Membrane-supported coplanar waveguides (CPW's) are needed for low-dispersive and low-loss millimeter-and submillimeter waves as well as for power sensor applications. This letter demonstrates CPW's on polyimid membranes micromachined on gallium arsenide (GaAs) that meet the requirements of a typical microwave monolithic integrated circuit (MMIC) process. The influence of the design parameters is simulated by finite difference in frequency domain (FDFD), in excellent agreement with the experiment. For a membrane CPW with ground to ground spacing of only 50 m and characteristic impedance of 115 , relative effective dielectric constants near 1.02 and attenuation of 0.14 dB/mm at 25 GHz have been achieved.

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