Coaxial Filter Research Articles

Design and Fabrication of a Five-Order Narrow-Band Coaxial Filter based on Cross-Coupling and Non-Cross-Coupling Methods

In this paper, the design, analysis, and fabrication of a novel coaxial filter based on folded topology are presented. First, two structures of cross-coupling and non-cross-coupling were proposed to achieve the best performance of the coaxial cavity. Second, to reach the smallest dimensions, a folded topology was chosen. Third, phase relationship and also matrix coupling are introduced for determining suitable phase shifts. The proposed method is verified by fabricating a five-order narrow-band coaxial cavity filter for a transverse electromagnetic (TEM) mode at 4 GHz. Finally, the simulation and measurement results of the coaxial cavity filter are presented. Good agreement between simulation and fabrication confirms the validity of the proposed methodology.

Robust cryogenic matched low-pass coaxial filters for quantum computing applications

Electromagnetic noise is one of the main external factors decreasing superconducting qubit coherence. Matched coaxial filters can prevent microwave and IR photons' negative influence on superconducting quantum circuits. In this report, we describe the design and fabrication process of matched coaxial filters for noise-sensitive measurements at millikelvin temperatures. A robust transmission coefficient and ultralow reflection loss of −20 dB in the frequency range up to 20 GHz is achieved. Fabricated low-pass filters have linear transmission and reflection characteristics with 3 dB-cutoff frequency of 1.5–2.5 GHz. A method for extracting the propagation constant and filter impedance from scattering parameter measurements is demonstrated. This method is experimentally approved on a filter with a compound of Cu powder and Stycast epoxy resin and a filter filled with ECCOSORB CR-110 epoxy resin. The proposed design and assembly technology are versatile for various compounds and provide highly repeatable geometric and microwave characteristics. Furthermore, we demonstrate that these low-pass coaxial filters can be effectively utilized to improve superconducting qubit relaxation due to suppressing standing waves originating from reflections in control coaxial cables.

Three Dimensional Printed Vertically-Stacked Single-/Multi-Band Coaxial Filters and RF Diplexers

This article reports on monolithically integrated and low form-factor vertically-stacked coaxial resonator-based single-/multi-band filters and radio frequency (RF) diplexers using stereolithography apparatus (SLA) additive manufacturing (AM). The proposed RF filtering/diplexer concepts exhibit the following unique features: 1) low form-factor due to the use of vertically stacked low-profile capacitively-loaded coaxial cavity resonators; 2) monolithic integration; and 3) versatile and highly selective transfer functions facilitated by the topological arrangements of the resonators within the filter volume that enable cross-couplings and can be exploited to increase selectivity. Theoretical filter design analysis using coupling routing diagrams (CRDs) and eigen-mode electromagnetic (EM) simulations are performed. The proposed concept is validated by the design, fabrication, and testing of four monolithically-integrated prototypes, namely a four-pole two transmission zeros (TZs) bandpass filter (BPF), a three-pole two TZs BPF, a second-order dual-band BPF, and a second-order diplexer operating at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> -band and exhibiting an effective quality factors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{eff}}s)$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 700.

A 100–180-GHz Coaxial Frequency Tripler Based on Copper Additive Manufacturing

This article presents a wideband coaxial D-band frequency tripler fabricated by copper additive manufacturing (AM). The central part of the tripler consists of two waveguide–coaxial transitions, a coaxial low-pass filter, an antiparallel Schottky diode chip, and an output impedance matching network. Most constitutions, except for the diode chip, are monolithically fabricated in one piece. The diode chip with additional thermal paths is specially designed to obtain a good thermal performance and better power handling. To facilitate the measurement, a waveguide fixture is also designed to convert the ports to standard waveguide ports (WR-19 and WR-6.5). The measurements show that the maximum output power of the tripler is 9.44 mW with about 182 mW of input power at 147 GHz and its 3-dB bandwidth is 45.2% from 108 to 171 GHz. Additionally, the tripler delivers <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 1.87 mW of output power and better than 10 dB of return loss over the 100–180-GHz range. To the best of authors’ knowledge, this is the first AM coaxial ultra-wideband frequency multiplier reported in the open literature.

