External Coupling Structure Research Articles

High‐performance two‐pole filter using self‐coupled resonators with frequency‐variant internal and external couplings

AbstractIn this article, a two‐pole filter with very high selectivity and second harmonic suppression is presented. The design is based on a novel configuration using self‐coupled half‐wave resonators with external frequency‐variant coupling (EFVC) structures. The self‐coupling allows placing two transmission zeros, produced by frequency‐variant interresonator coupling and the tapped feeds, close to the passband edges. The EFVC structure enables arbitrary positioning of these zeros without affecting in‐band performance. Thus, very high‐selectivity passbands can be realized. Additionally, the external coupling structures provide more zeros which are used to suppress spurious harmonics. The fabricated prototype second‐order filter at 2.35 GHz center frequency with 5.6% bandwidth shows a selectivity factor (ratio of 3‐ to 20‐dB bandwidths) of 0.535 and stopband up to 2.8 times the center frequency with minimum 20‐dB rejection.

An array structures of nanoparticle-coupled hyperbolic metamaterials for efficient SERS sensing

Hyperbolic metamaterials (HMMs) have been employed in the field of surface-enhanced Raman scattering (SERS) for their properties to support large-wave vector bulk plasmon polariton (BPP) waves, whereas the excitation of BPP is challenging to a certain extent. In addition, with the advance of SERS, the substrate for energy utilization has aroused increasing attention. An HMM-Ag nanoparticles (Ag NPs) platform based on patterned sapphire substrate (PSS) array structure was proposed in this study. With Ag NPs as the external coupling structure, the generated large-wave vector scattered light excited the BPP in the HMM and extended the energy into the Ag NPs gap. On that basis, a hot surface with a high density of “hot spots” was formed. PSS with excellent light trapping capability was employed as a substrate, which improved the energy utilization of the platform. Furthermore, the good hydrophobicity of the nanoparticle array structure further amplified the SERS signal. Lastly, the excellent performance of the platform was experimentally verified, the detection limits of CV and R6G reached 10-10 M and 10-11 M, respectively. Accordingly, it is believed that the plasma platform has promising applications in high-sensitivity sensing and biochemical detection.

Recyclable surface-enhanced Raman spectroscopy (SERS) platform fabricated with Ag-decorated ZnSe nanowires and metamaterial

In surface-enhanced Raman scattering (SERS), metal-semiconductor heterostructures have attracted a lot of interest because of their remarkable features. However, the use of organic substances in the fabrication of metal nanoparticles can result in contamination of the SERS substrate, which can negatively impact sensor performance. Here, we introduced new recyclable SERS substrates which include Ag-decorated ZnSe nanowires and hyperbolic metamaterial. The Ag-decorated ZnSe nanowires work as an external coupling structure for hyperbolic metamaterials, due to this structure exhibiting significant plasmonic effects as well as unique optical features. There exists overlapping and physical interaction between metal and semiconductor nanowires, as a result, both resonance energy and hot electron were transferred. Rhodamine 6G (R6G), malachite green (MG), and adenosine were used to assess the SERS performance of synthesized Ag-decorated ZnSe, which showed outstanding stability and a sensitivity limit of 10-12 M. The nanostructure's self-cleaning feature was demonstrated through photocatalytic degradation of R6G and MG molecules under visible light, enabling it to be reused multiple times and showing that it was not limited to a single organic molecule. The bifunctional structure not only offers a unique way of boosting SERS efficiency but is also considerable for photocatalytic behavior.

SERS Sensing Using Graphene-Covered Silver Nanoparticles and Metamaterials for the Detection of Thiram in Soil

Multilayer hyperbolic metamaterial (HMM)-based SERS substrates have received special consideration because they accommodate various propagation modes such as surface plasmonic polaritons (SPP). However, the SPP modes are difficult to generate in HMM due to their weak electric field enhancement. In this article, we designed novel SERS substrates consisting of graphene-covered AgNPs and HMM. The graphene-covered AgNPs work as an external coupling structure for hyperbolic metamaterials due to this structure exhibiting significant plasmonic effects as well as unique optical features. The localized surface plasmonic resonance (LSPR) of the graphene-covered AgNPs excited the SPP and thus formed a strong hot spot zone in the nanogap area of the graphene. The Raman experiment was performed using rhodamine 6G (R6G) and crystal violet (CV), which showed high stability and a maximum enhancement factor of 2.12 × 108. The COMSOL simulation further clarified that enhanced SERS performance was due to the presence of monolayer graphene and provided an atomically flat surface for organic molecules in a more controllable manner. Interestingly, the proposed SERS structure carries out quantitative detection of thiram in soil and can satisfy the basic environmental need for pesticide residue in the soil.

