MICROWAVE COUPLER

Abstract: A microwave coupled line device constructed to equalize even and odd mode delay and comprising an outer conductor and first and second inner conductors at least one of which has insulation bonded thereto and separated by the thickness of said insulation therebetween. There is also provided an insulating sleeve disposed in the outer conductor and adapted to accommodate the first and second inner conduc­ tors. Means are provided for filling the void between the insulating sleeve and the outer conductor with an insulating material preferrably having a dielectric constant in the range of 2.6-3.5.

Description: BACKGROUND OF THE INVENTION The present invention relates in general to coupled line devices and is concerned, more particularly, with quadrature hybrids and couplers including directional couplers constructed in accordance with the principals of the present invention and having in particular improved directivity and power handling capabilities. In accordance with the present invention the device has preferred high directivity and low power consumption. U.S. Patent 3,358,248 shows a previous version of a coupled line device including a pair of insulated inner conductors and a common outer conductor with the inner conductors spaced a distance corresponding substantially to a quarter wavelength at the center operating frequency. If the parallel transmission line center conductors could be imbeded in a uniform dielectric material, whether air or some other material, the propagation velocities will be equal. However, in practice this does not occur and in the device described in U.S. Patent 3,358,248, the conductors are not imbeded in a material having a uniform dielectric. For example, the coating on the wires typically has a relatively high dielectric constant which may be in the order of 2.7. In the previous construction which employed a teflon support bead, the teflon has a dielectric constant in the order of 2.0. This inconsistency in dielectric constants slows the odd mode propagation in comparison to the even mode. Also, the wires have a twist which can make the electrical length larger for the odd mode than for the even mode. Furthermore, there tend to be air voids between the wires and the surrounding teflon. These air voids, depending upon location, may either increase or decrease the odd mode velocity compared to the even mode velocity. Accordingly, it is an object of the present invention to provide an improved miniaturized coupled line device in which the propagations delay of both the even and odd modes are substantially equalized. Another object of the present invention is to provide an improved coupler in accordance with the proceeding object and which is characterized by high directivity over a wide frequency range. Another object of the present invention is to provide a coupled line device that may be constructed either as a TEM directional coupler or as a 3dB hybrid and which is characterized by relatively high power handling capabilities. Still another object of the present invention is to provide a high performance miniaturized coupled line device that is relatively easy and inexpensive to fabricate. A further object of the present invention is to provide an improved fabrication technique for a microwave coupler that enables all air voids to be filled thus improving operation and also preventing moisture entry into the device. Another object of the present invention is to provide an improved microwave coupler device that is constructed to furthermore provide improved center conductor cooling. The invention relates to a microwave coupled line device according to the preamble of claim 1 and known from Patent document DE-A-1466 350. The objectives of the inventions are attained by the features of the characterising portion of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Numerous other objects, features and advantages of the invention should now become apparent upon reading of the following detailed description taken in conjunction with the accompanying drawing, in which: FIG. 1 is a cross-sectional view through the wire line device of the present invention in a first embodiment; FIG. 2 is a cross-sectional view through an alternate embodiment in which the wire line device is round in construction rather than the square version shown in FIG. 1; FIG. 3 shows a third alternative embodiment of the invention in a cross-sectional view similar to the view of FIG. 2 but with the supporting sleeve removed; and FIG. 4 is a longitudinal sectional view of the embodiment of FIG. 1 showing the manner in which the wire line is arranged to form a directional coupler device. DETAILED DESCRIPTION With reference now to the drawing, and more particularly, FIG. 1 thereof, there is shown a cross section view of one embodiment of the invention or which is referred to herein as a square version employing an outer square brass tubing 10 which has an outer square dimension of 0.25 inch and an inner dimension of 0.222 inch. Disposed within the square brass tubing 10 is a teflon block or sleeve 12 having a through passage for receiving the inner conductors. The brass member 10 defines the outer