One-shot color mapping of a ray direction field for obtaining three-dimensional profiles integrating deep neural networks

A method for simultaneously and instantly obtaining both a three-dimensional (3D) surface and its inclination angle distribution from a single image captured by an imaging system equipped with a coaxial multicolor filter that integrates deep neural networks (DNNs) is proposed. The imaging system can obtain a light-ray direction in the field of view through one-shot color mapping. Light rays reflected from a 3D surface, even if it has microscale height variations with a small inclination angle distribution, can be assigned different colors depending on their directions by the imaging system. This enables the acquisition of the surface inclination angle distribution. Assuming a smooth and continuous 3D surface, it is possible to reconstruct the surface from a single captured image using DNNs. The DNNs can provide the height variations of the 3D surface by solving a nonlinear partial differential equation that represents the relationship between height variation and the direction of light rays. This method is validated analytically and experimentally using microscale convex surfaces.

Stochastic cooling notch filter developments for the high-precision spectrometer ring in the high intensity heavy-ion accelerator facility project.

Stochastic cooling of the high-precision spectrometer ring (SRing) at the High Intensity Heavy-Ion Accelerator Facility (HIAF) project in China, which is used mainly for experiments with radioactive fragment beams, is applied to speed up the cooling process of a stored ion beam. In this article, a new coaxial-type notch filter with an amplitude equalizer in the long branch and an optical-type notch filter with phase-stabilized optical fiber are discussed and evaluated for the SRing stochastic cooling system. Both prototypes of coaxial and optical notch filters are fabricated and tested. The minimum notch depth of coaxial and optical notch filters reaches to 26 and 40 dB, respectively. The performance of both coaxial notch filter and optical fiber notch filter is presented in this work. These developments will be used not only for the longitudinal stochastic cooling system but also have potential for the beam feedback system.

Modeling Investigation of Groove Effect on the Multipactor of Dielectric-Loaded Coaxial Low-Pass Filters

Multipactor is a common discharge phenomenon occurring in space microwave systems. The surface microstructure has been verified to be effective in mitigating multipactor. In this work, we design a square coaxial low-pass filter (SCLPF) with dielectric sheets loaded to check the multipactor dependence on the structure parameters of the loaded dielectric sheets, and further model groove structures on the sensitive area surface to lower the risk of multipactor. Simulation results indicate that the SCLPF loaded with alumina and PTFE exhibits favorable operational characteristics, and the multipactor threshold is significantly improved after introducing the surface grooves. Then, we investigate the effects of three typical groove parameters, groove depth, groove number, and aspect ratio, on the multipactor threshold of the SCLPF device. The results show that the multipactor threshold rises at first as the groove number and groove depth increase, and then the threshold reaches a saturation status. For a deeper analysis of multipactor, we discuss how the grooves shelter the secondary electrons, and further mitigate the electron avalanche. Furthermore, the mechanisms of threshold saturation under the effect of groove parameters are analyzed in detail, and a contour map for the multipactor threshold of PTFE-loaded SCLPFs is given, which makes significant sense for predicting the multipactor threshold of the devices with its sensitive surface being grooved. The regularity of modulating the multipactor threshold by the groove structures obtained in this study is of engineering significance for suppressing multipactor in microwave devices in practical applications.

Vertically Integrated Coaxial Resonator-Based Multiband Bandpass Filters Using SLA 3-D Printing

This letter reports on a novel multiband RF filtering concept and a compact low-loss integration scheme for coaxial resonator-based multiband bandpass filters (BPFs). Size compactness is achieved by: 1) vertically stacking its constituent resonators, so that the available 3-D volume is optimally occupied; 2) the use of subwavelength capacitively loaded coaxial resonators; and 3) monolithic integration enabled by stereolithography apparatus (SLA) additive manufacturing (AM). A unique coupling routing diagram (CRD) is proposed and implemented with capacitively loaded coaxial resonators that allow to independently control the passband and stopband frequencies and facilitate both symmetric and asymmetric responses. A dual-band and triple-band BPFs operating at sub-6 GHz were designed, manufactured, and tested demonstrating highly miniaturized form factors and passbands with in-band insertion loss (IL) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 0.2–0.3 dB, i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{eff}}$</tex-math> </inline-formula> : 640–1030.

