Based on a GaAs substrate integrated passive device (IPD) technology with varactor diodes, two millimeter-wave bandpass filters and one tunable bandpass filter operating in the 5G NR FR2 n258 band are designed. The first filter is a second-order bandpass filter with a center frequency of 30 GHz, a passband bandwidth of 5.5 GHz, a passband insertion loss of 1 dB, and a passband return loss greater than 15 dB. The second filter is a third-order bandpass filter with a center frequency of 33 GHz, a passband bandwidth of 4.5 GHz, a passband insertion loss of 1.7 dB, and a passband return loss greater than 15 dB. The third filter is a center-frequency-tunable bandpass filter with a tuning range of 25.5–27.5 GHz, a passband bandwidth of 2.5 GHz, and a passband insertion loss of 3.5–5 dB.

This article presents a synthesis method for on-chip fourth-order bandpass filters (BPFs) for 5G millimeter-wave (mmWave) applications. The method transforms the conventional $K$ -filter prototype into microstrip schematics comprising capacitively loaded microstrip (CLM) resonators and semi-lumped vias acting as impedance inverters. The approach enables rapid calculation of design parameters under varying bandwidth, center frequency, and harmonic suppression requirements. Two BPFs are designed and fabricated using the integrated passive device (IPD) process to validate the method. The first operates at 24 GHz with an insertion loss of 3.98 dB, a 3-dB fractional bandwidth (FBW) of 13.5% and 53-dB stopband attenuation. The second employs a cross-coupled structure at 26 GHz, achieving an insertion loss of 3.92 dB, a FBW of 12.5%, and transmission zeros (TZs) at 22.8 and 28.4 GHz, corresponding to a rectangular coefficient (20-dB BW/3-dB BW) of 1.53. The results validate the theoretical counterparts and demonstrate that the designed filters exhibit good passband selectivity and stopband suppression.

An on-chip reconfigurable dual-band millimeter-wave (mmWave) bandpass filter (BPF) is presented in a GaAs integrated-varactor platform. Independently tunable passbands with asymmetric reconfigurability are realized using a parallel-coupled topology comprising a varactor-loaded half-wavelength resonator and a dual-mode capacitor-loaded resonator, which effectively decouples the two bands, a functionality seldom demonstrated in reported on-chip mmWave filters. The lower band tunes from 25 to 26.5GHz with 10.2% FBW and 3.48-4.16dB insertion loss, whereas the upper band tunes from 35.25 to 37.25GHz with a reconfigurable 4.4-9.2GHz bandwidth and 3.7-5.15dB insertion loss. Good linearity is achieved, with a maximum IIP3 of 30dBm. Source-load coupling introduces transmission zeros (TZs) to enhance selectivity, and measured results agree well with simulations.

In conventional microwave filter design, extensive full-wave electromagnetic (EM) simulations often result in high computational cost and long design cycles. This paper proposes an automated optimization design framework, termed E-NASOD, which integrates surrogate modeling based on artificial neural networks (ANNs) with simulated annealing-particle swarm optimization (SA-PSO). ANNs are developed to model the mapping from structural parameters to S-parameter responses, and a weighted loss function is introduced to improve prediction accuracy in critical response regions, especially near the minima of the reflection response, while also improving the optimization landscape. In addition, a composite fitness function is formulated for filter synthesis and incorporated into SA-PSO for goal-oriented parameter search. A dielectric waveguide filter example using a cross-coupled structure is employed to validate the proposed framework. The results demonstrate that the proposed method is effective for both conventional and highly nonlinear microwave filter synthesis problems, while offering good stability, robustness, and improved design efficiency.

A compact quasi-elliptic bandpass filter (BPF) based on self-coupled quarter-wavelength resonators (SCQWRs) is proposed. The SCQWR is realized by vertically folding a microstrip line to form a self-coupled structure, which significantly reduces the circuit footprint and enhances the mixed coupling between resonators, enabling a quasi-elliptic response with two transmission zeros (TZs). Source-load coupling is further introduced through layout optimization to generate an additional controllable TZ. An equivalent circuit model is developed to explain the operating mechanism of the filter. For experimental verification, a second-order quasi-elliptic BPF is designed and fabricated based on the GaAs-IPD process. The fabricated filter exhibits a center frequency of 28 GHz, an insertion loss of 2.16 dB, and a 3-dB fractional bandwidth (FBW) of 12.9%. The maximum stopband attenuation is 41 dB with a compact core area of 0.034 lambda(0)& times;0.025 lambda(0).

