GB2501881A - A reconfigurable electromagnetic band gap impedance surface - Google Patents

A reconfigurable electromagnetic band gap impedance surface Download PDF

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Publication number
GB2501881A
GB2501881A GB201208008A GB201208008A GB2501881A GB 2501881 A GB2501881 A GB 2501881A GB 201208008 A GB201208008 A GB 201208008A GB 201208008 A GB201208008 A GB 201208008A GB 2501881 A GB2501881 A GB 2501881A
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United Kingdom
Prior art keywords
conductors
impedance
ebg
reconfigurable
load
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GB201208008A
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GB201208008D0 (en
Inventor
Nathan Clow
Ivor Leslie Morrow
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UK Secretary of State for Defence
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UK Secretary of State for Defence
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Priority to GB201208008A priority Critical patent/GB2501881A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H01Q15/006—Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces
    • H01Q15/0066—Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces said selective devices being reconfigurable, tunable or controllable, e.g. using switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
    • H01Q17/007—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems with means for controlling the absorption

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Abstract

A reconfigurable electromagnetic band gap (EBG) impedance surface comprises a plurality of conductive patches Pal - Pa6 disposed as an array above a ground plane GP with conductive pipes Pi1 Pi6 extending from respective patches. Conductors C1 C6 are arranged to extend into each respective conductive pipe Pi1 Pi6 without any direct connection to the pipe. Load impedances Za1 Za6, Zb1 Zb6 are provided for connection to the conductors C1-C6 such that the load impedance to at least one of the conductors can be independently adjusted in value relative to that of at least one of the other conductors. The values of the impedances are varied electrically, for example by electrically switching between different load impedances using switching circuitry SW1 SW6, and/or by electrically controlling a variable load impedance using varying circuitry. The load impedances may be capacitive and/or inductive and/or resistive, LC resonators, open circuit or short circuit terminations. Circuit board and dielectric materials may be used in the construction of the impedance surface. Some surface elements may be switched to an antenna feed AF3, AF4 and are able to send and/or receive radio frequency signals.

