Search Results (215)

A Chebyshev wideband balanced bandpass filter (BPF) with excellent common-mode (CM) suppression and an extended upper stopband is proposed, which is made up of a hybrid microstrip–slotline vertical transition structure and series short-ended slotline stubs. By means of the intrinsic CM rejection feature of slotline stubs, the CM noises of the circuit are effectively suppressed with a rejection level better than 31.7 dB over the frequency range of 1.7 to 14.5 GHz, while the differential-mode (DM) signal can pass through smoothly. In terms of odd-/even-mode equivalent circuits, the corresponding odd-/even-mode resonant frequencies can be solved expediently. Moreover, the synthesis algorithm is employed to achieve Chebyshev equal-ripple responses in the balanced filtering circuit, which significantly enhances the design efficiency of the proposed balanced filter. In addition, lowpass filters (LPFs)—which consist of two sets of dumbbell-shaped series slotline segments—are adopted to further improve the harmonic suppression level of the DM filtering circuit and significantly expand the upper stopband. Finally, the proposed Chebyshev wideband balanced BPF is fabricated and tested to verify the validity of the synthesis theory; experimental results agree well with simulation responses. Full article

This paper presents a metasurface filtering antenna based on unequal rectangular patch elements. The design is implemented with only two dielectric layers: the upper PCB carries the metasurface radiator, and the lower PCB supports a Y-shaped microstrip feeding network. A radiation null near 3.3 GHz is obtained by dividing the four corner units of the metasurface into 2 × 2 subarrays, which reshapes the current paths around the central aperture and causes destructive spatial radiation. For the upper stopband, a second null appears at 3.84 GHz because the fields coupled from the opposite-phase currents on the Y-shaped feed branches cancel in the far field. Measurements indicate that the antenna provides a 10 dB impedance bandwidth of 3.43–3.60 GHz, or 9.85% in fractional bandwidth. Within the passband, the measured average realized gain reaches 7.51 dBi. The lower and upper stopbands exhibit radiation suppression levels of 15.61 dB and 14.08 dB, respectively. The boresight cross-polarized field is also more than 20 dB below the co-polarized field, confirming satisfactory radiation quality. These results make the proposed antenna suitable for compact 5G front-end integration. The proposed design provides a balanced combination of low profile, compact aperture, measured gain, and two band-edge radiation nulls. Full article

This paper presents a miniaturized ultra-wideband high-pass filter integrated with a notch function based on low-temperature co-fired ceramic (LTCC). The design motivation is to realize continuous wideband high-pass transmission while rejecting a narrow in-band interference/leakage component in compact RF front-end modules. The proposed design employs a cascaded structure of a seventh-order quasi-elliptic HPF and a three-section $\lambda /4$ stub notch filter in a single multilayer LTCC chip. Multiple transmission zeros (TZs) are introduced to improve the lower-stopband selectivity, while the three-section coupled-line NF produces a tunable localized rejection band. The LTCC implementation further integrates multilayer capacitors, three-dimensional helical inductors, shielded strip-line coupling stubs, a grounding compensation capacitor, and an isolation wall to balance compactness, impedance matching, and parasitic suppression. The fabricated chip achieves an ultra-wide bandwidth of 2.35 octaves, a notch 20 dB FBW of 8.5%, an insertion loss below 2 dB, a 60 dB roll-off rate of 154.1 dB/GHz within the lower stopband, and a voltage standing wave ratio (VSWR) less than 2. Experimental results validate that the proposed compact chip meets communication requirements and is suitable for 5G base stations, radar systems, and other applications. The chip dimensions are 4.5 mm × 3.2 mm × 2.5 mm. Full article

We present FilterForge, a chat-driven VS Code environment that pulls the synthesis, analysis, simulation, and optimization stages of microwave bandpass filter design, normally coordinated by hand across tools written in different languages, into one workflow. A deployed Model Context Protocol (MCP) server exposes deterministic Python implementations of coupling-matrix synthesis, uniform predistortion, topology reconfiguration, a genetic-algorithm transmission-zero selector, a mode-matching engine for H-plane iris-coupled rectangular waveguide geometries, and a skill that generates PyAEDT/HFSS notebooks for various dimensioning design-curves. A language-model orchestrator turns natural-language requests into typed tool calls, while every reported quantity stays inside the deterministic kernels, so the numerics remain reproducible and model-agnostic. We evaluate the call layer on a 45-task benchmark across the five tool categories: gemini-3-flash reaches $96.3\%$ tool-selection and $94.8\%$ full-call accuracy with an $88.9\%$ pass³ rate, which an ablation traces to the curated tool-selection prompt rather than to raw model capability. The mode-matching engine is validated against full-wave HFSS on a six-pole 4 GHz Chebyshev filter tuned from the chat panel, and on an 8 GHz WR-112 counterpart taken end-to-end with no engineer in the loop, where a deterministic critique gates each round until a manufacturable geometry is reached. We then exercise the full workflow on two folded six-pole WR-90 cross-coupled filters at $10\mathrm{GHz}$, a high-selectivity design synthesized against a stop-band mask and a group-delay-equalized variant whose positive cross-coupling uses a pair of side-wall irises, the latter settling to a peak-to-peak in-band group-delay ripple below $1.5\mathrm{ns}$ while recovering the synthesized return loss. Full article

