US3916347A - Novel directional coupler for high-frequency electric signals - Google Patents

Novel directional coupler for high-frequency electric signals Download PDF

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Publication number
US3916347A
US3916347A US492777A US49277774A US3916347A US 3916347 A US3916347 A US 3916347A US 492777 A US492777 A US 492777A US 49277774 A US49277774 A US 49277774A US 3916347 A US3916347 A US 3916347A
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United States
Prior art keywords
piezoelectric member
regions
directional coupler
wave
input transducer
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Expired - Lifetime
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US492777A
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English (en)
Inventor
Alain Bert
Gerard Kantorowicz
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/74—Multiple-port networks for connecting several sources or loads, working on the same frequency or frequency band, to a common load or source
    • H03H9/76—Networks using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02637—Details concerning reflective or coupling arrays
    • H03H9/02685—Grating lines having particular arrangements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/0296—Surface acoustic wave [SAW] devices having both acoustic and non-acoustic properties

Definitions

  • the invention relates to a directional coupler comprising a piezoelectric crystal for high-frequency waves.
  • the known devices comprise a piezoelectric member on which input and output transducers are applied.
  • an electric signal is applied to the input transducer, it induces a mechanical wave in the piezoelectric member, the wave having the same frequency as the applied signal and propagating at the surface of the member.
  • the wave which is accompanied by a potential wave, reaches the output transducer and in turn induces a signal which is collected at the terminals of the output transducer.
  • the last-mentioned signal is somewhat delayed compared with the input signal owing to the time taken by the mechanical wave to propagate at the surface of the piezoelectric member.
  • delay electroacoustic devices are used to provide directional coupling of high-frequency waves by inserting a number of conductive strips between the input transducer and the output transducers on the surface of the piezoelectric member, the strips being large compared with the transducers in a direction at an angle, e.g. perpendicular, to the direction of propagation of the surface wave in question.
  • the conductive strips are in the form of conductors which are applied in stationary manner to the piezoelectric member.
  • the conductors are conventionally obtained by depositing metal on the surface of the piezoelectric member.
  • An object of the invention is to describe a directional coupler comprising a piezoelectric crystal and having adjustable characteristics.
  • FIG. 1 a plane view of a device of the prior art
  • FIG. 2 a perspective view of a device of the invention.
  • allel conductive strips 5 forming an assembly 50 are disposed between the transducers and also applied to the surface of member 1.
  • the transducers and strips are obtained e.g. by depositing metal on the surface of member 1 and occupy stationary positions thereon.
  • a high-frequency signal having a given frequency is applied between terminals 010 and 011 of transducer 1 and produces a surface mechanical wave which propagates along the piezoelectric member. If there were no strips 50, the wave would propagate on the surface of the piezoelectric member in an invariable direction depending on the orientation of the member. In the drawing, this direction is represented by arrow 10.
  • the wave would then induce a signal corresponding to the input signal in transducer 02.
  • the assembly 50 of strips 5 behaves like two guides for waves which are guided in the direction of the arrow, the guides being adjacent and coupled together by apertures which are formed in their common surface and which can occupy either some or all the area of this surface.
  • the two guides are e.g. two identical rectangular wave guides whose short sides are adjacent and parallel to the direction 10 in the central plane of the FIGS. 3, 4 and 5, partial plane views of three embodiments of the invention.
  • FIG. 1 is a diagrammatic plan view showing a piezoelectric member I, e.g. a known quartz wafer cut in a privileged direction, and four transducers 01,02, 03, 04 applied to member 1. A number of equidistant pardrawing.
  • a piezoelectric member I e.g. a known quartz wafer cut in a privileged direction
  • transducers 01,02, 03, 04 applied to member 1.
  • the wave initially propagates along the direction of arrow 11 and is gradually attenuated; owing to the aforementioned coupling, a wave at the same frequency appears in the second guide along arrow 12; the latter wave induces a signal in transducer 03.
  • the result is a coupling between transducer 01 and transducer 03, which adversely affects the coupling in relation to transducer 02 which would occur in the absence of strips 50.
  • the attenuation along the path 11 varies with the length of the wave guide sections; if the wave guide sections are short it may be partial, whereas if the sections are sufficiently long it may affect the entire initial wave.
  • the directionalcharacter of the coupling obtained by the prior-art devices depends on the number of strips 5 forming assembly 50; the proportion of energy received from transducer 01 by transducers 02 and 03 is dependent on the number of strips 5.
  • the strips, which are narrow, are usually disposed at a distance of M3 from one another, A being the wavelength of the aforementioned signal.
  • the strips are metal conductors applied to the surface of member 1, as in the prior art shown in FIG. 1, the coupling ratio of transducer 01 with each of transducers 02 and 03 is stationary for a given device. This is a disadvantage. Similarly, the operating frequency associated with the spacing between the strips is substantially stationary. This is another disadvantage.
  • the electroacoustic device for unidirectional coupling according to the invention is designed to obviate these disadvantages. This object is obtained in a manner which will be described hereinafter, with reference to FIG. 2.
  • FIG. 2 is a perspective diagram, showing a wafer 1 of piezoelectric material on which four transducers are disposed as in FIG. 1 and bear the same references as in FIG. 1.
  • a number of strips 6 represented by dotted rectangles are disposed between the transducers and form an assembly 60.
