Additional Transmission Zeros Research Articles

Design of IPD-based wideband bandpass filter chips with controllable transmission zeros

ABSTRACT In this brief, two novel wideband bandpass filter (BPF) chips with independently controllable transmission zeros are proposed. BPF I uses bridge T-type highpass and lowpass structures cascaded to achieve wideband filtering. On this basis, BPF II adds three pairs of LC resonant circuits to add additional transmission zeros while retaining the lowpass structures. The analytical methods of odd-even mode and ABCD matrix to S-parameter matrix are used to analyze and calculate two designs. For validation, two prototypes of proposed BPFs in integrated passive device (IPD) have been designed, fabricated, and measured. One prototype operates at 5.3 GHz, providing a 3-dB fractional bandwidth (FBW) of 46.9%, while the other prototype operates at 4.7 GHz, providing a 3-dB FBW of 57.6%. Moreover, the two chips exhibit minimum insertion losses of 1.55 dB and 1.5 dB, respectively, while occupying compact sizes of 2.27 mm × 0.83 mm and 1.7 mm × 0.88 mm.

Design of highly selective balanced bandpass filter with wide differential-mode stopband and high common-mode suppression

A highly selective and wide stopband bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) has been proposed. The BPF employs a box-like coupling structure consisting of two half-wavelength resonators and a dual-mode open stub loaded resonator, enabling the generation of two TZs and four TPs. Three controllable TZs are obtained by adding an annular spiral open stub to the terminal of the input and output coupling lines, which significantly improves the selectivity of the BPF. To achieve a wide stopband characteristic, a wide stopband unit with three additional TZs is cascaded within the structure. A balanced BPF is realized by introducing a microstrip-slotline-microstrip balun structure to the input and output ports of the proposed BPF. Experimental results validate the feasibility of the proposed BPF and balanced BPF applied in 2.45 GHz ISM band. The introduction of eight TZs gives the BPF a 20 dB rectangular coefficient of 1.3 with an upper stopband exceeding than 12 GHz. The balanced BPF can achieve 40 dB of high common-mode(CM) suppression in the passband, while differential-mode (DM) transmission is close to the performance of the proposed BPF. The minimum insertion loss for BPF and balanced BPF is 0.8 dB and 1.3 dB, respectively.

Wideband filtering power divider based on D-CRLH resonator

In this paper, a wideband filtering power divider (FPD) based on dual-composite left–right-handed (D-CRLH) resonator is proposed. The D-CRLH filter unit, featuring a parallel stepped impedance resonator (SIR), is used to replace the λ/4 transmission line of the Wilkinson power divider, which can make the FPD more compact. Due to the inherent characteristics of D-CRLH resonator, two transmission zeros can be generated on both sides of the passband, so the proposed power divider based on the D-CRLH resonator can achieve a quasi-elliptic filtering response. To further enhance anti-interference ability at low frequencies, a pair of open stubs is added to the output feedline to introduce an additional transmission zero on the low-frequency side of the power divider passband. Finally, isolation resistors are introduced on the input and output feedlines to improve the isolation between the output ports. For validation, a prototype with a center frequency of 3.6 GHz is fabricated and measured, with −10 dB fractional bandwidths (FBWs) of 58.3 %(2.55–4.65 GHz). The measurement results are basically consistent with the simulation results, and its isolation in the passband is all more than 13.8 dB.

Compact Waveguide Filters Using Novel Resonant Coupling Structures

In this article, new resonant coupling structures are proposed for designing miniaturized waveguide bandpass filters. The resonant coupling structure is constructed by adding one or two metal blocks in a relatively thick inductive iris, which can be considered as the integration of a resonator, the input, and output coupling structures. Positive or negative coupling can be realized by selecting a different number of metal blocks. The combination of different resonant coupling structures can be used to design higher-order filters with various transverse topologies, realizing different transmission zeros (TZs) distributions. In addition, the weak source–load coupling caused by the resonant coupling structures can introduce an additional TZ, which can further improve the out-of-band suppression level of the filter. For verification, two third-order waveguide bandpass filters based on all resonant coupling structures are designed and simulated to achieve different TZ distributions. Finally, a fifth-order waveguide bandpass filter employing both resonant coupling structures and classical rectangular cavities is designed and fabricated. The measured results verify the proposed method.

