External Quality Factor Research Articles

Dual‐band filtering power divider with independent in‐band power split ratio using a single quad‐mode dielectric resonator

A design approach is presented based on insights into power division among modes for a dual-band filtering power divider using a single multimode resonator. The relationship between the energy of the input port under different modes and the corresponding external quality factor (Qe) is analysed. Then, the power distribution among the in-band modes and between output ports can be all expressed by Qe. Therefore, the synthesis of a coupling matrix to achieve independent power distribution in the two bands is simplified. For further verification, a quad-mode dielectric resonator with independently controllable modes is designed. Based on this, dual-band filtering power dividers with equal and unequal power split ratios (1:1 in the lower band and 2:1 in the higher band) are simulated and implemented. The simulation and measurement agree, proving the correctness of the approach.

High-Order Modes Analysis and Its Applications to Dual-Band Dual-Polarized Filtering Cavity Slot Arrays

In this article, a series of filtering cavity slot arrays using high-order modes are investigated. It is found that each unit of the cavity slot arrays in the proposed high-order mode resonator is in phase with the same amplitude, which helps enhance the antenna gain and reduce the sidelobe level. Meanwhile, the filtering function is integrated into the design for frequency selectivity and harmonic mode suppression. The higher order response can be achieved by cascading more high-order mode resonators with required external quality factor ( Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ) and coupling coefficient ( K). The fractional bandwidth (FBW) and out-of-band suppression of proposed designs are also discussed. For proof-of-concept, a single-band third-order 4×5 filtering cavity slot array using a TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">450</sub> mode resonator and a dual-band dual-polarized third-order 4×3 filtering cavity slot array, using TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">430</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">340</sub> mode resonators, are fabricated and tested. The good agreement between the simulated and measured results verifies that the proposed design methodology is feasible for designing high-order mode filtering cavity slot array antennas.

A high-selectivity double-mode SIW bandpass filter utilizing the modified parallel coupled microstrip lines

ABSTRACT In this article, a high-selectivity double-mode substrate integration waveguide bandpass filter utilizing modified parallel coupled microstrip lines (MPCML) is presented. The designed method is analyzed in detail. Six metal vias are designed to perturb TE-101 mode and TE-103 mode. The resonant frequency of the perturbed TE-101 mode is shifted to high frequency, close to that of TE-102 mode, which caused the formation of passband. The resonant frequency of the perturbed TE-103 mode is shifted to high frequency, improving out-of-band performance. Simultaneously, the coplanar waveguide structure is used to adjust the external quality factor. Two rectangular slotlines are introduced to adjust center frequency and bandwidth slightly. Two rectangular stubs are designed for better source and load matching. Three transmission zeros (TZs) are obtained to improve the selectivity. The designed MPCML promotes the generation of TZs. Another TZ is obtained by the coupling between TE-102 mode and TE-103 mode. The designed filter operates at 14.4 GHz with bandwidth of 800 MHz. The measured return loss is better than 15 dB, and the minimum insertion loss is 1.60 dB. The measurement is agreed with the simulation.

A High-Power Ka-Band Radial Transit Time Oscillator With Over-Sized Extractor

Radial transit time oscillator (TTO) is a promising device to achieve a high-power Ka-band output. However, because the cavity number is limited, the power capacity of extractor and the radiation power are hard to improve. To solve this problem, a high-power Ka-band radial TTO with an over-sized extractor is proposed in this article. Taking the quasi-TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode as working mode, the electric field distribution, beam-loading conductance ratio, and external quality factor prove that the electric field in the extractor can interact with the radial intensity electron beam efficiently. Particle-in-cell (PIC) simulation results prove that a constant magnetic field or decreasing magnetic field can confine electron movement effectively. Setting the imposed diode voltage to be 400 kV, the corresponding current is 7.5 kA, and the microwaves with the power of 1.13 GW, the frequency of 32.15 GHz, and the efficiency of 38% can be generated. When the output power saturates, the maximum radial electric field on the surface of the extractor is only 980 kV/cm, which verified the high-power capacity of the over-sized extractor. Taking ohmic loss into consideration, the proposed radial TTO made of low-loss material (e.g., copper) is potential to output giga-watt level high-power microwaves (HPMs) at Ka-band.

