Abstract
In this work, the design, fabrication and characterization of micro-air-channel-based unit cells aimed at phase control exploitable in 5G-mmwave applications are reported. The basic unit cell consisted of rectangular dielectric blocks (RDB) placed onto a thin substrate, realized by means of a resin polymer. The RDB effective relative permittivity was changed by tuning specific design parameters and infill density percentage (ID%), that was engineered through the introduction of a number of uniformly distributed micro-air channels. The reflected phase variation was numerically quantified in terms of frequency range and ID%, thus proving that a controlled phase variation can be accomplished depending on air-channel number. The prototypes were fabricated by means of the micro-inverted Stereolithography (SLA). In order to assess the accuracy of the SLA technology on the dimensions imposed by the high aspect ratio of the structures, larger unit cells operating in the X band were first fabricated. The acquired technological know-how has been subsequently exploited to fabricate smaller unit cells operating at mmwave. Geometrical characterizations of the prototypes, performed via a visual system setup, put in evidence the technological challenges, especially faced to realize open micro-air channels. In particular, as smaller micro-channel were actually obtained for some samples, a consequent increase of the actual ID% and effective relative permittivity values was experienced by the related unit cells. Nonetheless, the experimental results performed on the fabricated prototypes in the X band and mmwave range were in good agreement with the numerical ones, confirming the phase variation vs. ID% trends of the simulated unit cell arrays.
Highlights
Fifth-Generation (5G) communications have recently attracted the attention of the scientific community and of the wider public due to their promise to enhance and accelerate the interconnection among devices and people [1]
The unit cells were designed to allow the control of the reflected phase: this goal was obtained by tuning the unit cell size and the infill density percentage (ID%), and so, the effective relative permittivity of the structures
Array configurations of unit cells having different sizes and ID% values were numerically analyzed via Finite Element Method (FEM) analysis; the numerical results showed that very small phase variation over a wide band can be obtained especially in the mmwave range, depending on the air-channel number
Summary
Fifth-Generation (5G) communications have recently attracted the attention of the scientific community and of the wider public due to their promise to enhance and accelerate the interconnection among devices and people [1]. The design of the unit cell is a delicate task, since the elements must introduce controllable phase shift, which can be generally accomplished by a variation of the effective relative permittivity (εr−eff). Dielectric resonator antennas (DRAs) located on a thin substrate were considered as unit cells for a RA operating in the Ka band (26-40 GHz) [4]: the relative permittivity variation and consequent phase shift were accomplished by changing the DRA length. As described, the ID% was implemented artificially by introducing a number of squared air micro-channels within each RDB: this action allowed to fine-tune the relative permittivity of each unit cell and, control the induced phase shift variation on a wider frequency range. Scattering parameter S11 and phase shift measurements were performed in the X band and mmwave range on the fabricated UC arrangements: results and discussion are reported in Sections V and VI
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