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EP0247794A2
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Matching asymmetrical discontinuities in transmission lines
Assignee: BTG International Ltd
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Filing: 1987-05-21
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Granted: —
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Expires: 2007-05-21
Abstract
Abstract The invention relates to matching asymmetrical discontinuities in transmission lines to give low reflection coefficients (less than five percent) over a wide frequency band (corresponding to at least an octave in wavelength). A group of asymmetrical discontinuities, such as impedance steps (24) and (25) in a waveguide (12,13), are matched by considering a reference plane (3O) whose position varies with frequency at which the reflection coefficient for waves transmitted in one direction is equal to that for waves transmitted in the opposite direction. Matching elements (26) and (27) are then provided which have a reflection coefficient at the reference plane which is equal and opposite to the reflection coefficient of the discontinuities. Matching is less difficult if the distance between the steps is less than a quarter of a guide wavelength at all frequencies in the wide band mentioned above and such an arrangement is a "reduced quarterwave transformer". The technique of using the reference plane can also be applied to a single impedance step where two matching elements on either side of the step are required. The invention has application to, for example, waveguide transitions (including coaxial to waveguide transitions), waveguide twists, waveguide tees, symmetrical waveguide five ports, planar transmission lines, optical transmission lines and dielectric lenses.
Inventors
- 👤 Frans Christiaan De Ronde
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 10:15
CPC Classifications
H; H01; H01P; H01P5/00; H01P5/02
Claims Analysis
Total Claims: 65
Claim 1
Independent Claim
76 words
A section of a transmission path for electromagnetic waves, comprising a group of asymmetrical discontinuities, and matching means so positioned that its reflection coefficient transferred to the reference plane, as hereinbefore defined, of the group of discontinuities, is substantially equal and opposite to the reflection coefficient at the said reference plane of the discontinuities over a frequency band corresponding to at least half an octave in wavelength and for each direction of transmission along the line.
Claim 2
Dependent Claim
76 words
A section of a transmission path for electromagnetic waves, comprising a group of asymmetrical discontinuities, and matching means so positioned that its reflection coefficient transferred to the reference plane, as hereinbefore defined, of the group of discontinuities, is substantially equal and opposite to the reflection coefficient at the said reference plane of the discontinuities over a frequency band corresponding to at least half an octave in wavelength and for each direction of transmission along the line.
Claim 3
Dependent Claim
70 words
A section of a transmission path according to Claim l wherein there is one discontinuity only in the said group and the matching means is formed by two reactive matching elements, one on one side of the reference plane and one on the other, the matching elements each being spaced by substantially one eighth of the guide wavelength at the centre frequency of the said band from the reference plane.
Claim 4
Dependent Claim
120 words
A section of a transmission path according to Claim 2 wherein the said section is a waveguide and the discontinuity is an impedance step with the result that the reflection coefficient at the said reference plane is substantially constant with frequency across the said band, and wherein the matching elements comprise a shunt inductive element in the lower impedance waveguide portion and a shunt capacitive element in the higher impedance waveguide portion, the vector sum of the reflection coefficients of the elements transferred to the said reference plane being substantially constant with frequency variation across the said band and equal but opposite to the reflection coeffient for the same direction of transmission of the impedance step at the reference plane.
Claim 5
Dependent Claim
110 words
A section of a transmission path according to Claim 2 wherein the said section is a mode converter between two portions of waveguide of different types, and the matching elements comprise a shunt inductive element in one waveguide portion and a shunt capacitive element in the other waveguide portion, the vector sum of the reflection coefficients of the elements transferred to the reference plane of the mode converter varying with frequency variation across the band in the same way as any such variation in the reflection coefficient of the transition between the two waveguide portions for the same direction of transmission at the reference plane but being of opposite sign.
Claim 6
Dependent Claim
82 words
A section of a transmission path according to Claim l wherein there are two discontinuities only in the said group and the matching means is positioned on one side of the reference plane and has a reflection coefficient which when transferred to the reference plane varies with frequency across the said band by substantially the same amount as the reflection coefficient of the two discontinuities at the reference plane for the same direction of transmission, the two coefficients being of opposite sign.