Dual-Band Power Divider With Wide Passbands and Wide Harmonic Suppression Utilizing Multi-Mode T-Stub Loaded Slotline Resonators

This brief proposes a novel dual-wideband slotline power divider (DWSPD) with ultrawide stopband, which is suitable for the multi-band wireless communication system application. The proposed DWSPD is mainly constructed with two multi-mode T-stub loaded slotline resonators (MTSRs), four folded slotline structures (FSSs), four microstrip-slotline transitions and two isolation resistors. The MTSR can generate four transmission poles (TPs), which forms two wide passbands. Furthermore, the FSS contributes to four additional transmission zeros (TZs), which enhances the harmonic suppression. The fabricated DWSPD demonstrates the 3-dB fractional bandwidths of 45.3% @2.25 GHz and 47.1% @4.37 GHz and the stopband with a suppression more than 18 dB @ up to 40 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17.8~f_{01}$ </tex-math></inline-formula> ). To the best of the author’s knowledge, the 3-dB FBWs and stopband achieve the best among the existing dual-band filtering power dividers (DBFPDs).

Direct Synthesis of Acoustic Wave Multiplexers Built on Fully Canonical Multiport Functions

This work proposes the first analytical method for the direct synthesis of multiplexers based on acoustic wave (AW) ladder filters connected in a star junction topology. It describes the computation of the polynomial representation of a multiport ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K} +$ </tex-math></inline-formula> 1 ports) network with fully canonical (FC) channels and derives a set of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> distorted channel polynomials from which each of the AW ladder filters is synthesized. The channel polynomials are distorted in a way such that when connected together at the star junction, the desired multiplexer response is obtained avoiding degradation due to channel loading. The method allows to freely set the fractional bandwidth (FBW), return loss (RL), and transmission zeros (TZs) of each channel enabling the search for multiplexers that fulfill the technological requirements of AW technology in terms of electromechanical coupling coefficient and area occupancy among others. Moreover, since the multiport network polynomials incorporate the complete effects of the loading between channels as, for example, additional TZs, the synthesized multiplexers depict an improvement of isolation when compared with a design based on only controlling the reflection phase of each channel filter. The proposed method is rigorously demonstrated by means of a synthesized multiplexer example providing the Butterworth–Van Dyke (BVD) elements of each channel filter. This approach avoids intensive optimization procedures and represents a useful technique for the design of carrier aggregation (CA) filter modules in a direct and controlled manner.

Synthesis Design of Wideband Bandpass Filter With High Selectivity and Harmonic Suppression

A novel wideband quasi-Chebyshev bandpass filter (BPF) with steep skirt selectivity and extended upper stopband is presented. It is comprised of two microstrip-to-microstrip vertical transitions with nonuniform slotline sections, which cascaded directly by a nonuniform microstrip connecting line. In terms of odd-/even-mode analysis, the in-band six poles which make up the wideband bandwidth can be explicitly derived. Moreover, the Chebyshev equal-ripple filtering responses with prescribed specifications can be conveniently achieved in desired passband by adopting synthesis theory. In order to suppress the second and third spurious harmonics, a modified circuit model based on synthesis method is further proposed. Two additional transmission zeros (TZs) TZ3, TZ4 can be generated at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3f_{0}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5f_{0}$ </tex-math></inline-formula> respectively by adjusting impedance ratio of slotline stubs properly under the condition of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{\mathrm {s1}} = \theta /4$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta _{\mathrm {s2}} = \theta /2$ </tex-math></inline-formula> , which widen the upper stopband bandwidth greatly and enhance harmonic rejection level effectively. Meanwhile, combing with the inherent periodic finite-frequency TZ5, TZ6 and TZ7, the upper stopband could be extended to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.22f_{0}$ </tex-math></inline-formula> with rejection level better than 14.6 dB. Besides, a pair of finite-frequency TZ1 and TZ2 caused by source-load coupling occur at both sides of passband to sharpen the cutoff slope of skirts remarkably. For verification, a prototype is fabricated and measured, the experimental results agree well with the theoretical predictions, which verify the validity of proposed method.

