A High Directivity Microstrip Coupler Technique - IEEE Xplore

and be less 10SSY.2 Above 7DB coupling, however, there
is no need for the cross-over; a single coupler can be
etched with the necessary tolerances for reproducibility.
In order to exploit the broadband possibilities of a
wiggly coupler, a 54 to 290 MHz 3 section 18DB coupler was
built. The 3 Sections were individually built and tested
before being patched together. Figure IV shows the coupling
and directivity performance of this coupler, built on glass
epoxy circuit board.
The side effects of wiggling seem to be to increase the
coupling for a given line spacing, and to slightly increase
the loss. When the wiggle spacing becomes an appreciable
fraction of a wavelength, the coupler will no longer appear
continuous, but this does not appear to be a serious limi–
tation until well above X band.
What has been described here is a technique for the broadband
equalization of the even and odd mode velocities of a
microstrip coupler. This technique makes possible simple,
multi-octave microstrip couplers of more than 20DB directivity.
1 H.E. Brenner “Perturbations of the critical parameters
of quarter-wave directional couplers” IEEE MTT and
J.E. Morris, IEEE TMTT, July 1968. Overlay Coupler
2 Julius Lange, IEEE TMTT, December 1969
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