Stripline Filters Research Articles

Design of planar metal stripline filter and diplexer with frequency‐dependent couplings

AbstractIn this letter, frequency‐dependent coupling (FDC) is introduced into the design of metal stripline filters and diplexers for the first time. FDC is a popular research method to introduce the finite‐position transmission zeros in the synthesis and design of filters in recent years. Finite transmission zeros are critical for filters to enhance the rejection ratios. To verify the realizability and effectiveness of FDC, a filter centered at 3.52 GHz and a diplexer operating at 2.55 and 2.65 GHz have been designed and fabricated. The planar filter and diplexer are compact in structure with multiple transmission zeros, whose resonators and cavity are integrated and formed, the cavity and cover plate are soldered together. We designed, assembled and tested the filter and diplexer, the synthesis results, the simulation results, and the tested results are well matched with each other. Compared with the dielectric waveguide filter, the planar stripline filter has better insertion loss, better harmonic suppression, and higher reliability, which is expected to be widely used in 5G base station filters.

Investigation on temperature stability of MEMS silicon‐based sixth‐order stripline filter

A double-layer silicon-based stripline filter with a center frequency of 20.76 GHz and a bandwidth of 2 GHz was designed by using an aggressive space mapping (ASM) and fabricated with Microelectromechanical Systems (MEMS) technology. The measurements agreed well with simulation, showing efficiency and accuracy of the ASM algorithm. Over temperature range of −50 to 80°C, the filter's performance such as insertion loss, bandwidth and central frequency were investigated and discussed, and the measured frequency drift is −55.5 ppm/°C and the bandwidth variation is ±4% over temperature range of −50 to 80°C. At 150°C after 1000 h of aging test, although the insertion loss of the filter slightly increased from 2.18 to 2.4 dB and the passband ripple deteriorated, the stopband rejection performance improved.

Investigation on temperature stability of MEMS silicon‐based sixth‐order stripline filter

A double-layer silicon-based stripline filter with a center frequency of 20.76 GHz and a bandwidth of 2 GHz was designed by using an aggressive space mapping (ASM) and fabricated with microelectromechanical systems (MEMS) technology. The measurements agreed well with simulation, showing efficiency and accuracy of the ASM algorithm. Over temperature range of −50 to 80°C, the filter's performance such as insertion loss, bandwidth and central frequency were investigated and discussed, and the measured frequency drift is −55.5 ppm/°C and the bandwidth variation is ±4% over temperature range of −50 to 80°C. At 150°C after 1000 h of aging test, although the insertion loss of the filter slightly increased from 2.18 to 2.4 dB and the passband ripple deteriorated, the stopband rejection performance improved.

High power and immunity high Q PMC packaged dual notch high power suspended defected stripline filter

Abstract In this paper, a novel high power high selective and high-Q packaged dual band air suspended stripline notch filter is presented. The notch frequencies, at 2.4 and 3.5 GHz, were designed using defected suspended stripline (DSS). Moreover, the filter was packaged and shielded using perfect magnetic conductor (PMC). The DSS were designed using two frequency independent non-coupled cascaded U shape resonators. It has been proved that the filter attenuation has a sharp rejection characteristic (measured) at the two resonance frequencies (27 dB at 2.4 GHz) and (30 dB at 3.5 GHz) with Quality factor = (18). So, the sharp measured filter attenuation performance was further enhanced to become 38 dB at the two frequencies. The achieved results are discussed and confirmed using different circuit, 3D EM and experimental measurements. The designed filter can find many medium powers up to 20 kW applications.

EBG Common-Mode 20-GHz Microstrip and Stripline Filters: Sensitivity to Design Parameters

In this article, design and characteristics of 20-GHz electromagnetic bandgap (EBG) common-mode (CM) filters for microstrip (MS) and stripline (SL) differential pairs are considered. CM filter notch (resonance) frequency, depth, and width at the -15 dB level are calculated from the mixed-mode S-parameters. The agreement between the measured and modeled S-parameters of the baseline structures validates the models and allows for further numerical experiments. The systematic analysis of the trends for both MS and SL filter characteristics as functions of various geometrical and material design parameters is presented. Sensitivity to various technological features (conductor surface roughness, trapezoid shape of the traces, and line length imbalance) is also analyzed. It is shown that the MS EBG structure is more sensitive and less monotonic to most of the design parameters than those for the SL. This is attributed to the less electromagnetic field containment and more complex mode structure in the MS structures as compared to the SL. Systematic sensitivity analysis allows for an optimal design of the EBG CM notch filters for any printed circuit board layer where a differential pair runs. Though the analysis is presented for 20-GHz EBG filters, most of the trends would be applicable to the filters for the other frequencies.

