Including Variable Impedance Patents (Class 333/253)
  • Publication number: 20140320238
    Abstract: The invention relates two lines each with two terminals. A first line provides a first terminal and a second terminal. A second line provides a first terminal and a second terminal. The lines extend in spatial proximity and are coupled. The two lines transport an electromagnetic signal fed into the line system. Distanced from the first terminal of the second line and distanced from the second terminal of the second line, at least one controllable element is arranged along the second line. The invention further relates to a switch, a controllable diplexer, a controllable frequency filter, a controllable attenuator and a controllable phase shifter.
    Type: Application
    Filed: April 29, 2014
    Publication date: October 30, 2014
    Applicant: Rohde & Schwarz GmbH & Co. KG
    Inventor: Rudolf FORSTMAIER
  • Patent number: 8823471
    Abstract: Certain exemplary embodiments can provide a rectangular waveguide and backshort adapted for using/studying millimeter and/or submillimeter waves. Exemplary sliding shorts can exhibit relatively low loss, relatively smooth phase variation with frequency and movement, and/or relatively good repeatability. Certain exemplary embodiments can resist transmission of power by reflecting substantially all power from an incident signal.
    Type: Grant
    Filed: May 28, 2010
    Date of Patent: September 2, 2014
    Inventors: James Stanec, Nicholas S Barker
  • Patent number: 8797126
    Abstract: The present invention relates to a tunable microwave arrangement (100) comprising a waveguide arrangement and tuning elements comprising a number of varactors for tuning an electromagnetic signal input to the waveguide arrangement. It comprises a substrate (1), a layered structure (20) comprising at least two conducting layers (2,3) and at least one dielectric layer (4) which are arranged in an alternating manner. The layered structure is arranged on the substrate (1) such that a first of said conducting layers (2) is closest to the substrate (1). It also comprises at least one surface mounted waveguide (5), a second of the conducting layers (3), most distant from the substrate, being adapted to form a wall of the surface mounted waveguide (5), which wall incorporates said tuning elements which are arranged to enable control of surface currents generated in said wall, hence loading the waveguide (5) with a tunable, controllable impedance.
    Type: Grant
    Filed: December 1, 2008
    Date of Patent: August 5, 2014
    Assignee: Telefonaktiebolaget L M Ericsson (Publ)
    Inventors: Spartak Gevorgyan, Anatoli Deleniv, Thomas Lewin, Per Ligander
  • Publication number: 20140184351
    Abstract: An exemplary embodiment of the present invention provides an improved dielectric waveguide named electrical fiber. The electrical fiber with a metal cladding may isolate the interference of the signals in other wireless channels and adjacent electrical fibers, which typically causes band-limitation problem, for a smaller radiation loss and better signal guiding to lower the total transceiver power consumption as the transmit distance increases. Also, the electrical fiber may have frequency independent attenuation characteristics to enable high data rate transfer with little or even without any additional receiver-side compensation due to vertical coupling of the electrical fiber and an interconnection device.
    Type: Application
    Filed: December 11, 2013
    Publication date: July 3, 2014
    Applicant: Korea Advanced Institute of Science and Technology
    Inventors: Hyeon Min BAE, Ha Il SONG, Huxian JIN
  • Patent number: 8447256
    Abstract: In accordance with some embodiments of the present disclosure an attenuating circuit comprises a balun configured to receive a radio frequency (RF) signal at first and second input ports and configured to output the RF signal. The circuit further comprises an attenuator coupled in parallel with the first and second input ports. A power level of the RF signal output by the balun is based at least partially on an impedance of the attenuator. The attenuator comprises a resistor ladder configured to receive at least a portion of the RF signal and a plurality of switches coupled to the resistor ladder. The plurality of switches are configured to open and close such that the impedance of the attenuator is a function of which switches are open and closed. Therefore, the power of the RF signal is controlled based at least on the opening and closing of the switches.
    Type: Grant
    Filed: August 11, 2011
    Date of Patent: May 21, 2013
    Assignee: Fujitsu Semiconductor Limited
    Inventors: Kurt B. Hausmann, Omid Oliaei
  • Patent number: 8044540
    Abstract: A SPDT or SPMT switch may include a transformer having a primary winding and a secondary winding, where a first end of the secondary winding is connected to a single pole port, where a first end of the primary winding is connected to a first throw port; a first switch having a first end and a second end, where the first end is connected to ground; and a second switch, where a second end of the secondary winding is connected to both a second end of the first switch and a first end of the second switch, where a second end of the second switch is connected to a second throw port, where the first switch controls a first communication path between the single pole port and the first throw port, and where the second switch controls a second communication path between the second throw port and the single pole port.
