GB2408152A - Optically controlled transmission line component - Google Patents

Optically controlled transmission line component Download PDF

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Publication number
GB2408152A
GB2408152A GB0326333A GB0326333A GB2408152A GB 2408152 A GB2408152 A GB 2408152A GB 0326333 A GB0326333 A GB 0326333A GB 0326333 A GB0326333 A GB 0326333A GB 2408152 A GB2408152 A GB 2408152A
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United Kingdom
Prior art keywords
transmission line
line component
conductive element
photoconductive material
terminal portion
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Granted
Application number
GB0326333A
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GB0326333D0 (en
GB2408152B (en
Inventor
Yiannis Costas Vardaxoglou
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ANTRUM Ltd
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ANTRUM Ltd
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Priority to GB0326333A priority Critical patent/GB2408152B/en
Publication of GB0326333D0 publication Critical patent/GB0326333D0/en
Publication of GB2408152A publication Critical patent/GB2408152A/en
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Publication of GB2408152B publication Critical patent/GB2408152B/en
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/2676—Optically controlled phased array
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/18—Phase-shifters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/18—Phase-shifters
    • H01P1/184—Strip line phase-shifters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P3/00—Waveguides; Transmission lines of the waveguide type
    • H01P3/02—Waveguides; Transmission lines of the waveguide type with two longitudinal conductors
    • H01P3/08—Microstrips; Strip lines

Abstract

The transmission line comprises two microstrip conductors 12, 21 separated by a dielectric substrate 40. A photoconductive silicon die 50 is placed over a gap in the microstrip 21 and is coupled to the terminal portion 31 of the conductor 21. The photoconductive material is illuminated by a infrared LED 60 to cause phase delay or insertion loss. A plurality of such components may be used as the delay elements in a steerable beam antenna.

