring, and a prong. The center conductor extends a length of the balun. The dielectric material surrounds the center conductor along the length of the balun. The tapered wall forms a portion of a tube between a first wall and a second wall. The first wall is opposite the second wall. The tapered wall is formed of a conductive material. The portion of the tube forms a slot exposing the dielectric material. The ring connects to the second wall of the tapered wall and is formed of the conductive material. The ring forms a tube surrounding the center conductor and the dielectric material. The prong connects to the ring to extend toward the first wall and is formed of the conductive material. The prong extends over a portion of the dielectric material exposed by the slot.

Abstract: A tunable phase shifter is provided that includes a spatial phase shift element and a conducting sheet. The spatial phase shift element includes a dielectric substrate and a conductive antenna element mounted on the dielectric substrate. The conducting sheet is mounted a distance from the spatial phase shift element and configured to reflect an electromagnetic wave through the spatial phase shift element. The conductive antenna element is configured to radiate a second electromagnetic wave in response to receipt of the reflected electromagnetic wave. The distance between the conducting sheet and the spatial phase shift element can be changed to adjust a phase shift of the reflected electromagnetic wave.

Abstract: A tunable phase shifter is provided that includes a spatial phase shift element and a conducting sheet. The spatial phase shift element includes a dielectric substrate and a conductive antenna element mounted on the dielectric substrate. The conducting sheet is mounted a distance from the spatial phase shift element and configured to reflect an electromagnetic wave through the spatial phase shift element. The conductive antenna element is configured to radiate a second electromagnetic wave in response to receipt of the reflected electromagnetic wave. The distance between the conducting sheet and the spatial phase shift element can be changed to adjust a phase shift of the reflected electromagnetic wave.

Abstract: An ultra-wideband, low profile antenna is provided. The antenna includes a ground plane substrate, a feed conductor, a top hat conductor, a shorting arm, and a ring slot. The feed conductor includes a first end and a second end. The first end is configured for electrical coupling to a feed network through a feed element extending from the ground plane substrate. The top hat conductor includes a generally planar sheet mounted to the second end of the feed conductor in a first plane approximately parallel to a second plane defined by the ground plane substrate. The shorting arm includes a third end and a fourth end. The third end is mounted to the top hat conductor, and the fourth end is mounted to the ground plane substrate. The ring slot is formed in the ground plane substrate around the feed element.

Abstract: A slow wave structure of a traveling wave tube is provided. The slow wave structure includes an input port, an output port, a first material, and a second material. The second material is mounted in the first material at periodic intervals in a direction of propagation of a radio frequency signal between the input port and the output port. The second material has a real part of permittivity that is negative and a real part of permeability that is positive at an operational frequency of the radio frequency signal.

Abstract: An antenna system that includes a ground plane substrate, a first antenna, and a second antenna is provided. The first antenna includes a first loop conductor electrically connected to a feed network and to the ground plane substrate, a second loop conductor electrically connected to the feed network and to the ground plane substrate, and a first conductor mounted to and electrically connected to a first edge of the first loop conductor and to a second edge of the second loop conductor. The second antenna includes a third loop conductor electrically connected to the feed network and to the first conductor, a fourth loop conductor electrically connected to the feed network and to the first conductor, and a second conductor mounted to and electrically connected to a third edge of the third loop conductor and to a fourth edge of the fourth loop conductor.

Abstract: An antenna system that includes a ground plane substrate, a first antenna, and a second antenna is provided. The first antenna includes a first loop conductor electrically connected to a feed network and to the ground plane substrate, a second loop conductor electrically connected to the feed network and to the ground plane substrate, and a first conductor mounted to and electrically connected to a first edge of the first loop conductor and to a second edge of the second loop conductor. The second antenna includes a third loop conductor electrically connected to the feed network and to the first conductor, a fourth loop conductor electrically connected to the feed network and to the first conductor, and a second conductor mounted to and electrically connected to a third edge of the third loop conductor and to a fourth edge of the fourth loop conductor.

Abstract: A slow wave structure of a traveling wave tube is provided. The slow wave structure includes an input port, an output port, a first material, and a second material. The second material is mounted in the first material at periodic intervals in a direction of propagation of a radio frequency signal between the input port and the output port. The second material has a real part of permittivity that is negative and a real part of permeability that is positive at an operational frequency of the radio frequency signal.