    Type: Grant
    Filed: September 23, 2009
    Date of Patent: October 25, 2011
    Assignees: Georgia Tech Research Corporation, Samsung Electro-Mechanics
    Inventors: Dong Ho Lee, Minsik Ahn, Kyu Hwan An, Wangmyong Woo, Chang-Ho Lee, Joy Laskar
  • Publication number: 20110169592
    Abstract: A co-axial microwave bolometer architecture is disclosed that uses thick-film processes to construct very small thermistors on a substrate that is selected for low heat transfer. Thermal isolation is further enhanced by making the planar electrodes from a metal with lower heat transfer than typical electrical metals. Furthermore, a resistor with very strong temperature coefficient (thermistor), is arranged such that connecting metal paths are arranged axially, and as generally flat, thin, planar conductors. Additionally, the substrate of the thermistor is selected to have very low conductivity of heat, so the thermistor element itself is well isolated thermally from its surroundings.
    Type: Application
    Filed: January 3, 2011
    Publication date: July 14, 2011
    Applicant: TEGAM, INC.
    Inventors: Jefferson D. Lexa, Andrew S. Brush, John D. Swank
  • Publication number: 20110133862
    Abstract: A tunable filter for enabling the adjustment of tuning characteristics includes: a housing, in which multiple cavities are defined by partitions; a resonator contained in the cavity; at least one sliding member installed over the resonator; a main cover coupled to an upper portion of the housing; and at least one tuning element coupled to a lower portion of the sliding member and made of a metallic material. The tuning element is coupled to the sliding member by a rotatable bolt, and the bolt is coupled to the tuning element at a point that is a particular distance away from a center of the tuning element. The tunable filter using a sliding system according to certain embodiments of the present invention has the advantage of enabling adjustment of tuning characteristics by way of the rotation of the tuning element, and accordingly, can be used adaptively in various environments.
    Type: Application
    Filed: August 7, 2009
    Publication date: June 9, 2011
    Inventors: Dong-Wan Chun, Kwang-Sun Park
  • Patent number: 7795988
    Abstract: The invention relates to a compact automatic impedance adapter in a waveguide, characterised in that the impedance is controlled by plungers, filling the entire guide with a magic-tee coupler plane E/plane H modifying the electrical and magnetic field, one plunger modifying the electrical field (E) in the guide and the second modifying the magnetic field (H).
    Type: Grant
    Filed: June 6, 2006
    Date of Patent: September 14, 2010
    Assignees: Centre National de la Recherche Scientifique, Univerisite des Sciences et Technologies de Lille-USTL
    Inventors: Frederic Bue, Christophe Gaquiere, Nicolas Vellas, Damien Ducatteau
  • Patent number: 6952144
    Abstract: Briefly, in accordance with an embodiment of the invention, an apparatus and method to increase efficiency of a power amplifier is provided. The apparatus may include a power amplifier, and a variable impedance matching circuit coupled to the power amplifier to improve the transmitter efficiency over a range of output power. The variable impedance matching circuit may be adapted to match the output impedance of the power amplifier. The method may include varying the impedance of a circuit coupled to the output of a power amplifier during operation of the power amplifier to match the output impedance of the power amplifier.
    Type: Grant
    Filed: June 16, 2003
    Date of Patent: October 4, 2005
    Assignee: Intel Corporation
    Inventor: Ronald D. Javor
  • Patent number: 6914538
    Abstract: A system and method for downhole power delivery. In one embodiment, the system delivers computer-regulated downhole power voltages, and may be configured to customize signal waveforms and power allocation on the various independent signal transmission modes to maximize the power capacity of the logging cable subject to its maximum voltage rating. In one embodiment, the system includes a standard multiconductor logging cable which supports orthogonal signal transmission modes on circumferentially spaced insulated conductors. A high-power power source on the surface is coupled to the insulated conductors in the cable to drive a power signal on the lowest impedance signal transmission mode. The system may further include multiple power sources operating on different independent signal transmission modes, and may also include multiple telemetry channels which share the power transmission modes via frequency multiplexing.