This paper introduces a highly sensitive microwave biosensor based on a defected ground structure (DGS) for label-free detection of minute volume liquid samples. The biosensor incorporates a resonant structure etched into the ground plane, which concentrates the electric field to form a strongly localized sensing “hot-spot”. This configuration significantly enhances sensitivity to minute variations in the dielectric properties of tiny volume samples. Using MEMS fabrication techniques, the DGS biosensor is integrated with a microfluidic channel capable of single-cell trapping, thereby enabling high-precision measurements at the single-cell level. An equivalent circuit model is developed and simulated to quantitatively correlate the sample’s dielectric constant with the resonant frequency. Experimental results demonstrate that the biosensor achieved frequency shifts on the order of MHz in tests involving microplastic particles and various tumor cell types, highlighting its high detection sensitivity and discrimination capability. Furthermore, a dual-branch DGS configuration is designed to enable dual-band sensing, and simulations are conducted to analyze the influence of microsphere dielectric properties on both resonant frequencies. The fabricated biosensor exhibits consistent performance across particles and cell-based assays, offering a viable and effective platform for the highly sensitive detection of minute volume biological samples.

This paper presents a miniaturized tunable bandpass filter chip fabricated using a gallium arsenide (GaAs) technology. In the layout design, a quasi-lumped element is utilized to replace conventional spiral inductors, complemented by on-chip PN-junction varactor diodes and Metal-Insulator-Metal (MIM) capacitors. The integration of a source-load coupling structure and grounded series LC resonators introduces three transmission zeros (TZs), enhancing the frequency selectivity. By independently tuning the coupling capacitance and the grounded series LC resonant structures, the operating frequency of the filter achieves continuous tunability. An equivalent circuit model is established to analyze the filter’s performance. For experimental verification, the proposed filter was fabricated and measured, occupying a compact die area of 1.35 × 1.365 mm2. The measured results demonstrate a center frequency tuning range from 5.4 to 6.2 GHz, showing good agreement with simulation and thus validating the proposed miniaturized continuously tunable filter.

Based on GaAs integrated passive device (IPD) technology, this paper proposes a millimeter-wave dual-mode bandpass filter. The proposed filter achieves size reduction by employing a capacitor-loaded microstrip-line structure and forming the passband through multiple resonant modes within a single resonator. Compared with a MIM-capacitor-free dual-mode filter fabricated using the same process and exhibiting similar electrical performance, the proposed design achieves a size reduction of 36.63%. On-chip measurement results demonstrate that the filter operates at a center frequency of 22.8 GHz, with an insertion loss of 2.15 dB and a maximum return loss better than 25 dB. The measured 3-dB fractional bandwidth is 16.70%, and the core circuit area, excluding the feed lines, is only 0.372 mm × 0.362 mm.

In this paper, a reconfigurable tri-band common-mode filter based on defected ground structure (DGS) is proposed. An extra second suppression band can be generated by introducing an embedded square resonator into traditional dumbbell-shaped DGS. The two suppression bands can be adjusted by tuning the geometrical parameters of the structures. Two pads are introduced for soldering varactors. The addition of two grounding branches creates the third suppression band, which extends the suppression bandwidth of the proposed structure. A prototype of the proposed filter is designed, manufactured, measured and evaluated. The results demonstrate that the proposed filter has a wide suppression band and a large tuning range.

This paper presents a compact fully tunable bandpass filter based on a single substrate integrated waveguide (SIW) cavity. By introducing two metalized via holes along the diagonal of the cavity, the degenerate modes TE102 and TE201 are split and coupled, which produces a second-order filtering response. Varactors are loaded on both surfaces to independently tune the center frequency and bandwidth. The filter exhibits a frequency tuning range of 2.22–2.24 GHz and a 3-dB bandwidth tuning range of 80–140 MHz. A prototype is fabricated and measured, showing good agreement between simulation and measurement. The measured insertion loss remains below 3.8 dB, and the return loss is better than 15 dB across the entire tuning ranges.

