A circuit assembly having a thin and large-area dielectric substrate and
improved grounding. To make the assembly, a circuit board comprising the
substrate, and a circuit pattern and a metal layer that are formed on
respective sides of the substrate. A bath of conductive bonding material
(e.g., a low melting point solder) is made inside a tray-like metal
chassis of the assembly. The circuit board is floated on the bath and
excessive portion of the conductive material is absorbed. A branch circuit
for branching a first path into at least two second paths is provided by
mainly using impedance transformers but by using fewest possible stub(s).
Also, the elements are arranged in symmetry around the axis through the
first path. This yields a wide operating frequency band. A
waveguide-microstrip line transition that is easy to work and low in
transition loss is provided by shaping the wider walls of the ridge
waveguide so as to spread out toward the end. Since doing this increases
the degree of freedom in design parameters, the width and the height of
the ridge can be fitted to that of the microstrip line and that of the
waveguide. The above elements is applicable to HF circuits, antennas and
communication systems.