Effects of defects and surface roughness on high-Q modes in ZnO microspheres

Photoluminescence (PL) spectra of high-Q ZnO microspheres of various degrees of inhomogeneity are studied. Multiple sharp resonance features with distinct patterns associated with whispering gallery modes (WGM) of these microspheres are observed. Relative WGM peak strengths in these PL spectra are found to be closely related to defects and the surface roughness of the microspheres. A theoretical model based on Mie theory and Green’s function method is used to simulate the optical emission spectra of these microspheres. The effects of defects and surface roughness can be characterized by a frequency-dependent external quality factor (Q ex ) with a prefactor. By adjusting the prefactor in Q ex and a parameter describing the contribution of stimulated emission in the PL spectra, we can fit the observed PL spectra well. Through this study, we gain a better understanding of the relation between the diffusive scattering and the lineshapes of spectral features in PL.

A high selectivity dual‐band bandpass filter using quadruple‐mode multi‐stub loaded ring resonator (SLRR)

A high selectivity dual-band filter is proposed based on the quadruple-mode multi-stub loaded ring resonator. The ring resonator can utmostly avoid bending the electromagnetic wave. Two external open stubs are employed to generate four transmission poles where the odd- and even-mode is utilized to analyze the resonant frequencies of the BPF. The internal stub effectively reduces the insert loss (IL) by improving the external quality factor Qe of the second passband. In addition, five transmission zeros are generated due to the multipath and self-resonance modes to improve the out-of-band selectivity of the proposed filter. The proposed filter centered at 2.65 and 4.84 GHz is designed, fabricated and measured. The simulated results agree well with the measured results.

Method for in situ and in operando cavity loaded Q extraction in superconducting rf accelerators

A novel method has been developed that allows extracting the loaded quality factor of particle accelerating radio-frequency cavities at any time during beam operation from acquired control system process parameters without the need of additional measurement equipment. Concurrently it assesses the attenuation in a cavities' power transmission line for any rf generator to rf cavity mismatch condition, and thus can correct calibration inaccuracies of measured forward and reflected power levels. The mathematical formalism is described. It is specifically derived for cryogenically cooled superconducting cavities for which the loaded quality factor can be equated with the external quality factor of the input power coupler. The described method has been applied for 418 superconducting cavities in operation at the Continuous Electron Beam Accelerator Facility at the Thomas Jefferson National Accelerator Facility. The validation of the method as well as its beneficial use as a diagnostic tool is demonstrated for a finite number of examples utilizing process variables archived during a period in the past when the linac beam current was ramped up multiple times. The method is in the process of being implemented in the machines' control system for an in situ and in operando evaluation of the power coupler's external quality factor.

Millimeter-Wave Dual-Band Bandpass Filter With Large Bandwidth Ratio Using GaAs-Based Integrated Passive Device Technology

In this letter, a millimeter-wave (mm-wave) dual-band bandpass filter is proposed with large bandwidth ratio by using gallium arsenide (GaAs)-based integrated passive device (IPD) technology. To realize small chip size, one dual-mode on-chip resonator is designed by using quasi-lumped capacitors and microstrip lines. In addition, multiple transmission zeroes are generated by further introducing both the electric and magnetic couplings between adjacent resonators. To realize large bandwidth ratio of two passbands, the external quality factors are investigated at both passband, and can be independently controlled. For demonstration, a 28-/50-GHz dual-band bandpass filter is designed, fabricated, and measured. The fractional bandwidth ratio is 7.8, which is much larger than the reported on-chip filters. Meanwhile, very low insertion loss of 0.58-dB is realized for the lower passband at 28 GHz, indicating the proposed dual-band bandpass filter a promising application in mm-wave wireless systems.