Description

24081 52 An opticaliv controllable transmission line component Embodiments
of the present invention relate to optically controllable transmission line components.
It would be desirable to be able to optically control the electrical properties of a transmission line. Optical control is very fast, immune to electrical interference and will not couple with the signal carried by the transmission line.
Current research into the optical control of the electrical properties of transmission line concentrates on using a bulk silicon substrate as the dielectric separating the transmission line from the ground plate. The transmission line runs along the upper surface of the silicon substrate and has a gap that is bridged by the underlying silicon substrate. The illumination of the silicon in the gap has some effect on the electrical properties of the transmission line.
However, such a technique is inefficient as it requires high power illumination. It is also difficult to control changes in the electrical properties of the transmission line.
According to one aspect of the present invention there is provided an optically controllable transmission line component comprising: a first conductive element; a second conductive element; a dielectric substrate separating the first conductive element and the second conductive element; and photoconductive material coupled to the second conductive element, wherein controlled illumination of the photoconductive material controls the electrical properties of the transmission line component.
Such a configuration is surprisingly sensitive to illumination and can be operated at low powers of illumination. 4 l
! 2 l The insertion loss of the transmission line component may be j controlled by controlling the intensity of the incident radiation illuminating the I photoconductive material.
The delay or phase shift introduced into the transmission line by the transmission line component may be controlled by controlling the intensity of the incident radiation illuminating the photoconductive material.
For a better understanding of the present invention reference will now be made by way of example only to the accompanying drawings in which: Fig 1A is a schematic illustration, in plan view, of a first transmission line component; Fig 1B is a schematic illustration, in side view, of the first transmission line component; Fig 2 is a schematic illustration o'f a steerable beam antenna; Fig 3A is a schematic illustration, in plan view, of a second transmission line component that is operable as a resonator; Fig 3B is a schematic illustration, in side view, of the second transmission line component that is operable as a resonator; Fig. 4 is a schematic illustration, in plan view, of a third transmission line component that is operable as an optical switch; Fig. 5 is a schematic illustration, in plan view, of a fourth transmission line component that is operable as an optically controllable phase shifter; Fig. 6 is a schematic illustration, in plan view, of a fourth transmission line component that is operable as an optically switchable antenna. \
The below described embodiments optically change the dielectric properties of a photoconductive material. The complex pemmittivity, and hence the characteristic impedance, of a semiconductor die is varied by the application of optical energy. This can be used to control the speed of electromagnetic wave propagation along a microstrip transmission line and/or the insertion loss of a component of the transmission line. The transmission line typically carries electromagnetic waves at a frequency from DC up to several THz.
Fig. 1A, 1B, 3A, 3B, 4, 5 and 6 each schematically illustrate an optically controllable microwave transmission line component 10 comprising: a reference conductive element 12 such as a ground plate; a first microstrip conductor 21 that terminates at a first terminal portion 31; a dielectric substrate 40 separating the reference conductive element 12 and the first microstrip conductor 21; and photoconductive material 50 electrically coupled to the temminal portion 31 of the first microstrip conductor 21, wherein controlled illumination of the photoconductive material, for example by IR LED 60, controls the electrical properties of the transmission line component 10 such as phase delay and/or insertion loss.
In one particular example, a first IR LED is mounted over the photoconductive material 50. The IR LED used has a mid-wavelength of 880nm, and 100mW peak power. The first photoconductive material was provided by a die of high resistivity bulk silicon. The die had a thickness of 300um and a resistivity >6000 Ohmcm. The major surface of the die is passivated (with an oxide or nitride layer), which means that less power is required from the LED. The microstrip conductors 21, 22 are copper interconnect formed on the upper surface of the dielectric substrate 40. The copper interconnect was 10um thick. The dielectric substrate used was RT Duroid which was1.25mm thick and has a relative permittivity of 2.2.
Embodiment of Fin. 1A and 1B Referring to Fig. 1A and 1B, the transmission line component 10, I further comprises a second microstrip conductor 22 that terminates at a second terminal portion 32. The second terminal portion 32 opposes the first terminal portion 31 of the first microstrip conductor 21 across a gap 42. The photoconductive material 50 couples to both the first terminal portion 31 and the second terminal portion 32. The photoconductive material 50, in this example, is a silicon die that overlies both the first temminal portion 31 and the second temminal portion 32 and bridges the gap 42.
Embodiment of Fin 2 Referring to Fig. 2, there is disclosed a steerable beam antenna 100. A transmission line 110 connects a plurality of antenna elements 102, 104 in parallel. The antenna elements may be patch antennae and are preferable of the same size and dimensions.
A first delay element 106 is connected prior to the input node 107 of a first antenna 102. A second delay element is connected between the input node 107 to the first antenna 102 and the input node 109 to the second antenna 104.
