This paper reports a Ka-band microstrip patch antenna fabricated using post-CMOS compatible process technology. The antenna uses an air cavity underneath the patch radiator that is supported on thin membrane. To start with, a thin dielectric film of silicon dioxide is deposited on <100> single crystal silicon substrates by RF sputtering process. The membrane is then realized using bulk micromachining technology. The antenna structure was analyzed and optimized using the finite-element method (FEM) based Ansoft High Frequency Structure Simulator software (version 9). The antenna structure mounted on a test jig with K-connector was used for testing its performance. The measured results of the fabricated prototype antenna agree quite closely with the simulated results. The fabricated antenna resonated at 36 GHz with -10 dB return loss bandwidth of 1.2 GHz. In the absence of access to well-established MEMS foundry, the RF sputtering process reported here can be advantageously used for rapid prototyping of many antenna structures.