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
  • H01P5/08—Coupling devices of the waveguide type for linking dissimilar lines or devices
  • H01P5/10—Coupling devices of the waveguide type for linking dissimilar lines or devices for coupling balanced lines or devices with unbalanced lines or devices
  • H01P5/107—Hollow-waveguide/strip-line transitions

Definitions

• the present invention relates to a waveguide to transmission line transition for coupling signals between transmission lines and waveguides.
• Such transitions are commonly used for transmission of microwave and millimeter wave energy.
• Microwave and millimeter wave energy can be transmitted through a number of different transmission media, including waveguides, microstrip and coplanar transmission lines and coaxial cables.
• waveguides are well suited for the transmission of energy on the surface of a semiconductor integrated circuit
• waveguides are suitable for transmission of energy over larger distances.
• transitions and adaptors can be configured in the form of fins, ridges and steps disposed in a waveguide.
• the ridges, fins, and steps are physically designed to transform the impedance of the waveguide to match that of the transmission line.
• the structures guide microwaves or millimeter waves from a waveguide into an interface, such as a microstrip transmission line.
• the performance of transitions with these elements depends critically on the dimensions of the elements. Often, fins and ridges are difficult to manufacture.
• coplanar and microstrip transmission lines have been coupled to waveguides by means of intervening transmission lines such as coaxial lines or finlines.
• the present invention avoids these intermediate transmission lines and has the advantages of lower fabrication cost, lower reflections, and increased reliability due to the elimination of very small and delicate connections in the case of small wavelength devices, e.g., millimeter wavelengths.
• Harris, U.S. Patent No. 4,544,902 shows a semiconductor probe coupling a coaxial cable to a rectangular waveguide.
• the reference describes a rectangular waveguide, a coaxial cable, a probe and a connector.
• a semi-conductor probe from the coaxial connector protrudes through a waveguide wall and is connected to the opposite wall of the waveguide.
• U.S. Patent No.4,725,793 describes a waveguide to microstrip converter in which a probe is formed, surrounded by a dielectric to keep it structurally stable, in a short circuit waveguide.
• a microstrip transmission line is formed on a substrate.
• An end of the probe which is not on the same substrate as the microstrip transmission line, is connected by soldering to the microstrip line.
• U.S. Patent No.3,924,204 describes a waveguide to microstrip converter in which a microstrip transmission line penetrates Into a waveguide through a slot.
• the transmission line includes a substrate with a conductor strip disposed thereon.
• the substrate enters the waveguide approximately one-quarter wave from the short circuit plane of the waveguide.
• the substrate apparently extends through the waveguide.
• the substrate of the probe is positioned in the waveguide so that the plane of the substrate is parallel to the length of the waveguide.
• the transmission line could be of a type that comprises a ground planar conductor, a layer of dielectric material, and a line conductor.
• the transmission line is coupled by extending the line conductor through a slot into the rectangular waveguide.
• the conductor and dielectric can extend partially or entirely across the waveguide.
• the probe and transmission line are disposed on the same substrate.
• Ponchak and Simons, NASA TM-102477, January 1990 describe a rectangular waveguide to coplanar waveguide transition.
• the probe and the transistors that form a transmission line are disposed on the same substrate.
• a sloping tapered ridge in a top broad wall of the waveguide protrudes and extends down to contact a groove-like slot which gradually tapers in the bottom wall of the rectangular waveguide.
• Dalman, U.S. Patent No. 5,017,892 & Cornell University Electronics Letters 21 June 1990 show a microwave waveguide to coplanar transmission line transition made of metal.
• the top wall of the waveguide is an integral part of the output transmission line.
• a signal entering the waveguide encounters a centrally located tapered fin which is shaped to gradually guide the wave to a slot formed in the top of the waveguide.
• the fin slopes in such a manner as to become the center conductor of the coplanar transmission line.
• the sidewalls of the slot provide separate ground planes.
• Prior art devices that use sloping fins are difficult to manufacture to the precise tolerances required for optimum performance and are difficult to position within a waveguide. Microwave transitions are complicated by intervening transmission and adaptor structures imposed between the waveguide and transmission line which can create unwanted reflections.
• the transmission line includes first and second ground plates disposed on opposite sides of a substrate which are connected by conductors formed through the substrate. These conductors substantially eliminate electric signal energy dissipation into the substrate to reduce energy loss.
• the substrate partially protrudes through a slot in the wall of a waveguide and couples energy with minimum reflection between the waveguide and the transmission line on the substrate.
• the substrate is galHum-arsenide and the flat strip conductors are gold.
• the additional conductors are preferably gold and are termed "via holes" or "plated-through holes”.
• Figure 1 is an isometric view of a waveguide to coplanar transition in accordance with one embodiment of the present invention.
• Figure 2 shows the measured reflection coefficient versus frequency of a scale model of the present invention.
• the present invention relates to a transition from a waveguide to a transmission line.
• a waveguide is a transmission medium that guides signals in the form of electromagnetic radiation.
• the waveguide is typically a hollow metallic pipe, usually with no material inside. In a preferred embodiment, the metal might be copper or aluminum.
• the waveguide can be rectangular, square, circular, cylindrical, ridged, elliptical, or any other suitable configuration.