Parametric Model for Coaxial Cavity Filter with Combined KCCA and MLSSVR

Aiming at the problems of poor data effectiveness, low modeling accuracy, and weak generalization in the tuning process of microwave cavity filters, a parametric model for coaxial cavity filter using kernel canonical correlation analysis (KCCA) and multioutput least squares support vector regression (MLSSVR) is proposed in this study. First, the low-dimensional tuning data is mapped to the high-dimensional feature space by kernel canonical correlation analysis, and the nonlinear feature vectors are fused by the kernel function; second, the multioutput least squares support vector regression algorithm is used for parametric modeling to solve the problems of low accuracy and poor prediction performance; third, the support vector of the parameter model is optimized by the differential evolution whale algorithm (DWA) to improve the convergence and generalization ability of the model in actual tuning. Finally, the tuning experiments of two cavity filters with different topologies are carried out. The experimental results show that the proposed method has an obvious improvement in generalization performance and prediction accuracy compared with the traditional methods.

Advanced Synthesis and Precise Design of Inline Fully Canonical Filters With High Selectivity

This article presents an advanced synthesis and novel designs of inline fully canonical filters with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> cascaded extracted pole (EP) sections, providing higher band-edge selectivity and suppressing interference from adjacent bands. The conventional fully canonical prototype is reconfigured to significantly facilitate filter design and fabrication. Moreover, to synthesize realizable circuits, a general node scaling method based on admittance matrix is implemented. All associated elements, especially the junction susceptances, can be scaled directly without the aid of inverters, avoiding intricate equivalent circuit transforms. Furthermore, the importance of precise control over the junction susceptances in filter design is discussed for the first time. Accurate junction susceptance enables the exact mapping from synthesized circuits to physical structures, preventing brute-force optimization. In particular, a new and compact EP structure in coaxial technique is proposed with flexibly tuned loading phase and accurately regulated junction susceptance. The good measurement results of a coaxial EP filter with four reflection zeros (RZs) and four transmission zeros (TZs) validate the effectiveness of the proposed theories. Also, this is the first reported coaxial fully canonical filter with only build-in capacitive couplings to avoid passive intermodulation (PIM).

Coaxial Low-Pass Filter Design and Manufacture

In this study, a low-pass filter with coaxial transmission lines is designed and produced. The objective for designing a coaxial low-pass filter was to utilize both low loss transmission and high breakdown voltage capability for high power microwave applications to enable the suppression of the second harmonic of the 4.4-6 GHz C-Band ( C-Band was selected as a proof of concept ) signals with minimal insertion loss. Microwave and 3D electromagnetic simulators were used in the filter design. The design was started by establishing an 11 th order Chebyshev low-pass filter prototype giving 0.05 dB ripple. Based on this prototype, a filter circuit consisting of capacitors and inductors as lumped elements was designed. The low and high impedances to be selected for the stepped impedance method, which is the basis of the transition to coaxial transmission lines, were decided and the most suitable impedances for manufacturing was determined. The filter using these impedances and designed with stepped impedance lines was transformed into the filter in which coaxial transmission lines are used. Coaxial transmission lines in the low-pass filter circuit consist of conductors with an insulating material in between. While the insulating material is selected as air in the high impedance sections of the transmission lines, it is PTFE (Polytetrafluoroethylene) with an insulating constant of 2.1 in the low impedance sections. The designed filter was manufactured. The basic properties of the manufactured filter were characterized by using RF measuring devices and compared with the designed filter. The measurements results prove that the frequency responses of the designed filter and the produced filter are very close to each other. Namely, a low-pass filter with a cutoff frequency of 6 GHz, a sharp suppression of about 45 dB at the stopband of 9 GHz and a return loss of 20 dB was designed and produced by using coaxial transmission lines. The novelty in our work can be stated that the power handling capability is increased by two techniques. The first one is that the highest transmission line radius preventing the higher order mode excitations is used to decrease the conductor loss. Teflon is covered around the low impedance lines to enhance the dielectric breakdown capability. Teflon inclusion is also used to decrease the practical low impedance level that improves the filter characteristics.