An Empirical Assessment and Validation of Redundancy Metrics Using Defect Density as Reliability Indicator

Software metrics which are language-dependent are proposed as quantitative measures to assess internal quality factors for both method and class levels like cohesion and complexity. The external quality factors like reliability and maintainability are in general predicted using different metrics of internal attributes. Literature review shows a lack of software metrics which are proposed for reliability measurement and prediction. In this context, a suite of four semantic language-independent metrics was proposed by Mili et al. (2014) to assess program redundancy using Shannon entropy measure. The main objective of these metrics is to monitor program reliability. Despite their important purpose, they are manually computed and only theoretically validated. Therefore, this paper aims to assess the redundancy metrics and empirically validate them as significant reliability indicators. As software reliability is an external attribute that cannot be directly evaluated, we employ other measurable quality factors that represent direct reflections of this attribute. Among these factors, defect density is widely used to measure and predict software reliability based on software metrics. Therefore, a linear regression technique is used to show the usefulness of these metrics as significant indicators of software defect density. A quantitative model is then proposed to predict software defect density based on redundancy metrics in order to monitor software reliability.

Development and vertical tests of 650 MHz 2-cell superconducting cavities with higher order mode couplers

650 MHz 2-cell superconducting cavities are proposed for the main ring of the Circular Electron–Positron Collider (CEPC). The cavity is designed with two detachable double-notch higher order mode (HOM) couplers to suppress the fundamental mode and extracted the HOM power. The present paper describes the design, fabrication, surface treatment and vertical tests of the cavities and HOM couplers. The performances of the cavity at 2 K is not affected after the installation of the HOM coupler. The maximum intrinsic quality factor Q0 of the cavity dressed with the HOM coupler reached 3.1×1010 at operation accelerating gradient. The vertical tests results showed that the fundamental mode external quality factor Qe of all HOM couplers is an order of magnitude larger than Q0 of the cavity. The HOM damping results for the 650 MHz 2-cell cavity were also measured at cryogenic temperature and compared with the simulated and measured results at room temperature. Two 650 MHz 2-cell cavities each with two HOM couplers will be assembled in the CEPC 650 MHz test cryomodule after helium vessel dressing.

Unbalanced-/Balanced-to-Unbalanced Diplexer Based on Dual-Mode Dielectric Resonator

The design of compact unbalanced-/balanced-to- unbalanced diplexer (U2U/B2U) based on full dual-mode dielectric resonator (DR) is investigated for the first time. The relationships of the external quality factors ( $Q_{e}$ ) under the two modes are analyzed. It is found that the $Q_{e}$ of two modes can be controlled independently, which makes the design procedure simple and efficient. Based on the analysis, both of the proposed U2U and B2U diplexer can be easily built by properly adding feeding probes for the DR without increasing the circuit size by altering the location of the feeding probes according to the distribution of the electromagnetic fields. To verify the proposed design concept, the diplexers mentioned above are simulated, implemented and measured. The isolation is achieved by the orthogonality between modes while the low insertion loss is obtained due to the high unloaded quality factor ( $Q_{u}$ ) of the dual-mode DR. The measurements are in accordance with the simulated results, showing low loss and good selectivity.

A 12-pole VHF band high selective high temperature superconducting filter

A 12-pole VHF band high temperature superconducting (HTS) filter with a spiral quarter-wavelength resonator is introduced. The coupling characteristics of the proposed resonator, cross structure and external quality factor is analyzed in detail. The HTS filter is fabricated on a 3-inch-diameter double-sided DyBa2Cu3O7 HTS thin film with a LAO substrate and measured with a low-temperature test system at 77 K. The measured filter has a center frequency of 119.93 MHz and a 1-dB passband of 10.04 dB. Due to the introduction of transmission zeros, the rectangular coefficient (BW60dB/BW1dB) of the measured filter is about 1.20, which shows excellent selectivity. The measured results are in good agreement with the simulated ones.

Quality Prediction and Control of Assembly and Welding Process for Ship Group Product Based on Digital Twin.

In view of the problems of lagging and poor predictability for ship assembly and welding quality control, the digital twin technology is applied to realize the quality prediction and control of ship group product. Based on the analysis of internal and external quality factors, a digital twin-based quality prediction and control process was proposed. Furthermore, the digital twin model of quality prediction and control was established, including physical assembly and welding entity, virtual assembly and welding model, the quality prediction and control system, and twin data. Next, the real-time data collection based on the Internet of Things and the twin data organization based on XML were used to create a virtual-real mapping mechanism. Then, the machine learning technology is applied to predict the process quality of ship group products. Finally, a small group is taken as an example to verify the proposed method. The results show that the established prediction model can accurately evaluate the welding angular deformation of group products and also provide a new idea for the quality control of shipbuilding.

