In this work, four designs of (Bi)CMOS on-chip antenna (OCA) at 90GHz and 140GHz are shown and compared, aiming at the difficult task of broadside radiation (off the top chip metal surface). A bowtie-shaped slot antenna is fabricated and expected to offer a gain of 1.5dB at 90GHz and 30GHz impedance bandwidth. Another design of slot antenna backed by a cavity, which is fully isolated from the circuits, gives a gain of 2 dB at 140GHz and 5 GHz bandwidth. Additionally, a design of a slot antenna based on an integrated waveguide in (Bi)CMOS showing 1 dB gain is proposed. At last, a proposed E-shaped patch antenna, which only occupies 0.7 mm 0.7 mm area, shows 2 dB gain with 10 GHz bandwidth. © 2011 IEEE.