Wide Stopband Research Articles

A New Concept of Partial Electric/Magnetic Walls for Application in Design of Balanced Bandpass Filters

In this paper, a concept of partial electric/magnetic walls is proposed and applied to design a class of balanced bandpass filters on (modified) doublet topology with differential-mode (DM) transmission zeros (TZs). It is first demonstrated that the partial electric/magnetic walls are equivalently attained along certain parts of these balanced filters. Using this concept, a dual-mode ring balanced bandpass filter on modified doublet topology with two DM TZs is designed, fabricated, and measured. Furthermore, another balanced bandpass filter on doublet topology with three DM TZs and wide upper stopband is designed and implemented, so as to exhibit the attractive application of the proposed concept. Good agreements between the expected response, simulated results, and measure results are observed.

Comprehensive structural and optical characterization of AlAs/GaAs distributed Bragg reflector

30-pair AlAs/GaAs distributed Bragg reflector (DBR), which has 1030 nm center reflectivity, is studied extensively by means of High Resolution X-ray Diffraction (HR-XRD) and reflectivity measurements. Theta/2-Theta measurements and dynamical simulations have been done for (002), (004) and (006) planes to determine strain and thickness of AlAs and GaAs layers in the DBR stack. Reciprocal space mappings (RSMs) are measured for same planes and also for (224) plane to find out tilt and relaxation of the DBR stack. Relaxation is not observed and it is confirmed with symmetric in-plane (400) Theta/2-Theta and RSM measurements. This is a first study in the literature according to the best of our knowledge. Finally, we have shown sensitivity of high angle diffraction planes to disorders in crystal. Angle-dependent reflectivity simulations have been also done and compared with measurements. 99.99% reflectivity is obtained with 99.5 nm stop bandwidth and 482.7 nm penetration depth.

High-Isolation and Wide-Stopband SIW Diplexer Using Mixed Electric and Magnetic Coupling

In this brief, a high-isolation and wide-stopband diplexer with controllable transmission zero (TZ) nearby the passband, is implemented using substrate integrated waveguide elements. The TZ is generated by the mixed electric and magnetic coupling scheme of $ {TE}_{ {101}}$ mode. It can be flexibly controlled by changing the length of rectangular apertures while keeping good wide-stopband performance unchanged. An ${X}$ -band diplexer with lower and upper channels centered at 9.5 GHz and 10.5 GHz was designed, fabricated, and measured to verify the proposed concept. Good agreement between simulation and measurement can be observed. The designed diplexer exhibits a high isolation level larger than 45 dB over the whole band and a wide stopband up to 20 GHz.

Design and fabrication of microstrip lowpass filter using asymmetric hairpin resonator

In this letter, a compact microstrip lowpass filter (LPF) is designed using serial connecting of two modified asymmetric hairpin resonators. The proposed design is consists of four open-circuited stubs that are used to suppress spurious harmonics in the stopband. The proposed filter has wide-stop band with attenuation level better than −28 dB from 2.16 up to 26.1 GHz and sharp roll-off. The proposed LPF has −3 dB cutoff frequency equal to 2.11 GHz, wide stopband width around 12th harmonic suppression and insertion loss less than 0.1 dB at about 85% of the passband. The excellent agreement is observed between the simulated results and measured values of the fabricated LPF.

Synthesis of X‐band trisection bandpass filters using hybrid structures of λ/4 and λ/2 resonators

AbstractThis paper presents the design of compact cross‐coupled microstrip trisection bandpass filters based on the hybrid structures of quarter‐wavelength (λ/4) and half‐wavelength (λ/2) resonators. The desired cross‐couplings for transmission zeros (TZs) are realized by parallel‐coupled transmission‐line sections (J‐inverter) or coupled via sections (K‐inverter) of λ/4 resonators. The main‐line couplings, on the other hand, are formed by mixed‐coupled λ/4 and λ/2 resonators. To validate the proposed hybrid configurations, two X‐band trisection filters with 6.5% and 6.2% fractional bandwidth were designed. The first filter generates a TZ below the passband, while the second one produces a TZ above the passband. Minimum insertion loss of 1.7 dB and 1.5 dB was observed for the two trisection filters, respectively, while the hybrid configurations caused significant size reduction in the overall filter size. Moreover, the first spurious response for the proposed filter topologies was pushed to 3fo, resulting in a wide stopband.

