EP0318198A1

EP0318198A1 - A dielectric waveguide

Info

Publication number: EP0318198A1
Application number: EP88310757A
Authority: EP
Inventors: Kailash C. Garg; Joseph C. Rowan; Jeffrey A. Walter
Original assignee: WL Gore and Associates Inc
Current assignee: WL Gore and Associates Inc
Priority date: 1987-11-27
Filing date: 1988-11-15
Publication date: 1989-05-31
Also published as: DK657888D0; NO885083L; IL88213A0; FI885138L; NO885083D0; FI885138A7; AU1886488A; FI885138A0; IE883452L; PT89066A; GB2212989A; JPH01170101A; GB8826691D0; DK657888A

Abstract

A dielectric waveguide for the transmission of electromagnetic waves is provided comprising a core (12) of a plastic material and having one or more layers of polytetrafluoroethylene (PTFE) cladding (14) overwrapped around the core. The core material is polystyrene, polychlorotrifluoroethylene, polyethylene, polypropylene, polysulfone or polycarbonate.

Description

This invention relates to a dielectric waveguide for the transmission of electromagnetic waves.
Electromagnetic fields are characterised by the presence of an electric field vector E orthogonal to a magnetic field vector H. The oscillation of these components produces a resultant wave which travels in free space at the velocity of light and is transverse to both of these vectors. The power magnitude and direction of this wave is obtained from the Poynting vector given by:
P = E x H (Watts /m²)
Electromagnetic waves may exist in both unbounded media (free space) and bounded media (such as a coaxial cable or a waveguide). This invention relates to the behaviour of electromagnetic energy in a bounded medium and, in particular, in a dielectric waveguide.
For propagation of electromagnetic energy to take place in a bounded medium, it is necessary that Maxwell's Equations are satisfied when the appropriate boundary conditions are employed.
In a conventional metal waveguide, these conditions are that the tangential component of the electric field, E_t, is zero at the metal boundary and also that the normal component of the magnetic flux density, B_n, is zero.
The behaviour of such a waveguide structure is well understood. Under excitation from external frequency sources, characteristic field distributions or modes will be set-up. These modes can be controlled by variation of frequency, waveguide shape and/or size. For regular shapes, such as rectangles, squares or circles, the well-defined boundary conditions mean that operation over a specific frequency band using a specific mode is guaranteed. This is the case with most rectangular waveguide systems operating in a pure TE₁₀ mode. This is known as the dominant mode in that it is the first mode to be encountered as the frequency is increased. The TE_mn type nomenclature designates the number of half sinusoidal field variations along the x and y axes, respectively.
Another family of modes in standard rectangular waveguides are the TM_mn modes, which are treated in the same way. They are differentiated by the fact that TE_mn modes have no E_z component, while TM_mn modes have no H_z component.
U.S. Patent 4,463,329 discloses a dielectric waveguide of a shaped article having a core of polytetrafluoroethylene and having one or more layers of expanded, porous polytetrafluoroethylene overwrapped on or around the core.
The dielectric waveguide disclosed in U.S. Patent 4,463,329 does not have such well-defined boundary conditions. In such a dielectric waveguide, fields will exist in the polytetrafluoroethylene (PTFE) cladding medium.
The absolute value of the decaying field at any point in the cladding is dependent upon a number of factors. These include the difference in dielectric constant between the core and cladding media, the frequency of operation, the physical dimensions involved and, of course, the applied field. On a given construction, more field will be induced in the cladding region at lower frequencies of operation. This effect is undesirable since the propagating wave becomes more "loosely bound" thus reducing stability characteristics and leading to a general deterioration in loss and VSWR performance. We have found that one means of overcoming this problem is to increase the dielectric constant of the core by using materials other than PTFE as described in U.S. Patent 4,463,329. Alternatively, at a given frequency the overall size of a waveguide may be reduced by using a smaller, higher dielectric constant core other than the PTFE as described in U.S. Patent 4,463,329.
According to the present invention there is provided a dielectric waveguide for the transmission of electromagnetic wave comprising a core of a solid plastic material, one or more layers of PTFE cladding overwrapped around said core, and an electromagnetic shielding layer covering said cladding. The or each cladding layer may be extruded, unsintered PTFE; extruded, sintered PTFE; expanded, unsintered, porous PTFE; or expanded, sintered, porous PTFE. Such cladding layer may contain a filler. The shielding layer preferably is aluminised KAPTON (Registered Trade Mark) polyimide tape. The dielectric waveguide may be further overwrapped with a tape of carbon-filled PTFE. The core may be polystyrene, polychlorotrifluoroethylene, polyethylene, polypropylene, polysulfone or polycarbonate.
An embodiment of the invention will now be particularly described, by way of example, with reference to the accompanying drawings in which:-

Figure 1 is a side elevation, with parts cut away, of a dielectric waveguide according to the invention and showing one launcher, and
Figure 2 is a cross-sectionsl view of the dielectric waveguide taken along the line 2-2 of Figure 1.

A dielectric waveguide for the transmission of electromagnetic waves is provided comprising a core of a plastic material and having one or more layers of polytetrafluoroethylene (PTFE) cladding overwrapped around the core. The core material is a material selected from the class consisting of polystyrene, polychlorotrifluoroethylene, polyethylene, polypropylene, polysulfone and polycarbonate.
Figure 1 shows a dielectric waveguide according to the invention. When launcher 20 with conventional flange 21 is connected to dielectric waveguide 10, within the dashed lines, electromagnetic energy enters the launcher 20. An impedance transformation is carried out in the taper 13 of the core 12 of waveguide 10 such that the energy is coupled efficiently into the core 12 of dielectric waveguide 10. Once captured by the core 12, propagation takes place through the core 12 which is surrounded by cladding 14. The core 12 is a plastic material and the cladding is polytetrafluoroethylene, preferably expanded, porous polytetrafluoroethylene tape oeverwrapped over core 12. Propagation uses the core/cladding interface to harness the energy. The core material is polystyrene, polychlorotrifluoroethylene, polyethylene, polypropylene, polysulfone or polycarbonate.
To prevent cross-coupling or interference from external sources, an electromagnetic shield 16 is provided as well as an external absorber 18. The shield is preferably aluminized KAPTON (Registered Trade Mark) polyimide tape, and the absorber is preferably carbon-filled PTFE tape.
The cross-sectional view of Figure 2 shows rectangular plastic core 12 overwrapped with PTFE tape 14 and also shows shield layer 16 and absorber layer 18.

Claims

1. A dielectric waveguide for the transmission of electromagnetic waves characterized by a core of a solid plastic material, one or more layers of PTFE cladding overwrapped around said core, and an electromagnetic shielding layer covering said cladding.

2. A dielectric waveguide according to claim 1 characterized in that the or each said cladding layer is of extruded, sintered or unsintered PTFE.

3. A dielectric waveguide according to claim 1 characterized in that the or each said cladding layer is of expanded, sintered or unsintered, porous PTFE.

4. A dielectric waveguide according to claim 1 characterized in that the or each said cladding layer contains a filler.

5. A dielectric waveguide according to claim 1 characterized in that said shielding layer is of aluminised KAPTON (Registered Trade Mark) polyimide tape.

6. A dielectric waveguide according to claim 7 characterized in that it is overwrapped with a tape of carbon-filled PTFE.

7. A dielectric waveguide according to claim 1 characterized in that said core is of polystyrene, polychlorotrifluoroethylene, polyethylene, polypropylene, polysulfone or polycarbonate.