Description

RECONFIGURABLE ELECTROMAGENTIC BAND GAP IMPEDANCE
SURFACE
Technical Field of the invention
This invention rdates to an electromagnetic band gap (EBG) impedance surface, in particular to a reconfigurable EBG impedance surface.
Background to the Invention
A known EBG impedance surface comprises a plurality of conductive patches above a ground plane, each conductive patch being connected to the ground plane by a conductor.
The EBG impedance surface substantially prevents the propagation of electromagnetic signals along the impedance surface over a band gap of electromagnetic frequencies, depending upon the geometry of the EBO impedance surface. For a detailed discussion of EBG impedance surfaces, refer to Sievenpiper, D, "High-Impedance Electromagnetic Surfaccs", Ph.D Disscrtation, Dcpt. Of Elcctrical Enginccring, LTnivcrsity of California, Los Angeles, CA, 1999.
EBG impedance surfaces can be used to provide low-profile antenna arrangements, with the band gap of the impedance surface being set to correspond to the frequency at which the antenna is driven. EBG impedance surfaces also find applications in beam-steering, wherein the reflection phase of an incoming signal may be varied across an EBG impedance surface by varying the values of various capacitances connected between the conductive patches of the EBG impedance surface, for example refer to US Patent Application Publication No. US 10/0066629.
GB Patent No. 2471010 of the same Applicant as the present application discloses an alternative EBG impedance surface that is provided by a plurality of ultra-wideband top-loaded monopole antenna arrangements that are grounded in a two-dimensional scattenng array surface. Such an impedance surface can exhibit a wider bandwidth band gap than previously known impedance surfaces.
I
It would be desirable to control the band gap of such a wide band EBG impedance surface, however known tuning techniques such as that described in US 20 10/0066629 of providing varactors between the conductive patches and biasing the conductive patches with voltages to set the capacitance of the varactors, or of that described in US2003/0052757 of altering the distance between the ground plane and the conductive patches, are inherently unsuited to the geometry of such a wide band EBG impedance surface.
In particular, in such a wide band EBG impedance surface there may not be any electrically conductive connection to the top-loading of the antenna arrangements for applying a bias voltage to varactors, and shieldings around the antenna alTangement monopoles may prevent much relative movement between the top loadings and the ground plane.
Altering the distance between the ground plane and the conductive patches as disclosed in US2003/0052757 also means that the impedance of all of the conductive patches are affected at the same time, which may be problematic for beam steering applications where different conductive patches need to be altered differently.
It is therefore an aim of the invention to provide an improved EBG impedance surface having a controllable band gap.
Summary of the Invention
According to an embodiment of the invention, there is provided a reconfigurable Electromagnetic Band Gap (EBG) impedance surface comprising: a plurality of conductive patches disposed in an array above a ground plane; a plurality of conductive pipes extending from respective ones of the conductive patches; a plurality of conductors extending into respective ones of the conductive pipes in a direction away from the ground plane, each conductor being electrically insulated from the respective conductive pipe; and load impedances suitable for connecting to the conductors, the value of load impedance to which at least one of the conductors is connected being independently electrically variable from the value of load impedance to which at least another one of the conductors is connected.
Accordingly, the band gap of the EBU impedance surface may be varied by altering the values of the impedances connected to the conductors. The values of the impedances are varied electrically, for example by electrically switching between different load impedances using switching circuitry, and/or by electrically controlling a variable load impedance using varying circuitry. This enables the values of the impedances to be easily changed. The load impedances connected to the conductors maybe independently varied to enaNe different areas of the EBG impedance surface to be set to different band gaps according to the particular application.
The load impedances may be at an opposite side of the ground plane from the plurality of conductive patches, with the plurality of conductors extending via through-holes in the ground p'ane. Placing the load impedances on the other side of the ground plane helps shield the load impedances and associated circuitry from the signals flowing on the conductive patches.
Advantageously, the plurality of load impedances may for example comprise one or more of capacitive load impedances. inductive load impedances. LC resonators, short circuit and open circuit terminations, or resistive load impedances.
There is no requirement for eveiy one of the conductors to be connected to a load impedance.
For example. one or more of the conductors may be connected to antenna feed point(s) instead of one or more of the load impedances.
The reconfigurable EBO impedance surface may further comprise control circuitry for setting the load impedances and/or antenna feed points that are connected to the various conductors.
For example. the control circuitry may be configured to set a first group of one or more of the conductors to be connected to the antenna feed point; a second group of the conductors surrounding the first group of the conductors to be connected to a first value of load impedance; and a third group of the conductors surrounding the second group of conductors to be set to a second value of load impedance different to the first value of load impedance.
The conductive patches above the second group of conductors may couple with the conductive patches above the first group of conductors to coflectivdy act as a patch antenna, and the conductive patches above the third group of conductors may act as an insulating region around the patch antenna, the second group of conductors being connected to load impedances allowing the corresponding conductive patches to conduct a particular frequency band of signals, and the third group of conductors being connected to load impedances preventing the corresponding conductive patches from conducting the particular frequency band of signals. Furthermore, the control circuitry may set the number of conductors in the second group differently for different frequency band signals, thereby controlling the effective dimensions of the patch antenna.