In this study, a novel aperiodic photonic crystal (PC) structure is designed using the golden ratio-based Lucas sequence, and its infrared (IR) transmission characteristics are investigated. Transmission behavior demonstrates a strong dependence on the number of unit cells and parity (even or odd) of the defect layer repetitions, enabling the formation of a predetermined number of resonant modes around the operating wavelength and broad photonic stopbands at longer wavelengths with sharp defect modes. With its high spectral tunability, the proposed new Lucas sequence-based structure represents a viable candidate for the design of high-performance optical filters and components. These findings indicate that novel Lucas sequence-based PC designs will provide new opportunities for manipulating light–matter interactions in future studies. Full article

With the large-scale commercialization of 5G and rapid evolution of 6G wireless systems, planar interdigital bandpass filters (BPFs) have become the core passive components for low-power RF front-ends. However, state-of-the-art filter design methods either rely heavily on empirical trial-and-error with 8–10 simulation iterations, or fail to resolve the inherent trade-off between center frequency tuning and stopband performance degradation, which cannot meet the demands of rapid customized design for 5G/6G multi-band scenarios. In this paper, a symmetric five-resonator three-segment patch-type interdigital BPF is taken as the research object. Through theoretical derivation, full-wave electromagnetic simulation, parametric scanning and orthogonal experiments, the quantitative mapping between structural parameters and filter performance is established. Notably, the directional tuning mechanism of the resonator’s narrow segment width on the first stopband is first revealed, which realizes lossless stopband optimization without disturbing the center frequency. On this basis, a three-stage standardized design procedure is proposed, which reduces design iterations from 8–10 to 3, shortens the design cycle by over 70%, and achieves 100% compliance of core design indexes. This work provides an implementable, low-threshold engineering method for rapid customized design of planar interdigital BPFs for 5G/6G RF front-ends. Full article

Existing ground-slotted coplanar waveguide (CPW) spoof surface plasmon polariton (SSPP) low-pass filters (LPFs) remain constrained by the difficulty of achieving a wide stopband while maintaining a compact size, as well as by undesired radiation leakage arising from their open-aperture slot configuration. To address these issues, a grounded coplanar waveguide spoof surface plasmon polariton (GCPW-SSPP) low-pass filter based on a multi-arm star-shaped slot (MASS) loading topology is proposed. An equivalent-circuit interpretation and full-wave dispersion analysis show that the multi-arm slots introduce enhanced distributed reactive loading, thereby lowering the asymptotic frequency and enabling compact SSPP implementations. The near-field characteristics further demonstrate tighter electromagnetic confinement, as reflected by an approximately 48% reduction in the electric-field confinement width along the z-direction. To alleviate the trade-off between miniaturization and wide-stopband performance in cascaded SSPP LPFs, the single-cell S-parameters of the proposed topology are investigated. A single MASS unit exhibits a sharp cutoff and a deep transmission notch, allowing a wide stopband to be obtained with fewer cascaded cells. Radiation characteristics are subsequently quantified by a loss-decomposition method, and the MASS topology is found to suppress the radiation leakage of open-aperture ground-slotted structures, yielding a maximum radiation-loss reduction of approximately 75%. To validate the design methodology, a MASS-loaded GCPW-SSPP LPF is designed, fabricated, and measured. The measured results are in good agreement with the simulated ones, confirming the effectiveness of the proposed scheme. By simultaneously achieving a wide stopband, compact size, and suppressed radiation leakage, the proposed filter offers a promising low-interference filtering solution for highly integrated microwave and RF front-end systems. Full article