Claim 7
Dependent Claim
57 words
A section of a transmission path according to Claim 5 wherein the discontinuities are impedance steps in the same sense separated by a quarter of a wavelength at a frequency above the said band, the steps having unequal reflection coefficients with the result that the position of the reference plane of the two steps varies with frequency.
Claim 8
Dependent Claim
29 words
A section of a transmission path according to Claim 6 wherein the said section is a waveguide, and the steps are changes in the cross-sectional area of the waveguide.
Claim 9
Dependent Claim
84 words
A waveguide according to Claim 7 wherein the matching means is formed by two spaced apart capacitive shunt elements positioned in the waveguide portion having the highest impedance, the capacitive elements being constructed and positioned to have a reflection coefficient which when transferred to the reference plane varies with frequency across the said band by substantially the same amounts as the reflection coefficient of the two discontinuities at the reference plane for the same direction of transmission, the two coefficients being of opposite sign.
Claim 10
Dependent Claim
79 words
A waveguide according to Claim 7 wherein the matching means is formed by a shunt inductive element positioned in the waveguide portion having the lowest impedance and constructed and positioned to have a reflection coefficient which when transferred to the reference plane varies with frequency across the said band by substantially the same amounts as the reflection coefficient of the two discontinuities at the reference plane for the same direction of transmission, the two coefficients being of opposite sign.
Claim 11
Dependent Claim
15 words
lO. A waveguide according to Claim 7, 8 or 9 including a tapered waveguide portion.
Claim 12
Dependent Claim
14 words
A waveguide according to Claim lO wherein the tapered portion is between the steps.
Claim 13
Dependent Claim
25 words
A waveguide according to Claim lO or ll wherein the tapered portion has at least one wall in the form of a constant radius curve.
Claim 14
Dependent Claim
133 words
A section of a transmission path according to Claim l wherein the transmission line is a mode converter between two portions of transmission line of different types, and the group of discontinuities comprises a transmission line section which is a quarter of a wavelength long at a frequency above the said band with the result that both the position of the reference plane and the reflection coefficient for the discontinuities vary with frequency, and wherein the matching means is positioned on one side of the reference plane and has a reflection coefficient which when transferred to the reference plane varies across the said band by substantially the same amount as the reflection coefficient of the discontinuities at the reference plane for the same direction of transmission, the two coefficients being of opposite sign.
Claim 15
Dependent Claim
75 words
A section of a transmission path according to Claim l3 wherein the matching means is formed by an inductive element, the inductive element being constructed and positioned to have a reflection coefficient which when transferred to the reference plane varies with frequency across the said band by substantially the same amounts as the reflection coefficient of the discontinuities at the reference plane for the same direction of transmission, the two coefficients being of opposite sign.
Claim 16
Dependent Claim
42 words
A section of a transmission path according to any of Claims l, 2, 5, 6 and 9 to l2 insofar as dependent on Claim 5, and Claims l3 and l4 wherein the matching means comprises at least one series connected reactive element.
Claim 17
Dependent Claim
33 words
A section of a transmission path according to any preceding claim comprising at least one of the following: waveguide, strip line, microstrip, slot line, coplanar line, coaxial line, two-wire line and optical waveguide.
Claim 18
Independent Claim
66 words
A method of matching a group of asymmetrical discontinuities in a transmission path comprising so positioning matching means that its reflection coefficient transferred to the reference plane as hereinbefore defined of the group of discontinuities, is substantially equal and opposite to the reflection coefficient of the discontinuities over a frequency band corresponding to at least half an octave in wavelength and for each direction of transmission.
Claim 19
Independent Claim
66 words
A method of matching a group of asymmetrical discontinuities in a transmission path comprising so positioning matching means that its reflection coefficient transferred to the reference plane as hereinbefore defined of the group of discontinuities, is substantially equal and opposite to the reflection coefficient of the discontinuities over a frequency band corresponding to at least half an octave in wavelength and for each direction of transmission.
