Classifications

• • 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
  • H01P3/003—Coplanar lines

Definitions

• the invention pertains to coplanar transmission ** lines having a small size and very low impedance utilized in microwave integrated circuits.
• Coplanar waveguide transmission lines have found increased application in microwave circuits.
• the basic configuration of such a coplanar waveguide transmission line is shown in Figure 1.
• This basic configuration was suggested by Chang P. Wen in 1969 in an article "Coplanar Waveguide: A Surface Strip Transmission Line Suitable for Nonreciprocal Gyromag- netic Device Application", IEEE Transactions on Microwave Theory and Techniques, vol. MTT-17, No. 2, Dec. 1969, p. 1087, ff.
• This transmission line is fabricated ' entirely upon one surface of a dielectric substrate 10 and includes a center strip 12 of width disposed on the upper surface of a dielectric substrate 10 within a channel 13 of width W 2 cut in a ground plane 11.
• the impedance of this type of coplanar waveguide transmission line is determined by the ratio of the strip width W-, to the channel width 2 and the die ⁇ lectric constant of the material of the substrate.
• the lowest realizable transmission line impedance is . about 25 ⁇ . This corresponds to a ratio W-,/W 2 of ap ⁇ proximately 0.95.
• much lower impedances are desirable in some instances for implementation of " • particular microwave circuits. Lower impedances have hitherfore not been achievable in coplanar waveguide transmission lines since unrealizably small gap sizes would be required to reduce the impedance much below 25 ⁇ .
• a coplanar waveguide transmission line is constructed by arrang ⁇ ing a plurality of separate coplanar waveguide trans ⁇ mission lines of reduced size parallel to one another with a fixed ratio of W,/W 2 .
• fingers extend perpendicularly from the sides of a main center conductor. These fingers are inter ⁇ leaved with grounded fingers, the ends of which adjacent the main center conductor of the transmission line are interconnected through bond wires. This arrangement forms a low impedance transmission line in shunt with the main transmission line.
• a composite line of interleaved fingers is arranged in cascade with the main line.
• the main line is flared and longitudinal channels formed therein. Internal fingers are disposed longitudinally in each of these channels. The internal fingers are grounded at each end through bond wires.
• Figure 1 is a perspective/cross-sectional view of a prior art coplanar waveguide
• Figure 2 is a top view of a shunt-covered low impedance coplanar microwave transmission line accord ⁇ ing to a first embodiment of the invention
• Figure 3 is a top view of a series-connected low impedance coplanar microwave transmission line accord ⁇ ing to a second embodiment of the invention
• Figure 4 is a cross-sectional view of the device shown in figure 2.
• FIG. 5 is a plot of the characteristic im ⁇ pedance of a portion of a coplanar microwave transmis ⁇ sion line of the invention.
• a center or main conductor 12 of a primary transmission line is formed on the surface of a dielectric substrate in a channel 13 surrounded by a ground plane 11, similar to the prior art arrangement.
• a number of fingers 14 extend orthogonally from both sides, in a symmetric fashion, from the main conduc ⁇ tor 12 of the transmission line.
• only 3 such fingers 14 on each side of the main conductor 12 are shown. However, it may be preferred to use a larger number of such fingers depending upon the transmission line impedance desired.
• the fingers 14 are formed within channels 15 formed in the ground plane 11. Within the channels 15 also are formed ground fingers 16 which are inter ⁇ leaved with the fingers 14. The ends of the ground fingers 16 nearest the main conductor 12 are shorted together and connected to ground by bond wires 18 and 19 while the opposite ends are connected directly to the main part of the ground plane 11.
• Figure 4 shows an enlarged cross-sectional view taken through the fingers 14 and 16 of the arrangement shown in Figure 2.
• Figure 4 also shows the electric and magnetic field patterns which are produced when signals are applied to the transmission line. Because of the symmetrical pattern of the electric and mag ⁇ netic fields, the computation of the impedance of the transmission line can be reduced to a simple, single cell field problem of a known solution so long as all of the gaps between the fingers 14 and 16 in the channel 15 have a fixed width (here indicated by S) and all of the conductors, both the fingers 14 and the fingers 16, have another fixed width (here indicated as W). In this analysis, each individual conductive finger 14 is considered to be a simple transmission line of impedance Zw.
• This impedance Z£__> is somewhat higher than would be observed if the neighboring fingers 14 were removed.
• a transmission line of the type of Figure 2 was constructed.
• W 0.002 in.
• S 0.001 in.
• W/S 2.0 for a val ⁇ ue Z of 62.7 ⁇ .
• an impedance of 3.14 ⁇ with a total composite line width of only 0.118 in. could be realized.
• a second embodiment of a transmission line of the invention is shown in the top view of Figure 3.
• the main conductor 12 is flared and divided into a plurality of parallel transmission paths 21 of reduced width by longitudinally-extending channels 22.
• Within the channels 22 are disposed longitudinally-extending internal fingers 23. Both ends of all of the internal fingers 23 are intercon ⁇ nected and connected to ground through bond wires 18
• the bond wires 18 and 19 maintain the ground potential on the isolated internal ground fingers 23.

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• Waveguides (AREA)

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• 1983
  • 1983-01-13 EP EP83900599A patent/EP0099398A1/de not_active Withdrawn
  • 1983-01-13 WO PCT/US1983/000051 patent/WO1983002687A1/en unknown
  • 1983-01-20 IT IT8367058A patent/IT8367058A0/it unknown
  • 1983-01-21 IL IL67723A patent/IL67723A0/xx unknown

Non-Patent Citations (1)

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