Miniaturized suspended strip-line bandpass filter based on spoof surface plasmon polaritons

In this letter, we propose the design of miniaturized suspended strip-line (SSL) filters based on spoof surface plasmon polariton (SSPP), a sub-wavelength mode confined tightly around artificial structures. To avoid using high-density lossy dielectric fillings, we place a periodic corrugated metallic strips (PCMS) structure in a rectangular metallic cavity. Two probes are positioned near the two ends of PCMS structure. Since PCMS structure support SSPP with shorter wavelength, it can be treated as low-loss artificial dielectrics with high permittivity εr equivalently. The cut-off frequency f lower of waveguide modes in the cavity will be reduced, which, plus the cut-off frequency f upper of SSPP, will produce a pass band between f lower and f upper. Due to high εr, low insertion loss and light weight of the PCMS structure, miniaturized band-pass filters can be implemented using such a configuration. We demonstrated a prototype operating a bandpass filter in 2.7–4.6 GHz. The cross-section of cavity is reduced by more than 75%. The filter is with quite low insertion loss only 0.1–0.3 dB. Both simulation and measurement results verify this design. This work provides an alternative to miniaturized, light-weight, high-efficiency SSL filters.

Design and characterisation of dual‐mode suspended‐substrate stripline filter

A new design technique of a dual-mode ring-resonator suspended-substrate stripline filter is reported here to achieve low passband insertion loss, high quality factor, and good spurious response. A fourth-order bandpass filter was designed and fabricated at the operational frequency of 2.07 GHz with two ring resonators packaged in a metallic cavity where each ring resonator is one wavelength long. The transmission zeros of the dual-mode filter are generated due to the phase cancellation between the two paths in a ring, thus a sharp-skirt selectivity filter response was achieved. Perturbation notch structure was implemented on each ring resonator to provide the electromagnetic coupling of two degenerate modes, thus a dual-mode response of the filter can be synthesised. Measurement results of the first dual-mode filter prototype showed a return loss and an insertion loss of better than 16.42 and 0.926 dB, respectively, while an out-of-band rejection of up to 55 dB was achieved. The novel filter design technique proved that no cross-coupling is required to obtain the transmission zeros of the filter, thus the sharp-skirt response was achievable.

Influence of Geometric Parameters and Permittivity of Stripline Filters on Resonator Coupling Coefficients

It has been proved that electromagnetic coupling coefficients K of resonators in stripline filters with homogeneous dielectric depend only on geometric parameters of the filter designs and are independent of relative permittivity er (if the dielectric is two-layer, coefficients K depend only on geometric parameters of the filter designs and ratio er2/er1). It has been shown that the revealed earlier influence of permittivity er and the operating frequency on K is only a consequence of the influence of the length of stripline resonators on K: the lesser is the length, the larger is coefficient K. It has been found that these propositions enable consideration of frequency characteristics of the same design of the bandpass filter in different frequency bands by changing er and performing slight changes in outermost resonators. The results of computer simulation of the transfer of frequency characteristics of a stripline bandpass filter from 3 GHz to 6 and 12 GHz with retaining the fractional bandwidth and selectivity are presented.

Interaction Features of Stepped-Impedance Stripline Resonators in Comb Filters

Mixed coefficients of coupling between the closely spaced stepped-impedance resonators in comb filters of stripline design have been investigated. Transmission zeros at frequencies f zi correspond to mixed coupling coefficients k i . These zeros can be moved with respect to the filter passband central frequency f0 by modifying the shape of resonators. It was proved that the reduction of gap between resonators made it possible to locate frequencies f z and f0 closer to one another. The existing restrictions on the minimal value of gap between resonators limit the degree of proximity between f z and f0. The N-resonator stripline comb filters with mixed coupling can have N−1 transmission zeros. The absence of cross-coupling links in stripline filters simplifies their construction. It has been established that the thickness of central conductors of stripline resonators affects the positive and negative mixed coupling coefficients. The paper presents measurement data of miniature stripline three-resonator comb filter having an enhanced selectivity at the expense of two transmission zeros. The central frequency of filter is f0 = 1850 MHz, the bandwidth BW = 100 MHz. The filter having dimensions 5.8×4.2×2 mm was implemented by connecting two ceramic substrates having relative dielectric permittivity e r = 92 and the metallized patterns deposited on them.