conductor. Within the hollow centrally disposed passage in the teflon sleeve 12 there are provided inner conductors which includes a first conductor 14 with its associated insulation 16. Similarly, there is a second inner conductor 18 with its associated covering or layer of insulation 20. In the embodiment described in FIG. 1, there is provided a thin wall mylar or polyester tubing 22 which is used to encapsulate the inner conductors and hold them in relatively fixed spaced interrelationship. It is noted that in the embodiment of FIG. 3 to be described hereinafter the tubing 22 is not used. In constructing the device of FIG. 1, once the inner conductors are disposed in the tubing 22, then the entire assembly is inserted into the teflon block 12 and the next step is to then fill the void, particularly the one that exists between the tubing 22 and the teflon block. In FIG. 1, as well as the other embodiments described herein, the inner conductors may be copper wire of no. 20 AWG. The insulation on each of wires may be of a type teflon/kaptan. As indicated previously, the tubing 22 may be a heat shrinkable mylar. The potting material is illustrated in FIG. 1 as filling areas 24 and 26. The area 24 is filled between the tubing 22 and the teflon sleeve 12. The area 26 is filled about the inner conductors and between the inner conductors and the tubing 22. The potting material may be Sylguard 170 A/B. This is used because of its relatively high dielectic constant. This is a silicone base which is liquid to which a catalyst is added which causes curing thereof. In the liquid state, the material is quite viscous and thus when injected into the areas disclosed in FIG. 1 fills all voids thus tending to equalize the odd and even mode velocities. This material is also of relatively high dielectric constant on the order of 2.9 particularly in comparison with the dielectric constant of the teflon sleeve 12 which is on the order of 2.0. By using this higher dielectric constant material there is a decrease of the odd mode velocities so as to provide equalization between the even and odd mode propagation velocities. The potting in these voids also fills any air spaces preventing moisture entry and improves the cooling of the center conductors. FIG. 1 fills all voids thus tending to equalize the odd and even mode velocities. This material is also of relatively high dielectric constant on the order of 2.9 particularly in comparison with the dielectric constant of the teflon sleeve 12 which is on the order of 2.0. The preferred range for dielectric constant is 2.6-3.5 but the range of dielectric constant that is used depends on the dielectric constant of the insulating sleeve and the insulation bonded thereto. By using this higher dielectric constant material there is a decrease of the even mode velocities so as to provide equalization between the even and odd mode propagation velocities. The odd mode velocity is slowed by the Kapton insulation and mylar insulation. The potting in these voids also fills any air spaces preventing moisture entry and improves the cooling of the center conductors. As indicated previously, the embodiment of FIG. 1 is a square version. In FIG. 2 there is provided a round version in that the teflon sleeve 12a is cylindrical. In the embodiment of FIG. 2 the metallic outer conductor 10 may be identical to the tubing used in FIG. 1. However, because the teflon is cylindrical and the outer conductor is square there is a void area filled with material 11 which may be the aforementioned material Sylguard 170A/B. The other part of the construction of FIG. 2 is substantially the same as shown and previously discussed in connection with FIG. 1. Thus, in the embodiment of FIG. 2 there are provided inner conductors 14 and 18 and insulation 16 and 20 thereon. There is also provided in the embodiment of FIG. 2 the heat shrinkable mylar tubing 22. The only other difference in the embodiment of FIG. 2 is that the dielectric compensating insulating material Sylguard 170 A/B is only disposed in the outer area between the tubing 22 and the teflon block. In the embodiment of FIG.1, this higher dielectric constant material was used in both areas 24 and 26. A further embodiment of the present invention is illustrated in FIG. 3. In FIG.3 the same reference characters have been used to identify the same parts as previously described in FIGs.1 and 2. The embodiment of FIG.3 is constructed without the use of the heat shrinkable mylar tubing 22. In this case the inner conductors with their attached insulation join together and are essentially force fitted into the opening in the teflon sleeve 12a. Thus, in this embodiment the open passage in the teflon sleeve may be made smaller so that there is an appropriate force fit and it is this force fit of the inner conductors into the teflon sleeve that maintains their alignment. Once aligned in the teflon sleeve, then the higher dielectric constant material is injected into the void area between the inner conductors and the teflon sleeve, as well as between outer conductors 10 and insulating sleeve 12A. In an alternate embodiment, the outer conductor 10 may be of circular cross section. Potting