The input to a first antenna element 102 is consequently delayed by the first delay element 106. The input to the second antenna element 104 is consequently delayed by the first delay element 106 and the second delay element 108. Varying the delay introduced by the delay elements steers the radiation beam created by the multiple antenna elements.
Only two antenna elements and two delay elements are illustrated in the Figure for conciseness. However, the steerable antenna may have multiple antenna elements each with an associated delay element prior to its input node.
i' The delay elements 106 and 108 may be provided by first and second Itransmission line components 10 as described herein in relation to Figs 1A, j1B, 3A, 3B, 4 and 5. Such a transmission line component 10 may be used as a tuneable phase shifter or delay line, where the phase introduced is dependent upon the radiation intensity illuminating the semiconductor material portion(s) 50, 52. Increasing the light intensity typically decreases the delay.
In an alternative configuration, the delay elements are arranged in parallel connection and each delay element is connected in series with an antenna element.
Embodiment of Fin 3 Referring to Figs. 3A and 3B, the transmission line component 10, further comprises a second microstrip conductor 22 that terminates at a second terminal portion 32 and a third terminal portion 33; and a third microstrip conductor 23 that terminates at a fourth terminal portion 34.
The second terminal portion 32 of the second microstrip conductor 22 opposes the first terminal portion 31 of the first microstrip conductor 21 across a gap 42. First photoconductive material 50 electrically couples to both the first terminal portion 31 and the second terminal portion 32. The first photoconductive material 50, in this example, is provided by a first silicon die that overlies both the first terminal portion 31 and the second terminal portion 32 and bridges the gap 42.
The third terminal portion 33 of the second microstrip conductor 22 opposes the fourth terminal portion 34 of the third microstrip conductor 23 across a gap 44. Second photoconductive material 52 electrically couples to both the third terminal portion 33 and the fourth terminal portion 34. The second photoconductive material 52, in this example, is provided by a second silicon die that overlies both the third terminal portion 33 and the fourth terminal portion 34 and bridges the gap 44.
The length of the second conductor 22 defines a resonant frequency of the transmission line component 10. The passband at a resonant frequency is determined by the length of the second conductor. The length equals '/.
wavelength in the dielectric substrate 40.The resonant frequency is typically within the microwave range of frequencies, but the principle is applicable to any frequency.
The described transmission line component 10 may form an optically tuneable resonator or an optically switchable bandpass filter. Illuminating the semiconductor materials 50, 52 changes the passband of the resonator.
In one particular example, a first IR LED is mounted over the first photoconductive material 50 and a second IR LED is mounted over the second photoconductive material 52. The IR LED used in this example has a mid-wavelength of 880nm, and 100mW peak power.
The first and second photoconductive material were provided by separate dies of high resistivity bulk silicon. The die had a thickness of 300um and a resistivity >6000 Ohmcm. The major surface of the die are passivated (with an oxide or nitride layer), which means that less power is required from the LED.
The microstrip conductors 21, 22, 23 are copper interconnect formed on the upper surface of the dielectric substrate 40. The copper interconnect was 1 Oum thick. The dielectric substrate used was RT-Duroid which was1. 25mm thick and has a relative permittivity of 2.2.
In operation, the exemplary resonator, at 4GHz, provides a delay of 2ns with no illumination and a delay 0.5ns when the IP LEDS are at 1/2 full power. The insertion loss of the resonator is low at 3dB.
The operation of the transmission line component 10 can be improved by the introduction of a secondary periodic conductive structure. In one implementation, a regular periodic arrangement of conductors is formed on the upper surface of the dielectric 40, surrounding but not touching the microstrip conductors 21, 22, 23. In another implementation, a conductive layer 41 is placed within the dielectric layer 40 just below the microstrip conductors 21, 22, 23. The conductive layer, illustrated in Fig. 3B by dotted S line 41, is parallel to the conductive microstrips. It has a plurality of regularly shaped holes arranged in a periodic two dimensional array. The holes may, for example, have the shape of a Jerusalem Cross. In an alternative implementation, the conductive layer 41 is replaced by a thin dielectric layer that has within it a plurality of regularly shaped conductive elements arranged as a periodic two dimensional array. The use of a secondary periodic conductive structure may also be used with the transmission line components of Figs. 1, 4, 5 and 6.
Embodiment of Fins 4 Referring to Fig. 4, the transmission line component 10 includes multiple identical dipole elements 60. Each of the dipole elements has first and second portions arranged symmetrically on either side of a microstrip 62.
Each of the first and second portions of the dipole elements 60 has a first microstrip conductor 21 that terminates at a first terminal portion 31 and overlies a dielectric substrate 40 and photoconductive material 50 (e.g. a silicon die) electrically coupled to the terminal portion 31 of the first microstrip conductor 21.
The first terminal portion 31 of the first microstrip conductor 21 terminates a dipole element 60 when the silicon die 50 is not illuminated and the photoconductive material 50 terminates the dipole element 60 when the silicon die is illuminated. The transmission line component 10 consequently has a greater insertion loss when it is illuminated. The insertion loss can therefore be controlled by the simultaneous illumination of the silicon dies at the ends of each of the dipoles 60.