Claim 20
Dependent Claim
105 words
A section of a transmission path for electromagnetic waves having a predetermined frequency range, comprising two impedance steps in the same sense with respect to transmission along the path, characterised in that the two steps are separated by a distance equal to a quarter of a wavelength as measured in the path at a frequency above the said frequency range, and together have a reference plane as hereinbefore defined, and in that the transmission path also comprises means having a reflection coefficient at the said reference plane which, over the said frequency range, is equal and opposite to the combined reflection coefficient of the steps.
Claim 21
Dependent Claim
105 words
A section of a transmission path for electromagnetic waves having a predetermined frequency range, comprising two impedance steps in the same sense with respect to transmission along the path, characterised in that the two steps are separated by a distance equal to a quarter of a wavelength as measured in the path at a frequency above the said frequency range, and together have a reference plane as hereinbefore defined, and in that the transmission path also comprises means having a reflection coefficient at the said reference plane which, over the said frequency range, is equal and opposite to the combined reflection coefficient of the steps.
Claim 22
Dependent Claim
120 words
A section of a transmission path according to Claim l wherein the section is a mode converter between a waveguide and an external coaxial line with the centre conductor of the coaxial line connected to a probe which projects into the waveguide for approximately a quarter of the guide wavelength at the centre frequency of the said band, the outer conductor of the coaxial line being connected to the waveguide walls, the group of discontinuities is formed by the projection of the inner conductor of the coaxial line into the waveguide, and the matching means is formed by at least one transmission line section which is electrically a quarter of a wavelength long at a frequency above the said band.
Claim 23
Dependent Claim
39 words
2O. A mode converter according to Claim l9 wherein the, or one of the, transmission line sections is formed by a section of further coaxial line connected between the probe and the waveguide wall, and the external coaxial line.
Claim 24
Dependent Claim
40 words
2l. A mode converter according to Claim l9 or 2O wherein the, or at least one of the, transmission line sections is formed by a step in the waveguide wall projecting into the waveguide around, but spaced from, the probe.
Claim 25
Dependent Claim
26 words
A mode converter according to Claim 2l, 22 or 23 wherein the waveguide is rectangular and the probe projects from one of the broad walls thereof.
Claim 26
Dependent Claim
82 words
A mode converter according to Claim 22 wherein the waveguide is short circuited in one direction from the probe at a distance which is a quarter of a wavelength from the probe at one of the following frequencies: a frequency near the centre of the band, a frequency near the top of the band, and a frequency near the bottom of the band, and the said matching means includes, at least for the latter two possibilities, additional matching stubs in the waveguide.
Claim 27
Dependent Claim
22 words
A mode converter according to Claim l9, 2O or 2l wherein the probe projects into the waveguide from transverse one end thereof.
Claim 28
Dependent Claim
60 words
A mode transducer according to Claim 23 wherein the probe extends into the waveguide in the direction of propagation in the waveguide, the group of discontinuities includes a section of the waveguide adjacent to the probe and having a dimension normal to the said direction which is a quarter of the guide wavelength at the centre of the said band.
Claim 29
Dependent Claim
42 words
A mode converter according to Claim 24 wherein the said matching means includes a step in waveguide opposite the corner and a capacitive stub in the waveguide about a quarter of a said guide wavelength from the end of the said probe.
Claim 30
Dependent Claim
127 words
Apparatus for radiating signals having frequencies in a predetermined band of at least half an octave, comprising a probe which projects from a conductive ground plane, and has a length electrically equal to a quarter wavelength at a frequency in the said band, and a coaxial line with inner conductor connected to the probe and outer conductor connected to the ground plane, characterised by matching means having a reference plane, as hereinbefore defined, which coincides at all frequencies in the said band with the reference plane of the transition between the coaxial line and free space, and the matching means having a reflection coefficient at the reference plane which is equal and opposite, at all frequencies in the said band, to the reflection coefficient of the transition.