Secondary electron emission suppression on alumina surface and its application in multipactor suppression

For the high-power microwave (HPM) components applied to the space environment, the seed electrons in the components may resonate with the radio-frequency electrical field and may further lead the secondary electron multiplication to occur, triggering off the phenomenon of multipactor. Multipactor deteriorates the performance of the components, and in severe circumstances, it is even possible to result in the failure of the components or the spacecraft. Alumina ceramic possesses good dielectricity, high hardness, good thermal isolation, low dielectric loss, etc., so it is widely used in HPM systems including dielectric windows, and many other microwave components. However, alumina ceramic possesses a relatively high level of secondary electron yield (SEY or &lt;i&gt;δ&lt;/i&gt;), indicating that the devastating effect of multipactor discharge is likely to be triggered off inside the alumina-filled HPM components in the space environment. In this work, the model of alumina loaded coaxil low pass fillter is simulated to verify that reducing the SEY of the alumina surface is effective and necessary to improve the multipactor threshold. After that, we use several technologies to achieve an ultralow SEY on the alumina surface. Firstly, a series of microstructures with different porosities and aspect ratios is fabricated. The results indicate that the microstructure with 67.24% porosity and 1.57 aspect ratio shows an excellent low-SEY property, which is able to suppress the SEY peak value (&lt;i&gt;δ&lt;/i&gt;&lt;sub&gt;m&lt;/sub&gt;) of alumina from 2.46 to 1.10. Then, various process parameters are used to fabricate TiN films on silicon sheets. Experimental results indicate that the TiN film achieves the lowest &lt;i&gt;δ&lt;/i&gt;&lt;sub&gt;m&lt;/sub&gt; of 1.19 when the gas flow ratio of N&lt;sub&gt;2&lt;/sub&gt;∶Ar is 7.5∶15. Thereafter, we deposit TiN ceramic coating onto the laser-etched microstructure samples, and an ultralow &lt;i&gt;δ&lt;/i&gt;&lt;sub&gt;m&lt;/sub&gt; of 0.79 is finally achieved on alumina surface. Then we implement a qualitative analysis to explore the influence of surface charge on the secondary electron emission and multipactor for the microstructured alumina surface, discuss the mechanism of low-SEY surfaces mitigating unilateral and bilateral multipactor. For verifying the actual effect of low-SEY technologies on the suppression of multipactor, we use the technologies of constructing microstructure and depositing TiN films on the alumina surface which is filled in the designed coaxial low pass filter. Finally, we obtain a significant improvement in the multipactor threshold for the filter, which increases from 125 W to 650 W, and the improvement is 7.16 dB. This work develops an effective method to reduce SEY for alumina, which is of great scientific significance in revealing the mechanism of multipactor for the dielectric-filled microwave components and also is of engineering application significance in improving the reliability of HPM components.

Tunable Coaxial Bandpass Filters Based on Inset Resonators

A new class of compact, high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> , tunable coaxial filter is presented in this article based on a novel inset resonator concept. The tuning concept is based on the displacement of movable resonators inside a properly modified metallic housing which features wide tuning capabilities and stable high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor performance with minimum variation throughout the tuning window. Various prototypes are designed and implemented to demonstrate and validate the proposed concept. A single tunable inset resonator is first designed and measured showing distinctive results of a 43% tuning range, stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 4100% ± 4%, spurious-free band up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.8\times f_{0}$ </tex-math></inline-formula> , and volume-saving up to 50% when compared with the conventional combline and half-wavelength structures. The design procedure for constant absolute bandwidth (CABW) tunable filters is then presented, and two different tunable inset filters are designed and implemented. First, a manually tunable four-pole filter is demonstrated with the merits of a wide 39.3% tuning range, while maintaining a constant bandwidth of 116 MHz ± 6% and a stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1820% ± 6%. Next, an automatically tunable third-order inset filter is designed and measured using high-accuracy piezomotors. Similarly, the measured results exhibit a wide 1.3-GHz tuning range from 2.65 to 3.95 GHz with a stable insertion loss that is less than 0.35 dB, a return loss that is better than 15 dB, and a good spurious performance up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.8\times f_{0}$ </tex-math></inline-formula> . To our own knowledge, the proposed tuning technique and tunable components represent state-of-the-art tuning range and stable high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> with minimal variation when compared with similar loaded-waveguide designs.