• the invention is preferably embodied as a transition between a waveguide and coplanar transmission line because there is less energy dissipation into the substrate of a coplanar transmission line.
• coplanar transmission lines are more preferred than microstrip transmission lines for use in millimeter wave integrated circuits because of their lower ground inductance, ease of surface probe testing, and accommodation of a thicker and less fragile substrate.
• microstrip transmission lines may be useful in certain applications and is considered to be within the scope of the present invention.
• the transition couples the dominant mode in a hollow, metallic, waveguide 1 to a transmission line 2.
• the waveguide is formed to define an interior volume 3 with open endfaces, to receive and deliver the signal.
• there are four walls including a first wall, a second wall, a third wall, and a fourth wall, 4, 5, 6, and 7 respectively.
• a substrate 8 has a first ground plate 9 in the form of a metallic coating that serves as a ground plane.
• the substrate could be any dielectric such as polystyrene, alumina or TEFLON.
• a second ground plate 10, which is a metallic coating covers the entire reverse side of the substrate 8 except within the rectangular waveguide 1.
• the second ground plate 10 acts as another ground plane.
• Two separated metalization layers, i.e., the first metalization layer 9a and the second metalization layer 9b, are formed on the first ground plate 9.
• a printed metallic line 11 on the substrate 8 in the center between the first metalization layer 9a and the second metalization layer 9b is the conductor of the transmission line.
• the portion of the printed metallic line 11 that extends into the waveguide 1 is considered the transition probe 12.
• the shape and width of probe 12 can be varied.
• the probe has a taper angle 13 measured from a base perpendicular to the metallic line 11.
• Probe 12 couples electric signals between waveguide 1 and transmission line 2. Because the metalization of ground plate 10 is removed within the waveguide, the probe 12 is not shielded by the ground plane. This ensures coupling between the coplanar line and the waveguide.
• Conductors 14 in the form of cylindrical metallic pins electrically connect the first ground plate 9 and the second ground plate 10 through the substrate 8. They are known as “via holes” or “piated-through holes” and are formed through the substrate close to the inside wall of the waveguide. This short circuits the electric field of dielectric modes to thereby achieve propagation of energy into the coplanar mode.
• coplanar lines are susceptible to less spurious energy dissipation into the substrate than microstrip transmission line, there is still some tendency for the energy from the waveguide to propagate within the substrate. This increases insertion loss which includes power lost in reflections between the waveguide and transmission line, ordinary impedance loss in electrical conductors, and the loss of power into the substrate which comprises the transmission line.
• Insertion loss is measured as the output power, measured under the center conductor, divided by the input power into the waveguide.
• the electrical conductors 14 are preferably formed through the substrate parallel to the electric field of electromagnetic radiation with the substrate. In Maxwell's equation, the electric field is zero measured parallel to a conducting surface. Thus, the additional conductors reflect the signal energy away from the substrate so that less energy is lost from propagation into the substrate. As a result, the signal only passes on the center conductor in the desired transmission line mode.
• the conductors 14 are formed close to the end of the portion of the substrate 8 that is not in the waveguide. It was empirically determined that a maximum spacing of .2 wavelengths between vias would minimize the loss of signal energy into the substrate.
• the transition functions by coupling the electric field in the waveguide 1 to the probe 12 of the transmission line extending into the waveguide.
• the via holes significantly improve operation by preventing the propagation of energy into the substrate. Without the conductors 14, this energy would be lost, e.g., by going off in spurious directions or reflected back into the rectangular waveguide. It is noted that in Figure 1 the width of the substrate 8 extending into the waveguide 1 is less than the width of the waveguide
• the portion of the substrate 8 inside the waveguide 1 may have a width equal to the full waveguide width. It has empirically been found that ultimate performance is relatively insensitive to probe and substrate width.
• the waveguide would usually extend in the direction of the viewer of Figure 1 and would be terminated with a short circuit at a distance of approximately one-quarter wavelength from the substrate's point of entry into the waveguide.
• the model has all dimensions 22.9 times the size of a typical millimeter-wave version of the transition and then gives identical performance at 1/22.9 times the millimeter-wave frequency in accordance with well accepted scaling laws for electromagnetic waves.
• the transition gave less than 1% reflected power over the 3.36 GHz to 4.41 GHz frequency range.
• a transition 22.9 times smaller would give this performance from 77 to 101 GHz.
• a short circuit was placed in the waveguide and a reflection coefficient close to unity was measured in the coplanar waveguide. This verifies that the transition does not radiate or couple into the dielectric substrate.
• a preferred embodiment of the invention has been described in the form of a rectangular waveguide to coplanar transmission line transition. Instead, the waveguide may be elliptical, circular, cylindrical, ridged, square, etc.
• the transmission line may be microstrip rather than coplanar.

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• Waveguides (AREA)
• Testing Or Measuring Of Semiconductors Or The Like (AREA)

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• 1993
  • 1993-04-02 TW TW082102464A patent/TW212252B/zh active
  • 1993-04-27 WO PCT/US1993/003904 patent/WO1993022802A2/en active Application Filing
• 1994
  • 1994-06-08 US US08/286,982 patent/US5867073A/en not_active Expired - Lifetime

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