This article presents a high-sensitivity biosensor based on a resonant slot structure with an embedded electrode. The electrodes are positioned at the center of the slot to concentrate the electric field, thereby significantly enhancing sensitivity. Through comparative analysis of various sensing structures and electrode dimensions, it is demonstrated that the proposed sensor exhibits substantially larger frequency shifts. The results underscore the sensor’s high sensitivity and its advantages for detecting trace liquid samples. The slot resonator structures are fabricated, and microfluidic channels are monolithically integrated using micro-electro-mechanical system (MEMS) technology. Experiments are conducted using low-volume bovine serum albumin (BSA) solutions at different concentrations, micro-particle suspensions, and clustered tumor cell suspensions. The slot sensor exhibits frequency shifts at the MHz level in response to individual micro-particles and cells, confirming its capability for high-sensitivity microwave detection. To reduce environmental interference, a low-temperature co-fired ceramic (LTCC) multilayer-based slot resonator with nonradiative characteristics is further developed. Integrated with a 3-D-printed microfluidic channel, the resulting millimeter-wave sensor achieves ultratrace sample detection. Measurements of BSA solutions show that a 2.5% change in concentration at the single-cell level induces a frequency shift of 10MHz, validating the high sensitivity of the sensor.

The layout method for radio frequency/monolithic microwave integrated circuit (RF/MMIC) is one of the key components in achieving MMIC design automation. This work proposes a multistage progressive automated layout framework addressing MMIC layout challenges under 0.25- mu m GaAs pseudomorphic high electron mobility transistor (pHEMT) technology. This framework employs dimensionality reduction from unsupervised learning, integrates practical layout design rules, and achieves automated layout through analytical optimization methods. Applied to multiple cases including filters, low-noise amplifiers (LNAs), and power amplifiers (PAs), the method successfully generated manufacturable layouts; the process achieves end-to-end automation from placement to routing, producing layouts that are verified to be design rule check (DRC) clean. Simulation-verified results demonstrate comparable performance to manual designs while achieving >= 10 & times; speedup over conventional methods. We believe this work contributes valuable attempts toward automated MMIC layout generation and advances progress in MMIC design automation.

In this paper, a tunable bandpass filter based on gallium arsenide (GaAs) integrated passive device (IPD) technology is designed and implemented. It adopts a two-resonator structure loaded with varactor diodes controlled by a single bias voltage, simplifying the control circuit and enhancing engineering practicality. To maintain constant absolute bandwidth during frequency tuning, the coupling section dimensions are adjusted to approximate the ideal relationship between coupling coefficient, external quality factor, and center frequency. Measurement results demonstrate that the filter has an insertion loss of less than 2.97 dB, a center frequency tuning range of 25.1–26.57 GHz, and a 3-dB absolute bandwidth stabilized at 4 ± 0.15 GHz.

This paper presents an S-band planar coupled bandpass filter (BPF) with high selectivity and a wide upper stopband. The passband is formed by using a dual-mode ring resonator. The input of signal relies on parallel-coupled lines and side-coupled lines which enhance selectivity either. A pair of shorted coupled lines are implemented to introduce high frequency transmission zeros, which can suppress the third harmonic of the transmission poles. The proposed filter is fabricated on Rogers 4350 B substrate. The measurement results indicate that the proposed filter has a passband ranging from 3.1 GHz to 3.5 GHz, and it exhibits excellent out-of-band suppression, which is over 40 dB from DC to 2.7 GHz and from 4 to 8 GHz, and greater than 20 dB from 4 to 10 GHz. The measurement results correspond well with the simulation results.

This paper presents an inter-digital coupled line structure loaded with composite stubs (ICL-CS) to achieve high selectivity and a broad frequency range. The design uses triple-line coupling to minimize in-band insertion loss and composite stubs to expand the passband and stopband of the bandpass filter (BPF). Compared to traditional triple-line coupling structures, the ICL-CS offers a significantly wider stopband. The cascade response of triple- line coupling and composite branch nodes is analyzed using an extended odd-even mode method, systematically evaluating the frequency response. Based on this structure, a high-performance BPF is proposed with a wide stopband and excellent selectivity. Experimental results show an operating frequency range of 8.3 GHz to 15.2 GHz, an insertion loss of 2.6 dB, a shape factor of 1.22, and an out-of-band rejection of 26 dB across the stopband range of 16.4 GHz to 34 GHz. This filter is highly suitable for three-dimensional heterogeneous wireless communication systems.