Brief Description of the Drawings
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Fig. I shows a schematic cross-sectional diagram of an EBU element suitable for forming a reconfigurable EBG impedance surface according to an embodiment of the invention; Fig. 2 shows a schematic plan diagram of the EBU element of Fig. I; Fig. 3 shows a schematic cross-sectional diagram of a reconfigurable EBG impedance surface according to an embodiment of the invention, formed with a plurality of the EBG elements of Fig.]; and Fig. 4 shows a schematic plan diagram of the reconfigurable EBG impedance surface of Fig. 3.
Detailed Description
The cross-sectional diagram of Fig. I shows an EBU element 100 suitable for forming an EBU impedance surface according to an embodiment of the invention. The EBG element 100 has a conductive patch Pa and a conductive pipe Pi, the conductive pipe Pi extending from the conductive patch Pa in a direction perpendicular to the conductive patch Pa, and being directly attached thereto. The conductive pipe Pi is filled with a dielectric material D that extends down to a ground plane GP, and that helps supports the conductive pipe Pi over the ground plane UP. The conductive pipe Pi is insulated and spaced apart from the ground plane CF by the dielectric material.
A conductor C extends into the pipe Fi, in a direction Dir away from the ground plane UP.
The conductor C is electrically insulated from the conductive pipe Pi by the dielectric material D. In an alternate embodiment, the dielectric material D may not extend all of the way down to the ground plane UP, and the dielectnc material D, conductive pipe Pi, and conductive patch Pa may simply be suppor ed by the conductor C. The conductor C passes through the ground plane UP via a through-hole TH, and at an opposite side of the ground plane from the conductive patch Pa the conductor C is connected to a load impedance Za via a switch SW. The switch SW cou'd alternatively connect the conductor C to an antenna feed AF, or to another impedance Zb, by changing the switch from the switch connection Sa to the switch connections Sb or Sc. The through hole TH allows the conductor C to pass through the ground plane without electrically connecting to the ground plane, In practice the conductor C may be formed in three sections, one section below the ground plane, one section above the ground plane, and one section passing through the ground plane, such as a via.
In this embodiment, the impedance Za is an inductive impedance and the impedance Zb is a capacitive impedance. The inductance value of the inductance Za is variable according to the variance signal Va, and the capacitance value of the capacitance Zb is variable according to the variance signal Vb. Therefore, a wide range of different impedances can be applied to the conductor C by selecting either the inductive impedance Za or the capacitive impedance Zb, and setting the actual value of the sdected impedance using either Va or Vb as appropriate.
The plan diagram of Fig. 2 shows a top view of the EBU element 100 of Fig. 1. The conductive patch Pa is square, the conductive pipe Pi has a circular cross section, and the conductor C extends along the longitudinal axis of the circubr pipe. Other combinations of conductive patch andlor conductive pipe shapes are also possible, for example rectangular or triangular shapes.
In use, electromagnetic energy is coupled between the conductor C and the patch Pa/pipe P1 of the EBG element. Therefore, the EBG element can receive and/or send electromagnetic energy via the conductor C. An embodiment of the invendon will now be described with reference to the cross-sectional diagram of Fig. 3, which shows six of the EBG elements 100 of Fig. I formed using two PCB's (Pnnted Circuit Boards) TL and BL. The reference signs used in relation to Fig. 1 are also used in Fig. 3, but with a number from 1 -6 appended to them according to which one of the six EBG elements they refer to. For example. the conductive patch Pa of each EBG element is labelled from Pal to Pa6. Not all of the possible reference signs are shown on Fig. 3 for the sake of clarity.
The top PCB TL has a plura'ity of conductive patches Pal -Pa6 formed upon it in an array above the ground plane GP. A plurality of respective conductive pipes Pil -Pi6 (only Pil and Pi6 explicitly marked in Figs) extend from the plurality of conductive patches Pal -Pa6.
A plurality of conductors CI -C6 (only Cl and C6 explicitly marked in Figs) extend into respective ones of the conductive pipes Pil -Pi6 in a direction away from the ground plane GP. Each conductor Cl -C6 is electrically insulated from the respective conductive pipe Pil -Pi6.
The ground plane GP is formed upon the bottom PCB BL, and has through-holes for the conductors Cl -C6 to pass therethrough and into a switching layer SL of the PCB BL. The switching layer comprises switching circuitry of switches SW1 -5W6 (only SW1 and SW3 explicitly marked in Figs). The state of the switching circuitry determines which load impedances Zal -Za6 (only Zal and Za2 explicitly marked in Figs) and Zb I -Zb6 (only Zbl and Zb2 explicitly marked in Figs) that each of the conductors Cl -C6 are connected to.
The load impedances Zal -Za6 and Zbl -Zb6 are formed in a load impedance layer ZL of the PCB BL, beneath the switching layer SL.
Each switch SWI -SW6 has corresponding switch connections Sal -Sa6 (only 5a5 and Sa6 explicitly marked in Figs). Sbl -Sb6 (only Sb5 and Sb6 explicitly marked in Figs), and Sd -Sc6 (only Sc5 and Sc6 explicitly marked in Figs), to which the switch may connect the conductors Cl -C6. Each switch connection is connected to one of the impedances Zal -Za6. Zbl -Zb6. or to an antenna feed AF1 -AF6.
Each one of the impedances Zal -Za6 is independently variable by corresponding variance signals Val -Va6 (only Va3 and Va4 explicitly marked in Figs), and each one of the impedances Zbl -Zb6 is independently variable by corresponding variance signals Vbl - Vb6 (only Vb3 and Vb4 explicitly marked in Figs). The impedances Zal -Za6 and Zbl -Zb6 each comprise varying circuitry for varying their impedance values according to the signals Val -Va6 and Vbl -Vb6.
The value of load impedance to which each of the conductors CI -C6 is connected is independently electrically variable from the value of load impedance to which at least another one of the conductors Cl -C6 is connected, either by switching the switches SWI -SW6, or by altering the variance signals Val -Va6 or Vbl -Vb6, or by any combination thereof.
The state of the switching circuitry SW I -SW6 is controlled by a control circuitry CC in a control layer CL of the PCB BL. Switch control signals for the switches SW1 -5W6 are passed from the control circuitry CC to the switch circuitry SW1 -SW6 via switch control SCTL. The control circuitry CC also generates the variance signals Val -Va6 and Vbi -Vb6, and so can independently control which impedance each conductor Cl -C6 is connected to, and what value that impedance is set at.