Acoustic waveguide filters made up of rigid stacked materials with elastic joints

The acoustic dispersion properties of monodimensional waveguide filters can be assessed by means of the simple prototypical mechanical system made of an infinite stack of periodic massive blocks, connected to each other by elastic joints. The linear undamped dynamics of the periodic cell is governed by a two degree-of-freedom Lagrangian model. The eigenproblem governing the free propagation of shear and moment waves is solved analytically and the two dispersion relations are obtained in a suited closed form fashion. Therefore, the pass and stop bandwidths are conveniently determined in the minimal space of the independent mechanical parameters. Stop bands in the ultra-low frequency range are achieved by coupling the stacked material with an elastic half-space modelled as a Winkler support. A convenient fine approximation of the dispersion relations is pursued by formulating homogenised micropolar continuum models. An enhanced continualization approach, employing a proper Maclaurin approximation of pseudo-differential operators, is adopted to successfully approximate the acoustic and optical branches of the dispersion spectrum of the Lagrangian models, both in the absence and in the presence of the elastic support.

Design of Balanced Filter with Wide Stopband by Using Discriminating Coupling

Abstract This paper presents a novel balanced filter with enhanced stopband by using discriminating coupling. The proposed design utilizes third-order quarter-wavelength coupled resonators to obtain the filtering responses. Discriminating coupling is applied between feedline and resonator. The circuit is theoretically analyzed and implemented for demonstration. The operating frequency is located at 2.4 GHz and the common-mode rejection is larger than 20 dB up to 9 GHz (3.75f0). Due to discriminating coupling, the differential mode out-of-band rejection is larger than 20 dB up to 18 GHz (7.5f0), which shows wide stopband.

Ultra-Compact TSV-Based L-C Low-Pass Filter With Stopband Up to 40 GHz for Microwave Application

In this paper, an ultra-compact low-pass filter (LPF) with wide stopband is proposed based on lumped L-C structure in through-silicon via-based 3-D stacked configuration. The spiral inductor (L), interdigital capacitor (C), and the proposed LPF are theoretically analyzed based on parasitic parameters and equivalent circuit models. To evaluate the characteristics, the proposed LPF is simulated by HFSS, fabricated with CMOS-process-compatible technology, and measured with de-embedding method. Simulation and measured results are in good agreement. Compared with the other literature, the proposed LPF has the most compact size of $0.028\lambda _{g }\times 0.017 \lambda _{g}$ . ( $\lambda _{g}$ is the guide wavelength at $f_{c}$ .) With the cutoff frequency at 10.05 GHz, the filter has an insertion loss of 0.14 dB and reflection loss over 13 dB from dc to 9 GHz in the passband. The suppression levels are better than 20 dB from 20.4 up to 40 GHz in the stopband.

An equivalent circuit model of a rectangular bracket shaped DGS and its microwave filter applications

Abstract A lumped-LC equivalent circuit to model a novel rectangular bracket shaped defected ground structure (DGS) is presented in this paper. The presented equivalent circuit can accurately predicate the frequency responses, in terms of the magnitude and phase responses of S parameters, of the studied DGS. The lumped LC parameters of the presented model are extracted based on a unit cell of the DGS. Further, the model is found to be applicable in microwave engineering, including microwave filter designs. Some design examples are presented and examined. The studied DGS based microwave filters characterize maximum passband flatness, sharp skirt between the passband and stopband and wide stopband. The studied equivalent circuit model can accurately predicate the frequency responses including the magnitude and phase of S parameters.

Optimal Design of the Band Structure for Beam Lattice Metamaterials

Sonic or acoustic metamaterials may offer a mechanically robust and highly customizable solution to open large band gaps in the low-frequency dispersion spectrum of beam lattice materials. Achieving the largest possible stop bandwidth at the lowest possible center frequency may be a challenging multi-objective optimization issue. The paper presents a first effort of analysis, systematization and synthesis of some recent multi-disciplinary studies focused on the optimal spectral design of beam lattice materials and metamaterials. The design parameter vector is a finite set including all the microstructural properties characterizing the periodic material and the local resonators. Numerical algorithms are employed as leading methodology for solving various instances of the optimization problem. Methodological alternatives, based on perturbation methods and computational modeling, are also illustrated. Some optimal results concerning the dispersion spectrum of hexachiral, tetrachiral and anti-tetrachiral materials and metamaterials are summarized. The concluding remarks are accompanied by preliminary ideas to overcome some operational issues in solving the optimization problem.

Dual‐wideband filter with wide high‐rejection band using composite resonators

A new type of dual-wideband bandpass filter using composite series and shunt resonators is proposed in conjunction with its direct synthesis and design theory. By making use of the transmission pole (TP) and the transmission zero of the composite resonators flexibly, a dual-wideband filter with a wide range of frequency and bandwidth ratios as well as a wide stopband can be realised. With a shunt capacitor introduced at each I/O port, extra TPs either in the low passband or in the high passband can be created, leading to more filter design options. To give a direct design procedure, a lumped-element prototype is first synthesised based on a target filtering function and a dedicated circuit extraction process. The filter layout can be realised using semi-distributed circuits and chip capacitors. Two practical schemes are introduced to suppress spurious resonances for a wide high-rejection stopband. Two filter examples are designed with a small and a large frequency ratio and a wide band suppressed spurious resonances. The unique filter response and good agreement between the designed and measured results demonstrate the superior performance of the proposed filter structure and the effectiveness of the synthesis and design theory.

