A compact air-gap-free reconfigurable reflectarray with integrated absorptive bandstop filtering functionality is proposed in this article. It consists of compact unit cells that integrate a wideband antenna element with two switchable bandstop filters. One of the filters is built by series resonators, while the other filter is built by shunt resonators. By switching between the two filters using p-i-n diodes, the unit cell provides a stable 180° phase difference within the reconfigurable intelligent surface (RIS) reflection band for reflective beam steering while exhibiting an out-of-band absorptive response, thereby providing scattering suppression. As a proof-of-concept, a $15 \times 15$ element prototype operating at a center frequency of 10 GHz with a focal-length-to-diameter (F/D) ratio of 0.94 was designed, fabricated, and tested. Measurement results demonstrate a beam-scanning range of ±50° in the principal planes with a maximum gain of 19.8 dBi, corresponding to an aperture efficiency (AE) of 17%. In the out-of-band suppression region, the measured gain is more than 10 dB below the in-band peak, effectively suppressing out-of-band scattering. The proposed integrated antenna–filter design successfully validates a method for creating multifunctional RIS platforms, suitable for applications requiring both spatial wave control and spectral filtering.
Exceptional points (EPs) in non-Hermitian systems have enabled high-sensitivity inductive wireless sensing, and divergent exceptional points (DEPs) further enhance sensitivity by exploiting pole singularities. However, DEP-based sensing faces two critical bottlenecks: the stringent strong-coupling condition severely limits the interrogation distance, and fabrication-induced parameter deviations render conventional coupling-based EP recalibration inapplicable, as altering the coupling would destroy the divergent response. To address these challenges, we propose a pseudo-Hermitian (PH) inductor–capacitor (LC) near-field inductive wireless sensing system with a unidirectional feedforward network (FFN) that electronically enhances the effective coupling coefficient via flux-linkage amplification. This scheme enables DEP operation under weak mutual inductance, extending the interrogation distance from 2 to 10 mm, representing a fivefold improvement over existing DEP schemes. On the readout side, we introduce a virtual impedance compensation method that generalizes the monitoring condition from Im( $Z_{\mathrm {in}}) =0$ to Im( $Z_{\mathrm {in}}) = s$ , allowing restoration of the EP and the preset divergent response without adjusting any circuit parameters. Experiments validate that the proposed system achieves ultrahigh sensitivity to minute perturbations, with a normalized frequency shift of $\Delta \omega \approx ~2.73$ under a 5% loss perturbation, significantly outperforming conventional parity–time (PT)-symmetric reference systems with a maximum shift of only $\Delta \omega \approx ~0.62$ . This work provides a new paradigm for high-performance inductive telemetry by jointly addressing the interrogation distance and calibration limitations of DEP-based sensors.
Pushed by the availability of large fractional band-widths (FBWs), many well-established applications are focusing on the W-band spectrum for product deployment. Achiev-ing broadband operation with a flat amplitude response is challenging in the W-band, primarily due to the inherent high-frequency loss of transceiver components. For W-band communication systems, a positive gain-equalization amplifier with high output power is required to maintain the waveform integrity of high-speed signals. Conventional active equalizers require additional DC power and compromise linearity, whereas traditional passive equalizers generate a gain slope through frequency-dependent attenuation, resulting in an inherent gain penalty. To overcome these limitations, the proposed vector-sum equalizer (VSE) shapes the equalization slope through frequency-dependent phase synthesis, enabling increasingly constructive combining at higher frequencies, while simultaneously achieving a high gain-equalization range and a compact circuit area. The results show that the proposed VSE provides a linear gain-equalization slope of up to 0.4 dB/GHz. Based on the proposed prototype, the proposed power amplifier (PA) with positive gain equalization is implemented in a 0.1 mu m gal-lium arsenide pseudomorphic high electron mobility transistor (pHEMT) process. According to the measurement results, the PA obtains a saturated output power (Psat) of 24.8 dBm and an output 1 dB compression point (OP1dB) of 22.2 dBm at 71 GHz. The 3 dB gain bandwidth is approximately 37.1 GHz from 67.6 to 104.7 GHz, corresponding to a FBW of 43%. Moreover, at 86 GHz, the gain, input return loss, and output return loss are 19.3, -7.9, and -14.2 dB, respectively.
This work presents a stretchable variable capacitor actuated by a flexible polyvinylidene fluoride (PVDF) unimorph for wearable electronic systems. Strain mismatch between the piezoelectric PVDF active layer and the polyethylene terephthalate (PET) passive layer induces large out-of-plane deformation, enabling wide-range capacitance tuning through air-gap modulation. To evaluate device performance under both rigid and deformable conditions, two versions of the capacitor were fabricated on different substrates. Experimental characterization shows that the device achieves a maximum capacitance tuning ratio of 10.45 at a bias voltage of 150 V; the rigid device exhibited a quality factor of 97 at 1 GHz, while the stretchable device exhibited a quality factor of 29 at 0.5 GHz. The effects of bias voltage and operating frequency on the capacitance and quality factor were systematically investigated. In addition, voltage-controllable capacitance tuning was retained under uniaxial stretching, highlighting the mechanical adaptability of the device. To demonstrate practical applicability, the variable capacitor was further integrated into a resistor-capacitor low-pass filter circuit. These results establish a PVDF-unimorph-actuated variable capacitor architecture for quasi-static frequency trimming and impedance reconfiguration in wearable and flexible electronic systems.
This article presents an analytical formulation of the electric ( $\Psi _{E}$ ) and magnetic ( $\Psi _{H}$ ) point spread functions (PSFs) for quantitative near-field microwave imaging (NFMI) using an open-ended rectangular waveguide probe. The derivation employs the volume equivalence principle (VEP) to model the interaction between the probe’s radiated electromagnetic field and inhomogeneities within a target medium, with explicit treatment of depolarization effects and the full vectorial character of the $\text {TE}_{10}$ mode field distribution. The first-order Born approximation is applied to linearize the scattering problem, and the Lorentz reciprocity theorem is used to evaluate the modal coupling at the waveguide aperture. The resulting $\Psi _{E}$ and $\Psi _{H}$ capture both transverse and longitudinal field components and are parameterized by the dielectric contrast and standoff distance between the target and the rectangular waveguide aperture. The analytical model is validated against ANSYS HFSS numerical simulations and benchmarked against a simplified astigmatic Gaussian-beam kernel for a $K$ -band waveguide at three standoff locations in front of the probe aperture. Furthermore, the analytical model results are verified against measurements collected using an experimental setup utilizing an $S$ -band rectangular waveguide; the measurements confirm the model’s spatial accuracy in a real scanning environment. The proposed framework enables the imaging problem to be cast as a linear convolution, offering a computationally efficient pathway for quantitative permittivity reconstruction without resorting to iterative inverse-scattering solvers.