The antenna feeds AFI -AF6 (only AF3 and AF4 explicitly marked in Figs) are connected to an antenna feed point AEP, which sends/receives any antenna signals to/from the conductive patches Pal -Pa6. The antenna feed point is also controlled by the control circuitry CC, and may send/receive antenna signals via the antenna feed point.
The state of the switching circuitry SWI -SW6 is shown with Cl, CS, and C6 connected to Zal, Za5, and Za6 (inductive impedances), with C2 and C4 connected to Zb2 and Zb4 (capacitive impedances), and with C3 connected to the antenna feed point AFP via antenna feed AF3. hi use the antenna feed point AFP receives a radio signa' from the control circuit CC, and the radio signal is transmitted from the conductive patch Pa3. The signals Vb2 and Vb4 set the load impedances Zb2 and Zb4 to a small value of shunt capacitance, moving the band gap of the conductive patches Pa2 and Pa4 to a higher frequency than the band of the radio signal, and allowing the conductive patches Pa2 and Pa4 to couple to and transmit the radio signal. The signals Val. Va5, and Va6 set the load impedances Zal, ZaS, and Za6 to a small value of shunt inductance, moving the band gap of the conductive patches Pal, Pa5, and Pa6 down into the band gap of the radio signal, and preventing propagation of the radio signal over those conductive patches.
The conductive patches thereby form a patch antenna, the conductive patches Pa2, Pa3, and Pa4 together forming the patch of the antenna, and the conductive patches Pal, Pa5, and Pa6 forming an ins&ating area around the patch of the antenna (since their band gap corresponds to the band of the radio signal). The size of the antenna patch may be varied according to the number of conducive patches Pa that are connected to a small capacitive impedance Zb, and so the size of the antenna patch may be set to suit the particular frequency band of the radio signal by switching the switch circuitry SW and controlling the variance signals Vb.
Many other possible applications for the independently variable impedance values will also be apparent to those skilled in the art, for example in beamforming, phased antenna arrays, directional reflector arrays.
Fig. 4 shows a schematic plan diagram of the BBG impedance surface of Fig. 3. The cross section of Fig. 3 is taken along the fine A-A marked on Fig. 4. Each conductive patches of the EBO impedance surface is labelled as being in one of three different groups, Cl -G3. The conductive patches Pa31, Pa3, and Pa32 labelled as being in the group Gl are connected to the antenna feed AF, and may be driven at different phases to provide beam-steering if desired. The different phases could for example be generated by the control circuitry CC controlling a switch connected to the conductor for the conductive patch Pa3 I to an inductive impedance Za in addition to the antenna feed AF, and by the control circuitry CC controlling a switch connected to the conductor for the conductive patch Pa32 to a capacitive impedance Zb in addition to the antenna feed AF.
The conductive patches labelled G2 all have their conductors connected to a small value of shunt capacitance, moving the band gap of the conductive patches G2 to a higher frequency than the band of the radio signal, and allowing the conductive patches G2 to couple to and transmit the radio signal. The conductive patches G2 according'y form a patch antenna having effective dimensions of three conductive patches wide by three conductive patches long. More or tess conductive patches may be configured to be within the group 02 to vary the effective size of the patch according to the band of the radio signal that is to be transmitted.
The conductive patches labelled 03 all have their conductors connected to a small value of shunt inductance, moving the band gap of the conductive patches G3 down into the band gap of the radio signal, and preventing propagation of the radio signal over those conductive patches. The conductive patches 03 therefore form a boundary around the patch antenna formed by the conductive patches 02.
In further embodiments, the number of conductive patches may be increased to increase the size of the EBO impedance surface, and mutipe patch antennas maybe formed on the EBO surface. Conductive patches between the patch antennas may be configured to prevent the patch antenna signals from propagating across the EBG impedance surface and interfering with one another.
Although the specific embodiment shows the EBG impedance surface formed by two PCB's, the use of PCB's is not essential and other supporting means for the various components and connections could alternatively be used. The PCB TL could be omitted entirely with the conductive patches and pipes being supported above the PCB BL by the didectric materiah Dl -D6 (on'y D2 and D3 expficitly marked in Figs).
Clearly, many other types of EBG element are also possible, for example the switches may not be implemented and the impedance value may be altered by varying the value of an impedance that is permanently connected to one of the conductors Cl -C6. The possibility to connect to an antenna feed may also not be available. The number of switch connections that the switch SW selects between may be only two, or may be greater than three. The switch SW maybe capable of connecting to more than one of the switch connections at the same time, for example if the switch SW is connected to the switch connections Sa and Sb at the same time then the conductor C is connected to both the impedance Za and the antenna feed AF at the same time, so that the impedance Za can alter the phase of a signal from the antenna feed AR The switch SW may be connected to both Za and Zb at the same to form an LC resonant circuit, for example if Za is inductive and Zb is capacitive. Although the specific embodiment has been described with reference to inductive and capacitive load impedances, other types of load impedance such as resistive impedance and open or short circuit terminations could alternatively, or additionally, be used depending on the particular application.
Although all the EBU elements of the reconfigurable EBU impedance surface are shown to be the same as one another in the specific embodiments, the EBG elements could be different to one another depending upon their expected function. For example only one or a few EBG elements of an EBG impedance surface may have the option to connect to an antenna feed.
and offly one or a few of the EBG elements may have the option to connect to particular types or values of load impedance.
Further embodiments falling within the scope of the appended claims will also be apparent to those skilled in the art.

