Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P5/00—Coupling devices of the waveguide type
  • H01P5/12—Coupling devices having more than two ports
  • H01P5/16—Conjugate devices, i.e. devices having at least one port decoupled from one other port
  • H01P5/18—Conjugate devices, i.e. devices having at least one port decoupled from one other port consisting of two coupled guides, e.g. directional couplers
  • H01P5/181—Conjugate devices, i.e. devices having at least one port decoupled from one other port consisting of two coupled guides, e.g. directional couplers the guides being hollow waveguides
  • H01P5/182—Conjugate devices, i.e. devices having at least one port decoupled from one other port consisting of two coupled guides, e.g. directional couplers the guides being hollow waveguides the waveguides being arranged in parallel
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/18—Phase-shifters
  • H01P1/182—Waveguide phase-shifters

Definitions

• This invention relates to hybrid couplers which introduce an inherent guadrature relationship, or 90° phase shift, to electromagnetic waves coupled between two waveguides and, more particularly, to a coupling device including phase shifters in each waveguide to compensate for the 90° phase shift.
• Hybrid couplers are widely used in microwave circuits for coupling a portion of the electromagnetic energy in one waveguide to another waveguide.
• the coupling ratio is one-half so as to produce an equal split of the power among the two waveguides.
• a smaller amount of the power such as one-quarter or one-tenth of the power may be coupled from one waveguide to the second waveguide.
• the two waveguides are brought contiguous to each other and in parallel relationship so as to share a common wall. An aperture in the common wall provides for the coupling of the electromagnetic energy.
• the hybrid coupler introduces a 90° phase shift to an electromagnetic wave coupled from the first waveguide to the second waveguide.
• phase shifter into the first waveguide, downstream from the coupling aperture, to equalize the phase shifts in the two waveguides.
• the 90° phase shift in the second waveguide is a phase lag and, accordingly, the phase shifter comprises a series of capacitive elements disposed along the first waveguide.
• the foregoing solution to the problem suffers from the disadvantage that a capacitive phase shifter of sufficient length to introduce the required 90° phase shift is unduly long and heavy for use in a microwave network for feeding an antenna.
• Such microwave networks typically have numerous waveguide branches.
• phase shifters have proven to be highly dependent on frequency with the resultant phase shift being frequency dispersive. Accurate compensation for the quadrature relationship has only been obtained for a single value or narrow range of frequency. Accordingly, the foregoing problem of the unwanted phase shift has not been resolved in a manner which allows for the reduction in size and weight of the microwave components.
• phase compensated waveguide hybrid coupler in which two waveguides are positioned in side by side relation, each of the waveguides being formed of metallic walls arranged with a rectangular cross section having two long walls joined by two short walls.
• the two waveguides share a common short wall.
• a coupling aperture is located within the common short wall to provide the hybrid coupling.
• a phase shift of -90° is introduced inherently by the hybrid coupling of electromagnetic energy from the first waveguide to the second waveguide via the aperture in the common wall.
• An input terminal of the coupler is located in the first waveguide on one side of the coupling aperture.
• phase compensation is attained by constructing a first phase shifter in the first waveguide adjacent the through port, and a second phase shifter in the second waveguide adjacent the coupled port.
• the first phase shifter is constructed of a set of capacitive irises located on a long wall of the waveguide and introducing a phase shift of -45°.
• the second phase shifter is constructed of a set of inductive irises disposed on a short wall of the waveguide and extending between the two long walls of the waveguide to provide +45° phase shift.
• the algebraic summation of the +45° compensatory phase shift with the -90° inherent phase shift introduces a net -45° phase shift in the second waveguide, which phase shift is equal to the -45° phase shift of the first waveguide.
• Each of the waveguides is provided with an abutment disposed on the short wall opposite the coupling aperture to provide a reduced cross section which enhances the coupling of the radiant energy via the coupling aperture.
• the abutments are constructed as a series of steps which are sufficiently small relative to the free space wavelength so as to introduce no more than a negligibly small reflection coefficient.
• the foregoing configuration of the compensated hybrid coupler is sufficiently wide band to allow for separate transmit and receive communi ⁇ cation channels for use in satellite communications.
• FIG. 1 is an end view of the compensated coupler of the invention
• FIG. 2 is a plan view of the coupler sectioned along the line 2-2 of FIG. 1;
• FIG. 3 is a longitudinal sectional view of the coupler taken along the line 3-3 in FIG. 1;
