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, low power consumption and high thermal transfer.
U.S. Pat. No. 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 imbedded in a uniform dielectric material, whether air or some other material, the even and odd mode propagation velocities will be equal. However, in practice this does not occur and in the device described in U.S. Pat. No. 3,358,248, the conductors are not imbedded 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 constant 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. Futhermore, 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 preceding 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 as a TEM directional coupler and which is characterized by relatively high power handling capabilities.
Another object of the present invention is to provide a coupled line device that may be constructed as a 3 dB hybrid in which is characterized by relatively high powered 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 resulting from the filling of air voids.