Symmetric microwave mixer with improved isolation

Balun coupled microwave circuit layout and structure comprising:

• a dielectric substrate;
• ground plane means on a bottomside of said substrate;
• a first balun secondary conductor pair having first and second conductors and a second balun secondary conductor pair having third and fourth conductors, each conductor pair being on the bottomside of said substrate with the respective conductors of each of said first and second pairs extending from said ground plane means towards each other and terminating in respective spaced ends facing each other at a separation gap therebetween;
• a transmission line on the topside of said substrate juxtaposed said first and second pairs of secondary conductors for interacting therewith to dual balun couple a field balanced between the first secondary conductor pair across said gap and a field balanced between the second secondary conductor pair across said gap;
• fifth and sixth conductors having topside coplanar sections on the topside of said substrate and having respective linking sections extending down through said substrate to respective bottomside coplanar sections on the bottomside of said substrate, said bottomside sections having spaced ends proximate the spaced ends of said first and second pairs of secondary conductors and said bottomside sections extending oppositely away therefrom;
• and
• a diode mixer having first and second separate, isolated sections, said first section comprising a first diode pair interconnecting the first and second conductors of said first secondary conductor pair and the bottomside section of said fifth conductor at coplanar connection points on the bottomside of said substrate for heterodyne modulation product signal generation, said second section comprising a second diode pair interconnecting the third and fourth conductors of said second secondary conductor pair and the bottomside section of said sixth conductor at coplanar connection points on the bottomside of said substrate for heterodyne modulation product signal generation.