• FIG. 4 is a longitudinal sectional view of the coupler taken along the line 4-4 of FIG. 1; and FIG. 5 is a graph of phase shift versus frequency for each of two phase shifting sections of the compensated coupler.
• a hybrid coupler 10 is constructed in accordance with the invention for the coupling of electromagnetic energy.
• the coupler 10 is formed of a first waveguide 12 and a second waveguide 14, each of which have rectangular cross-sectional form wherein the ratio of a long wall to a short wall is 2:1.
• a microwave frequency of 12 GHz For operation at a microwave frequency of 12 GHz
• waveguide type WR-75 is employed.
• Each of the waveguides have two long walls, namely a top wall 16 and a bottom wall 18, which are joined by short walls, namely outer sidewalls 20 and a common wall 22 which serves as an inner sidewall for each of the two waveguides 12 and 14.
• the coupler 10 is a very broad band device which, in the preferred embodiment of the invention has an operating range extending from 11.7 GHz to 14.5 GHz.
• the coupler 10 provides the dual functions of hybrid coupling plus phase compensation of electromagnetic energy between the two waveguides 12 and 14.
• the coupling of the electromagnetic energy is accomplished by a gate 24 located in the common wall 22.
• the gate 24 is always opened and has a fixed length approximately equal to one free-space wavelength of the electromagnetic energy, as measured along a longitudinal axis of either waveguide 12 or 14.
• the length of the gate 24 is reduced, for example, to 0.8 waveguide for 6 dB coupling .
• the coupler 10 has two output terminals, shown as a through port 26 and a coupled port 28, and located at ends of the waveguides 12 and 14 respectively.
• the coupler 10 further comprises an input port 30 located at an end of the first waveguide 12 opposite the through port 26, and an isolation port 32 located at an end of the second waveguide opposite the coupled port 28.
• the isolation port 32 is shown connected schematically to a resistor 34 which represents a nonreflecting load having an impedance matched to that of the second waveguide 14.
• a load (not shown) is constructed typically in the form of a well-known wedge which absorbs electromagnetic energy at the operating frequency of the coupler 10, and is conveniently mounted within a section of waveguide (not shown) connected to the isolation port 32 by flanges (not shown).
• the coupler 10 would be connected to components of a microwave circuit (not shown); such components may include waveguide fittings which would be connected in a conventional manner, as by flanges (not shown) to the ports 26, 28, and 30 of the coupler 10.
• the arrangement of the coupling gate 24 in the common sidewall 22 of the two waveguides 12 and 14 provides the configuration of a guadrature sidewall short slot hybrid coupler.
• Microwave signals coupled between the two waveguides via the gate 24 undergoes a lagging 90° phase shift, this phase shift being inherent in the well-known operation of a quadrature sidewall short slot hybrid coupler.
• phase shift is unwanted, and some sort of phase compensation is required to equalize the phase between the microwave signals of the two waveguides 12 and 14.
• the invention provides the requisite phase compensation by use of a set of four capacitive irises 36 located in the first waveguide 12 beyond the gate
• the configuration of the capacitive irises 36 in the waveguide 12 constitutes a phase shifter 40 which introduces a lagging phase shift of 45° at the through port 26.
• the configuration of the inductive irises 38 in the waveguide 14 constitutes a phase shifter 42 which introduces a leading phase shift of 45° at the coupled port 28.
• the combination of the -90° shift introduced at the gate 24 with the +45° shift introduced by the shifter 42 provides a net -45° shift at the coupled port 28 which balances the -45° shift introduced by the shifter 40 at the through port 26.
• the coupler 10 In order to use the coupler 10 in certain situations, such as a microwave circuit handling two- way communication via an antenna carried by a satellite, it is desirable to construct the coupler 10 with a bandwidth wide enough to accommodate a transmit channel and a receive channel spaced apart in the frequency domain by an empty band which prevents cross talk bet-we the two channels .
• the increased bandwidth of the- coupler 10 is attained by use of stepped abutments 44 located at the outer sidewalls 20 on a center line of the gate 24.
• the abutments 44 reduce the width of the waveguides 12 and 14 at the gate 24 to enhance coupling of radiant energy via the gate 24.
• Each of the abutments 44 is composed of three tiers having steps 46A-E and risers 48A-E.
• the dimensions of an abutment 44 may be adjusted to attain a desired bandwidth. Typical dimensions in terms of the free- space wavelength are as follows.
• the overall length is 1 1/4 wavelength
• the step 46C is 1/2 wavelength
• the steps 46B and 46D are each 1/4 wavelength
• the steps 46A and 46E are each 1/8 wavelength.
• the risers 48A and 48E are each 0.050 inches
• the risers 48B and 48D are each 0.045 inches
• the risers 48C on both sides of the step 46C are each 0.060 inch. It is noted that each of the risers is less than 1/10 of a wavelength so as to minimize reflections from the abutments 44.
• the two center irises 36 have an equal height of 1/8 wavelength, this being 0.110 inch at the operating frequency of the coupler 10.
