Abstract: An antenna includes: a substrate; a first reference electrode on a first surface of the substrate; a radiating element on a second surface of the substrate, feeding directions of a first port and a second port of the radiating element are different; and at least one transmission structure on the second surface of the substrate and connected to at least one of the first port and the second port. The transmission structure includes: a signal electrode, a second reference electrode on at least one side of the signal electrode, and at least one membrane bridge; the signal electrode feeds a microwave signal into the radiating element, is positioned in a space surrounded by the membrane bridge and the substrate, and is insulated from the membrane bridge through an interlayer dielectric layer; orthographic projections of the membrane bridge and the second reference electrode on the substrate are overlapped.

Abstract: A method for ascertaining a state variable of a magnetic actuator at a particular point in time. The method includes a step of reading in and a step of calculating. In the step of reading in, a first sensor value and at least one second sensor value are read in, the first sensor value representing a physical variable identical to that of the second sensor value, and the first sensor value having been detected after the second sensor value. In the step of calculating, the state variable is calculated using the first sensor value and the second sensor value as input variables to at least one approximation function.

Abstract: An RF applicator has an open-ended waveguide having an aperture and a dielectric cone extending through the aperture and is electrically connected to an RF source that is configured to generate RF energy pulses. A top fin is mounted to an inner top surface of the waveguide and comprises a conductive material, is electrically connected to the RF source, and has dimensions configured to optimize a bandwidth that the RF applicator applies to tissue. A bottom fin is mounted to an inner bottom surface of the waveguide and comprises a conductive material electrically isolated from the RF source, with dimensions configured to optimize a bandwidth that the RF applicator applies to tissue. A dielectric cone is inserted into the waveguide. A filler material between inner surfaces of the waveguide and the solid dielectric cone can fill gaps and has a dielectric constant similar to the dielectric cone.

Abstract: A full band waveguide orthomode transducer (OMT) includes first, second, and third waveguide sections coupled to one another, the first, second, and third waveguide sections respectively having a first port, a second port, and a third port. A first wire grid polarizer in the first waveguide section is transparent to electromagnetic signals having a first polarization and reflective of electromagnetic signals having a second polarization orthogonal to the first polarization. A second wire grid polarizer in the second waveguide section is transparent to electromagnetic signals having the second polarization and reflective of electromagnetic signals having the first polarization. The third waveguide section is configured to transmit and/or receive electromagnetic signals having the first polarization and/or the second polarization.

Abstract: A polarizing screen includes an arrangement of at least one, electrically conductive, polarizing cell, which at least one cell is frequency- and polarization-selective, for transforming the polarization of the electric component E of the transverse electromagnetic (TEM) wave, received with linear polarization, into an electromagnetic wave with circular polarization. The four lateral walls of each section of waveguide forming a polarizing cell are each open over their entire length due to a median continuous slot, parallel to the direction of propagation of the incident electromagnetic wave, so as to form four angled electrically conductive plates.

Abstract: Embodiments described herein perform incisions along the direction of the long axis of the waveguide, thereby exposing a trench structure which can be readily plated. Once divided and plated, the individual cut pieces can then be secured together to restore the original waveguide structure. In this fashion, multiple cut pieces can be secured together and used as “building blocks” to create a modular solution which can be used to provide a number of different customizable waveguide structures. Thus, embodiments described herein can perform plating procedures in a less expensive manner while achieving the benefits of ganged waveguide structures. Moreover, embodiments described herein can offer a modular approach to ganged waveguide design thereby allowing for end-user flexibility in testing.

Abstract: Systems, methods, and devices for diverting surface current on a display panel support plate are provided. An electronic transceiver device including a display panel may include a display back plate and a support plate, such that the support plate is disposed beneath the display back plate. The support plate may include an array of slots etched into the support plate, such that the array of slots may be used and positioned to divert an electromagnetic field on the support plate to redirect propagation of the surface current towards ground pins located on the display panel housing.

