Frequency reconfigurable impedance matching networks based on LTCC, fluidic and MEMS technologies for agile RF amplifiers

Abstract

New frequency reconfigurable impedance matching networks (MNs), or tuners, which can be used to realize various field programmable RF devices, such as amplifiers, are proposed. By enabling field programmability of RF devices, the proposed MNs make it possible to reduce considerably the component count in a multi-standard RF chain and to maximize hardware reuse. Both fluidic and MEMS (MicroElectroMechanical Systems) technologies are considered for designing alternative MNs covering different frequency bands. In both cases, Low Temperature Co-fired Ceramics (LTCC) technology is used as a low-loss 3D substrate in the MN realization in order to simultaneously achieve miniaturization, high integration levels and low-cost packaging solutions. First, the architecture and operation principle of the proposed RF impedance MNs, which are common to both fluidic and MEMS solutions, are introduced and discussed. The selected architecture is based on eight cascaded 2-state cells where each cell’s electric parameters alternate between two sets of values from one state to the other. In the fluidic approach, the cells are made of cavities over a coplanar waveguide and the two states correspond to when the cavity is empty and when the cavity is filled with deionized (DI) water. In the MEMS approach the cells are made of capacitive switches, with the up and down switch positions providing the two desired states. The design of the individual cells and entire cascaded turner are then undertaken. Analytical equations are developed and used to establish the initial dimensions ofthe individual cells, i.e., the fluidic cell and the MEMS switch and 3D field simulations are used to complete the design of the cells and the entire tuners. Alternative miniaturization approaches for the MEMS-based tuner are also investigated. Simulation results show that is possible to achieve good Smith chart coverage with the fluidic tuner for frequencies between 0.8 GHz and 2.4 GHz with a tuner that measures 26 mm X 10 mm X 1.5 mm, while he MEMS-based tuner provides comparable coverage for frequencies between 2 GHz and 7 GHz with a tuner that can be miniaturized down to 5.51 mm X 2.54 mm X 1.19 mm. Second, the fabrication and testing of the designed cells and tuners is undertaken. For the fluidic cells and tuner, the standard LTCC process is adequate for prototyping and has been used to fabricate and test multiple cells and tuners. Good agreement between simulations and measurements are observed for the individual cells and the entire tuner, confirming the predicted coverage. For MEMS solution, a new MEMS-on-LTCC process, necessary for fabricating the MEMS-based tuner is first developed to take into account the specificities of the LTCC substrate. Details about all process steps needed to build a capacitive switch on LTCC are elaborated. The encountered challenges are highlighted and some means to circumvent them are proposed. As an application, reconfigurable RF amplifiers using the developed fluidic and MEMS MNs are built. They show a gain varying around the maximum available gain at different points in the frequency bands of interest, i.e. [0.9GHz- 2.4 GHz] and [2 GHz- 7GHz] for the fluidic and MEMS based architectures respectively. Finally, perspectives for enhanced RF tuners are discussed. Introducing air- filled transmission lines in the MEMS based tuner as a way to reduce dielectric losses may improve the overall performances. Employing liquid metal instead of DI-water in fluidic tuner allows removing concerns about dielectric losses and enabling reconfigurabilty at higher frequencies. Modules for tuners’ automatic control and activation are also proposed.

Date	14 Feb 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Ammar B. Kouki (Supervisor)