Design of Dual-Band Dual-Mode Band-Pass Filter Utilizing 0° Feed Structure and Lumped Capacitors for WLAN/WiMAX Applications

Two dual-band second-order highly selective band pass filters operated at 3.5/5.5 GHz and 3.5/6 GHz for wireless local area network /worldwide interoperability for microwave access WLAN/WiMAX applications are introduced in this paper. The designed filters are inspired of utilizing two coupled open-loop resonators loaded with stub, spiral resonators and lumped capacitors. The filters are designed based on calculating the desired coupling matrix and the external quality factor. The first and the second filters are designed at the fundamental mode of 3.5 GHz then the first filter is loaded with two spiral resonators in the microstrip line to produce the desired band stop behaviour, which in turn achieves the second pass-band. However, the second band of the second filter is achieved by loading the stub with the lumped capacitors, which controls the second mode. The centre frequency of the second band is adjusted by varying the lumped capacitors values. The two designed filters have insertion loss less than 0.7 dB in the pass-band region, high selectivity with more than 4 transmission zeros and more than 20 dB attenuation level in the stop band region. The suggested filter has compact size and high selectivity with tunability behavior. The two filters are fabricated and measured to validate the simulated results.

A Varactor-Based Very Compact Tunable Filter with Wide Tuning Range for 4G and Sub-6 GHz 5G Communications.

A very compact microstrip reconfigurable filter for fourth-generation (4G) and sub-6 GHz fifth-generation (5G) systems using a new hybrid co-simulation method is presented in this manuscript. The basic microstrip design uses three coupled line resonators with λ/4 open-circuited stubs. The coupling coefficients between the adjacent and non-adjacent resonators are used to tune the filter at the required center frequency to cover the frequency range from 2.5 to 3.8 GHz. The coupling coefficient factors between the adjacent resonators are adjusted to control and achieve the required bandwidth, while the input and output external quality factors are adjusted to ensure maximum power transfer between the input and output ports. Two varactor diodes and biasing circuit components are selected and designed to meet the targeted performance for the tunable filter. The impedance bandwidth is maintained between 95 and 115 MHz with measured return losses of more than 17 dB and measured insertion loss of less than 1 dB. Computer simulation technology (CST) is utilized to design and optimize the presented reconfigurable filter, with hybrid co-simulation technique, using both CST microwave studio (MWS) and CST design studio (DS), is applied to build the model by considering the SPICE representation for the varactor switches and all electronic elements of the biasing circuit. The introduced reconfigurable microstrip filter is also fabricated using a Rogers RO3010 material with a relative dielectric constant of 10.1 and it is printed on a very compact size of 13 × 8 × 0.81 mm3. An excellent agreement is obtained between the simulation and measurement performance.

Microstrip Tunable Diplexer With Separately-Designable Channels

A microstrip tunable diplexer with two separately- designable channels and multiple transmission zeroes (TZs) using common element-loaded uniform impedance resonator (UIR) is proposed. The common UIR operating in third harmonic ( ${f} _{3}$ ) and fifth harmonic ( ${f} _{5}$ ) is used for designing the two diplexer channels. The stub is loaded at the voltage-null point of ${f} _{3}$ on the common UIR and the varactor is loaded at the open end of the stub. The varactor-loaded stub can separately tune ${f} _{5}$ but has no effect on ${f} _{3}$ so that the two channels can be separately designed. Meanwhile, the input port is tap-connected to the common UIR, which necessarily produces a common TZ between ${f} _{3}$ and ${f} _{5}$ , existing in both channel filtering responses. In the tunable high channel design (at ${f} _{5}$ ), the major design concept relies on choosing the properly values of three varactor diodes, the desired external quality factor and coupling coefficient can be easily obtained for realizing the constant absolute bandwidth (ABW). By properly choosing coupling schemes of the two channels, more TZs are realized at the desired locations. For demonstration, a diplexer with a fixed low channel and a tunable high channel with the constant ABW is designed, fabricated and measured.

