Compact Microwave Research Articles

Electromagnetic modeling and design of a novel class of complementary split-ring resonators

This research study reports the assessment of complementary split ring resonators based on Gielis transformation as basic elements for the design of high-performance microwave components in printed technology. From the electromagnetic simulation of said structures, suitable equivalent circuit models are extracted and analyzed. Physical prototypes are fabricated and tested for design validation. The obtained results confirm that the adoption of supershaped geometries enables the synthesis of very compact scalable microwave filters.

Dual mode microwave deflection cavities for ultrafast electron microscopy

This paper presents the experimental realization of an ultrafast electron microscope operating at a repetition rate of 75 MHz based on a single compact resonant microwave cavity operating in a dual mode. This elliptical cavity supports two orthogonal TM110 modes with different resonance frequencies that are driven independently. The microwave signals used to drive the two cavity modes are generated from higher harmonics of the same Ti:Sapphire laser oscillator. Therefore, the modes are accurately phase-locked, resulting in periodic transverse deflection of electrons described by a Lissajous pattern. By sending the periodically deflected beam through an aperture, ultrashort electron pulses are created at a repetition rate of 75 MHz. Electron pulses with τ = (750 ± 10) fs pulse duration are created with only (2.4 ± 0.1) W of microwave input power; with normalized rms emittances of ϵn,x = (2.1 ± 0.2) pm rad and ϵn,y = (1.3 ± 0.2) pm rad for a peak current of Ip = (0.4 ± 0.1) nA. This corresponds to an rms normalized peak brightness of Bnp,rms=(7±1)×106 A/m2 sr V, equal to previous measurements for the continuous beam. In addition, the FWHM energy spread of ΔU = (0.90 ± 0.05) eV is also unaffected by the dual mode cavity. This allows for ultrafast pump-probe experiments at the same spatial resolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be used for exciting the sample. Moreover, the dual mode cavity can be used as a streak camera or time-of-flight electron energy loss spectroscopy detector with a dynamic range >104.

A Dual-Mode Split-Ring Resonator to Eliminate Relative Humidity Impact

In this letter, a compact resonant-based dual-mode microwave sensor is proposed, aimed to eliminate the erroneous effect of relative humidity (RH) in microwave chemical sensing within the uncontrolled environment. A single split-ring resonator (SRR) is employed as the sensor core and the first resonance ( $f_{1}\sim 0.552$ GHz) and the second resonance ( $f_{2}\sim 1.03$ GHz) of the resonator are utilized to calibrate the potential measurement error arising from ambient RH. Simulations of the sensor’s design and sensitivity using the finite-element method were performed and presented, which are further confirmed by measurements for resonant profile variation considering RH change of 5%–70%. Using the proposed technique, SRR size reduction of 50% is achieved. In addition, common chemical materials of methanol, ethanol, 2-Isopropanol (IPA), and heptane are successfully detected, achieving clear distinction from the impact of external humidity.

Наблюдения эруптивных событий с помощью Сибирского радиогелиографа

We describe methods for monitoring eruption activity with the first phase of the multiwave Siberian Radioheliograph (SRH-48). We give examples of the recorded eruptive events: 1) rise of a prominence above the limb observed in the radio map sequence of April 24, 2017; 2) a jet recorded on August 2, 2017, whose cold matter screened a compact microwave source for several tens of minutes. The shading due to the jet appearance was observed on SRH-48 correlation curves as the so-called “negative” burst. Using the “negative” burst on the correlation curves of February 9, 2017 as an example, we show that the intervals with depression of the microwave emission of local sources are not always caused by shading of their emission. In this event, the radio brightness decreased within ten hour period of the increased quasi-stationary emission during the development of AR 12635 magnetic structure. Similar behavior was observed in EUV, SXR, and radio emission at 17 GHz.

Observation of eruptive events with the Siberian Radioheliograph

We describe methods for monitoring eruption activity with the first phase of the multiwave Siberian Radioheliograph (SRH-48). We give examples of the recorded eruptive events: 1) rise of a prominence above the limb observed in the radio map sequence of April 24, 2017; 2) a jet recorded on August 2, 2017, whose cold matter screened a compact microwave source for several tens of minutes. The shading due to the jet appearance was observed on SRH-48 correlation curves as the so-called “negative” burst. Using the “negative” burst on the correlation curves of February 9, 2017 as an example, we show that the intervals with depression of the microwave emission of local sources are not always caused by shading of their emission. In this event, the radio brightness decreased within ten hour period of the increased quasi-stationary emission during the development of AR 12635 magnetic structure. Similar behavior was observed in EUV, SXR, and radio emission at 17 GHz.