A Triple-Quasi-TEM-Resonance Dielectric Cavity for Bandpass Filter Design

This letter presents a triple-quasi-TEM-resonance dielectric cavity for compact bandpass filter design. The proposed dielectric cavity is silver coated and has three blind holes which form three distinct quasi-TEM mode resonators. The external coupling structure for the resonator is realized by tapping hole. The inter-resonator couplings are realized and controlled by slots on the outer surfaces of the dielectric block. A three-pole filter with two controllable transmission zeros is designed and implemented. The measured results agree well with the simulated results, verifying the proposed triple-resonance dielectric cavity structure and coupling mechanisms.

Bandpass Filter and Diplexer Based on Dual-Mode Dielectric Filled Waveguide Resonators

This paper presents the designs of a bandpass filter (BPF) and a diplexer based on the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> mode and the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">120</sub> mode of the dielectric filled waveguide resonators (DFWRs). The DFWR is designed by integrating a dielectric main body and a printed circuit board (PCB) cover. The PCB cover is electrically connected with the top surface of the dielectric body. For each mode, metallized blind holes can be set at its maximum electric-field points to excite or extract it and the other mode will not be influenced. Microstrip lines on the PCB are utilized to connect different pairs of the metallized blind holes to form the internal and external coupling structures. For verification, a BPF and a diplexer are designed, fabricated and measured based on the DFWRs. In measurement, the BPF is with a frequency band of 2.515 GHz - 2.675 GHz, an insertion loss of 0.6 dB, and a return loss of 20 dB. The two frequency bands of the proposed diplexer are 3.3 GHz - 3.4 GHz and 3.7 GHz - 3.8 GHz. For the two frequency bands, the measured insertion losses are 0.9 dB/0.85 dB and the isolations are better than 40 dB/50 dB.

A compact tunable balanced tri‐band bandpass filter with high selectivity using stub loaded resonator

AbstractIn this paper, a balanced tri‐band band‐pass filter (BPF) with the third independently tunable passband and the other two fixed ones based on a novel multi‐stub loaded resonator (MSLR) is presented. Due to the symmetrical circuit structure, the even‐and odd‐mode methods are applied to analyze the differential‐mode (DM) and the common‐mode equivalent circuits of the proposed resonator, and the correspondingly resonant characteristics can be obtained. With the approximate design of the MSLR, the first three DM resonant frequencies are employed to form the three DM passbands. Then, the external coupling structure can be controlled by coupled lines to meet the required specifications. Furthermore, the frequency tuning of the third DM passband can be realized by adjusting the varactors loaded at the end of the resonators. Finally, the source and load coupling is introduced to improve the frequency selectivity. For verification, a balanced tri‐band BPF with the tunable third DM passband was designed, manufactured and tested. The fabricated filter has central frequencies of the first two fixed bands located at 2.4 and 2.95 GHz, the third one tuning from 4.17 to 4.41 GHz, and the correspondingly fractional bandwidths (FBWs) are 12.3%, 3.5% and 1.9% ± 0.89%. The experimental results are in good agreement with the simulated ones.