material 11 will fill any small voids between circular conductor 10 and round insulating sleeve 12A. FIG. 4 is a longitudinal sectional deal showing the wire line construction of the present invention as embodied in a coupler device in which there are provided four terminal pairs A,B, C and D. When these terminal pairs are terminated in are constructed are suitable for operation over, for example, octave bandwidths in the 150MHz to 2GHZ band. The couplers are suitable for narrow band operation for frequencies well beyond 2GHz. The devices are available in either 0.25 square inch or 0.25 inch round cross-sections as illustrated herein. As a hybrid or coupler, the devices offer an VSWR of 1.1 or less, an isolation greater than 30dB and a power rating of 500 watts at 1GHz. Typically, a square cross section hybrid, 2.38 inches long, operates over a frequency range of 750 to 950MHz and weighs less than 0.5 ounces. When used as a directional coupler, the device displays equally good performance over a narrower band. Typically, a square cross section, 20dB directional coupler, 1.30 inches long, operates over a frequency range of 88 to 108MHz and weighs less than 0.5 ounces. A principal application of devices of the present invention is in printed circuit work, where it is inconvenient to achieve either quadrature hybrid or direction coupler performance using planar techniques. The exterior of the unit is tin plated for ease in soft soldering and epoxy bonding. The wires are cut and trimmed to simplify assembly. In an octave bandwidth version of the invention there is provided for quarter wave coupling (excluding losses) at mid band of 2.70dB ± .15dB. In addition, a narrow band version is available for frequency bandwidths less than 30% with mid band coupling (excluding losses) of 3.0dB ± .15dB. The modules are supplied cut to length. The length of a hybrid in inches is determined by dividing 1.97 by the center frequency in GHz. Having now described a limited number of embodiments of the present invention, it should now be apparent to those skilled in the art that numerous other embodiments are contemplated as falling within the scope of the present invention as defined by the appended claims. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included just for the sole purpose of increasing intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A microwave coupled line device operative over a frequency range embracing a predetermined central frequency, comprising, means (10) defining an outer conductor, first (14) and second (18) inner conductors at least one of which has insulation (16,20) bonded thereto and separated by the thickness of said insulating sleeve, preferably for a distance corresponding substatially to quarter wavelength at the center of the operating frequency and separated by a greater distance elsewhere, an insulating sleeve (12,12A) disposed in said outer conductor and adapted to accommodate said first and second inner conductors, CHARACTERIZED IN THAT insulating material means (24,26) are provided in a void between the insulating sleeve and the inner conductors, said insulating material means, having a relatively high dielectric constant in comparison with the dielectric constant of the insulating sleeve and in the range of a dielectric constant of 2.6 - 3.5, said insulating material means having a dielectric constant selected in comparison with the dielectric constant of the insulating sleeve so as to decrease the even mode velocities, so as to approach equalization between the even and odd mode propagation velocities. A microwave coupled line device according to claim 1, characterized in that each said first and second inner conductors have an insulation (16,20) thereon. A microwave coupled line device according to claim 2, characterized in that said insulating sleeve (12,12A) is of Teflon material. A microwave coupled line device according to claim 3, characterized in that said outer conductor (10) is a metal tubing. A microwave coupled line device according to claim 1, characterized in that a polyester sleeve (22) is disposed between said insulating sleeve (12,12A) and said inner conductors (14,18), the polyester sleeve being adapted to encase said inner conductors. A microwave coupled line device according to claim 1, characterized in that said insulating material means (24,26) has a dielectric constant on the order of 2.9 and greater than the dielectric constant of the insulating sleeve. A microwave coupled line device according to claim 6, characterized in that said inner conductors (14,18) each include copper wire. A microwave coupled line device according to claim 1, characterized in that said insulating sleeve (12) is square. A microwave coupled line device according to claim 1, characterized in that said insulating sleeve (12A) is round. A microwave coupled line device according any of the preceding claims, characterized in that further insulating material means (11) are provided in a further void defined between said insulating sleeve (12A) and the outer conductor (10).

Inventors: CHAPELL, HARRY
Applicants: SAGE LABORATORIES, INC.
Application year: 1984
Main classification: H01P5
IPC codes: H01P5