Low-Noise X-Band Tunable Microwave Generator Based on a Semiconductor Laser With Feedback

The stabilization of a relatively simple microwave oscillator tunable across the full X-band based on a laser subjected to optical feedback is achieved. Specifically, a resonance effect based on locking the two inherent dynamic frequencies of the system, as well as, optoelectronic feedback are utilized to achieve a sub-ps jitter and typical phase noise in the range of −107 dBc/Hz at 10 kHz offset from an oscillation frequency that can be tuned from 5.5 to 12.1 GHz. Further, the microwave signal is extracted from the laser-diode injection terminals and eliminates the need for multiple lasers, radio-frequency filters, and external RF sources. This architecture, therefore, realizes a compact and low-cost tunable microwave photonic oscillator.

A compact microwave device for monitoring insect activity in grain samples

We designed and fabricated a novel microwave device capable of detecting a single insect in grain samples. A test set-up was constructed by combining a planar active microwave resonator, a Peltier cell, and an insect cage. With the integration of a regenerative element, the active resonator had a quality factor as high as 21,600 even when placed in grain, an electrically lossy medium. The high sensitivity of the device allowed the characterisation of the activity of single adult insects Tribolium castaneum or Cryptolestes ferrugineus at different temperatures, as well as the reliable detection of single adult insects in grain samples. Our approach demonstrated the non-contact sensing technique that could assist in decision making for integrated pest management programs to monitor insects in stored grain.

A novel L-band slow wave structure for compact and high-efficiency relativistic Cerenkov oscillator

A novel L-band slow wave structure (SWS) for compact and high-efficiency relativistic Cerenkov oscillator is proposed. The SWS is composed of orthogonal array of two all-metal metamaterial units. Since the metamaterial used for constructing the SWS has a negative equivalent permittivity and permeability, the fundamental mode of the SWS has a negative dispersion and can work below cutoff frequency of circular waveguide with the same size, indicating that the structure has advantage of miniaturization. Analysis of high-frequency characteristics shows that interaction impedance of the fundamental mode (quasi TM01 mode) is greater than 70 Ω across operating frequency band, which indicates that this structure is expected to achieve the high efficiency of high power microwave sources. By adopting an orthogonal arrangement between metamaterial resonant units, the angular uniformity of electric field in SWS space is significantly improved, and the non-uniformity of electric field due to asymmetry of the metamaterial units is reduced. In addition, an L-band relativistic Cerenkov oscillator is constructed using this metamaterial SWS. In the acceleration voltage U = 550 kV, beam current I = 1.5 kA, and axial uniform magnetic field B = 1.5 T conditions, preliminary particle simulations show that the Cerenkov oscillator obtains a 240 MW average power at 1.405 GHz, with an efficiency of 29.1%, and axial length around one λ. This Cerenkov oscillator obtains a high power and efficiency in a miniature and compact microwave device.

Note: A compact microwave plasma enhanced chemical vapor deposition based on a household microwave oven.

I designed an efficient and compact microwave plasma enhanced chemical vapor deposition (MW-PECVD) based on a household 2.45 GHz microwave oven. In the MW-PECVD, the microwave plasma was sparked by a piece of Cu foil in a low pressure down to 1 Pa. The SiC plate is not only used to realize rapid microwave heating-up but also to prevent the reflected power from damaging the magnetron. To test the performance of the system, vertically oriented graphene nanosheets were fabricated on the Cu foil. The products were characterized by Raman spectra and scanning electron microscope.

Compact, high power and high efficiency relativistic magnetron with L-band all cavity axial extraction

To reduce the size and the weight of the relativistic magnetron (RM), a highly compact RM using an all cavity extraction and transparent cathode is investigated. Compared with the traditional RM design [Sayapin et al., IEEE Trans. Plasma Sci. 45(2), 6792062 (2017) and Sayapin and Shlapakovski, J. Appl. Phys. 109(6), 063301 (2011)] this configuration occupies only 0.55λ (radius) * 1.55λ (length). Both simulation and experimental results demonstrate that a microwave power of 508 MW is generated at 1.57 GHz when the input beam voltage is 369 kV and the corresponding efficiency is ∼33%. This provided work paths a way to finally achieve high power, high efficiency, and compact microwave sources.