  • the strips serve the same purpose as the strips in the preceding example. They are manufactured as shown hereinafter.
  • a layer of a material having the property of induced conductiveness when bombarded by electrons is disposed on the piezoelectric material 1.
  • the property referred to belongs to certain materials, which, when bombarded by an electron beam, become conductive at the place of impact of the beam and for a certain distance below the place of impact.
  • Such materials are known in electronics; an example is cadmium sulphide or CdS, which is used to make layer 20 in the example given.
  • Means are provided for producing a bombardment of the aforementioned kind in the device according to the invention.
  • the means comprise a thermionic cathode 31 having a heating filament (not shown), a control electrode 32, an electrode 33 and an electrode 34.
  • the beam from cathode 31 is accelerated towards layer 20 by a potential difference produced between electrodes 31 and 34 as shown in the drawing, by using a source (not shown) whose negative terminal is connected to the electrode 31 and whose positive terminal is connected to anode 34, i.e. to earth in the example shown.
  • Electrode 33 is in two parts and is raised to a potential which is between that of cathode 31 and earth, and can thus deflect the beam by producing a potential difference between its two parts, by means of connections 330 to a source (not shown), whereas electrode 32 is used for periodically interrupting the beam, as will be seen hereinafter.
  • the potential of the layer is fixed by a collector which collects the secondary electrons emitted by layer 20 when bombarded.
  • the drawings do not show the collector, which may either be a grid parallel to the layer 20 through which the'incident electrons travel, or a conductive deposit on the periphery of layer 20, or may be embodied in any other prior-art manner.
  • the gun assembly 30 may also comprise other electrodes, e.g. collimation electrodes, in accordance with any known electron-gun feature.
  • FIG. 2 does not show any of these electrodes, since they are not necessary for understanding the operation of the device.
  • FIG. 2 likewise does not show the negative-pressure casing inside which the bombardment occurs.
  • the electron beam bombards layer 20 at an energy of several kilovolts, e.g. 4 kilovolts in the case of cadmium suphide in the example. Owing to the bombardment, the conductivity of layer 20 increases at the place of impact of the electron beam, since free charge carriers are produced in the mass of layer 20 under the surface where the electrons impinge, the number of carriers depending on the nature of the layer material. In the case of cadmium sulphide (CdS), the number of carriers at the aforementioned acceleration voltage is about 1,000 times the number of incident electrons. The free carriers are distributed in the material to a depth not exceeding one tenth of a micron.
  • CdS cadmium sulphide
  • the number of free carriers produced per pulse is about 2 X 10 per cubic centimetre, corresponding to a resistivity of the order of 0.1 ohm cm.
  • the electron beam coming from cathode 31 is chopped by grid 32 into pulses each lasting 10 microseconds and repeating every thousandth of a second.
  • the two plates forming electrode 33 scan at the mains frequency, i.e. 50 cycles per second, the beam making an outward and return movement, per cycle of one hundredth of a second each.
  • the mains frequency i.e. 50 cycles per second
  • the beam making an outward and return movement, per cycle of one hundredth of a second each.
  • there are 10 pulses from the control grid each corresponding to a strip 6; accordingly 10 strips 6 are produced on layer 20 during a scanning cycle. For clarity, only some of the strips have been shown.
  • the conductivity of the strips is renewed at each transit. of the electron beam. The strips remain permanently conductive during scanning.
  • the recombination time of the free carriers produced in layer 20 during the transit of the electron beam through a strip is substantially greater than the time between two successive transits of the beam through the strip. Accordingly, the beam travels a second time through the strip before the conductivity produced therein by the previous transit has had time to disappear owing to the recombination of the free carriers. To obtain satisfactory operation, this time should also be substantially greater than the period of the acoustic wave. The first of these conditions can easily be obtained from the aforementioned data and results in the second condition at the operating frequencies, e.g. 50 MHz.
  • the conductivity disappears when the strip cease to be scanned for a time longer than the recombination time; according to the preceding data, the recombination time is quite short, i.e. a few thousandths of a second. Consequently, if a number of strips 6 are formed on layer 20, they can be erased if they are no longer maintained by the electron beam. Consequently, after a first set of strips 6 has been produced, a different set can be produced without the device preserving any trace of the preceding set.
  • the device in FIG. 2 operates in the same manner as the device in FIG. 1.
  • the strips 5 forming assembly 50 and represented by conductors deposited on the surface of substrat l occupy a stationary position thereupon
  • the strips 6 which serve the same purpose as strips 5 in FIG. 1 can be moved on film 20 by acting in known manner on the frequency of the current pulses and on the scanning characteristics of the electron beam and film 20. It is thus possible to displace the strips with respect to one another, i.e. to modify the pitch of the array formed by assembly 60 of strips 6 and to vary the number of strips, etc. Consequently, couplers according to the invention have different properties from similar prior-art couplers.
  • a single coupler can operate at different freresults in a modification in the coupling ratio between the input transducer and the two output transducers 02 and03, i.e; in the proportion of the wave energy 'applied to the input transducer which is collected by each of the output transducers.
  • the number of strips can be-varied so as to transfer practically .all the initial wave from pathv 11 to path 12, i.e. towards terminals 030 and 031 of transducer'03, or alternatively to transfer only'part of the initial wave to transv ducer 03, the remainder goingto transducer 02 and being sampled between the terminals 020 and 021 thereof.