Wideband slot-coupled dielectric resonator-based filter

A simple and novel slot-coupled dielectric resonator-based filter (DRF) with wideband performance is proposed, and the designed geometric parameters of the filter are discussed in detail. The proposed filter comprises a substrate, a microstrip line, and three dielectric resonators (DRs), which are positioned on the center of the corresponding slots to obtain a wide stopband response. Numerical simulations show that the wideband DRF has a center frequency of 6.5 GHz, which is consistent with the experimental measurement results. The simulation, as well as the experimental results demonstrate that the distance between the adjacent DRs is a key parameter that can be used to tune the bandwidth of the wideband DMF. The physical mechanism of the DRs is also revealed through analysis of the electromagnetic field distribution results. Additionally, the influence of the DRs on the stopband frequency is also discussed. The results indicate that the DRs play a critical role in the proposed filter. Furthermore, this paper presents the first report on a wideband DRF.

Control of resonance mode using a fine-structured grating: toward a high resolving power filter.

A band-stop filter with high resolving power is designed for mid-infrared spectroscopic sensing and imaging applications. By utilizing a truncated grating consisting of multiple gold nanowires in each unit cell of the periodic structure, compression of the stop bandwidth and improvement of the resonance extinction are realized simultaneously. It shows only a single stop band at ∼4.474 μm with 15dB extinction and >80% background transmission over a wide spectral range. The obtained narrow linewidth (∼1.45 nm) enables a spectral resolving power higher than 3000. Flexible control of the filtering performance is investigated by adjusting the variety of geometrical parameters. Moreover, the structure may have potential applications in refractive index sensing.

Compact and Broadband Microstrip Band-Stop Filters with Single Rectangular Stubs

In this research, a compact and broadband microstrip line quarter-wavelength open circuited stub, which is the core of the band-stop filter, is studied from the viewpoint of the characteristic impedance ratio between the main transmission line and the stub line. Furthermore, a circuit pattern in which an inductive diaphragm is inserted at the stub attachment point using a stepped impedance structure is examined, and an evaluation of frequency adjustment and miniaturization is investigated. The results are compared with the well-known radial stub. Good agreement was obtained between the measured and simulated values up to 5 GHz. Good stop bandwidth was obtained, and the validity of the proposed method is confirmed. The application to other frequency bands is straightforward. The proposed structure is applicable as an alternative to the existing radial stub used for bias T to prevent the reverse flow of the Radio frequency (RF) signal to direct current (DC) source. It is also applicable for the waveguide E-plane band-stop filter, for preventing unwanted leakage from narrow gaps by substituting to a short-circuited stub with a capacitive window, by using the same approach used in the microstrip line H-plane discontinuity.

A compact lowpass filter with ultra-high figure-of-merit for integrating with Class-F/F−1 power amplifiers

This Paper presents a microstrip lowpass filter (LPF) with compact size, and ultra-wide stopband. The structure consists of a semi-circular shaped resonator (SCSR) and circular patches as the suppressing cell. The proposed LPF has a − 3 dB cutoff frequency at 1.53 GHz. It also has suitable performances such as an extended stopband width from 1.62 to 19.1 GHz (with the attenuation level of more than − 20 dB), ultra-sharp transition-band of 0.09 GHz (from − 3 to − 20 dB). Low insertion loss, high return loss and flat group delay in the region of the passband are very significant properties of this LPF. A proper agreement between the simulation and measurement results has been achieved after the fabrication and testing. Proposed LPF has an ultra-high figure-of-merit (FOM) of 126168, showing its strong efficiency. Forasmuch as harmonic control circuits (HCCs) play a key role in designing Class-F/F−1 power amplifiers (PAs); the asymmetric high performance LPFs can be used at the input and output of these PAs in the HCC section. Therefore, the proposed LPF can be suggested for this application.