Abstract: An antenna system is provided. The antenna system includes a coaxial cable, an antenna, and an impedance matching structure. The coaxial cable includes a center conductor extending a length of the coaxial cable, a dielectric material surrounding the center conductor along the length of the coaxial cable, and a conductive shield surrounding the dielectric material along the length of the coaxial cable. The antenna includes a conductor having an electrical length of half a wavelength at a selected operating frequency. The impedance matching structure includes a second center conductor mounted between an end of the center conductor of the coaxial cable and a feed end of the antenna. The impedance matching structure is configured to match an impedance of the coaxial cable to an impedance of the antenna.

Abstract: An ultra-wideband, low profile antenna is provided. The antenna includes a ground plane substrate, a feed conductor, a top hat conductor, a shorting arm, and a ring slot. The feed conductor includes a first end and a second end. The first end is configured for electrical coupling to a feed network through a feed element extending from the ground plane substrate. The top hat conductor includes a generally planar sheet mounted to the second end of the feed conductor in a first plane approximately parallel to a second plane defined by the ground plane substrate. The shorting arm includes a third end and a fourth end. The third end is mounted to the top hat conductor, and the fourth end is mounted to the ground plane substrate. The ring slot is formed in the ground plane substrate around the feed element.

Abstract: An electrically small receiver system is provided. The receiver system includes a plurality of antennas and a signal processing circuit. The plurality of antennas includes a first antenna configured to receive a first signal and a second antenna configured to receive a second signal. The signal processing circuit includes a phase shifter configured to apply a phase shift to the received second signal. The phase shift applied by the phase shifter is a function of an angle of incidence of the second signal measured relative to a boresight direction of the plurality of antennas. The signal processing circuit is configured to form an output signal that is a combination of the received first signal and the phase shifted second signal.

Abstract: A transmitter supporting multiple-input, multiple-output communications is provided. The transmitter includes a signal processor, a plurality of feed elements, and an aperture. The signal processor is configured to simultaneously receive a plurality of digital data streams and to transform the received plurality of digital data streams into a plurality of analog signals. The number of the plurality of digital data streams is selected for transmission to a single receive antenna based on a determined transmission environment. The plurality of feed elements are configured to receive the plurality of analog signals, and in response, to radiate a plurality of radio waves toward the aperture. The aperture is configured to receive the radiated plurality of radio waves, and in response, to radiate a second plurality of radio waves toward the single receive antenna.

Abstract: A lens is provided. The lens includes a first two-dimensional (2-D) grid of capacitive patches and a first sheet layer. The first sheet layer includes a dielectric sheet and a second 2-D grid of capacitive patches. The dielectric sheet has a front surface and a back surface. The first 2-D grid of capacitive patches is mounted directly on the back surface of the dielectric sheet, and the second 2-D grid of capacitive patches is mounted directly on the front surface of the dielectric sheet. The first 2-D grid of capacitive patches is aligned with the second 2-D grid of capacitive patches to form a time delay circuit at each grid position of the aligned 2-D grids.

Abstract: An electrically small receiver system is provided. The receiver system includes a plurality of antennas and a signal processing circuit. The plurality of antennas includes a first antenna configured to receive a first signal and a second antenna configured to receive a second signal. The signal processing circuit includes a phase shifter configured to apply a phase shift to the received second signal. The phase shift applied by the phase shifter is a function of an angle of incidence of the second signal measured relative to a boresight direction of the plurality of antennas. The signal processing circuit is configured to form an output signal that is a combination of the received first signal and the phase shifted second signal.

Abstract: An electrically small receiver system is provided. The receiver system includes a plurality of antennas and a signal processing circuit. The plurality of antennas includes a first antenna configured to receive a first signal and a second antenna configured to receive a second signal. The signal processing circuit includes a first resonant loop and a second resonant loop. The first resonant loop is mounted to receive the first signal from the first antenna. The second resonant loop is mounted to receive the second signal from the second antenna. The first resonant loop and the second resonant loop are coupled such that the first output signal and the second output signal are generated as a function of the first signal and the second signal. A phase difference between the first output signal and the second output signal is greater than a phase difference between the first signal and the second signal.

Abstract: An ultra-wideband, low profile antenna is provided. The antenna includes a ground plane substrate and a radiating element. The radiating element includes at least two loop sections, wherein each of the at least two loop sections is electrically connected to a feed network and to the ground plane substrate. The radiating element is configured to radiate over a first frequency band when the feed network provides an in-phase input signal to the at least two loop sections and to radiate over a second frequency band when the feed network provides an out-of-phase input signal to the at least two loop sections. The second frequency band includes a lower frequency than the first frequency band.