  • strips 6 can beprovided which are partly in the form of conductors 61 on the surface of material 1 and partly in the form of regions 62 of a layer (not shown) made conductive by induced conductivity; each region 62 is disposed between two portions of conductors 61, as shown in the drawing. Coupling occurs only when the electron beam bombards regions 62; no coupling occurs in the absence of such bombardment. In this case, the regions need not necessarily be scanned and there can be a permanent bombardment during the whole time when the filter is used.
  • the piezoelectric material has the property of conductivity induced by electron bombardment, so that layer 20 is unnecessary.
  • FIGS. 4 and 5 show two other embodiments of cow plers according to the invention.
  • the piezoelectric member 1 comprises two adjacent parts 100 and 101 which are normally insulated from one another with regard to the transmission of the electromechanical wave.
  • Each part 100 and 101 bears metal conductors 61 as in the preceding example, the conductors being diagrammatically shown as fixed lines.
  • each part operates separately and provides coupling (which is not in any way directional) between the transducers at the two ends thereof.
  • coupling occurs under the conditions explained with reference to FIGS. 1 and 2.
  • the electronic bombardment can be maintained during the whole time during which directional coupling is required.
  • FIG. 5 is an alternative embodiment of FIG. 4, wherein the two adjacent parts 100 and 101 are made of different piezoelectric materials having different propagation rates. The two parts are coupled in the same way as before. Note that the last-mentioned feature would be difficult to obtain using an electron beam bombardment to produce the strips 6 in their whole by induced conductivity.
  • the devices according to the invention comprise a piezoelectric member which, at the system of strips 60, is covered with a material such as cadmium sulphide,
  • Thesame devices can be constructed as mentioned in connection with, FIG. 4,- using a singlemate rial which is both piezoelectric andcan be given induced conductivity.
  • Cadmium sulphideitself can be used. for this purpose, and gallium arsenide is equallyusefuh .In the examples described, we have assumedthat there are two outputtransducers. Allthe foregoing applies equally well to devices comprising more than two output transducers.
  • A-directional coupler for high-frequencyn-waves comprising, on a piezoelectric member, an input transducer to'which a high-frequency wave is applied and a number of output transducers collecting thecorresponding wave transmitted to the surface of the piezoelectric-member, and a number of conductive strips disposed between the input transducer and the output transducers at an angle to the direction of the highfrequency wave in the piezoelectric member, characterised in that it comprises means producing an electron beam, means causing the beam to strike regions of said piezoelectric member, means to endow said regions with the property of being electrically insulating, said regions being made conductive at the place of impact owing to free charge carriers being produced therein, means for chopping the beam into pulses, the impact of the beam on each region occuring during one of the pulses, and means causing the beam to periodically scan the regions at'a period less than the recombination time of the free'charge carriers.
  • a directional coupler characterised in that said means to endow said regions with the property of being electrically insulating is a layer of an electrically insulating material covering said piezoelectric member on that of its faces struck by the electron beam.
  • each conductive strip is made up of two portions of metal conductors separated from one another and a region which is made conductive by electron bombardment and is in contact with the aforementioned two portions.
  • a directional coupler characterised in that the piezoelectric member is made up of two separate pieces placed side by side and connected transversely to the aforementioned portions, each of the two portions forming one of the strips being at least partly disposed on one of the aforementioned two pieces.
  • a directional coupler according to claim 4 characterised in that the two pieces making up the piezoelectric member are made of the same material.
  • a directional coupler according to claim 4 characterised in that the two pieces making up the piezoelectric member are made of different materials.
  • a directional coupler for high-frequency waves comprising, on a piezoelectric member, an input transducer to which a high-frequency wave is applied and a number ,of output transducers collecting the corresponding wave transmitted to the surface of the piezoelectric member, and a number of conductive strips disposed between the input transducer and the output transducers at an angle to the direction of the highfrequency wave in the piezoelectric member, characterised in that it comprises means producing an electron beam, means causing the beam to strike regions of said piezoelectric member, means to endow said regions with the property of being electrically insulating, said regions being made conductive at the place of impact owing to free charge carriers being produced therein, means for chopping the beam into pulses, the impact of the beam on each region occuring during one of the pulses, and means causing the beam to periodically scan the regions at a period less than the recombination time of the free charge carriers, the device also comprising means associated with the deflecting means for modifying the spacing between the regions and thus
  • a directional coupler for high-frequency waves comprising, on a piezoelectric member, an input transducer to which a high-frequency wave is applied and a number of output transducers collecting the corresponding wave transmitted to the surface of the piezoelectric member, and a number of conductive strips disposed between the input transducer and the output transducers at an angle to the direction of the highfrequency wave in the piezoelectric member, characterised in that it comprises means producing an electron beam, means causing the beam to strike regions of said piezoelectric member, means to endow said regions with the property of being electrically insulating, said regions being made conductive at the place of impact owing to free charge carriers being produced therein, means for chopping the beam into pulses, the impact of the beam on each region occuring during one of the pulses, and means causing the beam to periodically scan the regions at a period less than the recombi' nation time of the free charge carriers, the device also comprising means for modifying the number of the aforementioned regions and consequently modifying the coup