Design of Compact Quasi-Elliptic Bandpass Filters Based on Coaxial Inset Resonators

This article reports a novel inset resonator configuration for coaxial filter applications with quasi-elliptic responses. The design and analysis of the inset resonator are discussed in detail and accurately modeled as a capacitively-loaded stepped-impedance half-wavelength resonator featuring more compactness, high quality factor, and enhanced spurious responses in comparison with conventional half-wavelength and combline resonators. Additionally, the operating frequency can be tuned intrinsically through the displacement of the coaxial resonator, eliminating the need for any additional tuning elements and maintaining a stable quality factor. Two quasi-elliptic inset resonator type filters are implemented in planar and longitudinal coupling configurations, respectively. The first takes the form of a folded four-pole 2.93 GHz filter with two symmetrical transmission zeros. The fabricated filter has a compact structure of 29.76 cm 3, an insertion loss better than 0.73 dB, a return loss better than 18 dB, and a wide spurious-free band up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5\cdot f _{0}$ </tex-math></inline-formula> . The second inset-type quasi-elliptic filter is realized in a longitudinal inline arrangement. An example of a 2.53 GHz three-pole filter is presented with a closely-positioned transmission zero, wide spurious-free band ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 3\cdot f _{0}$ </tex-math></inline-formula> ), and a very compact structure of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$55.7\times 33\times 33$ </tex-math></inline-formula> mm 3.

Coaxial filters of distributive lattices

Coaxial filters of distributive lattices

Fully shielded and self‐packaged compact quarter‐mode substrate integrated coaxial line bandpass filter for X and K ‐band

In this work, a dual-mode substrate integrated coaxial line (SICL) bandpass filter supporting single-band and dual-band operation for widely spaced passbands located in X and K - band is proposed. Firstly, a cavity conceived with shorted half-wavelength SICL line is investigated. For enhanced miniaturization, a new SICL cavity is developed from the short-circuited half-wavelength SICL line which is bisected along the fictitious magnetic wall to derive its half-mode and quarter-mode counterparts. A fully shielded compact dual-mode dual-band filter is realized by coupling two quarter-mode cavities. The proposed SICL based filter realized using standard PCB fabrication process demonstrates ease of design and enhanced flexibility in exciting the higher order mode to attain the second-passband. The experimental results indicate widely spaced passbands with 3-dB bandwidth of 3.18 GHz and 0.27 GHz centered at 9.61 GHz and 19.12 GHz, respectively. The proposed compact SICL based quarter-mode filter occupies only 0.15 λ g 2 lateral area.

Ultralow electron emission yield achieved on alumina ceramic surfaces and its application in multipactor suppression

Alumina ceramics used in microwave systems are susceptible to the multiplication of secondary electron emission on the surface due to the influence of resonance between electrons and the radiofrequency electric field, and a detrimental multipactor effect may therefore be triggered. For the alumina-loaded microwave components, it is essential to achieve low secondary electron yield (SEY) on the inserted alumina surfaces to mitigate multipactor. In this work, to achieve an ultralow SEY surface of alumina, two recognized low-SEY treatments were combined. For the primary SEY suppression, a series of microstructures were fabricated on the alumina surfaces with varied porosity and aspect ratio at the hundred-micrometer scale by infrared laser etching. The microstructure with 52.14% porosity and 1.78 aspect ratio showed an excellent low-SEY property, which could suppress the SEY peak value ( δ m ) of alumina from 2.46 to 1.00. For the secondary SEY suppression, the SEY dependence of TiN coating on sputtering parameters was studied, and the lowest δ m of 1.19 was achieved when the gas flow ratio of Ar:N2 was 15:7.5. Thereafter, by depositing TiN ceramic coating onto the laser-etched porous samples, an ultralow SEY, with δ m of 0.69, was achieved on the alumina surfaces. The simulation work revealed the impact of dielectric surface charge on electron multiplication and revealed a mechanism of using low-SEY surfaces to inhibit multipactor. Some coaxial filters filled with alumina were fabricated for verification; the results revealed that the multipactor threshold increased from 125 W to 425 W after applying the TiN-coated porous alumina, and to 650 W after treating another multipactor-sensitive area with the same low-SEY process. This work developed an advisable method to sharply reduce SEY, which is of great significance for the multipactor mitigation of alumina-loaded microwave components.