Dual-band suspended stripline filter based on electric metamaterials

Dual-band suspended stripline filter based on electric metamaterials

Planar three-resonator bandpass filters with cross coupling

New designs of planar three-resonator bandpass filters with cross coupling having a large variety of frequency characteristics are considered. In addition to better one-sided selectivity, such filters implement symmetric amplitude–frequency characteristics with an attenuation pole at each side of the passband. These filters can also have constant delay time in the passband. Concatenation of the proposed three-resonator filters leads to multiresonator filters with high selectivity determined by two attenuation poles at each side of the passband. It is found that the type of connection of the middle resonator in the circuit of a three-resonator filter with cross coupling results in substantial differences in amplitude–frequency characteristics. The results of modeling of different frequency characteristics are presented. It is shown that filters have small dimensions, which are comparable to overall dimensions of microwave ceramic filters. For example, dimensions of a three-resonator stripline filter designed for a frequency of 1.9 GHz are 9.4 × 5 × 2 mm for the permittivity of the filter material er = 92 and dimensions of a six-resonator filter are 10 × 9.4 × 2 mm.

Protecting Against Damage from Refraction of High Power Microwaves in the DIII-D Tokamak

Several new protective systems are being installed on the DIII D tokamak to increase the safety margins for plasma operations with injected ECH power at densities approaching cutoff. Inadvertent overdense operation has previously resulted in reflection of an rf beam back into a launcher causing extensive arcing and melt damage on one waveguide line. Damage to microwave diagnostics, which are located on the same side of the tokamak as the ECH launchers, also has occurred. Developing a reliable microwave based interlock to protect the many vulnerable systems in DIII-D has proved to be difficult. Therefore, multiple protective steps have been taken to reduce the risk of damage in the future. Among these is a density interlock generated by the plasma control system, with setpoint determined by the ECH operators based on rf beam trajectories and plasma parameters. Also installed are enhanced video monitoring of the launchers, and an ambient light monitor on each of the waveguide systems, along with a Langmuir probe at the mouth of each launcher. Versatile rf monitors, measuring forward and reflected power in addition to the mode content of the rf beams, have been installed as the last miter bends in each waveguide line. As these systems are characterized, they are being incorporated in the interlock chains, which enable the ECH injection permits. The diagnostics most susceptible to damage from the ECH waves have also been fitted with a variety of protective devices including stripline filters, thin resonant notch filters tuned to the 110 GHz injected microwave frequency, blazed grating filters and shutters. Calculations of rf beam trajectories in the plasmas are performed using the TORAY ray tracing code with input from kinetic profile diagnostics. Using these calculations, strike points for refracted beams on the vacuum vessel are calculated, which allows evaluation of the risk of damage to sensitive diagnostics and hardware.

Classes of reconfigurable band‐reject filters realising constant absolute bandwidth in two distinct states

This study presents the synthesis and design of novel band-reject filters whose frequency characteristics can be reconfigured between two distinct states, each of which is centred at a different resonant frequency. The absolute bandwidth of the reconfigurable filters in the two distinct states is maintained constant by virtue of introducing two new resonator types which are thoroughly studied and analysed in this work. The synthesis of two prototype networks realising a common electrical specification is illustrated and each network is subsequently transformed into two types of band-reject filters comprising novel coupled-line sections. The presented circuit concepts are then validated through the simulation of a suspended-substrate stripline filter modelled utilising high frequency structure simulator (HFSS) which realises an absolute bandwidth of 200 MHz in the two distinct states centred at 1180 and 1485 MHz. The HFSS filter model is manually reconfigured between the two distinct states upon terminating stubs within each of its resonator structures as either open circuit or short circuit. The performance of the HFSS filter model shows close correspondence to the performance of the synthesised prototype network, thus demonstrating the validity of the proposed circuit principles.

Coupling coefficient of quarter-wave resonators as a function of parameters of comb stripline filters

The relationship of the coupling coefficient of quarter-wave resonators operating on the main resonance frequency f0 as a function of different parameters of comb filters made of sections of symmetric striplines has been analyzed. It has been found out that the coupling coefficient increases with the rise of relative dielectric permittivity of striplines, their thickness and the resonance frequency. The measured characteristics of the stripline 4-resonator comb filter with central frequency f0 = 2.4 GHz built on dielectric material with er = 9.7 are also presented.

