High Stopband Rejection Research Articles

A Miniaturized Bandpass Filter with Wideband and High Stopband Rejection Using LTCC Technology

This paper designs an L-band wide stopband bandpass filter by applying low-temperature cofired ceramic (LTCC) technology to the global positioning system (GPS) frequency band. Taking the Chebyshev filter as a prototype, an equivalent collector element (capacitive and inductor) structure is adopted to fully use the three-dimensional package structure of LTCC to reduce the filter size. The filter is integrated into an eight-layer LTCC dielectric, and the series–parallel connection of the collector elements in the resonance unit is utilized to produce out-of-band transmission zeros, while the input and output ports’ capacitance is adjusted to control the bandwidth. Harmonic suppression is achieved by cascading two new compact stopband filters, while the size increase is insignificant due to LTCC technology. The simulation results are as follows: the center frequency is 1.575 GHz, 1 dB relative bandwidth is 6.3%, insertion loss in the passband is as slight as 1.6 dB, return loss is better than 30 dB, rejection bandwidth up to 16 GHz is more than 44 dB, and the volume of the whole filter is 6.2 × 3.7 × 0.78 mm3.

Metamaterial inspired electromagnetic bandgap filter for ultra-wide stopband screening devices of electromagnetic interference

Presented here is a reactively loaded microstrip transmission line that exhibit an ultra-wide bandgap. The reactive loading is periodically distributed along the transmission line, which is electromagnetically coupled. The reactive load consists of a circular shaped patch which is converted to a metamaterial structure by embedded on it two concentric slit-rings. The patch is connected to the ground plane with a via-hole. The resulting structure exhibits electromagnetic bandgap (EBG) properties. The size and gap between the slit-rings dictate the magnitude of the reactive loading. The structure was first theoretically modelled to gain insight of the characterizing parameters. The equivalent circuit was verified using a full-wave 3D electromagnetic (EM) solver. The measured results show the proposed EBG structure has a highly sharp 3-dB skirt and a very wide bandgap, which is substantially larger than any EBG structure reported to date. The bandgap rejection of the single EBG unit-cell is better than − 30 dB, and the five element EBG unit-cell is better than − 90 dB. The innovation can be used in various applications such as biomedical applications that are requiring sharp roll-off rates and high stopband rejection thus enabling efficient use of the EM spectrum. This can reduce guard band and thereby increase the channel capacity of wireless systems.

Design and Fabrication of a MEMS Bandpass Filter with Different Center Frequency of 8.5-12 GHz.

The design simulation and fabrication results of a bandpass filter based on micro-electro-mechanical system (MEMS) switches are presented in this paper. The MEMS filter element consists of a MEMS capacitance switch and two resonant rings that are fixed onto coplanar waveguide lines through anchor points. The micromachine characteristics of the filter could be optimized to change the center frequency from 8.5 to 12 GHz by improving the geometrical parameters; other electrical parameters of the filter, such as stopband rejection, insertion loss, and return loss at each center frequency, were simulated and calculated. In order to evaluate the MEMS filter design methodology, a filter working at 10.5 GHz fabricated with an aluminum top electrode was used, and it displayed a low insertion loss of 1.12 dB and a high stopband rejection of 28.3 dB. Compared with the simulation results, these proposed filter showed better electrical performance. Our results demonstrated that the filter with the integrated RF MEMS switch not only provides the benefit of reduced size compared with a traditional filter, but also improves stopband rejection, insertion loss, and return loss.

Broadband dual‐band bandstop filters based on step‐impedance stubs and transmission‐line networks

In this paper, a novel basic structure of a dual-band bandstop filter (DBSF) without coupled lines is proposed. In order to improve the performance, some optimizations are made to the basic structure, and two DBSF structures with multi-transmission zeros and multi-transmission poles are obtained. These filters have the advantages of simple structure, high selectivity, and high stopband rejection, among which the deepest stopband can be better than 45 dB. In addition, an extraction method of transmission zeros and transmission poles based on the S-parameter theory is proposed. The ideal 3-dB fractional bandwidths of the basic structure are 37.8% and 18.7%, respectively, 54.1% and 25.9% for the first improved structure, respectively, and 75.1% and 34.2% for the second improved structure, respectively. EM simulation results and measured results are highly unified to verify the proposed filter structure.