Reconfigurable Filter for Bandpass-to-Absorptive Bandstop Responses

A frequency tunable filter with a bandpass-to-absorptive bandstop reconfigurable characteristic is studied, designed and validated theoretically and experimentally. To control the filter bandwidth and impedance matching performance, variable capacitors are used in each external and internal coupling structure, and, by using equivalent circuits, the required frequency responses of two different modes are obtained. Two single-pole double-throw switches embedded in the transmission lines running from the source to the load accommodate external coupling structures to control the operational mode of the proposed filter. All commercially available electronics such as switches and varactor diodes are placed on the microstrip line layer, and the frequency-tunable substrate integrated waveguide (SIW) resonators are coupled to the transmission line through coupling slots. In the absorptive bandstop mode, the stopband is tuned from 1.83 GHz to 2.49 GHz, while the passband can be tuned from 1.86 GHz to 3.3 GHz in the bandpass mode. In both modes, more than 10 dB in return loss over the frequency tuning range of interest has been achieved. Theoretical, simulated, and measured results are in good agreement, which validate the proposed filter structure.

External Coupled Millimeter Wave Magnetron With Simple Diffraction Output

We proposed an external coupling structure of the millimeter wave magnetron that has the potential to utilize the diffraction output for axial power extraction. For such a structure, a 24-vane anode resonator operated in the $\pi $ mode was tightly coupled to an external coupling structure operated in the $2\pi $ mode through slots in the back walls of alternate cavities of the anode resonator. Moreover, we designed and simulated a Ka-band external coupled magnetron (ECM) in order to demonstrate the effectiveness of the new configuration. The simulation results showed the achievement of maximum microwave power of 108 kW at 35.0 GHz, with 29.6% efficiency.

Superconducting tunable filter with constant bandwidth using coplanar waveguide resonators**Project supported by the National Natural Science Foundation of China (Grant No. 61371009) and the National High Technology Research and Development Program of China (Grant No. 2014AA032703).

In this paper we propose a two-pole varactor-tuned superconducting filter using coplanar waveguide (CPW) spiral-in-spiral-out (SISO) resonators. Novel internal and external coupling structures are introduced to meet the requirements for a tunable filter with a constant absolute bandwidth. The fabricated device has a frequency tuning range of 14.4% at frequencies ranging from 274.1 MHz to 317.7 MHz, a 3-dB bandwidth of 5.14 ± 0.06 MHz, and an insertion loss of 0.08 dB–0.70 dB. The simulated and measured results are in excellent agreement with each other.

Energy Leakage and Characteristic Analysis of HMSIW and Implement in Multi-layered Structure Equalizer Design

The phase constant and attenuation constant of half mode substrate integrated waveguide (HMSIW) are calculated using an improved quicker multi-line method in this paper. A mathematical method is proposed to analyze the energy leakage of HMSIW theoretically. The radiation and leakage character of electromagnetic field at open face of HMSIW is different with different relative permittivity. An equalizer loaded multi-layered HMSIW resonant cavities is proposed based on the energy leakage excitation without external coupling structure. Compared with the other planar circuits, these structures have superiorities of small size, simple structure, low loss and high Q, suitable for the miniaturization development, and are easily integrated with other circuits. Furthermore, this proposed equalizer has a simpler design procedure than other HMSIW equalizers without resonant frequency deviation.

K-Band Frequency Tunable Substrate-Integrated- Waveguide Resonator Filter With Enhanced Stopband Attenuation

In this paper, we present a K-band substrate-integrated waveguide resonator bandpass filter structure. The filter uses an antisymmetric mode of the resonator for the first time. A design method for the external coupling structure of the resonator utilizing the antisymmetric mode is described. In addition, a methodology for suppressing neighboring resonances close to the passband is demonstrated. This method can enhance stopband attenuation performance without additional loss. The proposed filter can tune the center frequency by adjusting tuning components. In order to verify the proposed filter structure and design method, we have fabricated and measured a K-band filter and demonstrated higher order filter design.