Dual-Band Coaxial Filter and Diplexer Using Stub-Loaded Resonators

This article presents a simple design of a coaxial dual-band cavity filter and diplexer using stub-loaded resonators (SLRs). Based on the resonance characteristics of a coaxial SLR, the first two resonant frequencies can be tuned over a wide range by adjusting their structural parameters. Controllable external quality factors can be acquired by using the modified tapping structure for the two designated passbands. A coupling window and a coupling pin are proposed to obtain the expected coupling coefficients in the two bands. To demonstrate this concept, a third-order dual-band bandpass filter and an eight-pole diplexer are designed and fabricated. The measured results agree well with the full-wave simulation results.

Compact Wide-Stopband Dual-Band Balanced Filter Using an Electromagnetically Coupled SIR Pair With Controllable Transmission Zeros and Bandwidths

This brief presents a dual-band balanced filter with wide stopband, controllable transmission zeros and bandwidths, and compact size based on a newly designed electromagnetically coupled stepped impedance resonator (SIR) pair. The proposed SIR contains three different impedance lines, which can lead to more degrees of design freedom for resonant frequency control. Two electrical length ratios of the SIR can be individually tuned to obtain two desired differential-mode (DM) resonant frequencies for dual-band design, while keeping the first spurious frequency far away for wide-stopband design. Moreover, an inherent common-mode (CM) suppression can also be obtained without adding extra structures due to the discriminating CM resonant frequencies. The mechanism of transmission zeros (TZs) generation is also investigated by means of phases and admittance analysis. It reveals that four TZs around the two operating bands can be flexibly controlled via adjusting the ratio of magnetic and electric coupling coefficients of the SIR pair as well as the coupling space of the feeding lines, which have greatly enhanced the passband selectivities and the band-to-band isolation. Subsequently, the graphs of coupling coefficients and external quality factors for the filter design are extracted, showing sufficient degrees of design freedom for bandwidth control. The proposed dual-band balanced filter is finally fabricated and measured at 1.75 GHz and 3.64 GHz, respectively. Measured results are in good agreement with the simulated ones. Compared with the state-of-the-art works, the proposed circuit performs a deeper and wider stopband of $4.5{f}_{1}^{d}$ with 40dB attenuation (where ${f}_{1}^{d}$ is the fundamental frequency), and more than 50-/45-dB in-band CM suppressions with compact size ( $0.14\lambda _{g} \times 0.27{\lambda }_{g}$ , where ${\lambda }_{g}$ is the guided wavelength of the fundamental frequency).

Differential Dual-Band Filter Using Ground Bar-Loaded Dielectric Strip Resonators

In this letter, a new differential dielectric strip resonator (DSR) filter with dual passbands is proposed. By loading a pair of ground bars underneath the traditional half- wavelength ( $\lambda /2$ ) DSR with high permittivity (supported by a low-permittivity substrate with the bottom ground plane), the TM10 and TM30 modes can be controlled to be in a close spacing. Meanwhile, both of them can be differentially excited for the design of the differential dual-band bandpass filter (BPF). The external quality factors and coupling coefficients for both bands can be independently controlled through proper layout; meanwhile, the common-mode (CM) suppression in the two differential-mode (DM) passbands is more than 25 dB. Finally, a differential DSR BPF with dual-band response operating at 8.13 and 11.13 GHz is given to verify the proposed idea.

Novel Diplexer and Triplexer Designs Avoiding Additional Matching Circuits Outside Filters

Diplexers and triplexers are widely used in communication systems for separating frequency bands in different channels. Design issues related to preventing additional matching circuits, integrating two or three band input resonators into one-band resonator size, systematically designing each band external quality factor (Q L ), and avoiding loading effects are often encountered. To overcome these bottlenecks, stub-loaded resonators that feature in various negligible band loading effects are used to design proposed diplexers and triplexers. In particular, the stub-loaded resonator (SLR), used in the proposed triplexers and costing only one-band resonator size, achieves a negligible loading effect systematic procedure for designing the three bands required as external quality factors and resonant frequencies. Each SLR of the triplexers uses an integrated matching circuit in the resonator instead of an additional matching circuit outside the resonator. To our knowledge, a tapped-line feed resonator that can independently design three band external quality factors (Q Ls ) and meet matching requirements by using one-band resonator size has not been reported thus far. All the currently proposed circuits have been verified and fabricated on RO4003C substrates.