Tunable 1.25–2.1-GHz 4-Pole Bandpass Filter With Intrinsic Transmission Zero Tuning

A new concept of tuning transmission zeros (TZs) in 4-pole tunable bandpass filters is demonstrated. In this work, the tuning elements that were conventionally used for bandwidth control are also utilized for adjusting the TZs at the same time. As a result, the selectivity of the tunable filter can be controlled without increasing the filter order and complexity. A 4-pole stripline filter is used to demonstrate this concept. The filter can be continuously tuned from 1.25 to 2.1 GHz and two TZs are employed to improve the stopband suppression to $> {\hbox{60 dB}}$ at 200 MHz from the passband. These TZs can also be moved from the upper stopband to the lower stopband without any auxiliary tuning elements to significantly change the stopband suppression. The high rejection filter is useful in wireless systems and cognitive radios with large interferers.

Compact interdigital filters with transmission zeros in LTCC technology

This article presents a simple topology for the implementation of cross-couplings between nonadjacent resonators in interdigital stripline filters. This topology affords the inclusion of transmission zeros maintaining a cross-sectional structure similar to that of a stripline. Therefore, the manufacturing cost is very close to an all-pole prototype. Two design strategies for the coupling structure are discussed: one of them achieving filters with enhanced performance. Both strategies have been assessed implementing prototypes in low-temperature cofired ceramic LTCC technology. The fabricated filters exhibit operating frequencies at 5775 MHz and 8000 MHz with 2.6% and 3.75% pass-band fractional bandwidths, respectively, and up to 60 dB IL in the rejection band. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:560-570, 2014.

Power Handling Capability of Transmit HTS Stripline Filter with Shuttle-shape Resonators

The power handling capability and frequency response of transmit high-temperature superconducting stripline filter with shuttle-shape resonators were investigated. A cascaded quadruplet (CQ) design is used to produce a pair of attenuation poles for obtaining sharp cutoff characteristics. The shuttle-shape resonators improve power handling and out-of-band rejection. An electromagnetic simulator based on the moment method was used to design a four-pole SL CQ filter with shuttle-shape resonators (5.0-GHz center frequency and 100-MHz bandwidth). The filter was fabricated using YBa2Cu3O7-d thin films on an Al2O3 substrate and was formed Au ground plane. The filter showed good frequency response. From the result of the power-handling capability, the filter showed a liner property until 7.9W.

Subharmonic Mixer Based on EBG Technology

We present the design of a submillimeter-wave mixer based on electromagnetic band gap (EBG) technology and using subharmonic local oscillator (LO) injection. The indicated device converts an incoming submilimeter wavelength signal into a 1-5 GHz intermediate frequency (IF) signal by mixing it with a subharmonic LO signal. The mixer consists of a dual-band receiver and two coplanar stripline (CPS) filters, collocated on top of a three-dimensional (3-D) EBG structure. A four-element array of the proposed receivers was designed, fabricated and tested. The configuration demonstrated reasonable performance: conversion loss below 8 dB and noise temperature below 3000 K. The presented concept can be used for higher frequencies, provided the availability of sufficiently powerful LO sources.

Stripline combline filters on substrates designed on high-permittivity ceramic materials

Stripline bandpass combline filters designed on high-permittivity ceramic materials are analyzed. In order to form coupling between codirectional quarter-wave resonators, they are connected in the regions of their short-circuited ends by a stripline conductor. Features of the characteristics of such filters are revealed and compared with the parameters of other ceramic microwave filters. Experimental characteristics of a stripline filter designed on a ceramics with permittivity ɛr = 38 are presented. The experimental results are in good agreement with results of computer simulation.

Use of double-layer coupling circuit and additional patch conductors to improve power handling capability of HTS transmit filter

Abstract The use of a double-layer coupling circuit and additional patch conductors is proposed for improving the power handing capability of high-power high-temperature superconductor transmit filters with stripline (SL) structure. A double-layer coupling circuit is formed through the substrate between the edge of the resonator and the end of the feed line. This reduces the current concentration compared with that of a conventional gap-coupled circuit due to the large gap between the resonator and feed line of the double-layer coupling circuit. The additional patch conductors (placed in the upper layer of the resonator edge) improve the power handling capability by reducing the local magnetic field concentration. The current density distribution of two-pole SL dual-mode filters with a 5.0-GHz center frequency and 100-MHz bandwidth and with an Al2O3 substrate with a relative dielectric constant of 9.9 was investigated. An electromagnetic simulator based on the moment method was used to design the filters, and the maximum current densities at the edges of the resonator as a function of frequency were simulated. The results showed that the maximum current density in an SL filter with a double-layer coupling circuit and patch conductors was approximately 30% less than that of the conventional gap-coupled filter.