Application of Krank

• Decision Date: 11 March 1971
• Docket Number: Patent Appeal No. 8447.
• Citation: 58 CCPA 976,438 F.2d 609
• Parties: Application of Wolfgang KRANK and Gunther Mohring.
• Court: U.S. Court of Customs and Patent Appeals (CCPA)

58 CCPA 976, 438 F.2d 609 (1971)

Application of Wolfgang KRANK and Gunther Mohring.

Patent Appeal No. 8447.

United States Court of Customs and Patent Appeals.

March 11, 1971.

Jay M. Cantor, Washington, D.C., attorney of record, for appellants.

S. William Cochran, Washington, D.C., for the Commissioner of Patents. R. V. Lupo, Washington, D.C., of counsel.

Before RICH, ALMOND, BALDWIN, and LANE, Judges, and FORD, Judge, United States Customs Court, sitting by designation.

LANE, Judge.

This appeal is from the decision of the Patent Office Board of Appeals affirming the rejection of all claims in appellants' application serial No. 363,166, filed April 28, 1964, for "Elliptical Waveguide for Electromagnetic Waves." We affirm.

The specification states that it was old in the art to use smooth-walled waveguides of elliptical cross-section, the elliptical shape contributing good (wide-band) electrical transmission characteristics as compared with tubes of circular cross-section. It was also old to use waveguides having corrugated or bellows-like surface configurations, since this feature lent mechanical flexibility to the waveguides. The specification goes on to say:

Experience gained with corrugated tubes and bellows-type tubes as cable sheaths, lead sic; led? to the expectation that a corrugated tube or bellows-type tube of elliptical cross-section would meet the mechanical requirements of a waveguide, at least under certain conditions. However, it could not be expected that the electrical relations would be as simple as for smooth walled elliptical tubes. It was rather to be expected that the depth of the corrugations as well as their pitch would have considerable influence on the electrical behavior which could not be predicted by calculations. It was, therefore, necessary to rely on empirical results which were difficult to ascertain because of the multiplicity of parameters involved.

Appellants, apparently through experiments, found that if the ratio of the eccentricity es of the ellipses formed by the corrugation depressions to the eccentricity e1 of the ellipses formed by the corrugation ridges is held in the range of 1.025 to 1.075, preferably at 1.050, good flexibility and good transmission characteristics are obtained. If the ratio es/e1 is less than 1.025, indicating for normal sizes and thicknesses that the corrugations are not very deep, little flexibility is obtained. If the ratio exceeds 1.075, excellent flexibility is obtained, but a "detour factor" due to the deep corrugations results in a significant increase in damping or attenuation of the transmitted waves.

Appellants also found that if the corrugations are formed by a continuous helical depression in the waveguide surface, as opposed to the bellows-like configuration, the helical pitch should not be greater than one-eighth the operating wavelength, in order to prevent the occurrence of "reflection peaks." None of these specification assertions has been challenged by the Patent Office.

Claim 1 reads:

A low-loss corrugated waveguide which is coilable on a drum comprising a hollow tube having corrugation crests and corrugation troughs; said waveguide having an elliptical cross-section wherein the elliptical area varies along the longitudinal axis of said hollow tube from a large ellipse at a cross-section including a corrugation crest to a small ellipse at a cross-section including a corrugation trough; said large ellipse having a major axis of length D1, a minor axis of length d1, and an eccentricity e1 equal to 1-(d1/D1)2; said small ellipse having a major axis of length Ds, a minor axis of length ds, and an eccentricity es equal to 1-(ds/Ds)2; and the ratio es/e1 being greater than 1.025 and less than 1.075, whereby to provide minimal electrical damping factor and maximum flexibility for winding said waveguide on a drum.

Claim 2 adds the limitation that the corrugations are helical; claim 3 adds the further limitation that the ratio of eccentricities is 1.05. Claim 4 depends from claim 2 and adds the limitation that the helical pitch is no greater than 1/8 the operating wavelength. Claim 5 depends from claim 1 and specifies bellows-like corrugations; claim 6 depends from claim 5 and further specifies that the ratio of eccentricities is 1.05.

All claims stand rejected as obvious over a patent to Schuttloffel and Krank¹ (Krank being one of the appellants here) in view of Ragan² and Lines.³

Schuttloffel discloses a helically corrugated waveguide as illustrated in Figs. 1 and 2 of the patent. Schuttloffel states that the waveguide has "an elliptical cross section" which may be made by "pressing or flattening a corrugated hollow line with a round cross section."

Ragan discloses a bellows-type corrugated rectangular waveguide having rounded corners, as shown in his Fig. 5.45.

In both Schuttloffel and Ragan a principal object is to provide waveguides having mechanical flexibility without significant impairment of electrical transmission properties.

Lines need not be discussed in any detail. It is relied upon primarily to show that to obtain both...