To address the challenging needs of small size, wide bandwidth, and low-frequency applicability, a novel phase shifter implementation is introduced that utilizes tunable active differential inductors within all-pass networks. The inductor tuning is used to achieve phase shifts up to 180°. A switchable active balanced-to-unbalanced transition (balun) circuit is included in front of the all-pass network to complement its phase shift capability by another 180°. In addition, the all-pass network is followed by a variable-gain amplifier to correct for gain variations among the phase shifting states and act as an output buffer. Although active inductors have previously been used in the design of various components, to the best of our knowledge this is the first time that they have been used in an all-pass phase shifter. The approach is demonstrated with an on-chip design and implementation exhibiting wideband performance for S- and L-band applications by utilizing the 0.5-μm TriQuint pHEMT GaAs monolithic microwave integrated circuits (MMIC) process. Specifically, the presented phase shifter 1 x 3.95 mm² die area and operates within the 1.5-3-GHz band (i.e., 2:1 bandwidth) with 10-dB gain, less than 1.5-dB root-mean-square (rms) gain error and less than 9° rms phase error. Comparison with the state-of-the-art MMIC phase shifters operating in S- and L-bands demonstrates that the presented phase shifter exhibits a remarkable bandwidth performance from a very compact footprint with low-power consumption. Consequently, it presents an alternative for the implementation of wideband phase shifters where all-passive implementations will consume expensive die real estate.

A millimeter (mm)-wave beam steering antenna consisting of L lens antenna subarrays (LASs) is introduced. Each LAS hosts an M-element feed antenna array at its focal plane. The desired feed antenna of each LAS is excited through a single-pole multiple-throw (SPMT) switching network. The pole of each SPMT is connected to a mm-wave phase shifter (PS). The SPMT and PS states can be utilized jointly to steer the radiation pattern. For a given aperture size, the LAS size (i.e., L) can be adjusted to make a tradeoff between the total number of PSs (L) and switch throws (M). This can reduce the PS-related hardware complexities. The concept is demonstrated through a 38 GHz antenna consisting of L = 4 LAS. Each LAS is capable of hosting an M = 5 element aperture-coupled patch antenna array. The antenna prototype uses a single-patch antenna per LAS with mechanical movement to demonstrate the concept without the SP5T networks. The antenna performs with 8.5% |S ₁₁ | <; -10 dB bandwidth, 15.7 dBi gain, 5.2° H-plane half-power beamwidth, and 75° field of view.

Capability of 3D printing for developing wideband multilayered antenna systems packaged with active RF circuit components remains relatively unexplored. To address this gap, this manuscript demonstrates wideband patch antenna that is integrated with a polarization selection switch. Antenna bandwidth is enhanced with customized substrate thicknesses and stacked patch layers. Switch is integrated with 3D vertical transitions to achieve wide bandwidth, smaller packaging, and low-loss. To enable future antenna array applications, a detailed investigation is also presented to maximize the performance of the microstrip feed lines by adjusting the substrate thickness and deposition process. The antenna consists of 13 dielectric and conductive layers. Specifically, the manuscript demonstrates the lowest attenuation in the literature for a fully printed microstrip line with 0.25 dB/cm measured loss at 18 GHz. The antenna operates with more than 80% radiation efficiency and 45% bandwidth. The polarization switch is embedded within the antenna structure. The antenna retains a high cross-polarization ratio of 20 dB due to 3D feed line transitions and symmetric location of the switch with respect to the antenna feeds.

A microfluidic-based reconfiguration approach is presented for realizing a reflection phase shifter. The phase shifter consists of quadrature hybrid coupler with reflective microstrip line terminations. A selectively metallized plate (SMP) that can be repositioned inside a microfluidic channel is brought in close proximity (<;10 μm) of the reflective microstrip line terminations to vary their electrical lengths through capacitive RF short mechanism. The concept is demonstrated through a 9.5 GHz X-band phase-shifter design. Specifically, the design exhibits a footprint of 24 × 15 mm ² , operates with <;0.95 dB insertion loss, and attains the 360° phase shift with a total of 9.5 mm SMP motion resulting in 1.95 s total actuation time with the selected external micropumps. These phase shifters may be suitable for applications that prioritize low-loss and high power handling capability over reconfiguration speed.

Data rate and energy efficiency performance of mmWave wireless communication systems consisting of a new lens antenna subarray (LAS) based hybrid multiple input multiple output (MIMO) architecture is investigated. The LAS architecture degenerates into traditional hybrid MIMO architecture (TA) or single lens antenna array architecture (SLA) when the lens diameter of the subarray is reduced or enlarged, respectively. It is shown that under mmWave channel scattering conditions, LAS architecture operates with a data rate approaching that of TA while significantly exceeding the data rate of the SLA. Due to the reduced hardware complexity and power consumption, LAS architectures operate with a significantly improved energy efficiency. In an example system consisting of 64 and 16 transmitter and receiver antennas with 2 RF chains, it is shown that the LAS architecture operates with 2× energy efficiency and 98% spectrum efficiency. In a larger hybrid MIMO antenna systems, LAS architecture is expected to benefit even more.

An essential method to investigate neuromodulation effects of an invasive neural interface (INI) is magnetic resonance imaging (MRI). Presently, MRI imaging of patients with neural implants is highly restricted in high field MRI (e.g., 3 T and higher) due to patient safety concerns. This results in lower resolution MRI images and, consequently, degrades the efficacy of MRI imaging for diagnostic purposes in these patients. Cubic silicon carbide (3C-SiC) is a biocompatible wide-band-gap semiconductor with a high thermal conductivity and magnetic susceptibility compatible with brain tissue. It also has modifiable electrical conductivity through doping level control. These properties can improve the MRI compliance of 3C-SiC INIs, specifically in high field MRI scanning. In this work, the MRI compliance of epitaxial SiC films grown on various Si wafers, used to implement a monolithic neural implant (all-SiC), was studied. Via finite element method (FEM) and Fourier-based simulations, the specific absorption rate (SAR), induced heating, and image artifacts caused by the portion of the implant within a brain tissue phantom located in a 7 T small animal MRI machine were estimated and measured. The specific goal was to compare implant materials; thus, the effect of leads outside the tissue was not considered. The results of the simulations were validated via phantom experiments in the same 7 T MRI system. The simulation and experimental results revealed that free-standing 3C-SiC films had little to no image artifacts compared to silicon and platinum reference materials inside the MRI at 7 T. In addition, FEM simulations predicted an ~30% SAR reduction for 3C-SiC compared to Pt. These initial simulations and experiments indicate an all-SiC INI may effectively reduce MRI induced heating and image artifacts in high field MRI. In order to evaluate the MRI safety of a closed-loop, fully functional all-SiC INI as per ISO/TS 10974:2018 standard, additional research and development is being conducted and will be reported at a later date.