Abstract: An antenna array that can include a plurality of antenna cells positioned in a global coordinate system of the antenna array. Each of the plurality of antenna cells has a respective local coordinate system and can include a radiating element having a predetermined angle of rotation defined in the global coordinate system and an antenna port coupled to the radiating element, the antenna port being positioned at a particular set of coordinates in the respective local coordinate system. The particular set of coordinates of the antenna port of each of the plurality of antenna cells can be the same.

Abstract: A radar system to detect and track objects in three dimensions. The radar system including antennae, transmit, receive and processing electronics is all in a small, lightweight, low-cost, highly integrated package. The radar system uses a wide azimuth, narrow elevation radar pattern to detect objects and a Wi-Fi radio to communicate to one or more receiving and display units. One application may include mounting the radar system in an existing radome on an aircraft to detect and avoid objects during ground operations. Objects may include other moving aircraft, ground vehicles, buildings or other structures that may be in the area. The system may transmit information to both pilot and ground crew.

Abstract: An antenna array that can include a plurality of antenna cells positioned in a global coordinate system of the antenna array. Each of the plurality of antenna cells has a respective local coordinate system and can include a radiating element having a predetermined angle of rotation defined in the global coordinate system and an antenna port coupled to the radiating element, the antenna port being positioned at a particular set of coordinates in the respective local coordinate system. The particular set of coordinates of the antenna port of each of the plurality of antenna cells can be the same.

Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

Abstract: Conventional coaxial wiring devices present a problem in that the management of the manufacturing process therefor is difficult. A coaxial wiring device according to the present invention includes a first member, a second member, and a conductor plate.

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes at least one transceiver configured to modulate data to generate a plurality of first electromagnetic waves. A plurality of couplers are configured to couple at least a portion of the plurality of first electromagnetic waves to a transmission medium, wherein the plurality of couplers generate a plurality of mode division multiplexed second electromagnetic waves that propagate along the outer surface of the transmission medium. Other embodiments are disclosed.

Abstract: A microwave device, such as a waveguide, transmission line, waveguide circuit, transmission line circuit or radio frequency part of an antenna system, is disclosed. The microwave device comprises two conducting layers arranged with a gap there between, and a set of periodically or quasi-periodically arranged protruding elements fixedly connected to at least one of said conducting layers, thereby forming a texture to stop wave propagation in a frequency band of operation in other directions than along intended waveguiding paths, thus forming a so-called gap waveguide. All protruding elements are connected electrically to each other at their bases at least via the conductive layer on which they are fixedly connected, and some or all of the protruding elements are in conductive or non-conductive contact also with the other conducting layer. A corresponding manufacturing method is also disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

Abstract: A waveguide antenna assembly conformable to the configuration of a supported device for transceiving signals of a predetermined radio frequency range comprising at least two collaterally aligned conductive layers configured in a conformable loop so as to form an electrically isolating channel dimensionally configured for support of the waveguide modes of the predetermined frequency range, an aperture for electromagnetically transceiving the signals, wherein the aperture extends along a surface of the electrically isolating channel such that the aperture extends between the outer edge of the inner surface of the first conductive layer and the second conductive layer, a back short spaced apart from the aperture a predetermined distance equal to a resonant length of the waveguide mode wavelength so as to provide a circuit impedance between the first conductive layer and the second conductive layer for tuning the waveguide to transceive the signals, excitation points coupled to the aperture to propagate waveguide

Abstract: A system for operating a damper comprises a flue pipe assembly, and a damper movable between an open position and a closed position within the flue pipe assembly. At least one thermoelectric generator is coupled to a surface of the flue pipe assembly. Operation of the damper is achieved by the thermoelectric generator harvesting thermal energy from the flue pipe assembly and converting it into usable electrical energy for actuation of the damper.