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
US492777A 1973-08-02 1974-07-29 Novel directional coupler for high-frequency electric signals Expired - Lifetime US3916347A (en)

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FR7328289A FR2239810B1 (enrdf_load_stackoverflow) 1973-08-02 1973-08-02

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DE (1) DE2436727A1 (enrdf_load_stackoverflow)
FR (1) FR2239810B1 (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4079342A (en) * 1976-09-15 1978-03-14 Sperry Rand Corporation Fanned multistrip coupler filters
US4126839A (en) * 1976-02-26 1978-11-21 Sony Corporation Surface acoustic wave apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57173416U (enrdf_load_stackoverflow) * 1981-04-28 1982-11-01

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3516027A (en) * 1968-08-05 1970-06-02 Us Army Variable surface-wave delay line
US3560891A (en) * 1969-03-24 1971-02-02 Westinghouse Electric Corp Reflection phase shifter utilizing microstrip directional coupler
US3585531A (en) * 1969-04-29 1971-06-15 Westinghouse Electric Corp Magnetically variable microstrip directional coupler deposited on ferrite substrate
US3836876A (en) * 1971-05-05 1974-09-17 Secr Defence Acoustic surface wave devices

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3516027A (en) * 1968-08-05 1970-06-02 Us Army Variable surface-wave delay line
US3560891A (en) * 1969-03-24 1971-02-02 Westinghouse Electric Corp Reflection phase shifter utilizing microstrip directional coupler
US3585531A (en) * 1969-04-29 1971-06-15 Westinghouse Electric Corp Magnetically variable microstrip directional coupler deposited on ferrite substrate
US3836876A (en) * 1971-05-05 1974-09-17 Secr Defence Acoustic surface wave devices

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4126839A (en) * 1976-02-26 1978-11-21 Sony Corporation Surface acoustic wave apparatus
US4079342A (en) * 1976-09-15 1978-03-14 Sperry Rand Corporation Fanned multistrip coupler filters

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DE2436727A1 (de) 1975-02-13
FR2239810B1 (enrdf_load_stackoverflow) 1976-04-30
FR2239810A1 (enrdf_load_stackoverflow) 1975-02-28

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