The HMC329 chip is a miniature passive double balanced mixer which can be used as an upconverter or downconverter from 25 - 40 GHz in a small chip area of 0.84 mm x 0.55 mm. Excellent isolations are provided by on-chip baluns, and the chip requires no external components and no DC bias. The mixer chip is designed to be used in Local Multi- Point Distribution Systems (LMDS), microwave point to point radios, and SATCOM applications. Measurements were made with the chip mounted and ribbon bonded into in a 50-ohm microstrip test fixture that contains 5-mil alumina substrates between the chip and K-connectors. Measured data includes the parasitic effects of the assembly. RF connections to the chip were made with 0.076 mm (3-mil) ribbon bond with minimal length <0.31mm (<12 mil).