Abstract: Disclosed are various systems and methods directed to the launching of a guided surface wave embodying a modulated signal using a guided surface waveguide probe. A modulated signal is generated and coupled to a guided surface waveguide probe. A resulting guided surface wave is launched that decays exponentially as a function of distance.

Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes at least one transceiver configured to modulate data to generate a plurality of first electromagnetic waves. A plurality of couplers are configured to couple at least a portion of the plurality of first electromagnetic waves to a transmission medium, wherein the plurality of couplers generate a plurality of mode division multiplexed second electromagnetic waves that propagate along the outer surface of the transmission medium. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, an apparatus including a waveguide, an antenna, and a transmitter. The transmitter can facilitate transmission of first electromagnetic waves via the antenna, the first electromagnetic waves having a fundamental mode. The waveguide can facilitate propagation of the first electromagnetic waves at least in part on a surface of the waveguide. The waveguide can be positioned at a location that enables the first electromagnetic waves to induce second electromagnetic waves having fundamental and non-fundamental modes that propagate on a surface of a transmission medium. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

Abstract: Disclosed are various embodiments for superposition of guided surface wave launched along the surface of a lossy medium such as, e.g., a terrestrial medium by exciting a guided surface waveguide probe. In one example, among others, a system includes an array of guided surface waveguide probes configured to launch guided surface waves along a surface of a lossy conducting medium and an array control system configured to control operation of waveguide probes in the array via one or more feed networks. The array control circuit can control operation of the guided surface waveguide probes to maintain a predefined radiation pattern produced by the guided surface waves. In another example, a method includes providing voltage excitation to first and second guided surface waveguide probes to launch guided surface waves with the voltage excitation provided to the second guided surface waveguide probe delayed by a defined phase delay.

Abstract: The present application discloses a dual open-ended waveguide (DOEWG) antenna apparatus. The apparatus may include a plurality of radiating elements configured to radiate electromagnetic energy. Each radiating element may have an associated amplitude and phase. The apparatus may further include a waveguide configured to propagate an electromagnetic signal from a waveguide feed to the radiating elements. The radiating elements are arranged in a plurality of doublets. Each doublet includes at least two radiating elements and is coupled to the waveguide via a respective doublet neck. At least one doublet in the plurality of doublets is coupled to the waveguide via a doublet neck that has a first height proximate a first radiating element in the at least one doublet and a second height proximate a second radiating element in the at least one doublet in which the first height is different from the second height.

Abstract: Aspects of the subject disclosure may include, for example, a coupler including a receiving portion that receives a first electromagnetic wave conveying first data from a transmitting device. A guiding portion guides the first electromagnetic wave to a junction for coupling the first electromagnetic wave to a transmission medium. The first electromagnetic wave propagates via at least one first guided wave mode. The coupling of the first electromagnetic wave to the transmission medium forms a second electromagnetic wave that is guided to propagate along the outer surface of the transmission medium via at least one second guided wave mode that differs from the at least one first guided wave mode. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a transmission system having a coupling device, a bypass circuit, a memory and a processor. The coupling device can facilitate transmission or reception of electromagnetic waves that propagate along a surface of a transmission medium. The memory can store instructions, which when executed by the processor, causes the processor to perform operations including restarting a timer to prevent the bypass circuit from disabling the transmission or reception of electromagnetic waves by the coupling device. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, an apparatus including a waveguide, an antenna, and a transmitter. The transmitter can facilitate transmission of first electromagnetic waves via the antenna, the first electromagnetic waves having a fundamental mode. The waveguide can facilitate propagation of the first electromagnetic waves at least in part on a surface of the waveguide. The waveguide can be positioned at a location that enables the first electromagnetic waves to induce second electromagnetic waves having fundamental and non-fundamental modes that propagate on a surface of a transmission medium. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes at least one transceiver configured to modulate data to generate a plurality of first electromagnetic waves. A plurality of couplers are configured to couple at least a portion of the plurality of first electromagnetic waves to a transmission medium, wherein the plurality of couplers generate a plurality of mode division multiplexed second electromagnetic waves that propagate along the outer surface of the transmission medium. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes at least one transceiver configured to modulate data to generate a plurality of first electromagnetic waves. A plurality of couplers are configured to couple at least a portion of the plurality of first electromagnetic waves to a transmission medium, wherein the plurality of couplers generate a plurality of mode division multiplexed second electromagnetic waves that propagate along the outer surface of the transmission medium. Other embodiments are disclosed.