A Charge-Sharing IIR Filter With Linear Interpolation and High Stopband Rejection

This article introduces a new discrete-time (DT) charge-sharing (CS) low-pass filter (LPF) that achieves high-order filtering and improves its stopband rejection while maintaining a reasonable duty cycle of the main clock at 20%. It proposes two key innovations: 1) a linear interpolation of the sampling capacitor and 2) a charge re-circulation of the history capacitors for deep stopband rejection. Fabricated in 28-nm CMOS, the proposed IIR LPF demonstrates a 1–9.9-MHz bandwidth (BW) programmability and achieves a record-high 120-dB stopband rejection at 100 MHz while consuming merely 0.92 mW. The in/out-of-band IIP3 is +17.7 dBm/+26.6 dBm, and the input-referred noise is 3.5 nV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\mathrm{ Hz}}$ </tex-math></inline-formula> .

Broadband Dual-Polarized Differential-Fed Filtering Antenna Array for 5G Millimeter-Wave Applications

This article presents a novel broadband dual-polarized filtering patch antenna array using low-temperature cofired ceramic (LTCC) process for 5G millimeter-wave (mmW) applications. The filtering antenna element is implemented using a ± 45° polarized patch antenna fed by two pairs of differential L-type probes. An additional square ring and open strips are connected to each probe, resulting in radiation nulls and realizing the lower/upper stopband rejection level over 24 dB with skirt selectivity. The cross coupling among these structures not only introduces filtering responses, but also contributes to broadening the passband of 24.25–29.5 GHz covering 5G n257/n258/n261 bands. The antenna performance is validated by equivalent circuits based on transmission line models, which reveals clearly the principles of filtering antenna step by step and provides guidelines for further designs. The proposed filtering antenna element is expanded to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> filtering antenna array with shunt-fed feeding networks. The spacing between elements is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.48~\lambda _{0}$ </tex-math></inline-formula> . The measured results demonstrate that the array performs good filtering characters including high stopband rejection, high selectivity, and wide upper stopband up to 40 GHz, where the antenna efficiency (considering radiations from all the directions) is less than 5%. In addition, the differential feeds provide symmetric radiation patterns with low cross-polarized counterparts. Compared with other reported works, the proposed filtering antenna/array has excellent performances of wideband, high stopband rejection and wide upper stopband for potential 5G mmW applications.

Design of coaxial dual‐band filter with high stopband rejection

This paper proposes a design of dual-band coaxial filter with high stopband rejection. By setting the half-window coupling structures and loaded resonators, the stopband rejection of the dual-band coaxial filter can be significantly improved. An L band coaxial dual-band filter is designed and measured as an example. The stopband rejection of the design is increased from 2.7 times to 3.52 times the center frequency of the filter, which verifies the proposed method.

Compact, Wide Stopband, Shielded Hybrid Filter Based on Quarter-Mode Substrate Integrated Waveguide and Microstrip Line Resonators

A novel miniaturized bandpass filter (BPF) with high stopband rejection based on a hybrid structure is proposed with shielded quarter-mode substrate integrated waveguide (QMSIW) and microstrip technologies. The shielded QMSIW cavity provides a high-quality ( $Q$ ) factor with substantial size reduction. This filter exhibits flexible response with four poles and two controllable transmission zeros (TZs) by incorporating two quarter-wavelength microstrip resonators into two back-to-back QMSIW resonators. The working principles for higher order mode suppression and filter coupling topology are carefully illustrated by eigen-mode simulation, coupling matrix, and field distribution analysis, respectively. Compared with the reported works, the proposed four-order BPF demonstrates advantageous features in terms of a compact size of $0.62\,\,\lambda _{0}\times 0.62 \,\,\lambda _{0}$ , a low insertion loss of 1.2 dB, a wide passband (22.7%), and a high stopband rejection (better than 36 dB).

Microwave photonic notch filter with integrated phase-to-intensity modulation transformation and optical carrier suppression.

We demonstrate for the first time, to the best of our knowledge, an on-chip microwave photonic (MWP) notch filter with high stopband rejection and integrated optical carrier suppression in a phase modulator-based system. The notch filter was achieved through phase modulation to intensity modulation (PM-to-IM) transformation and dual-sideband-processing using a network of three ring resonators (RRs) in a low-loss silicon nitride (Si3N4) platform. We show simultaneous PM-to-IM conversion and optical carrier processing for enhancing the filter performance using a single RR. We achieve filtering with a high stopband rejection of >55dB, an optical carrier suppression up to 3 dB, a radio frequency link gain of 3 dB, a noise figure of 31 dB, and a spurious-free dynamic range of 100dB⋅Hz2/3. These experiments point to the importance of vectorial spectral shaping of an MWP spectrum for advanced functionalities.