This paper proposes a novel low-pass frequency selective surface (FSS) with high-frequency rejection. Through theoretical derivation of the equivalent circuit model (ECM), an additional transmission pole can be generated below the transmission zeros by cascading two band-stop FSSs incorporated with an air spacer, therefore enhancing the low-pass performance. Based on the above findings, a compact and simple FSS is designed, which consists of two dual band-stop FSS with an air spacer. The staggered distribution of the four transmission zeros substantially broadens the stopband. The full-wave simulation result shows that the proposed FSS has an ultra-wide out-of-band rejection with transmission coefficient under −10 dB from 4.42 GHz to 27 GHz (143%), while maintaining a relatively good low-pass characteristic under 4.42 GHz with a maximum insertion loss of 1.36 dB. The full-wave simulation result matches closely with the ECM result. Full article

This paper presents a flexible conformal beam-scanning leaky-wave antenna (LWA) array based on a PI-ABS composite substrate and spoof surface plasmon polariton (SSPP) structure for Ku-band (12–18 GHz) applications. The proposed design features periodically symmetric gradient linear metallic stubs and interleaved tapered radiating patches to realize efficient SSPP slow-wave transmission, −1st spatial harmonic radiation, and open-stopband (OSB) suppression simultaneously. Benefiting from the flexible PI-ABS composite structure, the antenna maintains stable radiation performance under different curvatures, overcoming the mechanical instability and beam-scanning sensitivity of conventional flexible LWAs. The four-element conformal array achieves continuous beam scanning from −67° to 32° with a peak gain of 16.5 dBi and radiation efficiency above 58% across the entire band. Both simulation and measurement results validate that the proposed design integrates flexible conformality, wideband beam scanning, and high radiation efficiency, providing a novel solution for conformal wireless communication systems. Full article

The high-density integration of low-temperature co-fired ceramic (LTCC) filters inevitably induces complex parasitic coupling. Traditional designs rely on forced isolation to mitigate this issue, often at the expense of increased physical footprints. To overcome this limitation, this paper proposes a strategy for the controlled utilization of parasitic effects. Methodologically, localized grounding structures are introduced to construct a controlled electromagnetic boundary. The system’s main path exhibits alternating inductive-capacitive (L-C) coupling, with a single explicit capacitive cross-coupling introduced between specific nodes (resonators 2 and 5). Based on the principle of multi-path signal cancellation, this explicit path synergizes with the implicit parasitic environment. By satisfying conditions of equal amplitude and a 180° phase difference at specific frequencies, a high-order hybrid network is equivalently reconstructed, generating four transmission zeros (TZs). A compact sixth-order LTCC filter was fabricated and tested. Measured results demonstrate a fractional bandwidth (FBW) of 38.6%, a shape factor of 1.16 (based on the 20-dB/3-dB bandwidth ratio), and a 20-dB upper stopband extending beyond $4.28f_0$. In conclusion, the rational utilization—rather than forced isolation—of inherent parasitic effects provides an effective solution for enhancing frequency selectivity and stopband performance in high-density integrated RF front-ends. Full article

With the rapid development of software-defined radio (SDR) technology, a digital, software-reconfigurable, and flexible solution is provided for microwave radiometers, particularly suitable for atmospheric water vapor and oxygen detection with wideband, multi-channel requirements, significantly improving system efficiency. Meanwhile, digitization helps improve channel consistency and address nonlinearity issues, while the digital zero-balancing mechanism implemented through adaptive integration is more suitable for digital platforms. This paper proposes a digital Dicke-type radiometer system based on an SDR platform, using Xilinx RFSoC XCZU47DR (AMD, San Jose, CA, USA) as the core hardware to achieve single-chip integration of RF signal sampling, digital local oscillator generation, and signal processing. The system implements a 46-channel channelized receiver (23 channels each for K-band and V-band) on an FPGA using a polyphase filter bank. The prototype filters achieve 70 dB stopband attenuation and 0.5 dB passband ripple, with each polyphase branch requiring only 25 coefficients, significantly reducing hardware resource consumption. An adaptive integration method is proposed, where an adaptive switch controller dynamically adjusts the hot source injection time ratio by calculating the power difference between adjacent integration periods, enabling the Dicke zero-balancing mechanism to operate entirely in the digital domain. Furthermore, a complete hardware transfer model is established for three signal branches (antenna, hot source, and matched load), and full-chain calibration of all 46 channels is performed using a liquid nitrogen cold source, with calibration reliability verified through blackbody measurements. Experimental results demonstrate brightness temperature consistency better than 0.7 K, with a sensitivity of less than 0.15 K for the K-band and less than 0.21 K for the V-band at 1 s integration time. Full article