Abstract: Aspects of the subject disclosure may include, for example, a transmission device that includes at least one transceiver configured to modulate data to generate a plurality of first electromagnetic waves. A plurality of couplers are configured to couple at least a portion of the plurality of first electromagnetic waves to a transmission medium, wherein the plurality of couplers generate a plurality of mode division multiplexed second electromagnetic waves that propagate along the outer surface of the transmission medium. Other embodiments are disclosed.

Abstract: Techniques for implementing series-fed antenna arrays with a variable dielectric waveguide. In one implementation, coupling elements with optional controlled phase shifters are placed adjacent each radiating element of the array. To avoid frequency sensitivity of the resulting array, one or more waveguides have a variable propagation constant. The variable waveguide may use certain materials exhibiting this phenomenon, or may have configurable gaps between layers. Plated-through holes and pins can control the gaps; and/or a 2-D circular or a rectangular travelling wave array of scattering elements can be used as well.

Abstract: A method and apparatus for a polarizer. The apparatus comprises a dielectric rod, a first array of slots, and a second array of slots. The first array of slots and the second array of slots are formed in sidewalls of the dielectric rod. The first array of slots is substantially opposite to the second array of slots. The first array of slots and the second array of slots are configured to shift a first component orthogonal to a second component in a signal traveling through the dielectric rod by around 90 degrees with respect to each other. The dielectric rod may be a solid material or comprised of layers of dielectric substrates with metal tabs.

Abstract: Implementations for exciting two or more modes via modal decomposition of a pulse by a wave launcher are generally disclosed.

Abstract: Electromagnetic slow wave structures (SWS) comprised of arrays of conductive obstacles are formed inside conductive parallel-plate waveguides These SWS may be formed using, for example, MEMS manufacturing processes at the wafer level on substrates including ceramic and silicon. An effective relative permittivity in the range of 15 to 40 may be obtained at millimeterwave frequencies. The SWS can be made absorptive by incorporating resistive losses in a plate of the PPW. Applications of these slow wave structures include delay lines and bootlace lens beamformers for microwave and millimeterwave antenna systems.

Abstract: A parallel capacitor varactor shunt switch device may include a shunt layer, a coplanar waveguide (CPW) layer, and a tunable thin film dielectric layer that is interposed between the shunt layer and the CPW layer. The tunable thin film dielectric layer electrically isolates the shunt layer from the CPW layer. The shunt layer includes a plurality of parallel shunt lines. The CPW layer includes a CPW signal transmission line with two CPW ground lines parallel to the CPW signal transmission line. A plurality of varactor areas equal in number to the plurality of parallel shunt lines are defined in the CPW signal transmission line, each varactor area corresponding to an overlap of the CPW signal transmission line with a respective shunt line and each respective parallel shunt line and its corresponding varactor area defines a capacitor.

Abstract: A twist for coupling radiation between orthogonal waveguides is provided. The twist includes at least three cavities opening from at least one of a first X1-Y1 surface and a second X2-Y2 surface of a metal block. A first cavity has a first opening in a first Y-Z plane and a second opening in a second Y-Z plane offset from the first Y-Z plane by a first length. A second cavity shares the second opening with the first cavity and has a third opening in a third Y-Z plane offset from the second Y-Z plane by a second length and has at least two heights and at least two widths. A last cavity shares a next-to-last opening in a next-to-last Y-Z plane with a next-to-last cavity. The last cavity has a last opening in a last Y-Z plane offset from the next-to-last Y-Z plane by a last length.