Compact Substrate Integrated Waveguide Wideband Bandpass Filter With Post-Manufacturing Tuning Capabilities

In this paper, a miniaturized wideband bandpass filter in coaxial substrate integrated waveguide (SIW) technology is presented. To improve the response selectivity and coupling control, a multi-layer structure has been implemented, introducing both strong magnetic and electric couplings. To reduce the physical size of the device, surfaced-mounted device (SMD) capacitors have been integrated on the top layer. These allow both resonant frequency and capacitive coupling level control. Thus, a 4-th order Chebyshev filter with an absolute bandwidth (BW) of 2.9 GHz centered at 5.35 GHz has been designed, fabricated and measured. An extremely small filter size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7 \times 7$ </tex-math></inline-formula> ,mm2 has been obtained. A study of manufacturing tolerances are also presented in this paper, together with a post-manufacturing response correction allowed by the SMD elements. As it is shown in the paper, the filter’s out-of-band rejection can be easily enhanced by introducing additional transmission zeros (TZs).

Compact filters based on dual‐mode gap waveguide cavities and 3D printing technology

AbstractThe design of compact dual‐mode/band filters based on gap waveguide and 3D printing technology is presented in this paper. The spatial power divider is designed to arrange the external coupling. And the multi‐slot middle plate is devised to manage the coupling between the dual‐mode cavities, introducing the non‐resonating modes to produce additional transmission zeros and improving the selectivity. Moreover, the dual‐mode/band filters structure are built up and optimized for 3D printing technology. Finally, the fabricated filters are measured to verify the design.

Compact Half-Mode SIW Filter With High Selectivity and Improved Stopband Performance

In this letter, a novel filter with high selectivity is proposed using a hybrid multilayer half-mode substrate-integrated waveguide (HMSIW). First, a rectangular HMSIW is used to realize a third-order cross-coupling topology, which could introduce a transmission zero (TZ) on the left side of the passband. Then a ring microstrip resonator is added to form the new dangling block, which realizes the fourth-order response with an additional TZ located on the right side of the passband. Sharp skirt and high selectivity are then achieved. In addition, since each mode of the HMSIW has different external coupling strengths at the same feeding position, harmonic suppression can be achieved easily by moving the feeding position. Therefore, a good stopband can be obtained with decent out-of-band performance. Size reduction is also achieved through the multilayer HMSIW and hybrid microstrip structures as well.

A Compact, Hybrid SIW Filter With Controllable Transmission Zeros and High Selectivity

A novel, highly selective, and compact filter with controllable transmission zeros (TZs) is proposed in this brief. The hybrid structure of the proposed filter is based on the substrate integrated waveguide (SIW) and microstrip line resonators. The negative magnetic coupling was introduced through a full-wavelength microstrip line resonator, and the additional TZ was added by the cross-coupling of indirectly connected resonators in the traditional box-like topology. Consequently, high selectivity is achieved with TZs located at both sides of the passband. The independent control of the left and right TZs can be realized by controlling the cross-coupling and external coupling. The proposed work achieves good performance, including sharp skirt characteristics, compact size, and low loss. As a validation of the concept and performance, a filter prototype designed following the procedure is fabricated and measured.

A novel asymmetrical interdigital coupled line‐based penta‐band bandpass filter design with enhanced selectivity employing square complementary split ring resonator

This article demonstrates design of a novel miniaturized penta-band bandpass filter (BPF) having enhanced selectivity with 10 transmission zeros (TZs) employing asymmetrical interdigital coupled lines and square complementary split-ring resonators (SCSRR). The arrangement of a split in open-circuited stubs with SCSRR presents an independently controllable additional TZ. The measured minimum insertion losses and shape factors are 1.1, 0.95, 1.35, 1.5, 1.65 dB and 2.1, 1.6, 1.7, 1.85, 1.7, respectively. Hence, this futuristic design structure with five passbands prominently delivers improved selectivity and low-insertion loss compared with other progressive multi-band BPFs. The fabricated penta-band BPF's physical area is 17.5 × 28.5 mm2 and renders five passbands operating at 1.8, 2.4, 3.5, 4.9, and 5.8 GHz for GSM, Wi-Fi, Wi-Max, public safety applications, and WLAN applications, respectively.

