This paper presents the design, fabrication and “on-wafer” characterization of multi-membrane-supported and polymer-cavity-backed monopole antenna and 2× 1 patch antenna array operating in the 135-GHz frequency range. The designs were fabricated on two-layer benzocyclobutene (BCB) material membrane obtained by micromachining of the low resistivity silicon. The silicon material is removed underneath the monopole antenna to produce a cavity surrounded by metal and filled with polymer. This polymer filled cavity provides a better support to the membrane than conventional air cavity which is extremely important for practical applications. In the meantime, the higher synthesized effective dielectric permittivity of the BCB-polymer mixed region than BCB-air mixed one provides the possibility for compact antenna array designs. The proposed monopole antenna shows a measured impedance bandwidth from 124 to 136 GHz for |S11| less than -10 dB and maximum measured gain of 6.74 dBi at 131 GHz; while the 2×1 patch antenna array achieved a measured impedance bandwidth from 126.5 to 138 GHz for |S11| less than -10 dB and maximum measured gain of 8.66 dBi at 130 GHz.