Coupled Loops for High-Frequency Chip-to-Antenna Interconnection at 24 GHz

Abstract

This paper examines the use of two coupled loops as an alternative method of connection for high-frequency signals between passive elements on microwave laminates and integrated circuits (ICs) replacing traditional interconnect methods such as wire bonds and solder bumps, which require costly post back-end-of-line processing. The loops harness both electric and magnetic fields in order to create the interconnection. Additionally, they can be placed around the perimeter of the IC where they would not occupy space that may be required for other components such as spiral inductors. In order to test the chip-to-antenna system, the interconnect was fabricated with one metallic loop on a low-loss microwave laminate and another on a 0.13- μm CMOS IC. These loops were then stacked in order to couple the signal from an IC onto a planar antenna array (printed on the laminate). This antenna-to-chip system was measured to have a center frequency near 23 GHz, with fractional bandwidth of 15%, and a peak antenna gain over 5 dBi; the transmission loss in the loop coupling is estimated to be 0.5 dB at 19 GHz (89% power transfer). The radiation pattern from the antenna (a four-element uniform array of bow-tie dipoles) has a 3-dB beamwidth of 16 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> in the elevation plane and 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> in the azimuth plane, making it potentially useful for application in mass-produced automotive radar systems, where harsh conditions create demand for a more robust interconnect method than wire bonding.