Claim 31
Dependent Claim
127 words
Apparatus for radiating signals having frequencies in a predetermined band of at least half an octave, comprising a probe which projects from a conductive ground plane, and has a length electrically equal to a quarter wavelength at a frequency in the said band, and a coaxial line with inner conductor connected to the probe and outer conductor connected to the ground plane, characterised by matching means having a reference plane, as hereinbefore defined, which coincides at all frequencies in the said band with the reference plane of the transition between the coaxial line and free space, and the matching means having a reflection coefficient at the reference plane which is equal and opposite, at all frequencies in the said band, to the reflection coefficient of the transition.
Claim 32
Dependent Claim
39 words
A mode converter according to Claim l9 wherein the, or one of the, further transmission line sections is formed by a section of further coaxial line connected between the probe and the ground plane, and the external coaxial line.
Claim 33
Dependent Claim
43 words
A mode converter according to Claim l9 or 2O wherein the, or at least one of the, further transmission line sections is formed by a step in the ground plane projecting in the same direction as, and around, the probe but spaced therefrom.
Claim 34
Dependent Claim
181 words
3O. Two sections of a transmission path according to Claim l together providing a twist for coupling two waveguides twisted in relation to one another, wherein each section has first and second portions, the first portion of the two sections comprises respective rectangular waveguides twisted in relation to one another and the two second portions are joined together and form a short intermediate waveguide, the intermediate waveguide having an opening with first and second regions which allow wave propagation between the first and second regions and the first and second waveguides, respectively, each region at least partially including a ridge in the general direction of propagation through the opening, the ridge having a transverse axis at an angle between the directions of corresponding transverse axes of symmetry of the waveguides, in each said section the group of discontinuities is formed by the interface between the first and second waveguide portions, and the matching means for each said section comprise a capacitive element in that section and an inductive element common to both sections formed by the interface of the intermediate waveguide.
Claim 35
Dependent Claim
112 words
3l. A twist for coupling two rectangular waveguides when the waveguides are twisted in relation to one another, comprising conductive walls defining an opening which when the twist is positioned between two rectangular waveguides twisted in relation to one another allows communication between electromagnetic fields in the waveguides and in the opening, characterised in that the walls also define a ridge having an axis of symmetry in the general direction of propagation through the opening, the ridge also having an axis of symmetry transverse to the said direction which in use is angularly displaced from the directions of both of transverse axes of symmetry of the waveguides which correspond with one another.
Claim 36
Dependent Claim
112 words
3l. A twist for coupling two rectangular waveguides when the waveguides are twisted in relation to one another, comprising conductive walls defining an opening which when the twist is positioned between two rectangular waveguides twisted in relation to one another allows communication between electromagnetic fields in the waveguides and in the opening, characterised in that the walls also define a ridge having an axis of symmetry in the general direction of propagation through the opening, the ridge also having an axis of symmetry transverse to the said direction which in use is angularly displaced from the directions of both of transverse axes of symmetry of the waveguides which correspond with one another.
Claim 37
Dependent Claim
48 words
A twist according to Claim 3O or 3l including matching means mounted on the ridge which either alone, or with further matching means, in operation provides matching over at least half an octave in the band of operation of waveguides which are in operation coupled by the twist.
Claim 38
Dependent Claim
26 words
A twist according to Claim 32 wherein the twist provides matching over the full working band of waveguides which are in operation coupled by the twist.
Claim 39
Dependent Claim
31 words
A twist according to any of Claims 3O to 33 wherein the said opening has two opposed ridges which give the opening a cross-section in the general form of an "H".
Claim 40
Dependent Claim
33 words
A twist according to any of Claims 3O to 33 wherein said opening has the general form of an "L", and the ridge projects from the intersection of the arms of the "L".
Claim 41
Dependent Claim
62 words
A twist according to Claim 32 or any of Claims 33 to 35 insofar as dependent on Claim 32 wherein the further matching means is not provided, and the ridge-mounted matching means comprises a pair of spaced projections on the ridge, or a pair of spaced projections on each ridge, each projection being transverse to the ridge on which it is mounted.
