Claims
- 1. A tunable waveguide stub, comprising:
- a waveguide sized for use with frequencies of interest between 1 and 1000 GHz;
- a thin insulator in the waveguide;
- a metallic bar movably mounted within the waveguide and insulated therefrom by the insulator; and
- a series of openings completely through the metallic bar forming sections of high impedance alternating with sections of the bar having low impedance to provide an adjustable short circuit in the waveguide for the frequencies of interest.
- 2. The tunable waveguide stub claimed in claim 1, wherein the openings each form a section of high impedance having a length equivalent to a portion of a wavelength at the frequencies of interest.
- 3. The tunable waveguide stub claimed in claim 1, wherein the openings each form a section of high impedance having a length equivalent to substantially the same portion of a wavelength at the frequencies of interest.
- 4. The tunable waveguide stub claimed in claim 1, wherein the openings are regularly shaped and spaced.
- 5. The tunable waveguide stub claimed in claim 4, wherein the sections of high impedance formed by each opening are in the range of about one eighth to one quarter wavelength at the frequencies of interest.
- 6. The tunable waveguide stub claimed in claim 5, wherein the sections of high impedance formed by each opening are on the order of one eighth wavelength at the frequencies of interest.
- 7. The tunable waveguide stub claimed in claim 6, wherein the openings are circular.
- 8. The tunable waveguide stub claimed in claim 6, wherein the openings are rectangular.
- 9. The tunable waveguide stub claimed in claim 4, wherein the sections of low impedance formed by the portion of the bar between each opening are in the range of about one eighth to one quarter wavelength at the frequencies of interest.
- 10. The tunable waveguide stub claimed in claim 9, wherein the sections of low impedance formed by the portion of the bar between each opening are on the order of one eighth wavelength at the frequencies of interest.
- 11. A method of tuning a waveguide stub, comprising the steps of:
- snugly mounting a metallic bar for motion in a waveguide sized for use with frequencies of interest between 1 and 1000 GHz;
- insulating the bar from the waveguide; and
- forming an adjustable short circuit in the waveguide with a series of openings completely through the metallic bar creating sections of high impedance alternating with sections of the bar having low impedance.
- 12. The method of tuning a waveguide stub claimed in claim 11, wherein the openings each form a section of high impedance having a length equivalent to a portion of a wavelength at the frequencies of interest.
- 13. The method of tuning a waveguide stub claimed in claim 11, wherein the openings each form a section of high impedance having a length equivalent to substantially the same portion of a wavelength at the frequencies of interest.
- 14. The method of tuning a waveguide stub claimed in claim 11, wherein the openings are regularly shaped and spaced.
- 15. The method of tuning a waveguide stub claimed in claim 14, wherein the sections of high impedance formed by each opening are in the range of about one eighth to one quarter wavelength at the frequencies of interest.
- 16. The method of tuning a waveguide stub claimed in claim 15, wherein the sections of high impedance formed by each opening are on the order of one eighth wavelength at the frequencies of interest.
- 17. The method of tuning a waveguide stub claimed in claim 16, wherein the openings are circular.
- 18. The method of tuning a waveguide stub claimed in claim 16, wherein the openings are rectangular.
- 19. The tunable waveguide stub claimed in claim 14, wherein the sections of low impedance formed by the portion of the bar between each opening are in the range of about one eighth to one quarter wavelength at the frequencies of interest.
- 20. The tunable waveguide stub claimed in claim 19, wherein the sections of low impedance formed by the portion of the bar between each opening are on the order of one eighth wavelength at the frequencies of interest.
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 USC 202) in which the Contractor has elected to retain title.
1. Field of the Invention
The present invention relates to adjustable backshorts for making variable length waveguide stubs by producing short circuits in the waveguides at high frequencies. In particular, this invention relates to non-contacting backshorts for use with frequencies in the 1 to 1000 GHz range.
2. Description of the Prior Art
Conventional waveguide systems utilize adjustable short circuits to tune the waveguides and produce more complex waveguide components. At higher frequencies, contacting backshorts--as described below with reference to FIG. 1--are normally used because of the very small physical dimensions of the waveguides. The contact area in such backshorts is critical and must make good contact to produce an acceptable short circuit. These backshorts provide good short circuits over the entire waveguide band.
However, the contacting areas of such waveguides eventually degrade from sliding friction. It is often difficult to achieve and maintain a uniform contact between the backshort and the waveguide walls at higher frequencies where the waveguide dimensions become fractions of a millimeter.
Some of these limitations have been overcome by the development of noncontacting backshorts, which are described in more detail with reference to FIG. 2 below. Noncontacting backshorts use a thin insulator of plastic film sold under the trademark "MYLAR" to prevent contact between the backshort and the waveguide and to permit the backshort to slide smoothly therein without appreciable wear.
Such noncontacting backshorts utilize a series of high and low impedance sections in order to produce a good radio frequency, or rf, short circuit and therefore a large reflection. The series of high and low impedance sections are typically placed at .lambda..sub.g /8 to .lambda..sub.g /4 in length, where .lambda..sub.g is the wavelength in the waveguide.
However, at very high frequencies above 100 GHz, the thin high impedance sections become too thin to easily fabricate and the conventional noncontacting backshort is no longer strong enough to slide snugly in the waveguide.
What is needed is a backshort for producing short circuits in waveguides that has the advantages of noncontacting waveguides but is sufficiently rugged and easy to fabricate for use at high frequencies in the range of 1 to 1000 GHz.
The preceding and other shortcomings of the prior art are addressed and overcome by the present invention that provides, in a first aspect, a method of tuning a waveguide stub by snugly mounting a metallic bar for motion in a waveguide sized for use with frequencies of interest between 1 and 1000 GHz, insulating the bar from the waveguide, and forming an adjustable short circuit in the waveguide with a series of openings through the metallic bar creating sections of high impedance alternating with sections of the bar having low impedance.
In another aspect, the invention provides a tunable waveguide stub, including a waveguide sized for use with frequencies of interest between 1 and 1000 GHz, a thin insulator in the waveguide, a metallic bar movably mounted within the waveguide and insulated therefrom by the insulator, and a series of openings through the metallic bar forming sections of high impedance alternating with sections of the bar having low impedance to provide an adjustable short circuit in the waveguide for the frequencies of interest.
The foregoing and additional features and advantages of this invention will become further apparent from the detailed description and accompanying drawing figure or figures that follow. In the figures and written description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawing figures and the written description.
US Referenced Citations (4)
Non-Patent Literature Citations (2)
| Entry |
| McGrath et al, "Development of a 600-700 GHz SIS Receiver", Symposium proceedings, First Int'l Symposium on Space Terahertz Technology, pp. 409-433, Mar. 1990. |
| Brewer et al, "Dual-Harmonic Noncontacting Millimeter Waveguide Backshorts: Theory, Design, and Test" IEEE Transactions on Microwave Theory and Techniques, pp. 708-714, 1982. |
Patent Grant
5138289