ABSTRACTThe design of monolithic microwave integrated circuits (MMICs) is a laborious process that involves exploring a vast design space, requiring multiple iterations to identify the optimal circuit design. In this research, we propose a design approach that combines GPU‐based high‐performance computing and transfer learning techniques. To improve modularity and reusability, we decompose the MMIC into multiple substructures and then combine these substructures to restore the overall circuit structure and performance. To achieve this, we adopted schematic simulation, which is more time‐efficient, to construct a data set and pre‐train the circuit substructure models. We then fine‐tune the pre‐trained models using a limited amount of electromagnetic (EM) simulation data, aiming to obtain layout‐level subcircuit models. Leveraging the parallel processing capabilities of neural network models, we employ GPU to conduct extensive exploration and design within the circuit design space, utilizing cascade connection theory to optimize the performance of the complete circuit. We apply this methodology to a low‐noise amplifier (LNA) circuit operating in the 6–13 GHz frequency range, achieving favorable outcomes.

This paper introduces a highly accurate equivalent circuit extraction method for microstrip filters, capable of producing precise equivalent circuit models with a normalized mean square error (NMSE) of less than 0.003. The extracted equivalent circuit models are well-suited for circuit simulations and serve as a powerful tool for the simplified design of tunable filters. To demonstrate the effectiveness of the method, a fourth-order tunable filter with fixed bandwidth and adjustable center frequency, as well as a fifth-order tunable filter with adjustable center frequency and bandwidth, was designed and implemented. The results from circuit simulations, electromagnetic field simulations, and experimental measurements exhibit strong consistency, confirming the reliability and practicality of the proposed method.

A reconfigurable common mode (CM) suppression filter for high-rate all pass differential circuits is proposed. This reconfigurable filter uses a compact defect ground structure (DGS) loaded with two varactors to reach consecutive reconfigurability of its operating frequency and a wide common mode rejection dynamic region within the bandwidth. Varactors play a crucial role in expanding the available bandwidth and downsizing the filter. All DGS units and U-shaped wires are symmetrically deployed under the differential line. By adjusting the capacitance of the varactors, a reconfigurable common mode band-stop characteristic can be obtained, which can be continuously adjusted in the range from 3.29 to 14.68 GHz. Corresponding fractional tuning range of the filter reaches 100%. The entire structure occupies an area of 3mm x 10mm.

In this article, the common-mode suppression filters (CMF) are synthesized using deep reinforcement learning algorithm called proximal policy optimization (PPO). The Latin hypercube is firstly employed to sample the parameters of complementary split-ring resonator structure, which is used as a reflective CMF. Then, with the help of PPO algorithm, a resistor-equipped defected ground structure is developed to absorb the reflective common-mode noise. To prove the feasibility of the proposed optimization method, two samples are designed and tested. The first sample is an absorptive CMF with absorption band located at 5 GHz, and the second sample is with dual absorption bands located at 2.4 GHz and 5 GHz. The results demonstrate that the proposed approach enables the automatic design of CMF.

In this article, a transmission space separation (TSS) structure is proposed to reconcile the contradiction between high loss for common-mode (CM) noise and low loss for differential-mode (DM) signal in the region of resistor-free absorptive CM filter (A-CMF) design. To meet the essential requirement for implementing A-CMF, which should contain nonzero real impedance parts, two matching components based on substrate integrated waveguide (SIW) cavity and defect ground structure (DGS) are employed. For both matching components, their equivalent circuit models (ECMs) are developed, and the impact of key parameters on the resonance points and resistance is discussed in detail. Then, two types of single-band A-CMFs are proposed based on matching components, and the transformation from directional A-CMF to bidirectional A-CMF is also discussed. The proposed A-CMFs can achieve an absorptive band at 5 GHz with absorptions of 97% and 99%, while the DM transmission performances maintain sub-3-dB insertion loss until 8.5 GHz. To meet the requirement of broadband absorption of CM noise, a band-enhanced A-CMF is proposed, fabricated, measured, discussed, and evaluated. The measured and simulated results aligned well with each other. The band-enhanced A-CMF can realize a 0.6-GHz absorption band at 5 GHz and maintains sub-3-dB insertion loss until 8.7 GHz. Furthermore, to examine the portability of TSS structure, the A-CMFs based on substrate integrated suspended line (SISL) and 3-D through-silicon via (TSV) processes are designed. An SISL prototype is fabricated, measured, and evaluated, and good agreement between simulation and measurement results is realized.