A COMPACT TRIPLE-BAND PASSBAND FILTER USING MULTI-STUB LOADED RESONATOR AND ASYMMETRICAL SIRS

This letter presents a compact triple-band passband filter with high frequency selectivity. The first and second passbands are formed by a multi-stub loaded resonator. The bandwidth of the second passband can be independently adjusted by tuning the coupling strength between the two loaded open stubs. The third passband is implemented using two asymmetrical stepped impedance resonators (SIRs) with a tapped line structure as external coupling form. The asymmetrical SIRs also serve as one part of the external coupling structure of the multi-stub loaded resonator so as to achieve a compact circuit size. Additionally, a source-load coupling is introduced, thus, multiple transmission zeros are generated to improve the frequency selectivity. After a detailed introduction of the operation principle, a triple-band passband filter with centre passband frequencies of 1.5, 2.6 and 3.6 GHz is designed and fabricated. The measured results verify the effectiveness of the proposed filter. As key components of the multi-band wireless service system, the multi-band passband filters have been extensively studied for past decades. They should have a compact size, flexible design freedom, high frequency selectivity and sufficient suppression of the parasitic harmonic modes. Many approaches have been utilized to implement multi-band filters. The most common method is based on SIRs (1-3), whose first two resonant modes can be controlled by properly selecting the relevant impedance or strip width ratio. But this method often suffers from a large circuit size and limited design freedom. The stub loaded multi-mode microstrip resonator (4-7) and the degenerate modes of perturbed ring resonators (8- 14) can also be utilized to construct multi-band filters. In (15), the multi-stub loaded resonator was used to implement a dual-band passband filter with independently controlled bandwidth by inserting a half-wavelength resonator between the loaded open stubs so as to introduce two signal paths. The transmission zeros generated by the direct source-load coupling improved the isolation between the passbands greatly and suppressed the parasitic harmonic modes to achieve a wider upper stopband. Following (15), in this letter, a compact triple-band passband filter with high frequency selectivity is proposed, whose first two passbands are implemented using the multi-stub loaded resonator in (15). The third passband is formed by using two asymmetrical electronically coupled SIRs. The SIR has a tapped line structure as the external coupling form. Simultaneously, as one part of the input/output structure of the multi-stub loaded resonator, the SIR not only accomplish the external coupling of the multi- stub loaded resonator, but also can introduce source-load coupling to improve frequency selectivity. Thus, the multi-stub loaded resonator combined with two SIRs achieves triple-band passband filtering function, while the circuit size does not increase considerably. Structure and design of the filter are in detail introduced in the remainder. A triple-band passband filter with center frequencies of 1.5, 2.6 and 3.6 GHz is fabricated and measured. The measured results verify the effectiveness of the proposed filter.

Micromachined 38 GHz cavity resonator and filter with rectangular-coaxial feed-lines

Micromachined, multilayer cavity resonators and filters at 38 GHz are demonstrated. Each layer is made of gold-coated silicon, structured by deep reactive etching. Two external coupling structures by coaxial feed lines are proposed to suit the fabrication process. The measured resonator gives an unloaded Q-value of 343 at 38 GHz. Methods to further improve the resonator quality-factors are discussed. The measured insertion loss of the filter is 1.01 dB, the 3 dB bandwidth is from 36.53 to 39.13 GHz, and the return loss is better than −15 dB over the frequency range from 37.0 to 38.6 GHz.

Novel planar, square-shaped, dielectric-waveguide, single-, and dual-mode filters

This paper presents a novel concept of a square-shaped dielectric-waveguide resonator, which can easily realize a dielectric-waveguide cross-coupled filter or a dielectric-waveguide dual-mode filter, using the conventional printed circuit board (PCB) process. This planar dielectric-waveguide resonator has a higher Q value than a microstrip resonator. The physical mechanisms of both single- and dual-mode filters are elucidated. Some new coupling structures are developed for undergoing the PCB process. Filter design procedures are detailed. Design curves for the coupling coefficients of internal- and external-coupling structures are determined by full-wave finite-element-method electromagnetic calculations. Measurement results are highly consistent with theory for all trial filters. This study offers an effective means of producing low-cost high-performance planar circuit filters.

Fast-wave heating of a toroidal plasma near the ion cyclotron frequency

The absorption coefficient of the magnetosonic wave at the ion cyclotron resonance is evaluated, in the limit of rare collisions, for a toroidal plasma with due allowance for the effect of the rotational transform. It is found that, when the parallel wave number kz imposed by the external coupling structure is small, the power absorption is much larger than that previously evaluated; it is independent of kz and does not vanish, as in a uniform magnetic field, for kz = 0. The plasma loading of an external coupling structure and the radial dependence of the absorbed power are evaluated. A critical radius above which the toroidal modes overlap, allowing for a small Q-value of the launching structure over a wide density range, is deduced.