    Type: Grant
    Filed: August 30, 2002
    Date of Patent: July 5, 2005
    Assignee: Halliburton Energy Services, Inc.
    Inventors: Gary K. Baird, Carl Dodge, Thomas E. Henderson, Francisco Velasquez
  • Patent number: 6794962
    Abstract: The invention reduces the size of waveguide circuits. The invention proposes to change the cross section of a waveguide in a curved part. Thus, a curved element according to the invention makes it possible at the same time to make a change in waveguide cross action.
    Type: Grant
    Filed: October 30, 2002
    Date of Patent: September 21, 2004
    Assignee: Thomson Licensing S.A.
    Inventors: Philippe Chambelin, Jean-François Pintos, Philippe Minard
  • Patent number: 6472951
    Abstract: A series of tuning brackets are mounted on the microwave waveguide manifold at positions between the input waveguide/filter couplings. These brackets constrain the manifold and are constructed with adjustment screws extending through the brackets and mechanically connected to the manifold. The movement of the adjustment screw will tend to deform the manifold dimensions resulting in a fine adjustment of the wavelength (&lgr;) of the multiplexer.
    Type: Grant
    Filed: January 5, 2000
    Date of Patent: October 29, 2002
    Assignee: Space Systems/Loral, Inc.
    Inventors: S. Jerry Fiedziuszko, Stephen C. Holme, Norman L. O'Neal
  • Patent number: 6191664
    Abstract: A manifold is constructed with a primary manifold section to which the input wave guides are connected and a tuning section attached to the output of the primary manifold section. The tuning section is constructed of a deformable material which allows the dimpling of the internal wall to alter the impedance of the waveguide system for the purpose of fine tuning the impedance matching of the manifold.
    Type: Grant
    Filed: May 24, 1999
    Date of Patent: February 20, 2001
    Assignee: Space Systems/Loral, Inc.
    Inventors: Slawomir J. Fiedziuszko, David J. Dunker
  • Patent number: 6075422
    Abstract: A high power microwave or radio frequency network is disclosed which utilizes [2] two movable capacitive probes in order to provide complete vector tuning [in 4 axis by] utilizing the capacitive reactance of the two capacitive probes to provide [2] two tuning axis and the inductive reactance of two fixed inductive posts to provide [the] two additional [axis] axes of tuning, thereby allowing four axes of tuning with the movement of only two members, the capacitive probes. A third capacitive probe/inductive post set can be added to the two probe configuration for extremely high reflection correction at all phase angles.
    Type: Grant
    Filed: June 1, 1998
    Date of Patent: June 13, 2000
    Assignee: R.F. Technologies, Inc.
    Inventor: George M. Harris
  • Patent number: 5939953
    Abstract: An E-H matching apparatus includes an E-plane branch waveguide connected to an E-plane of a waveguide body, an H-plane branch waveguide connected to an H-plane of the waveguide body, and plungers provided in the E-plane branch waveguide and the H-plane branch waveguide, respectively. The plungers are moved to establish impedance matching between the waveguide and a load. The H-plane branch waveguide has a bend portion formed in close proximity to the waveguide body.
    Type: Grant
    Filed: October 7, 1997
    Date of Patent: August 17, 1999
    Assignee: Fujitsu Limited
    Inventors: Toshiya Yogo, Atsushi Okuda, Masaaki Yano, Tomoyuki Mori
  • Patent number: 5908811
    Abstract: This invention pertains to monolithic filters of the band-pass or band-reject type which a single crystal ferroelectric material having an electric field dependent permittivity. The filters are comprised of: a first layer of a single crystal dielectric material; a second layer of a single crystal high T.sub.c superconductor material; a third layer of a single crystal ferroelectric material; and a fourth layer of high T.sub.c superconductive microstrip lines configured into the various filter circuits, including resonator circuits and transformer circuits. The filters are capable of operating at power levels up to 0.5 MW at a temperature slightly above the Curie temperature to avoid hysteresis.
