DC to 40 GHz coaxial-to-microstrip transition for 100- mu m-thick GaAs substrates

The design, design approach, and test results are presented for a simple coaxial-to-microstrip transition. The approach provides improved performance over the basic coaxial-to-microstrip transition by causing a TEM-to-quasi-TEM transformation through a tapering of the coaxial line for 432+or-51 mu m (<<6% of lambda /sub 0/ at 40 GHz) prior to impinging a portion of the resultant quasi-TEM field directly across the microstrip's dielectric at the coaxial-microstrip interface. Tests show that the return loss for the transition into a 50- Omega microstrip line on a 100- mu m-thick GaAs substrate is better than 16.9 dB per transition from 200 MHz to 40 GHz. A cover having a height of 1.9 mm and a width of 2.6 mm had little or no influence on test results.<
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