RF-MEMS for 5G applications: a reconfigurable 8-bit power attenuator working up to 110 GHz. Part 2-Experimental characterisation of the RF behaviour

摘要

RF-MEMS technology is indicated as a key enabling solution to realise the high-performance and highly-reconfigurable passive components that future 5G communication standards will demand for. In this work, divided in the previous Part 1 and the current Part 2, a novel design concept of an 8-bit reconfigurable power attenuator manufactured in the RF-MEMS technology available at the CMM-FBK, in Italy, is presented, tested and discussed. As reported in Part 1, the device features electrostatically controlled MEMS ohmic switches, in order to select/deselect resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. In the current Part 2, fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated in a full 3D Finite Element Method (FEM) environment. Despite the attenuator complexity, the simulation approach leads to accurate prediction of the experimental behaviour. The device exhibits attenuation levels (S21) in the range from - 10 to - 60 dB, up to 110 GHz. In particular, the S21 shows flatness from 15 down to 3-5 dB, from 10 MHz to 50 GHz, while less linear traces up to 110 GHz. A comprehensive discussion is developed around the voltage standing wave ratio (VSWR), employed as quality indicator for the attenuation levels. Finally, margins of improvement at design level are also discussed, in order to overcome the limitations of the presented RF-MEMS device.