In one particular example, the microstrip 82 is formed from copper and has a 50 ohm impedance. Ten dipole pairs are arranged symmetrically on either side either side of the copper microstrip 82. The microstrip 82 is 4.4 mm wide and the dipoles are 31 mm long and 1 mm wide. The separation between dipoles is about 5.0mm. The silicon die extension have a size of 1 mm x 5mm.
A high power IR LED with a mid range wavelength of 880nm and a peak power of 100mW is positioned over each silicon die extension 50. At 3.8 GHz, there is a switching of 25dB from the non-illuminated state to the state in which the LEDs receive half their peak power.
Although, in the example of Fig. 4, each dipole element 60 has its own photoconductive material 50 coupled to its terminal portion 31, in other implementations only some of the dipole elements 60 would have a photoconductive material coupled to their terminal portions. Thus in this alternative implementation, only a sub-set of the dipole elements are extended using illumination and less illumination sources may be used.
Although in this example, the dipole elements are linear and the illumination of photoconductive material associated with a dipole element 60 increases its length, in other implementations the dipole elements may include secondary and tertiary loadings of the dipole and the associated photoconductive material associated with a dipole element 60 may be used to change the effective shape of the dipole element 60. A secondary loading is a dipole element extending from the primary dipole element 60 and a tertiary loading is a dipole element extending from the secondary loading.
Embodiment of Fin 5 Referring to Fig. 5, the transmission line component 10 includes multiple identical dipole elements 60. Each of the dipole elements has first and second portions arranged symmetrically on either side of the microstrip 62. Each of the first and second portions of the dipole elements 60 has a first microstrip conductor 21 extending from the microstrip 82 that terminates at a first terminal portion 31 The transmission line component 10 additionally comprises a second microstrip conductor 22 that terminates at a second terminal portion 32 and a third terminal portion 33. The second terminal portion 32 of the second microstrip conductor 22 opposes the first terminal portion 31 of the first S microstrip conductor 21 across a gap 42. The third terminal portion 33 terminates the dipole element 60. The photoconductive material 50 electrically couples to both the first terminal portion 31 and the second terminal portion 32. The first photoconductive material SO, in this example, is provided by a first silicon die that overlies both the first terminal portion 31 and the second terminal portion 32 and bridges the gap 42. An LED is positioned at each silicon die to illuminate it.
When the photoconductive material 50 is not illuminated, the dipole elements 60 terminate at the first terminal portion 31. When the photoconductive material 50 is illuminated the dipole element 60 terminates with the third terminal portion 33- the dipole is extended.
The transmission line component 10 consequently has a greater insertion loss when it is illuminated. The insertion loss can therefore be controlled by the simultaneous illumination of the silicon dies within each dipole element 60.
The transmission line component 10 described in relation to Figs 4 and may be used as an optically controlled switch. The transmission line components described in relation to Figs 4 and 5 may also be used as an optically controlled attenuator, where the amount of attenuation is controlled by the amount of radiation incident on the silicon dies.
Embodiment of Fin 6 Referring to Fig 6, there is described a transmission line component 10 similar to that described with reference to Figs 3A and 3B. The transmission line component 10 additionally comprises a fourth microstrip conductor 24 I connected to a midpoint of the second microstrip conductor 22. The fourth and second microstrip conductors may be integrated as a single microstrip.
Such a transmission line component 10, may be used as an optically switchable antenna, where the fourth microstrip conductor 24 is the antenna I feed.
Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, the terminal portions 31, 32, 33, 34 of the respective microstrip conductors may taper towards a point or edge at their terminus. For example, the sides of the silicon die may be treated to improve internal reflection of incident radiation.
The silicon die and microstrip connector may be in direct contact or a dielectric gap may intervene. Although the embodiments have been described using a silicon die as an example of a photoconductive material, it should be appreciated that other photoconductive materials are suitable e.g. such as polysilicon, GaAs, photoconductive polymers etc. The photoconductive material may, for example, be in the form of a die or may be deposited in-situ into the gap beween microstrip conductors. Although in the preceding paragraphs the conductive microstrips and dipole elements have been described as linear conductive strips, in other implementations they may have secondary and tertiary loadings as described with reference to Fig. 4.
Although in the preceding paragraphs, the photoconductive material has been used to extend the length of a conductive element, in other implementations it may be used to otherwise change the shape of a conductive element..
Although in the preceding paragraphs, the photoconductive material has been used in relation to a microstrip it may alternatively or additionally be used to optically control the shape or configuration of other conductive elements such as secondary periodic conductive structures or the reference conductive element 12.
Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. l