A Novel Bandstop Filter Based on Two-Port Coaxial Cavities for the Installation of Metallic Mode Stirrers in Microwave Ovens

Metallic stirrers are commonly used in mode-stirred reverberation chambers but are less common in microwave ovens, because the use of a metallic axis creates a coaxial port in the cavity wall where the axis is introduced, which may result in significant microwave leakage levels. However, due to electromagnetic, mechanical, temperature, or chemical requirements, metallic axes must be used in some cases. In this paper, we present a high power coaxial filter that enables the use of metallic stirrers in microwave applications. The filter employs two-port coaxial cavities that are analyzed to determine their design parameters. These cavities are coupled via coaxial lines to achieve proper attenuation levels. The cavities were designed using commercial electromagnetic (EM) software, and a filter prototype was validated using vector network analyzer (VNA) measurements. The simulated and measured results show that a three-stage configuration can achieve attenuations greater than 70 dB at the 2.45 GHz ISM band, allowing the use and external handling of the metallic axis inserted into microwave ovens with negligible microwave radiation leakage.

Varactor-graphene-based multi-reconfigurable triplet filter with independent tuning of frequency and amplitude

In this paper, a multi-reconfigurable filter which consists of three identical varactor-graphene-loaded coaxial substrate integrated waveguide (SIW) resonators is presented. The center frequency and transmission amplitude of the proposed filter is independently reconfigurable by means of electrically controlling the values of the varactor capacitance and the graphene resistance, respectively. Tuners and their bias circuits are mounted on the surfaces of the SIW resonator to adjust the tuning of resonant frequency and unloaded quality factor, which enable to realize the frequency and amplitude of the presented multi-reconfigurable filter. In addition, the proposed filter applies a cascaded triplet topology to generate a transmission zero at the upper side in order to enhance skirt selectivity and out-of-band rejection. The circular shape of the resonator provides great flexibility and produces an additional compactness of the filter. The proposed multi-reconfigurable coaxial SIW filter is designed and fabricated, with high-Q varactors and graphene thin sheets as frequency and amplitude tuning elements, respectively, exhibiting the following reconfigurable characteristics: (a) a wide tuning range of 0.58–1.01 GHz with a constant 1 dB fractional bandwidth of 2 ± 0.2%. (b) A continuous tuning range of amplitude at any center frequency in the achievable frequency band. For instance, the proposed filter can be tuned with an amplitude range of 3.02–19.8 dB by varying the value of the graphene sheet resistance at 1.01 GHz. (c) Free combination of the arbitrary center frequency and attenuation level. The proposed filter with tunable filtering and attenuating responses has widely potential in reconfigurable wireless communication systems and radar systems due to its high integration and versatility.

Glass-Based Bandpass Filters for New Radio (NR) K-/Ka-Band Communications

Highly miniaturized substrate integrated coaxial (SIC) bandpass filters (BPFs) are presented for new radio (NR) communications. They are based on glass-integrated two-post SIC resonators and mixed electromagnetic (EM) couplings that contribute to two poles and one transmission zero (TZ) to the overall BPF transfer function. The concept can be extended to high-order quasi-elliptic configurations shaped by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2N$ </tex-math></inline-formula> poles and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> TZs by readily cascading <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> two-post SIC cavities through inter-stage transmission lines (TLs). A high-frequency glass-based integration platform is explored as a low-loss and high-frequency integration mechanism. To practically validate the concept, three glass-integrated BPF prototypes were designed, manufactured, and tested. They include a: 1) two-pole/one-TZ BPF with a passband centered at 26 GHz, fractional bandwidth (FBW) of 21%, and a TZ at 32 GHz; 2) two-pole/one-TZ BPF with a passband centered at 26.7 GHz, FBW of 11%, and a TZ at 23.6 GHz; and 3) a four-pole/two-TZ BPF with a passband centered at 26.7 GHz, FBW of 11%, and two TZs at 24 and 31.3 GHz.