Claims (16)

  1. CLAIMS1. A reconfigurable Electromagnetic Band Gap IEBG) impedance surface compnsing: a plurality of conductive patches disposed in an array above a ground plane; a plurality of conductive pipes extending from respective ones of the conductive patches; a plurality of conductors extending into respective ones of the conductive pipes in a direction away from the ground plane, each conductor being electrically insulated from the respective conductive pipe; and load impedances suitable for connecting to the conductors, the value of load impedance to which at least one of the conductors is connected being independently electrically variable from the value of load impedance to which at least another one of the conductors is connected.
  2. 2. The reconfigurable EBG impedance surface of claim 1, wherein the value of load impedance to which at least one of the conductors is connected is independently electrically variable from the value of load impedance to which at least another one of the conductors is connected by the reconfigurable EBU impedance surface further comprising switching circuitry for connecting different ones of the load impedances to the conductors.
  3. 3. The reconfigurable EBG impedance surface of claim I or 2, wherein the value of load impedance to which at least one of the conductors is connected is independently electrically variable from the value of load impedance to which at least another one of the conductors is connected by the reconfigurable EBU impedance surface further comprising varying circuitry for valying the impedance va'ue of load impedances connected to the conductors.
  4. 4. The recontigurable EBG impedance surface of any preceding claim, wherein the load impedances are at an opposite side of the ground plane from the plurality of conductive patches, and wherein the plurality of conductors extend via through-holes in the ground plane.
  5. 5. The reconfigurable EBG impedance surface of any preceding claim, wherein the plurality of load impedances comprise capacitive load impedances and inductive load impedances.
  6. 6. The reconfigurable EBG impedance surface of any preceding claim, wherein the plurality of load impedances comprise LC resonators.
  7. 7. The reconfigurable EBG impedance surface of any preceding claim, wherein the plurality of load impedances comprise short circuit and open circuit terminations.
  8. 8. The reconfigurable EBG impedance surface of any preceding claim, wherein the plurality of load impedances comprise resistive load impedances.
  9. 9. The reconfigurable EBG impedance surface of any preceding claim, wherein the plurality of conductive pipes are each spaced apart from the ground plane by dielectnc material.
  10. 10. The reconfigurable EBG impedance surface of any preceding claim, wherein each conductive pipe is electrically insulated from the respective conductor by a respective dielectric material.
  11. 11. The reconfigurable EBG impedance surface of any preceding claim, further comprising an antenna feed point suitable for connecting to one or more of the conductors.
  12. 12. The reconfigurable EBG impedance surface of claim 11, further comprising antenna switching circuitry for connecting the antenna feed point to selected ones of the conductors.
  13. 13. The reconfigurable EBG impedance surface of any preceding claim, further comprising control circuitry configured to control the toad impedance values connected to the conductors.
  14. 14. The reconfigurable EBG impedance surface of claim 13 when appended to claim 12, or claim 13 when appended to claim II, wherein the control circuitry is further configured to control which conductors are connected to the antenna feed point.
  15. 15. The reconfigurable EBG impedance surface of claim 14, wherein the control circuitry is configured to set: a first group of one or more of the conductors to be connected to the antenna feed point; a second group of the conductors surrounding the first group of the conductors to be connected to a first value of load impedance; and a third group of the conductors surrounding the second group of conductors to be set to a second value of load impedance, and wherein the control circuitry sets the number of conductors in the second group differently for different frequency band signals at the antenna feed point.
  16. 16. A reconfigurable EBG impedance surface substantially as described herein with reference to the accompanying drawings.
GB201208008A 2012-05-08 2012-05-08 A reconfigurable electromagnetic band gap impedance surface Withdrawn GB2501881A (en)