Novel Selective Feeding Scheme Integrated With SPDT Switches for a Reconfigurable Bandpass-to-Bandstop Filter

This paper demonstrates a new technique for designing high performance reconfigurable bandpass-to-bandstop filters by employing a ring resonator and a selective feeding scheme integrated with single-pole double-throw switches (SPDT). The transformation from bandpass-to-bandstop mode and vice-versa is achieved by connecting or disconnecting two λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /4 open-circuited stubs on the ring using PIN diodes. SPDT switches are employed for electronic switching between two different feeding line sections. In the bandpass state the resonator presents two transmission zeros near the edges of the passband and four attenuation poles inside the passband, enhancing the filter's performance, thus achieving excellent sharp rejection with high roll-off-rate (ROR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20dB</sub> ). On the other hand, high stopband rejection with wide bandwidth, good return loss and good skirt-band attenuation rates are achieved in the bandstop state. Even- and odd-mode analysis is adopted and closed-form expressions are derived to describe the filter's behaviour. To verify the validity of the proposed design, a prototype filter was fabricated and measured. In measurement, a 65% 3-dB bandwidth bandpass filter (BPF) with an insertion loss of 0.86 dB was switched to a 70% 20-dB bandwidth bandstop filter (BSF) with more than 40 dB stopband rejection.

A compact SIW bandpass filter using DMS-DGS structures for Ku-band applications

This paper presents a design of compact SIW (substrate integrated waveguide) bandpass filter for application in Ku-band Transmit up-convert frequency (i.e., 13.7–14.1 GHz) used for satellite communications. Based on Defected Microstrip Structure-Defected Ground Structure combination (DMS-DGS), this SIW filter structure is designed to improve passband and stopband performance. By merging circular ring slot (CRS) with interdigital DGS, better passband characteristics with sharp stopband attenuation are obtained. To validate the design, the filter is fabricated using Rogers substrate. The size measures 23.8 mm × 10 mm and operates at a center frequency of 13.9 GHz. Measured results of the filter agree well with the simulated results. Also, designed BPF filter has advantage of low insertion loss, better return loss, compact size and high stopband rejection.

Bandpass filter using coupled‐line‐stub cascaded structure with high stopband rejection

AbstractA compact fifth‐order bandpass filter (BPF) with high stopband rejection level is proposed using a coupled‐line‐stub cascaded structure (CLS‐CS). Based on transversal signal‐interference technique, the CLS‐CS is introduced to improve the characteristics of the filter, generating four new transmission zeros (TZs) close to band edge. The positions of all TZs are calculated through input impedance deduction. For demonstration, a BPF prototype centered at 2.1 GHz is designed with measured 3‐dB fractional bandwidth of 39% (1.68‐2.50 GHz) and stopband rejection levels of over 28.9 dB, which validates the proposed idea.

Dynamic Filtering of Microwave Signals Through Brillouin-Based Polarization-Sensitive Balanced Detection

A new photonic technique to implement both stopband and passband microwave filters is presented and demonstrated. The principle of operation relies on controlling the state of polarization of the band of interest using stimulated Brillouin scattering-based polarization rotation and the optoelectronic conversion of this polarization-structured signal by means of a polarization sensitive balanced photodetection. Using the proposed architecture, the filter response can be dynamically switched to implement a stopband or a passband response with the same scheme, thus enhancing its flexibility and application potential. Experiments with a single stage show that very high stopband rejection can be implemented, 67 dB, which for the best of our knowledge is the highest stopband rejection for a photonic microwave notch filter reported to date. Measurements also show that the filter response can be dynamically changed to implement a bandpass response.

A quad‐band bandpass filter using sept‐mode double square‐ring loaded resonator

AbstractA quad‐band bandpass filter (BPF) using a sept‐mode double square‐ring loaded resonator (DSRLR) is presented in this article. Based on the symmetrical geometric construction of the DSRLR, the even‐ and odd‐mode analysis with theoretical equations is employed to analyze the proposed BPF, and current density are obtained. Additionally, multimode splitting and resonant characteristics of the proposed DSRLR are explored. Accordingly, the design procedure is given after a pair of feedlines with dual‐finger structure is added to the I/O ports to introduce extra transmission zeros (TZs). Four TZs—including two created by the dual‐finger feedlines—are produced to separate four passbands that exhibit a sharp skirt and high stopband rejection. Finally, a microstrip quad‐band BPF is fabricated on a Teflon substrate with four measured passbands centered at 2.46, 3.41, 6.65, and 9.09 GHz with insertion losses of 0.68, 0.73, 0.81, and 1.23 dB, respectively. A satisfactory agreement is achieved between the measurement results and full‐wave simulation results.

