A novel DGS-Marchand balun from 40 to 80 GHz with IF-tap for mixer design

Novel wideband planar Marchand baluns in the millimeter wave range from 40 to 80 GHz are presented. The circuits can be fabricated in a regular thin-film process due to less stringent specifications by using defected ground structure (DGS) technology. The return loss of the balun is better than 10 dB from 40 -80 GHz and better than 15 dB from 43-73 GHz. The amplitude balance is better than 2 dB from 40-80 GHz and better than 0.5 dB from 43-73 GHz. The phase balance error is smaller than 8deg over the entire frequency range. Simulation and measurement results are fitting very well. Several additional versions of the proposed balun are presented providing IF-paths to build a complete double-balanced mixer circuit. To show the applicability of the baluns, a low cost hybrid ring mixer for an IF of 500 MHz has been fabricated. Measurement results show a flat conversion loss of about 9 dB from 33 -69 GHz. Further measurement results for a second mixer for IF frequencies up to 23 GHz are presented.