Design of Microstrip Dual-Mode Wideband Bandpass Filter with Controlled Center Frequency and Bandwidth Using Bandstop Filter Topology

ABSTRACT This paper discusses a new method for designing a microstrip dual-mode, sharp skirt, wideband bandpass filter with controlled center frequency and bandwidth from bandstop filter topology. A meander closed loop resonator with directly connected orthogonal feed lines provides a Bandstop filter (BSF) with reduced size. A pair of L-shaped open stubs introduced along the diagonal axis D-D1 realizes a wide passband within the rejection band (0.93–4.13 GHz) of the bandstop filter with sharp stopbands on either side of the passband. Furthermore, the effect of L-shaped open stubs susceptance on passband edges is demonstrated. A quarter wavelength stepped impedance shunt stub (SISS) connected at is proposed to achieve additional transmission zeros in the upper and lower rejection bands to improve the sharpness of filter response. Both center frequency and bandwidth of the proposed filter are controlled by the impedance ratio (R) of the SISS element. The proposed filter is simulated using ADS, fabricated and measured using Vector Network Analyzer (VNA). A good agreement is achieved between simulated and measured results.

Multi-band planar diplexers with sub-sets of frequency-contiguous transmission bands

AbstractA class of multi-band planar diplexer with sub-sets of frequency-contiguous transmission bands is reported. Such a radio frequency (RF) device is suitable for lightweight high-frequency receivers aimed at multi-band/multi-purpose mobile satellite communications systems. It consists of two channelizing filters, each of them being made up of the in-series cascade connection of replicas of a constituent multi-passband/multi-embedded-stopband filtering stage. This building filtering stage defines a multi-passband transfer function for each channel, in which each main transmission band is split into various sub-passbands by the multi-stopband part. In this manner, each split passband gives rise to several sub-passbands that are imbricated with their counterpart ones of the other channel. The theoretical RF operational principles of the proposed multi-band diplexer approach with sub-sets of imbricated passbands are detailed by means of a coupling–routing–diagram formalism. Besides, the generation of additional transmission zeros in each channelizing filter for higher-selectivity realizations by exploiting cross-coupling techniques into it is also detailed. Furthermore, for experimental demonstration purposes, a microstrip proof-of-concept prototype of second-order octo-band diplexer in the frequency range of 1.5–2.5 GHz that consists of two quad-band channelizing filters with pairs of imbricated passbands is developed and characterized.

High-order and tunable balanced bandpass filters using mixed technology resonators

AbstractThis paper reports on high-order balanced bandpass filters (BPFs) that are continuously tunable in terms of frequency and bandwidth and can be intrinsically switched-off. They use a hybrid integration scheme based on two different types of capacitively loaded resonators—ceramic coaxial and microstrip—that reduce the filter size, enhance its out-of-band selectivity and common-mode suppression, and allow for multiple levels of transfer function tuning. High selectivity is obtained in the differential mode due to the high number of poles and transmission zeros present. The common mode is highly suppressed through the introduction of additional transmission zeros and resistively loaded resonators. Furthermore, the use of ceramic coaxial resonators results in supplementary transmission zeros that are used to lower the out-of-band transmission in the differential mode. Multiple levels of tuning are obtained by reconfiguring only the frequency of the BPF's resonators. For experimental validation, a tunable mixed-technology microstrip prototype was manufactured and measured at S-band. It exhibited frequency tuning between 2.22 and 2.94 GHz, bandwidth tuning between 104 and 268 MHz, and an intrinsically switched-off mode with isolation &gt;50 dB in the differential mode. For all states, the common mode was suppressed by at least 35 dB at the center frequency and within a wide range.