Claim 42
Dependent Claim
74 words
A twist according to Claim 32 or Claims 33 to 36 insofar as dependent on Claim 32 wherein the reflection coefficient transferred to the reference plane, as hereinbefore defined, of the ridge-mounted matching means is substantially equal and opposite to the combined reflection coefficient at the said reference plane of the discontinuities formed by the interface between the twist and one of the waveguides and the interface between the twist and the other waveguide.
Claim 43
Dependent Claim
47 words
A twist according to Claim 37 wherein the magnitude of the said combined reflection coefficient decreases with frequency across the band of operation and distance between the projections of the, or each, pair is a quarter of the guide wavelength at a frequency above the said band.
Claim 44
Dependent Claim
66 words
A twist according to any of Claims 3O to 38 so constructed that it can be positioned, in operation, in two different angular positions relative to the two waveguides it couples and in one of these positions the polarization of the field in one waveguide is opposite to the polarization of the field in the said one waveguide when the twist is in the other position.
Claim 45
Dependent Claim
45 words
4O. A twist according to any of Claims 3O to 39 including coupling means for coupling the twist between two waveguides, the coupling means being arranged to allow the twist to be rotated with respect to two waveguides to which it is, in operation, coupled.
Claim 46
Dependent Claim
24 words
4l. A twist according to Claim 4O wherein the coupling means is arranged to allow the waveguides to be rotated relative to one another.
Claim 47
Dependent Claim
55 words
Two sections of transmission path according to Claim l together forming a waveguide tee, each section being in the form of a right-angle waveguide corner, the two corners being back-to-back with one end of each section forming one respective port for the tee and the other ends of the sections together forming a third port.
Claim 48
Dependent Claim
65 words
A waveguide tee according to Claim 42 wherein the tee comprises first and second waveguides joined end to end and a third waveguide opening into the junction of the first and second waveguides at right angles thereto and along one broad side of the junction, the said sections of transmission path being formed by the first and second waveguides and half the third waveguide, respectively.
Claim 49
Dependent Claim
114 words
A waveguide tee according to Claim 43 wherein each of the first and second waveguides includes a length of reduced cross-sectional area which is less than a quarter of a wavelength long at all frequencies over the band of the waveguides, the third waveguide contains an inductive matching element, the said matching means comprising the said length of reduced cross-sectional area and the matching element to match the impedance steps where the third waveguide opens into the first and second waveguides, and each first and second waveguide also includes a corner matching element to substantially remove reflections due to change of direction of propagation between the first and second waveguides and the third waveguide.
Claim 50
Dependent Claim
40 words
A waveguide tee according to Claim 43 or 44 including a coaxial or suspended strip line with one end opening into the first and second waveguides opposite the region where the third waveguide opens into the first and second waveguide.
Claim 51
Dependent Claim
89 words
A waveguide tee according to Claim 45 in the form of a "magic tee" wherein the centre conductor of the coaxial or suspended strip line projects from the surface opposite the region where the third waveguide opens into the first and second waveguides for a distance equal to a quarter of a wavelength at a frequency in the said band and the said line is matched to the waveguide by a transmission line section which is a quarter of a wavelength long at a frequency above the said band.
Claim 52
Dependent Claim
56 words
A waveguide tee according to Claim 43 or 44 in the form of a complete waveguide "magic tee" including a fourth waveguide opening into the junction of the first and second waveguides at right angles thereto and along one narrow side of the junction, and further matching means for matching the fourth waveguide to the junction.
Claim 53
Dependent Claim
71 words
A magic tee according to Claim 47 insofar as dependent on Claim 44 wherein the further matching means comprises a planar conductive plate projecting into the third waveguide from the said matching element for a distance, in the third waveguide, substantially equal to a quarter of a wavelength at the centre frequency of the said band, the plane of the plate coinciding with the plane of symmetry of the magic tee.
Claim 54
Dependent Claim
49 words
A magic tee according to Claim 48, including a conductor projecting from, and perpendicular to, the wall of the tee opposite the end of the fourth waveguide and contacting the edge of the planar conductive plate facing the said wall at a point adjacent to the said matching element.