    Type: Grant
    Filed: March 3, 1997
    Date of Patent: June 1, 1999
    Inventor: Satyendranath Das
  • Patent number: 5670918
    Abstract: A waveguide matching circuit in the form of a rectangular tube, open at both ends, and in which a high-frequency signal propagates along a central axis perpendicular to the open end; at least two screws for regulating a capacitive susceptance which are provided along a line having a predetermined angle to the axis line of the waveguide at a predetermined position on a wide face of the waveguide, and are respectively disposed at an interval of one eighth of a guide wavelength .lambda.g in the direction along the axis line; and at least two inductance rods narrowing the width between two internal sidewalls of the waveguide, disposed at the same interval as corresponding capacitive susceptance regulating screws.
    Type: Grant
    Filed: July 23, 1996
    Date of Patent: September 23, 1997
    Assignee: NEC Corporation
    Inventor: Keiichi Umezu
  • Patent number: 5663694
    Abstract: A microwave switch selectively directs a microwave signal along first and second signal paths. The switch includes a microwave transmission member, a microwave chamber formed by the transmission member for containing an ionizable gas, input and output ports formed by the transmission member to communicate with the microwave chamber and a triggered plasma generator which is configured to generate, in response to a voltage trigger signal, a trigger electron density N.sub.t in the gas. The microwave signal increases the trigger electron density N.sub.t to a reflective electron density N.sub.r. Consequently, the microwave signal is reflected along a first path from the input port when the trigger electron density N.sub.t is present and is directed along a second path to the output port when the trigger electron density N.sub.t is absent. A plurality of these microwave switches is arranged to form a tunable microwave short.
    Type: Grant
    Filed: March 8, 1996
    Date of Patent: September 2, 1997
    Assignee: Hughes Electronics
    Inventors: Dan M. Goebel, Joseph Santoru, Robert L. Poeschel, John W. Gerstenberg
  • Patent number: 5473294
    Abstract: A novel planar variable power divider, using waveguide technology, includes two hybrids and two variable phase shifters. The variable power divider includes a variable phase shifter based on a 3 dB hybrid circuit terminated by two sliding non-contacting moveable short circuits. The differential phase spreading of the phase shifter has been reduced to less than one-sixth of typical transmission line dispersion by the compensating short terminations. As a consequence, electrical performance achievable over a 16% bandwidth is significantly improved with respect to heretofore-known variable power dividers. The variable power divider also provides for planar integration, wideband performance, medium-high power handling capabilities and low loss.
    Type: Grant
    Filed: March 6, 1995
    Date of Patent: December 5, 1995
    Assignee: Alenia Spazio S.p.A.
    Inventors: Roberto Mizzoni, Rodolfo Ravanelli
  • Patent number: 5387884
    Abstract: A method and apparatus for adjusting the impedance of an electromagnetic energy-actuated device. An auxiliary test flange includes a substantially planar metallic member. An internal aperture matches the dimensions of the waveguide cavity formed at the mating ports of adjacent electromagnetic energy-actuated devices. The member includes an access groove for a metallic stub, permitting the stub to be inserted from an edge of the member into the aperture. Measurements of energy transfer are made as the stub is inserted to thereby adjust either the capacitive or inductive impedance to energy transfer. After a predetermined degree of energy transfer is observed, one or the other of the devices may be modified by the addition of a permanent auxiliary flange or directly modified in accordance with the optimized aperture reduction.
    Type: Grant
    Filed: July 13, 1993
    Date of Patent: February 7, 1995
    Assignee: Litton Systems, Inc.
    Inventor: John C. Porcello
  • Patent number: 5148131
    Abstract: An end portion (14a) of a center conductor (14) of a coaxial cable (16) protrudes transversely into a tubular waveguide (10) near an end thereof. A piston (22) having a stepped inner wall (24) closes the end of the waveguide (10). The inner wall (24) is formed with two or more steps (24a,24b,24c) which protrude axially into the waveguide (10) by different distances (L1,L2,L3), reducing the return loss and extending the bandwidth of the coaxial cable-to-waveguide transition.
    Type: Grant
    Filed: June 11, 1991
    Date of Patent: September 15, 1992
    Assignee: Hughes Aircraft Company
    Inventors: Kurt Amboss, Stephen L. Hart
  • Patent number: 5138289
    Abstract: A noncontacting waveguide backshort is provided for use with frequencies of interest between 1 and 1000 GHz including a relatively rugged metallic bar movably mounted within the waveguide in a MYLAR insulator. A series of regularly shaped and spaced circular or rectangular openings are made in the metallic bar to form sections of high impedance alternating with sections of the bar having low impedance. This creates a periodic impedance variation which serves to provided an adjustable short circuit in a waveguide for the frequencies of interest.
