CA2449596A1 - Dielectric cable system for millimeter microwave - Google Patents

Abstract

The subject of the invention is a cable-like device called "FiberGuide" that conducts millimeter wave energy from one place to another in a manner similar to a fiber optics cable, with the shield and spacing to ensure the lowest possible loss, plus the methods of interfacing of the said cable-like device to each other as well as to traditional microwave structures such as metallic resonating cavities and metallic waveguides.

Description

Dielectric Cable System For Millimeter Microwave DESCRIPTION
Introduction Issue of the optimal method of transmitting energy from one place to another with the highest possible efficiency and the lowest possible losses is encountered in every area of engineering in practically every application dealing with electrical, electromagnetic or acoustic forms of energy. Such optimal solutions are very different at each of the spectral range. At low frequency of electromagnetic energy, when it is referred to as electrical energy we transmit power through electrical cables consisting of two isolated conductors (single phase AC, or DC) or more conductors (3 or more phase AC). In the domain of high frequency signals, typically 1 OOkHz-1 GHz the optimal choice of a cable is coaxial cable consisting of a center conductor surrounded by a dielectric insulator and surrounded by a conductive shield, or a twisted pair cable similar to the one for low frequency AC power but with controlled impedance and low-loss dielectric insulation. Beyond about SGHz up to about 30GHz the optimal, the least lossy and most convenient way of transmitting microwave energy are metalic waveguides. Beyond 30GHz however, metallic waveguides are becomming increasing lossy which makes it difficult to transmit microwave power over large distances. At those frequency, in the so-called millimeter microwave range such waveguides are limited in practical applications to about couple of meters distance due to high losses. From millimeter microwave up to the optical range of electromagnetic energy, dielectric waveguidesloptic fibers become the most optimal way of energy transmission.
Explanation of terms:
Waveguide: tubular circular or rectangular in cross section hollow structure made of conductive material (e.g. metal), that conducts electromagnetic energy along its length and inside it.
Dielectric Waveguide: tubular circular or rectangular in cross section solid structure that conducts electromagnetic energy along its length inside and in the immediate vicinity outside of it.
Fiber Optic Cable: Dielectric Waveguide applied in the optical range.
"FiberGuide": dielectric waveguide in foam isolation that is used for cinducting millimeter microwave energy; the subject of this patent.
Coupler: mechanical device that allows joining two waveguides (dielctric waveguide to dielectric waveguide or dielectric waveguide to metal waveguide) together such that the energy transmission is unhidered.

EMBODIMENT OF THE INVENTION
In this embodiment, designed to transmit millimeter microwave at 70-90GHz, dielectric waveguide consists of a polipropylene or PTFE cable/wire with diameter of about 2mm (see FIG.1 ) surrounded by air filled foam that has a very low dielectric constant, and made out of material of very low dielectric losses at those frequency. The material of choice is polypropylene or PTFE. The whole structure is surrounded by a metallic or metallized (from the inside} shield or a sleeve. A material of choice would be silver or aluminum coated polyester foils underneath PVC jacket, or copper foil underneath a PVC or PTFE jacket .
An alternative cross section (to circular) for the center waveguide is rectangular with approx 2:1 aspect ratio, to allow retaining the definite polarization plane of the transmitted wave.
Coupler for joining two dielectric cables together.
The couple consists of a plastic pipe a few cm long, threaded inside from both ends, see FIG.2. Inner diameter of the pipe is a fraction of millimeter smaller than the outer diameter of the Dielectric Cable outer sleeve. One end is threaded with a right-hand-side thread, the other left-hand side such, that when the dielectric cable is pushed from both end, both ends of the cables may be screwed in simultaneously by turning the pipe, until both open sections of the cables will meet in the middle. Since the millemeter microwave fit is tolerant to within quarter-wavelength, that is about 1 mm in this case, the fit need not be as tight and precise as in case of optical fiber junction. In this particular example a 0.5 or even 1 mm gap may be tolerable.
RESULTS OF PROTOTYPE TESTING
[To be included]
Conclusions:
The laboratory tests prove the concept and demonstrate that it works

Claims (5)

1. A device composed in the shape of wire made out of plastic material that acts as a dielectric waveguide for millimeter microwave electromagnetic radiation

2. The device of claim 1 wherein the wire has circular, eliptical or rectangular cross-section.

3. The device of claim 1 and 2 wherein the plastic wire is surrounded by a insulating foam that has lower dielectric constant than the wire of claim 1.

4. The device of claim 1,2 and 3 that is shielded by an outer sleeve made out of a material harder than the foam of claim 3.

5. The device of claim 1, 2, 3 and 4 wherein the shield of claim 4 may be a composite material that is transparent, absorbing or reflective to microwaves.