Claim 55
Dependent Claim
92 words
5O. A waveguide tee comprising first and second waveguides joined end to end, a third waveguide opening into the junction of the first and second waveguides at right angles thereto and along one narrow side of the junction, and a conductor of a transmission line projecting asymmetrically into the junction parallel to the narrow sides of the waveguides, characterised in that the transmission line is so positioned, and shorted at such a distance from the junction, that waves reflected from the transmission line substantially cancel waves reflected back into the third waveguide.
Claim 56
Dependent Claim
92 words
5O. A waveguide tee comprising first and second waveguides joined end to end, a third waveguide opening into the junction of the first and second waveguides at right angles thereto and along one narrow side of the junction, and a conductor of a transmission line projecting asymmetrically into the junction parallel to the narrow sides of the waveguides, characterised in that the transmission line is so positioned, and shorted at such a distance from the junction, that waves reflected from the transmission line substantially cancel waves reflected back into the third waveguide.
Claim 57
Dependent Claim
30 words
5l. A waveguide tee according to Claim 5O wherein the transmission line is a coaxial line and the said conductor is the centre conductor thereof and extends across the junction.
Claim 58
Dependent Claim
54 words
Two sections of transmission path according to Claim l together forming a strip line tee, each section being in the form of a conductor separated from a ground plane by dielectric material, each conductor forming a corner with the conductors on one side of each corner joined to form a port for the tee.
Claim 59
Dependent Claim
70 words
A strip line tee according to Claim 52 wherein the said group of asymmetrical discontinuities for each transmission line section comprise a taper in the conductor for that section extending from the corner towards the said port, and the matching means for each transmission line section comprise a pair of capacitive stubs from the conductor for that section near that end of the taper which is remote from the junction.
Claim 60
Dependent Claim
42 words
Five sections of transmission path according to Claim l which meet at a common junction, the said group of asymmetrical discontinuities for each transmission line section being the discontinuity at the junction, and the said matching means being located at the junction.
Claim 61
Dependent Claim
99 words
A five port waveguide junction according to Claim 54 wherein each section of transmission path includes a rectangular waveguide and a portion of the junction, the junction is in the form of a chamber into which the waveguides open with the planes of symmetry of the waveguides which are parallel to the broad sides thereof angularly separated by substantially 72°, and wherein the matching means for the sections of transmission line are provided by an inductive diaphragm for each waveguide near the point where that waveguide opens into the chamber and a plurality of capacitive elements inside the chamber.
Claim 62
Dependent Claim
79 words
A waveguide junction according to Claim 55 wherein the chamber is cylindrical, the waveguides open into the cylindrical side of the chamber, and the capacitive elements are five conductive planar probes in the form of segments of an annulus symmetrically mounted, with its centre on the axis of the chamber, on a dielectric substrate substantially bisecting the chamber at right angles to its axis, and with spaces between the probes opposite the openings of the waveguides into the chamber.
Claim 63
Dependent Claim
76 words
A transmission path for use over a predetermined band of frequencies extending over at least half an octave according to Claim l wherein the group of discontinuities comprises two interfaces between dielectrics having different dielectric constants, the interfaces being a quarter of a wavelength apart at a frequency above the said band, and the dielectric between the interfaces having a dielectric constant value between those of the dielectric constants on the other sides of the interfaces.
Claim 64
Dependent Claim
35 words
A transmission path according to Claim 57 wherein the matching means comprises an inductance or a capacitance distributed over a planar region parallel to the region between the interfaces and separated from the said region.
Claim 65
Independent Claim
84 words
A method of transmitting electromagnetic waves along a transmission path according to Claim l wherein the group of discontinuities comprises two interfaces between different dielectrics, the dielectric between the interfaces having a dielectric constant value between those of the dielectric constants on the other sides of the interfaces, the method comprising transmitting waves over a band of frequencies at least half an octave wide, the highest frequency in the band having a wavelength which is more than four times the distance between the interfaces.
References Cited (Backward Citations)
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