Semiconductor-substrate integrated 3D-micromachined W-band helical antennas

This paper investigates for the first time concepts of W-band dielectric-core helix antennas which are fabricated by three-dimensional micromachining into the volume of a semiconductor (high-resistivity silicon) wafer substrate. The maximum antenna gain is achieved by free-etching the antenna but loading the core of the helical antenna with a dielectric-rod tailor-made out of the substrate, and by properly modifying the geometry of the substrate-integrated ground plane. The simulation results show that an optimized antenna concept has a return loss S11 of -22.3 dB at the nominal frequency of 75 GHz, and a 3dB-bandwidth of 2.5 GHz. For the whole band from 69 to 84 GHz, the reflection coefficient is better than -10 dB. A maximum gain of 13.2 dB and a half-power beamwidth (HPBW) of smaller than 40° are obtained for a single antenna. The front-to-back (F/B) ratio is better than 23.5 dB with an axial ratio of 0.94. An eight-element helix line array is demonstrated and has a maximum gain of 22.3 dB with a HPBW of 7° in the y-z plane and an F/B ratio of 23.71 dB.