Claims (34)

1. An optically controllable transmission line component comprising: a first conductive element; a second conductive element; a dielectric substrate separating the first conductive element and the second conductive element; and photoconductive material coupled to the second conductive element, wherein controlled illumination of the photoconductive material controls the electrical properties of the transmission line component.
2. A transmission line component as claimed in claim 1, wherein the photoconductive material is semiconductor material.
3. A transmission line component as claimed in claim 2, wherein the photoconductive material is silicon.
4. A transmission line component as claimed in claim 3, wherein the photoconductive material is a silicon die.
5. A transmission line component as claimed in any preceding claim, wherein the controllable electrical properties include phase delay and/or insertion loss.
6. A transmission line component as claimed in any preceding claim wherein the photoconductive material, when illuminated, provides at least a portion of a secondary periodic structure.
7. A transmission line component as claimed in any one of claims 1 to 5, wherein the second conductive element is a reference conductive element of the transmission line and the photoconductive material, when illuminated, varies the electrical properties of the reference conductive element.
8. A transmission line component as claimed in any one of claims 1 to 5, wherein the first conductive element is a reference conductive element of the transmission line and the second conductive element is a conductor of the transmission line, wherein the photoconductor material, when illuminated, varies the electrical properties of the conductor.
9. A transmission line component as claimed in claim 8, wherein the photoconductive material is electrically coupled to a terminal portion of the second conductive element.
10. A transmission line component as claimed in claim 8 or 9 wherein the conductor is a microstrip.
11. A transmission line component as claimed in any one of claims 9 or 10, wherein the second conductive element is a portion of a dipole element of the transmission line component
12. A transmission line component as claimed in claim11, wherein the terminal portion of the second conductive element terminates the dipole element when the photoconductive material is not illuminated and the photoconductive material terminates the dipole element when the photoconductive material is illuminated.
13. A transmission line component as claimed in claim 11, wherein illuminating the photoconductive material controllably increases the insertion loss of the transmission line component.
14. A transmission line component as claimed in claim 1 1, further comprising: a third conductive element that terminates at a terminal portion, opposing the second conductive element across a gap, wherein the photoconductive material electrically couples to the terminal portion of the third conductive element. l l
15. A transmission line component as claimed in claim 14, wherein a semiconductor die bridges the gap.
16. An optically controlled switch comprising a transmission line S component as claimed in any preceding claim.
17. An optically controlled attenuator comprising a transmission line component as claimed in any one of claims 1 to 16.
18. A transmission line component as claimed in any one of claims 8, 9 or 10, further comprising: a third conductive element that terminates at a temminal portion opposing the second conductive element across a gap, wherein the photoconductive material electrically couples to the terminal portion of the third conductive element.
19. A transmission line component as claimed in claim 18, wherein the third conductive element is a microstrip.
20. A transmission line component as claimed in claim 18 or 19, wherein a semiconductor die bridges the gap.
21. A transmission line component as claimed in any one of claims 18 to 20, further comprising a fourth conductive element that terminates at a terminal portion, wherein the third conductive element additionally terminates at a terminal portion opposing the terminal portion of the fourth conductive element across a second gap, bridged by second photoconductive material.
22. A transmission line component as claimed in claim 21, wherein the fourth conductive element is a microstrip.
23. A transmission line component as claimed in claim 21 or 22, wherein a second semiconductor die bridges the second gap.
24. A transmission line component as claimed in any one of claims 21 to 23, wherein the length of the third conductive element defines a resonant frequency of the transmission line component.
S
25. An optically tuneable resonator comprising a transmission line component as claimed in any one of claims 21 to 24.
26. An optically controllable bandpass filter comprising a transmission line component as claimed in any one of claims 21 to 24.
27. A transmission line component as claimed in any one of claims 18 to 23, further comprising a fifth conductive element connected to a midpoint of the third conductive element.
28. A transmission line component as claimed in claim 27 wherein the fifth and fourth conductive elements are a microstrip.
29. An optically switchable antenna comprising a transmission line component as claimed in any one of claims 18 to 23, 27 or 28.
30. A phase shifter comprising a transmission line component as claimed in any one of claims 1 to 24.
31. A delay line comprising a transmission line component as claimed in any one of claims 1 to 24.
32. A directional antenna system comprising a transmission line component as claimed in any one of claims 1 to 24.
33. An optically controllable transmission line component substantially as hereinbefore described with reference to and/or as shown in the drawings.
34. Any novel subject matter or combination including novel subject matter I disclosed, whether or not within the scope of or relating to the same invention as the preceding claims. s
GB0326333A 2003-11-12 2003-11-12 An optically controllable transmission line component Expired - Fee Related GB2408152B (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4636794A (en) * 1984-07-26 1987-01-13 Mcginn Vincent P Photo-conductive element operative in the microwave region and a light-steerable antenna array incorporating the photo-conductive element
US5481232A (en) * 1995-04-19 1996-01-02 New Jersey Institute Of Technology Optically controlled multilayer coplanar waveguide phase shifter
US5574464A (en) * 1995-10-17 1996-11-12 Northrop Grumman Corporation High-speed switching device for monostatic impulse radar
WO2001002070A1 (en) * 1999-07-02 2001-01-11 Sony Computer Entertainment Inc. Entertainment system, entertainment apparatus, recording medium, and program
WO2001020707A1 (en) * 1999-09-16 2001-03-22 Telefonaktiebolaget Lm Ericsson (Publ) A switchable microwave device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4636794A (en) * 1984-07-26 1987-01-13 Mcginn Vincent P Photo-conductive element operative in the microwave region and a light-steerable antenna array incorporating the photo-conductive element
US5481232A (en) * 1995-04-19 1996-01-02 New Jersey Institute Of Technology Optically controlled multilayer coplanar waveguide phase shifter
US5574464A (en) * 1995-10-17 1996-11-12 Northrop Grumman Corporation High-speed switching device for monostatic impulse radar
WO2001002070A1 (en) * 1999-07-02 2001-01-11 Sony Computer Entertainment Inc. Entertainment system, entertainment apparatus, recording medium, and program
WO2001020707A1 (en) * 1999-09-16 2001-03-22 Telefonaktiebolaget Lm Ericsson (Publ) A switchable microwave device

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GB0326333D0 (en) 2003-12-17
GB2408152B (en) 2008-03-05

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Effective date: 20151112