Abstract: Dispersive properties of a linear dispersive delay line are retained in a spiral configuration by constraining the radius of curvature depending on a desired propagation mode. The compact form factor spiral can be either a continuous spiral or a piecewise linear approximation. The spiral comprises a highly dielectric waveguide such as titanium dioxide or barium tetratitanate. Preferably, a spacer with a low dielectric constant and a microstrip are disposed on the top surface. The microstrip prevents attenuation of low frequencies, thereby increasing the operating frequency range. A second dielectric spacer and a second microstrip can be deposited on the bottom surface of the waveguide. Alternatively, the bottom surface of the waveguide can face a ground plane. The waveguide can be fed by horns or half-horns.

Abstract: A polarization converter may include an annular waveguide comprising an inner conductor having an outer surface and an outer conductor having an inner surface coaxial with the outer surface of the inner conductor. A plurality of loading structures may be disposed within the annular waveguide to form a plurality of regions within the annular waveguide including an alternating sequence of high phase shift regions and low phase shift regions along a direction of propagation of an electromagnetic wave. The plurality of loading structures may be configured to introduce a predetermined relative phase shift between orthogonally polarized first and second components of the electromagnetic wave for a predetermined operating frequency band. The plurality of loading structures may be further configured to suppress propagation of one or more higher order modes in the annular waveguide over the operating frequency band.

Abstract: A microwave pulse compressor has an elongated, cross-sectionally oversized waveguide resonator for decreasing the attenuation of the resonator, thereby increasing the resonator's QO The increased Q of the resonator guide results in more stored energy and greater output pulse power. The pulse compressor is symmetrically constructed to suppress high order modes that can be generated in oversized waveguides.

Abstract: A feed network may include a cylindrical common waveguide terminating in a common port and an orthomode transducer having a first port for coupling a first linearly polarized mode to the cylindrical common waveguide and a second port for coupling a second linearly polarized mode to the cylindrical common waveguide, the second linearly polarized mode orthogonal to the first linearly polarized mode. A filter-polarizer element may be disposed within the cylindrical common waveguide. The filter-polarizer element may be rotatable about an axis of the cylindrical common waveguide. The filter-polarizer element may be configured to cause a predetermined relative phase shift between a first signal and a second signal propagating in the cylindrical common waveguide. The filter-polarizer element may be further configured to suppress propagation of at least one undesired mode in the cylindrical common waveguide.

Abstract: In one or more embodiments described herein, there is provided an apparatus comprising input and output waveguides, and a carbon nanotube array. The array is positioned to electromagnetically couple the waveguides. The array has a slow-wave factor associated therewith, the speed of propagation of waves through the array being determined by this slow-wave factor. The array also has a first interface region. The apparatus further comprises a tuning element positioned to oppose the first interface region of the array to define a tuning distance. The slow-wave factor is affected by this tuning distance, and the tuning element is configured to be movable with respect to the first interface region so as to vary this tuning distance and thereby control the speed of propagation of waves through the array.

Abstract: Various exemplary embodiments relate to an antenna feed configured to receive a signal having a wavelength. They antenna feed may include a cylindrical body and four pin groups. Each pin group may include two pins in close proximity extending across the center of the cylindrical body. One of the two pins may be rotated approximately 22.5° from the angle of the other pin. Each pin group may be spaced approximately one quarter of a wavelength away from each other, and may be rotated approximately 22.5° from the angle of the previous pin group.

Abstract: A recess waveguide microwave chemical plant for production of ethene from natural gas and a process for production of ethene using the plant. The plant includes a recess waveguide, a mode transducer and coupling orifice plate, an adjustable short-circuiting plunger, and a chemical reactor; wherein with the recess waveguide as a main body, the mode transducer and coupling orifice plate is at the left side of the recess waveguide, the adjustable short-circuiting plunger is at the right side of the recess waveguide, and the chemical reactor is across the recess waveguide.

