Fluidically Tunable Frequency Selective/Phase Shifting Surfaces for High-Power Microwave Applications

Abstract

We examine fluidically tunable periodic structures acting as highly-selective frequency selective surfaces (FSSs) or spatial phase shifters (SPSs) capable of providing phase shifts in the range of 0 -360 . These devices are multi-layer periodic structures composed of non-resonant unit cells. The tuning mechanism is based on integrating small, movable liquid metal droplets with the unit cells of the periodic structure. By moving these liquid metal droplets by small distances within the unit cell, the structure's frequency response can be tuned continuously. Using this technique, a fluidically tunable FSS with a fifth-order bandpass response is designed and its tuning performance is examined for various incidence angles and polarizations of the incident EM wave. Additionally, electronically tunable counterparts of the same structure are also designed and their tuning performances are examined under short-duration high-power excitation conditions. It is demonstrated that such electronically tunable FSSs/PSSs demonstrate extremely nonlinear responses. Since the fluidically tunable structure examined in this work does not use any nonlinear devices, its response is expected to remain linear for such short-duration high-power excitation conditions. The tuning performances of these fluidically tunable periodic structures are also experimentally demonstrated by fabricating three prototypes and characterizing their responses in a waveguide environment.

Harmonic-Suppressed Miniaturized-Element Frequency Selective Surfaces With Higher Order Bandpass Responses

“…They also have been used to design tunable FSSs [17], [25] as well as FSSs for high-power microwave (HPM) applications [25]- [26].…”

Large-scale fluidic tuning of sub-wavelength periodic structures

“…The aforementioned studies examining liquid-tunable FSSs focused on characterizing the tuning capabilities of such structures at the unit cell level [11]- [12]. However, in a large tunable periodic structure, multiple unit cells exist and they have to be controlled simultaneously.…”

“…Recently, our group proposed a new fluidic tuning technique for designing tunable periodic structures with subwavelength periodicities [11], [12]. This technique does not rely on using any electronic devices and eliminates the need for using biasing networks or individually integrating active elements with each unit cell of the periodic structure.…”

“…The technique is based on embedding capillary tubes filled with liquid metal slugs within a periodic structure composed of subwavelength capacitive and/or inductive surface impedances. By moving the liquid metal droplets within the unit cell of the structure the capacitance values of the capacitive surface impedances can be changed in a continuous fashion very much like what is done using electronic varactor [12]. Using such liquid varactors, tunable miniaturized-element frequency selective surfaces were designed and experimentally demonstrated at the unit cell level.…”

“…This liquid tuning approach offers a wider tuning bandwidth compared to other liquid tunable FSSs utilizing liquid dielectrics. Moreover, it has been also shown that this class of tunable FSS is expected to be capable of handling significantly higher transient power levels as it does not use electronic devices that are inherently nonlinear [12].…”