Design and fabrication of double AlGaN/GaN distributed Bragg reflector stack mirror for the application of GaN-based optoelectronic devices

In this work, a near-ultraviolet (380 nm) double Al0.2Ga0.8N/GaN distributed Bragg reflectors (DBRs) stack mirror was designed and fabricated. The double DBRs stack mirror consists of a 30-pair Al0.2Ga0.8N/GaN DBRs centered at 375 nm and a 20-pair Al0.2Ga0.8N/GaN DBRs centered at 385 nm. Our simulation results show that the method of double DBRs stack mirror design can broaden the stopband width greatly and increase the reflected angle efficiently, compared with the single Al0.2Ga0.8N/GaN DBRs mirror. In experiment, the double Al0.2Ga0.8N/GaN DBRs stack mirror and the reference Al0.2Ga0.8N/GaN DBRs mirror were grown on sapphire substrate by metalorganic chemical vapor deposition. The measured stopband width of the double DBRs stack mirror (~ 25 nm) is more than two times that of the reference DBRs mirror (~ 11 nm), which consists well with our simulation results. It is reasonable to believe that this work could provide a valuable information to obtain AlGaN/GaN DBRs with wide stopband width that can be used in the fabrication of GaN-based resonant cavity light-emitting diodes and vertical cavity surface emitting lasers.

Wide Stopband Bandpass Filter Implemented by Stepped Impedance Resonator and Multiple In-Resonator Open Stubs

Stepped impedance resonator (SIR) has been widely used for applications in wide stopband bandpass filters. However, the reported SIR wide stopband bandpass filters are limited in either stopband performance or design complexity. Here we propose an approach to improve the stopband performance and reduce the design complexity simultaneously. Two in-resonator open stubs are adopted in a SIR (with tap-feeding) to stagger the frequencies of higher-order modes (compared with other SIR) and produce two adjustable transmission zeros without affecting the fundamental properties. For a SIR filter employing such a structure, the spurious passbands are doubly deteriorated by the staggering and up to four transmission zeros. At the same time, the fundamental passband is not affected, which significantly reduces the design complexity. As a result, not only wide stopband but also high-suppression stopband can be obtained in a simple design. A prototype based on the substrate integrated coaxial line (SICL) is experimented showing an impressive stopband performance. Agreeing with the simulation well, the measured stopband is extended up to about 12 f 0 with the suppression of 40 - 50 dB (f 0 is the center frequency). The proposed technique could be very useful to design a bandpass filter with a wide and high-suppression stopband efficiently.

A Dual-Band Balanced-to-Balanced Power Divider With High Selectivity and Wide Stopband

A dual-band balanced-to-balanced (BTB) filtering power divider (FPD) is presented, which can achieve an in-phase power division with high selectivity. The proposed FPD is composed of microstrip-to-slotline transition structures (MTSTSs), T-shaped slotline, and multiple stub-loaded resonators (SLRs). A dual-band differential-mode (DM) response with a steep filtering performance is generated by employing SLRs. By adjusting the electrical lengths of SLRs and the gaps between each resonator and microstrip lines, the fractional bandwidth (FBW) is controllable. By introducing slotline resonators loaded with surface-mounted resistors, the isolation between the two output ports is increased. Meanwhile, a wide DM stopband with a high rejection level is obtained. Moreover, good wideband common-mode (CM) suppression is achieved intrinsically, thereby simplifying the design procedure greatly. To verify the theoretical prediction, one FPD prototype is fabricated. A good agreement between the simulated and measured results is observed. To the best of authors' knowledge, the proposed dual-band BTB FPD is first ever reported.

Lowpass Filter with Wide Stopband Based on T-Shaped Resonator Loaded Step-Impedance Hairpin Resonator

A lowpass filter with wide stopband based on stepped impedance hairpin resonator is proposed. Multiple transmission zeros are created in the stopband region by different size T-shaped resonator to achieve wide stopband. A lowpass filter with 3dB cutoff frequency (fc) at 3.2GHz is designed, simulated and fabricated. Experimental results indicate that stopband can be extended to more than 7fc with a rejection level of 20dB after loading T-shaped resonator. The insertion loss is lower than 0.4dB and return loss is better than 16dB in the passband. Excluding the feed lines, the size of the filter is less than 0.26λg X 0.06λg. The modified filter is of good value in engineering application for its small size, sharp cutoff frequency response and wide stopband.

Compact High-Isolation Multiplexer With Wide Stopband Using Spiral Defected Ground Resonator

In this paper, the compact wide-stopband diplexer/triplexer is presented. The spiral defected ground resonator (SDGR) is analyzed by using the equivalent model. Based on the symmetry of the SDGR, a diplexer and a triplexer are implemented with a miniaturized size and a wide stopband. Each filter of the channels in the diplexer or triplexer can be independently controlled and exhibits a constant fractional bandwidth. To validate the design concept, the diplexer and the triplexer are designed, fabricated, and measured. The isolation between the channels is greater than 30 dB, and the measured out-of-band suppression is greater than 10 dB in the very wide frequency range. The measured results agree well with the simulation ones.