Junction between two microwave transmission lines of different field structures

DETAILED DESCRIPTION A junction according to our invention ensures full coupling between two kinds of line which can be produced as planar structures on substrates having high dielectric constants.
More particularly, the coupling links a slot line having an asymmetrical field structure and a line having a symmetrical field structure, i.
e.
a microstrip line.
The interest in such a transition, which is very simple, is enhanced by the facts that slot lines have many applications, more than other kinds of line, as they are usually employed in the field of filters, ferrites, couplers, and circuits containing semiconductor components, and that it is possible to associate them with series arrangements consisting of localized members, whereas parallel arrangements are needed in the case of the other types of lines.
From the point of view of its electrical behavior, the transition according to our invention needs to be capable of transmitting microwave energy under the most favorable conditions of voltage standing-wave ratio and insertion loss over a wide frequency band.
Before describing a transition which meets the above requirements, it may be useful to give some definitions.
FIGS.
1a and 1b, are plan and sectional views of a slot line 1 formed by an elongate gap 10 in a ground-plane layer 2 which is applied to a dielectric substrate 3.
The dielectric support provides a mechanically solid base for metal conductors which are generally applied by known photo-etching or photolithographic production techniques.
In a slot-type propagation line, virtually the entire energy is propagated in the dielectric 3 and is concentrated between the edges 4 and 5 of the slot or gap 10.
The thickness of the dielectric substance depends on its nature, and the width of the slot line thus determines the characteristic impedance of the line.
The dielectric substance may be polytetrafluorethylene, a beryllium oxide, an alumina ceramic, quartz, or a ferrite.
In FIG.
1b the lines of force of the electrical field E are shown dotted whereas those of the magnetic field H are solid