Waveguide to microstrip line coupling apparatus
View Patent ↗Electrical coupling apparatus providing transition between a high radio frequency waveguide and a perpendicularly oriented microstrip line without use of a shorting cap fixes an open end of the waveguide perpendicularly to a dielectric substrate. The microstrip line is carried on the substrate and couples through a hole in the waveguide wall to a microstrip patch on the substrate within the waveguide having a resonance with the waveguide encompassing a predetermined high radio frequency bandwidth of signals to be conducted by the apparatus. A plurality of parallel conducting members form a via fence aligned with the waveguide wall and extending through the substrate to electrically connect the waveguide to a planar ground conductor that covers the opposite side of the substrate, including the area under the open end of the waveguide.
1. High frequency electrical waveguide to microstrip line coupling apparatus comprising:
a waveguide comprising a generally cylindrical wall;
a substrate having a ground plane conductor one side and a microstrip line coupled to a microstrip patch on an opposite side, the microstrip patch having a resonance with the waveguide encompassing a predetermined high radio frequency bandwidth of signals to be conducted by the apparatus, the waveguide having an end perpendicularly attached to the substrate surrounding and substantially centered on the microstrip patch and further having a wall opening adjacent the substrate through which the microstrip extends; and
a via fence comprising a plurality of parallel conductors aligned with the waveguide wall and extending through the substrate to electrically couple the waveguide to the ground plane conductor, the ground plane conductor extending substantially across the entire area of the substrate bounded by the via fence.
2. The high frequency waveguide to microstrip line coupling apparatus of claim 1 wherein the microstrip line is coupled to the microstrip patch through a quarter wavelength impedance transformer.
3. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 2 wherein the microstrip line, quarter wavelength impedance transformer and microstrip patch comprise a single, continuous electrical conductor.
4. The high frequency waveguide to microstrip line coupling apparatus of claim 1 wherein the patch has a pair of opposite sides generally aligned with the microstrip line having edge lengths tuned to help determine the predetermined high radio frequency bandwidth.
5. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 4 wherein the microstrip patch is substantially rectangular.
6. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 4 wherein at least one of the opposite sides is bent toward the other to provide a longer current path than that of a straight side having the same end points, whereby the tuned wavelength of the microstrip patch is longer than that produced by straight sides having the same ends.
7. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 6 wherein the at least one of the opposite sides is at least partially arcuate.
8. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 7 wherein the at least one of the opposite sides comprises one of a circular arc and an elliptical arc.
9. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 6 wherein the opposite sides are both arcuate.
10. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 6 wherein at least one of the opposite sides comprises at least two non-parallel lines, at least one of which is a straight line segment.
11. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 10 wherein the at least one of the opposite sides comprises a plurality of straight line segments.
12. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 11 wherein each of the opposite sides comprises a plurality of straight line segments.
13. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 4 wherein at least one of the opposite sides comprises a convex portion between a pair of concave portions.
14. The high frequency electrical waveguide to microstrip line coupling apparatus of claim 1 wherein the microstrip line and microstrip patch comprise a single, continuous electrical conductor.