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GB2501881A true GB2501881A (en) 2013-11-13

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003047030A1 (en) * 2001-11-27 2003-06-05 Sciperio, Inc. Multiband or broadband frequency selective surface
US20030112186A1 (en) * 2001-09-19 2003-06-19 Sanchez Victor C. Broadband antennas over electronically reconfigurable artificial magnetic conductor surfaces
US6806846B1 (en) * 2003-01-30 2004-10-19 Rockwell Collins Frequency agile material-based reflectarray antenna
US20040263420A1 (en) * 2003-04-11 2004-12-30 Werner Douglas H Pixelized frequency selective surfaces for reconfigurable artificial magnetically conducting ground planes
US20070182639A1 (en) * 2006-02-09 2007-08-09 Raytheon Company Tunable impedance surface and method for fabricating a tunable impedance surface
GB2471010A (en) * 2009-06-09 2010-12-15 Secr Defence An electrically small, ultra-wideband, top-loaded monopole antenna

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030112186A1 (en) * 2001-09-19 2003-06-19 Sanchez Victor C. Broadband antennas over electronically reconfigurable artificial magnetic conductor surfaces
WO2003047030A1 (en) * 2001-11-27 2003-06-05 Sciperio, Inc. Multiband or broadband frequency selective surface
US6806846B1 (en) * 2003-01-30 2004-10-19 Rockwell Collins Frequency agile material-based reflectarray antenna
US20040263420A1 (en) * 2003-04-11 2004-12-30 Werner Douglas H Pixelized frequency selective surfaces for reconfigurable artificial magnetically conducting ground planes
US20070182639A1 (en) * 2006-02-09 2007-08-09 Raytheon Company Tunable impedance surface and method for fabricating a tunable impedance surface
GB2471010A (en) * 2009-06-09 2010-12-15 Secr Defence An electrically small, ultra-wideband, top-loaded monopole antenna

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