• the remaining two irises 36, at the ends of the set of irises, have an equal length of approximately 1/16 wavelength, the length measuring 0.080 inch at the operating frequency of the coupler 10, this being shorter than the height of the central irises 36.
• the thickness of each of the irises 36, as measured along the axis of the waveguide 12, is 1/8 wavelength.
• the spacing on centers between successive ones of the irises 36 is 1/4 of the guide wavelength.
• the width of each of the irises 36, as measured in a direction transverse to the waveguide axis, is approximately 0.2 inch.
• the length of the segment of the wall 22 adjacent the capacitive irises 36 is 1.7 inch.
• the capacitive irises 36 are centrally spaced between the two sidewalls 20 and 22. While the capacitive irises 36 are shown as extending upwardly from the bottom wall 18, it is noted that, alternatively, they may be constructed as extending downwardly from the top wall 16.
• the two center inductive irises 38 extend from the outer sidewall 20 a distance of 0.115 inch, and the remaining two irises 38 at the outer ends of the set of irises extend from the sidewall 20 a shorter distance, namely 0.110 inch.
• the spacing between centers of the inductive irises 38 is 1/4 of the guide wavelength.
• the thicknesses of the inductive irises 38, as measured along an axis of the waveguide 14, is approximately 1/8 free-space wavelength.
• Coupler 10 Other dimensions of the coupler 10 are as follows.
• the section of the common wall 22 adjacent the input port 30 measured 0.7 inch.
• the spacing between the sidewalls 20 and 22 in each of the waveguides 12 and 14 is 0.75 inch, this being approximately 3/4 wavelength.
• the overall length of the coupler 10 is 3.6 inch.
• brass or aluminum is employed in the fabrication of both the waveguide walls as well as the irises 36 and 38, and the abutments 44. Both of the metals provide adequate electrical conductivity, the aluminum being employed when it is desired to reduce weight.
• Both the abutments 44 and the inductive irises 38 extend the full distance between the. top wall 16 and the bottom wall 18.
• capacitive irises can be constructed which extend the full distance between the short walls, the desired phase shift and bandwidth has been obtained in the preferred embodiment by constructing the capacitive irises 36 with a width, as noted above, which extends only partway the two sidewalls 22 and 20 of the first waveguide 12.
• the coupler 10 operates as a Ku-band sidewall short slot hybrid coupler with phase compensation introduced into the output terminals 26 and 28.
• the phase compensation is non-dispersive in frequency, and the phase shift structures permit the construction of the coupling device in a compact light-weight assembly for use in broadband power division networks.
• the capacitive phase shifter 40 introduces a phase shift of -45° at the through port 26.
• the inductive phase shifter 42 introduces a +45° phase shift in the second waveguide 14, which phase shift is algebraically combined with the -90° phase shift introduced by the hybrid coupling .
• FIG. 5 shows a feature of the invention wherein the frequency dispersive characteristics of the phase shifters 40 and 42 track each other.
• the phase shift introduced by a phase shifter at one frequency differs somewhat from the phase shift introduced at another frequency.
• the coupler 10 is to be employed over a wide range of frequencies and, accordingly, any frequency dependency of phase shift must also be correcte . While the nominal values of phase shift of the inductive iris 38 and the capacitive iris 36 are
• the actual values of phase shift vary from the nominal value as a function of frequency.
• the inductive phase shifter 42 introduces a phase shift in excess of +45° at lower values of frequency, the value of phase shift dropping towards the nominal value for higher values of frequency.
• the phase shift introduced by the capacitive phase shifter 40 is smaller than the nominal value for lower values of frequency, and increases to the nominal value at higher frequencies.
• the difference between the phase shifts introduced by the series of inductive irises and the series of capacitive irises remains constant at 90° over the range of frequencies in the band of interest.
• the coupler 10 compensates for frequency induced variations in phase shift so as to provide for a broadband compensation of the inherent 90° phase shift associated with a hybrid coupler.
• the upper trace for the series of inductive irises accurately tracks the lower trace representing the series of capacitive irises.

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• Waveguide Switches, Polarizers, And Phase Shifters (AREA)

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ID=25126833

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Cited By (6)

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Citations (4)

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• 1985
  • 1985-10-02 US US06/782,677 patent/US4688006A/en not_active Expired - Lifetime
• 1986
  • 1986-09-17 EP EP86906083A patent/EP0240543B1/en not_active Expired - Lifetime
  • 1986-09-17 WO PCT/US1986/001913 patent/WO1987002189A1/en active IP Right Grant
  • 1986-09-17 DE DE8686906083T patent/DE3687310T2/de not_active Expired - Fee Related
  • 1986-09-17 JP JP61505016A patent/JPS63500840A/ja active Granted

Patent Citations (4)

Non-Patent Citations (1)

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