A Low-Cost Microwave Filter with Improved Passband and Stopband Characteristics Using Stub Loaded Multiple Mode Resonator for 5G Mid-Band Applications

This paper presents the design and implementation of a printed circuit microwave band-pass filter for 5G mid-band applications, using a Stub Loaded Multiple Mode Resonator (SL-MMR) technique. The objective of this article is to introduce a low-cost microstrip filter with improved passband and stopband characteristics, based on a mathematical analysis of stub loaded resonators. The filter cost is reduced by selecting the low-cost FR4 dielectric material as a substrate for the proposed filter. Based on the transmission line model of the filter, mathematical expressions are derived to predict the odd-mode and the even-mode resonant frequencies of the SL-MMR. The mathematical model also highlights the capability of controlling the position of the SL-MMR resonant frequencies, so that the 5G sub-band that extends along the range (3.7–4.2 GHz) can perfectly be covered with almost a flat passband. At the resonance frequency, a fractional bandwidth of 12.8% (500 MHz impedance bandwidth) has been obtained with a return loss of more than 18 dB and an insertion loss of less than 2.5 dB over the targeted bandwidth. Furthermore, a pair of parasitic elements is attached to the proposed filter to create an additional transmission zero in the lower stopband of the filter to enhance the suppression of the filter stopband. The measured and simulation results are well agreed, and both reveal the acceptable performance of the stopband and passband characteristics of the filter.

A Substrate Integrated Waveguide Bandpass Filter Based on the Modified CSRRs and the Z shaped slot

ABSTRACT In this paper, a substrate-integrated waveguide (SIW) bandpass filter using the modified complementary spilt-ring resonators (MCSRRs) and the Z-shaped slot is presented. Based on the combination of MCSRRs and the Z-shaped slot, four layouts with MCSRRs in different directions are designed and their distributions of electromagnetic fields are analyzed in some detail. Simultaneously, the causes of the passband generation and change are explained. By comparing the performance of the four layouts, a bandpass filter with the advantages of compact structure, easy integration, and low insertion loss is designed on the basis of face-to-face layout. An additional transmission zero is obtained by introducing the Z-shaped slot. The selectivity is improved duo to two transmission zeros. The proposed filter allows the electromagnetic wave to be propagated in the passband below the cutoff frequency of the waveguide characteristic. To validate the design, the filter is fabricated and tested, and the tested results are consistent with the simulated results.

High Performance Balanced Bandpass Filters With Wideband Common Mode Suppression

Two compact and high selectivity balanced bandpass filters with excellent common mode rejection are designed in this brief. Compared with the half-wavelength microstrip transmission line, 180° phase shift is realized by two small swap structures, which are composed by double-sided parallel-strip line (DSPSL), and this way can easily realize a wideband common mode rejection with compact circuit size. Two out-of-band transmission zeros are introduced by the dual-mode ring resonator in the first proposed structure; thus, high selectivity can be achieved. In the second filter, shorted/open coupled microstrip lines are added between the dual-mode ring resonator and 180° swap structure, two additional transmission zeros can be achieved. Finally, two prototypes center at 2.2 GHz are fabricated, and the measured 3-dB bandwidths for the differential mode are 23.6% and 11.8%, respectively.

High-Performance Wideband Balanced Bandpass Filter Based on Transversal Signal-Interference Techniques

A novel high-performance wideband balanced bandpass filter based on transversal signal-interference techniques is proposed in this article. Two signal-propagation paths consisted of coupled lines structure are used to realize two transmission zeros for the differential mode passband. Folding coupled lines are used to reduce the size of the balanced filter, and the source-load cross-coupling lines can generate additional transmission zeros to suppress the common mode signal. To validate the design, a prototype with center frequency at 2.2 GHz for long-term evolution (LTE)-band with 3-dB fractional bandwidths of 65.4% for the differential mode is designed and fabricated.

Compact Multi-Mode Filtering Power Divider with High Selectivity, Improved Stopband and In-band Isolation

This letter presents a new compact multi-mode filtering power divider (FPD) design based on co-shared FPD topology with sharp frequency selectivity, improved out-of-band harmonic rejection and port-to-port isolation. Power splitting and quasi-elliptic filtering functions are achieved by masterly integrating only one triple-mode resonator. By loading different open-circuited stubs at the input/output ports, multiple additional transmission zeros (TZs) are generated at both lower and upper stopband, resulting in an improved stopband performance. Meanwhile, a better port-to-port isolation is obtained by adopting frequency-dependent resistor-capacitor parallel isolation network. The proposed multi-mode FPD design stands out from those in the literature by both nice operation performance and compact topology with only one resonator. For demonstration purposes, one triple-mode FPD prototype and its improved one are implemented, respectively. Measured results exhibit the superiority of the FPD design.