Abstract: Provided is a phase shifter using a substrate integrated waveguide (SIW). The phase shifter includes: a substrate; and a waveguide integrated on the substrate, wherein the waveguide includes an input port, an out port, two columns of via walls which are separated by a width of the waveguide and are arranged parallel to each other, and either a plurality of air holes which are formed to shift a phase of a signal between the input port and the output port or a plurality of rods, each including an air hole and a dielectric material inserted into the air hole.

Abstract: Disclosed herein is a transmission apparatus including a first transmission block configured to modulate a carrier-wave signal having a predetermined frequency on the basis of a first input signal, thereby outputting a first transmission signal; and a second transmission block configured to modulate a carrier-wave signal having a predetermined frequency on the basis of a second input signal, thereby outputting a second transmission signal; wherein a first input point for inputting the first transmission signal outputted from the first transmission block into a waveguide and a second input point for inputting the second transmission signal outputted from the second transmission block into the waveguide are shifted by a distance for providing a predetermined phase difference between the first transmission signal and the second transmission signal.

Abstract: A method of changing phase of a microwave electromagnetic beam in free space is provided wherein a cascade of device layers is located transverse to a path of the microwave beam. Each of the device layers have one or more columns. Each column has a device combination series-coupled to an adjacent device combination in the column. Each device combination has a first device having inductive characteristics at microwave frequencies and a second device series-coupled to the first device. The second device has at microwave frequencies characteristics of a fixed capacitance in parallel with a variable capacitance. The capacitance of one or more of the second devices is variable to establish a desired phase shift and a desired frequency band edge within a desired frequency pass band.

Abstract: A terahertz interaction circuit is provided. The terahertz interaction circuit includes a waveguide and an electron beam tunnel. The waveguide has a folded shape and in which an electromagnetic wave propagates. The electron beam tunnel is formed to penetrate through the waveguide. An electron beam passes through the electron beam tunnel. The waveguide includes a ridge portion in which a portion of a surface of the waveguide protrudes into the waveguide.

Abstract: In one or more embodiments described herein, there is provided an apparatus comprising input and output waveguides, and a carbon nanotube array. The array is positioned to electromagnetically couple the waveguides. The array has a slow-wave factor associated therewith, the speed of propagation of waves through the array being determined by this slow-wave factor. The array also has a first interface region. The apparatus further comprises a tuning element positioned to oppose the first interface region of the array to define a tuning distance. The slow-wave factor is affected by this tuning distance, and the tuning element is configured to be movable with respect to the first interface region so as to vary this tuning distance and thereby control the speed of propagation of waves through the array.

Abstract: An adjustable assembly apparatus includes a waveguide phase shifter and a waveguide multiplexer. The waveguide phase shifter has a first flange structure and the waveguide multiplexer has a second flange structure. The second flange structure and the first flange structure are embedded, and the polarization directions of the waveguide phase shifter and the waveguide multiplexer are orthogonal. In an embodiment, the first flange structure includes a bulge, the second flange structure includes a recess, and the bulge is embedded in the recess. The polarization directions of the bulge of the waveguide phase shifter and the recess of the waveguide multiplexer differ by 90 degrees.

Abstract: A right circular cylindrical body of an isotropic dielectric such as a cross-linked styrene copolymer, has respective pluralities of mutually parallel grooves formed in its axial end faces, spaced apart by an intermediate portion whose dimension c is a half wavelength. The axial lengths a, b of the grooves are such that when a wave passes through the body, a quarter wavelength phase difference is produced between a component of a wave having its E-vector parallel to the grooves and a component of the wave having its E-vector orthogonal to the grooves. Alternatively the plate may consist of two or more discrete bodies whose grooves are dimensioned to produce a total differential phase shift of one quarter wavelength.