    Type: Grant
    Filed: December 21, 1990
    Date of Patent: August 11, 1992
    Assignee: California Institute of Technology
    Inventor: William R. McGrath
  • Patent number: 4688008
    Abstract: A waveguide shorting device having a shorting block and a wedge is disclosed. The shorting block contains a channel which is tapered so that it matches a taper of the wedge. A screw extends through the shorting block and engages a threaded hole in the wedge. Tightening the screw causes the wedge to be received in the channel and the shorting block to expand. Expansion of the shorting block clamps the shorting piston in a locked position within a waveguide.
    Type: Grant
    Filed: February 3, 1986
    Date of Patent: August 18, 1987
    Assignee: Motorola, Inc.
    Inventors: David R. Pollard, Robert H. Goldbach
  • Patent number: 4686497
    Abstract: An adjustable waveguide short circuit using a thin partition or rectangular pin parallel to the E-field in the waveguide and movable along longitudinal slots centrally located on the two broad walls of the waveguide.
    Type: Grant
    Filed: June 12, 1986
    Date of Patent: August 11, 1987
    Assignee: GTE Laboratories Incorporated
    Inventor: Douglas D. Tang
  • Patent number: 4631503
    Abstract: A waveguide or waveguide phase shifter is terminated with a short circuit provided by a rigid conductive block which is sized to be a close tolerance fit within the waveguide. The block has grooves in its faces adjacent to the waveguide walls. The walls of the waveguide are deformed to project into these grooves to permanently secure the waveguide to the block.
    Type: Grant
    Filed: June 27, 1985
    Date of Patent: December 23, 1986
    Assignee: RCA Corporation
    Inventor: Paul R. Brown
  • Patent number: 4604592
    Abstract: An electrically controlled radio frequency tuner used in conjunction with an antenna. The antenna used both as a transmitter and a receiver. The tuner eliminating waveform reflection and circulator feedthrough of transmitted signals which heretofore reflected back into the receiver creating a noise threshold that decreased the sensitivity of the receiver.
    Type: Grant
    Filed: April 19, 1984
    Date of Patent: August 5, 1986
    Assignee: The Boeing Company
    Inventor: George T. Pinson
  • Patent number: 4502023
    Abstract: In a method of fabrication of a module formed by a semiconductor diode which oscillates in millimeter waves and by a variable-capacitance diode, the oscillating diode is mounted on a pedestal at the center of a support base. A ring of fused silica for supporting a metallic disk of predetermined diameter serves to form a radial space between two metallic surfaces with a view to readily obtaining oscillation in a predetermined frequency band. A similar ring is welded at one end to the opposite face of the disk and at the other end to another metallic base fitted with a central variable-capacitance diode. Flexible connections bonded to the diodes are clamped between the rings and the disk. The module may be incorporated in a tunable oscillator.
    Type: Grant
    Filed: June 14, 1982
    Date of Patent: February 26, 1985
    Assignee: Thomson-CSF
    Inventor: Michel Heitzmann
  • Patent number: 4465989
    Abstract: In a temperature-stabilized microwave filter, each resonant cavity (5) is tuned by means of a tuning rod (10) of a thermally stable material. A first end of each tuning rod (10) extends into the respective cavity (5) without touching its surface. A second end is clamped, remotely of the cavity (5), into the filter body (1-2). At the position of this second end the filter body (1-2) has a bore (13) of substantially the same diameter as the tuning rod (10). The tuning rods (10) are clamped by pairs of retaining screws (15) accommodated in clearance holes in the filter body on one side of a longitudinal groove (21) intersecting the bore (13) and anchored into the filter body (1-2) on the other side of the groove (21).
    Type: Grant
    Filed: October 20, 1982
    Date of Patent: August 14, 1984
    Assignee: Compagnie Industrielle Des Telecommunications
    Inventors: Jean-Pierre Boujet, Gerard Gaille, Charles Jousselin
  • Patent number: 4380747
    Abstract: The invention relates to ultra-high frequency filters with variable capacitance tuning devices tunable in a wide frequency range.Each tuning device comprises two coaxial fingers, namely a fixed finger and a finger movable in the filter body. One of these fingers is hollow and the other has a tuning plunger, whose end is cylindrical and which is displaceable, e.g. by screwing in the body of the finger. The minimum capacitance obtained with a minimum penetration of the plunger, its end being level in the vicinity of the end of the corresponding finger, is adjustable by displacing the movable finger relative to the fixed finger. The supplementary variable capacitance is obtained by plunging the tuning plunger into the hollow finger.