In this study, we propose a novel approach to enhance upper stop-band attenuation in a split-ring resonator-based bandpass filter by partially inserting W-type hexaferrite films into a strategically placed mechanical hole. The hexaferrite exhibits a substantial increase in magnetic loss tangent in the desired band owing to ferromagnetic resonance, considerably improving attenuation in the upper stop-band while maintaining an acceptable insertion loss in the pass-band. The obtained results indicate that selectively placing the hexaferrite film enhances out-of-band rejection by up to 4 dB, with a slight degradation of 0.84 dB in pass-band insertion loss. Before inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.01 dB at 28 GHz and an attenuation of 20.04 dB at 32 GHz. By contrast, after inserting the hexaferrite film, the bandpass filter exhibited an insertion loss of 1.95 dB at 28 GHz and an attenuation of 24.45 dB at 32 GHz. Full article

Colloidal crystals are periodic arrays of monodisperse particles that exhibit optical stopbands, which can be experimentally observed as a Bragg reflection characterized by a specific Bragg wavelength and width. Precise control of these characteristic parameters is essential for applications in structural color materials, sensors, and tunable photonic crystals. Although the Bragg reflection wavelength can be widely tuned by adjusting the lattice spacing via changes in particle size and concentration, controlling the width over a wide range—such as through expansion—is challenging because it is intrinsically determined by the refractive index contrast between the colloidal particles and their surrounding medium. In this study, the Bragg reflection width of non-close-packed colloidal crystals immobilized in an elastomer film was successfully expanded by adjusting the photoinitiator concentration and ultraviolet light intensity for photopolymerization. Expansion was attributed to the superposition of Bragg reflections at different wavelengths, resulting from spatial variations in the lattice spacings of the non-close-packed colloidal crystals formed during photopolymerization. Owing to the solvent-free and highly flexible nature of the elastomer-immobilized, non-close-packed colloidal crystal film, the Bragg reflection wavelength was readily tuned by mechanical compression while maintaining the expanded Bragg reflection width, thereby advancing the practical applications of structural color materials. Full article

This study introduces two compact wideband substrate-integrated waveguide (SIW) filters fabricated using thin-film technology. The wideband bandpass response is achieved by incorporating interdigital capacitor (IDC) structures into a half-mode SIW (HMSIW) transmission line. An equivalent LC circuit model is formulated to analyze the influence of IDC parameters on the generation of transmission zeros. For the first filter (BPF 1), a third-order IDC coupling configuration is employed, resulting in a 1 dB passband spanning 11 GHz to 18 GHz, a minimum insertion loss of 0.66 dB, three transmission zeros that enhance stopband performance, and a compact core dimension of $0.49{\lambda }_g\times 0.29{\lambda }_g$. For further miniaturization, a modified HMSIW transmission line incorporating a metal-insulator-metal (MIM) capacitor at the equivalent magnetic wall is proposed. This design effectively reduces the transverse dimension of the waveguide while maintaining the original cutoff frequency. Utilizing this configuration, the second bandpass filter (BPF 2) was designed and fabricated employing double-layer ceramic thin-film technology. The resulting filter exhibits a 1 dB passband spanning 10 GHz to 18 GHz, a compact footprint measuring $0.44{\lambda }_g\times 0.23{\lambda }_g$, a minimum insertion loss of 0.58 dB, and features three transmission zeros. The fabricated and measured results of both filters show good agreement with simulations. Compared with previously reported wideband SIW filters, the proposed designs demonstrate comprehensive advantages in fractional bandwidth, insertion loss, out-of-band suppression, and circuit size, providing effective filtering solutions for high-density integration of microwave and millimeter-wave RF systems. Full article

This paper presents the design and experimental validation of a compact low-pass filter based on a quasi-eight-shaped defected ground structure (DGS). The study begins with a single DGS resonator that perturbs the ground-plane current distribution, introducing additional effective inductance and capacitance. An equivalent circuit model is developed to provide physical insight into the resonant mechanism and to establish the relationship between the DGS geometry and the electromagnetic response. By incorporating microstrip stubs on the top layer, the resonant structure is transformed into a low-pass filtering configuration with improved passband characteristics. Subsequently, a higher-order topology composed of two identical quasi-eight DGS units and three microstrip stubs is implemented to significantly enhance the rejection performance and extend the stopband bandwidth. The fabricated prototype exhibits a measured cutoff frequency of approximately 2.1 GHz, with an insertion loss lower than 1 dB in the passband. A wide stopband extending from 2.8 GHz to 8 GHz is achieved, with attenuation exceeding 26 dB. The close agreement between the equivalent circuit model, full-wave electromagnetic simulations, and measured results confirms the effectiveness and physical consistency of the proposed design. Owing to its compact planar implementation and strong harmonic suppression capability, the proposed filter is suitable for microwave front-end and antenna applications. Full article