Comments on "Reduced-length rat-race couplers"

For original paper see ibid., vol.50, no.12, p.2593-8. A rat-race coupler having three equal arms of arbitrary electrical length has been analyzed. It has been shown that an infinite number of solutions exist for the coupler design, some of them having lower electrical lengths than a conventional coupler. Theoretical predictions have been verified by implementing, in microstrip technology, a 19λ/18 length coupler operating at 0.9 GHz. The purpose of this paper is to analysis general hybrid ring having sections of length λ/n, n integer, and obtained general expressions for the S-parameters. It was shown that the existing designs for 3-dB power division (i.e., the rat-race coupler) and for arbitrary power division, follow as special cases. Also presented was a general design method for the 3-dB hybrid-ring, which led to a number of new designs, many of them having smaller electrical circumferences.