    Type: Grant
    Filed: February 25, 1981
    Date of Patent: April 19, 1983
    Assignee: Thomson-CSF
    Inventors: Jean C. Curtinot, Xavier Delestre, Jean Fouillet
  • Patent number: 4376923
    Abstract: The tuning device comprises a hollow cylindrical part and a moving rod which penetrates a cavity by passing from one side to the other of the hollow cylindrical member. This cylindrical member is fixed and integral with the cavity. It has an end located within the cavity, the end being longitudinally cut to form n slots (n being an integer greater than 1) for forming n elastic members, which are covered with an electrolytic silver deposit. Joined silver contacts are welded to the end of the elastic members to provide the contact with the moving rod and prevent poor conduction of surface currents due to wear to the electrolytic deposit at the contacts.
    Type: Grant
    Filed: March 4, 1981
    Date of Patent: March 15, 1983
    Assignee: Thomson-CSF
    Inventors: Jean C. Curtinot, Xavier Delestre, Jean Fouillet
  • Patent number: 4293828
    Abstract: An arrangement for suppressing interference waves and harmonic waves in traveling wave tubes has a short circuit slide in an output wave guide in which the slide has a groove in the form of a .lambda./4 or .lambda./2 wave guide element in its frontal surface which is the effective short circuit plane. The groove has an attenuation element arranged therein.
    Type: Grant
    Filed: February 4, 1980
    Date of Patent: October 6, 1981
    Assignee: Siemens Aktiengesellschaft
    Inventor: Franz Gross
  • Patent number: 4240050
    Abstract: In order to cancel unwanted reflected waves in a waveguide system, two micrometer-driven stub tuners are inserted in a waveguide bend. A first tuner is inserted through the outer bend wall to extend axially along one leg of the bend and includes a dielectric rod having a reflecting slug at its tip. Axial movement of the rod permits the variable position of the slug to vary the phase of the wave which it reflects. The second tuner includes a metal rod, which enters the waveguide transversely from the inner wall of the bend, diametrically across from the entrance of the dielectric rod, and permits adjustment of the magnitude of the wave which it reflects.
    Type: Grant
    Filed: June 29, 1979
    Date of Patent: December 16, 1980
    Assignee: Weinschel Engineering Co., Inc.
    Inventor: Robert C. Powell
  • Patent number: 4216450
    Abstract: The present invention relates to millimeter waveguide shorts and methods for making said shorts wherein an exemplary rectangular cross-sectioned waveguide short comprises a base substrate such as steel shimstock or foil having a width equal to the associated millimeter waveguide, a raised portion disposed laterally on both sides of the substrate at alternate quarter-wavelength sections adjacent one end of the substrate. The raised portions comprise a first layer of good electrically conductive material disposed on the substrate and a second layer of an insulating material formed atop the first layer. Alternatively, the exposed substrate sections can be gold plated. A preferred method comprises the steps of masking alternate quarter-wavelength sections of the exposed major surfaces adjacent one end of the substrate, depositing the first layer material on the unmasked quarter-wavelength sections and depositing the second layer material on the exposed major surfaces of the first layer material.
    Type: Grant
    Filed: November 1, 1978
    Date of Patent: August 5, 1980
    Assignee: Bell Telephone Laboratories, Incorporated
    Inventors: Richard A. Linke, Martin V. Schneider
  • Patent number: H1244
    Abstract: A device for absorbing resonances in a large circular cavity such as a microwave rotary joint that utilizes a horizontally positioned resonance absorber positioned in the balun cavity to absorb the resonances or undesired modes. The resonance absorber forms a folded slot with a resistor across its arms to interrupt the circumferential flow of current in the rim of the cavity without affecting the normal desired mode.
    Type: Grant
    Filed: October 30, 1992
    Date of Patent: October 5, 1993
    Assignee: United States of America
    Inventor: Gary E. Evans