Experimental study of multihole directional couplers providing a rippled response

The directivity versus frequency of a multihole waveguide coupler may be expressed as a polynomial whose complex roots, if placed off the unit circle, provide the opportunity of a rippled response. Two designs using seven equispaced holes, one each with 3.0 and 0.5 dB ripple, were implemented at X-band, and experimental validation of the theory has been excellent.<
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