Miniaturized-Element Frequency Selective Surface Metamaterials: A Solution to Enhance Radiation of RFICs

In this article, a technique to improve the radiation characteristics of an active CMOS circuit is presented. A miniaturized-element frequency selective surface (MEFSS) cover is utilized on top of the chip to provide gain enhancement, which is essential for many applications such as radar and communication systems. This is important due to the restrictions on the thickness of metallic layers, losses in substrate, and limitations in real estate. The MEFSS cover consists of partially reflecting surface (PRS) and high-impedance surface (HIS) creating a Fabry-Pérot-type cavity (FPC). When the MEFSS structure is used, the height of FPC can be reduced without causing any deterioration to the antenna radiation. A proximity patch antenna is embedded in the HIS layer, which is fed by a small metallic trace on the last layer of chip using the coupling mechanism. By utilizing the transverse-equivalent network (TEN) of the structure and imposing the resonance condition, the geometrical parameters of the MEFSS unit cell is calculated. For demonstration purposes, a scaled MEFSS cover for gain enhancement at the center frequency of 10 GHz is designed, fabricated, and tested. The measured results, which are in agreement with simulations, show that the proposed technique is reliable in practice and gain enhancement of 9 dB can be achieved for a single-patch antenna.