Wideband Diplexer With Narrow Channel Spacing Using Hybrid Bandpass-Bandstop Structures

In this paper, a wideband diplexer with narrow channel spacing is designed by using hybrid bandpass-bandstop structures. Two wideband bandpass structures are designed with the transmission zeros at the upper or lower passband edges to achieve high skirt selectivity. Two bandstop structures based on half-wavelength coupled lines are integrated to the two bandpass structures to introduce additional transmission zeros and thus the skirt selectivity is further improved. Accordingly, two channel filters with high skirt selectivity and high stopband rejection are designed to realize a wideband microstrip diplexer with very narrow channel spacing. For verification, a wideband diplexer operating at 1.71-2.17 GHz and 2.30-2.70 GHz is implemented, which covers multiple frequency bands for different mobile systems. The measured results show excellent performance of passband flatness, high in-band isolation of better than 35 dB and low minimum insertion losses of 0.46 and 0.50 dB for the two channels.

High Stop Band Rejection for Ceramic Loaded Waveguide Filters

This Paper describes the design procedure of a compact narrowband ceramic loaded filters with wide out of band response. The idea of loading the waveguide filter resonators with ceramic TEM blocks and ceramic ridge blocks are presented. Resonator loading with silver plated transverse electromagnetic (TEM) hole and silver plated ridge ceramic blocks offers wide spurious free bandwidth 2.45 times of center frequency. Simulated and measured results of six pole chebyshev Ceramic ridge loaded filter and simulated results of Ceramic TEM loaded filter are presented in this paper showing excellent out-of-band performance.

Realization of transmission zeros for bandpass filter using inductive-coupled stub-loaded resonators

AbstractThis article proposes a bandpass filter with three controllable transmission zeros (TZs) using three inductive-coupled stub-loaded resonators (SLRs). Different from other works, the proposed SLR can create one transmission pole and one TZ. With the TZs above the passband, high stopband rejection level is achieved. Moreover, the K-inverters are realized by short-circuit stubs between two adjacent SLRs. A general synthesis method for this kind of filter is described. For verification, a filter centered at 2.44 GHz with 0.18 GHz bandwidth is designed. The measured results show that the filter has three TZs at 3.1, 3.9, and 5 GHz. With those TZs, the filter's stopband rejection level is greatly improved.

Compact multi‐order bandpass filter with high stopband rejection performance

This Letter presents a multi-order bandpass filter (BPF) based on unit cells, which are constructed by coupled lines and microstrip stubs. This BPF unit cell features ultra-wide upper stopband and excellent stopband rejection performance. The external quality factors and coupling coefficients of unit cells are analysed in detail for multi-order BPF design, where transmission lines are adopted as a coupling structure for easy post-fabrication tuning. Following filter coupling matrix theory, two- and three-pole Chebyshev-response BPFs are designed and measured, centred at 1.0 GHz with 3-dB fractional bandwidth of 10%. Experimental results demonstrate excellent out-of-band rejection performances. In two-pole BPF, the upper stopband can reach 4.8 GHz (4.8 f 0 ) with the rejection level of 37 dB. In three-pole BPF, within the stopband frequency of 3.4 GHz (3.4 f 0 ), the rejection level is better than 55 dB, while the upper stopband can be extended to 6.5 GHz (6.5 f 0 ) with the suppression level of above 26.8 dB.

Compact Wideband Reflective/Absorptive Bandstop Filter With Multitransmission Zeros

Novel wideband reflective bandstop filters (RBSFs) and absorptive bandstop filters (ABSFs) with high stopband rejection (SR) and good frequency selectivity are proposed. Based on a coupled line (CL) with an open-circuited stub, a broad stopband response with three transmission zeros (TZs) is implemented in a compact circuit configuration. Two modified CL structures are loaded at the ports resulting in two additional TZs. In addition, a grounded resistor is introduced to absorb unwanted signals in the stopband. For demonstration, the five-zero RBSFs and three-zero ABSFs operating at 2 GHz are designed and built. The reflective filter shows a 35-dB SR with 79.5% relative bandwidth (RB). The absorptive filter with 69.5% RB of 24-dB SR achieves an all-passband 12.2-dB return loss. Good agreements between simulated and measured results are observed.

High-Selectivity Wideband Bandpass Filter Using Simple Coupled Lines With Multiple Transmission Poles and Zeros

A compact fifth-order wideband bandpass filter (BPF) using simple coupled lines with sharp rolloff skirts is proposed in this letter. Five transmission poles within the passband and eight deep transmission zeros from 0 to $2\!f_{0}$ ( $f_{0}$ denotes the center frequency of the passband) can be realized through input impedance calculations. For demonstration, a wideband BPF prototype centered at 2.05 GHz with high-stopband rejection is designed and fabricated, whose measured 3-dB fractional bandwidth is of 60% (1.44–2.66 GHz). Good agreement between the simulations and measurements validates the design idea.