Compact microwave plasma device for surface treatment

Compact microwave plasma device for surface treatment

3D printed microwave cavity for atomic clock applications: proof of concept

The authors present the realisation and characterisation of an additively manufactured (AM) microwave resonator cavity for double-resonance (DR) vapour-cell atomic clocks. The design of the compact microwave cavity is based on the loop-gap resonator approach, previously demonstrated for conventionally-machined aluminium components. In the present study, the resonator is fabricated by AM using a metal-coated polymer. A resonance frequency at the desired 6.835 GHz rubidium atomic frequency is obtained. When employed in an atomic clock setup, the AM cavity enables a DR signal of <500 Hz linewidth and of nearly 20% contrast, thus fulfilling the stringent requirements for DR atomic clocks. A clock short-term stability of 1 × 10−12 τ −1/2 is demonstrated, comparable to state-of-the-art clock performances.

Design of a compact microwave absorber using parameter retrieval method for wireless communication applications

A novel compact microwave absorber with 10 dB absorption level in 1.8–2.1 GHz frequency band for the wireless communication applications is investigated. A robust equivalent circuit (EC) model of the structure is developed and rigorously analysed using a non-resonance constituent parameter extraction technique. The EC model and the proposed topology developed on a low-cost FR-4 substrate of thickness 0.048λ L (λ L = wavelength at lower operating frequency) have been analysed for different polarisations and are in close agreement with each other. The structure has also been experimentally verified and good agreement among analytical model, full wave simulation, and the experimental results is observed. The absorber shows the high cost-effective bandwidth (BWCE = 81.14) in comparison to many recently reported works which proves its compactness and novelty.

Compact Microwave Power Limiter with HTSC Element

Compact Microwave Power Limiter with HTSC Element

Application of Gielis transformation to the design of metamaterial structures.

In this communication, the use of Gielis transformation to design more compact metamaterial unit cells is explored. For this purpose, transformed complementary split ring resonators and spiral resonators are coupled to micro-strip lines and theirbehaviour is investigated. The obtained results confirm that the useof the considered class of supershaped geometries enables the synthesis of very compact scalable microwave components.

Far field focusing for a microwave patch antenna with composite substrate

Modeling for a compact microwave antenna structure on base of a miniaturized rectangular patch antenna with composite substrate and magnetic superstrates is made in this study by using FDTD simulations. The resonant frequency of the antenna structure is supposed to be 15 GHz. The design of the antenna with composite substrate and without superstrate is made up by using the microwave miniaturization concept for rectangular patch antennas created by first author of this study. The optimal distance between the superstrate and antenna surface is found by using Fabry-Perot cavity theory as maximum values of power directivity and efficiency of the antenna is achieved. The comparative analysis with regard to some far and near field parameters of the above antenna structures and the antenna with dielectric substrate having same value of the relative permittivity is performed.

COMPUTATIONALLY EFFICIENT TWO-OBJECTIVE OPTIMIZATION OF COMPACT MICROWAVE COUPLERS THROUGH CORRECTED DOMAIN PATCHING

COMPUTATIONALLY EFFICIENT TWO-OBJECTIVE OPTIMIZATION OF COMPACT MICROWAVE COUPLERS THROUGH CORRECTED DOMAIN PATCHING

Low-cost multiband compact branch-line coupler design using response features and automated EM model fidelity adjustment

Design closure of compact microwave components is a challenging problem because of significant electromagnetic (EM) cross-couplings in densely arranged layouts. A separate issue is a large number of designable parameters resulting from replacement of conventional transmission line sections by compact microstrip resonant cells. This increases complexity of the design optimization problem and requires employment of expensive high-fidelity EM analysis for reliable performance evaluation of the structure at hand. Consequently, neither conventional numerical optimization algorithms nor interactive approaches (e.g., experience-driven parameters sweeps) are capable of identifying optimum designs in reasonable timeframes. Here, we discuss application of feature-based optimization for fast design optimization of dual- and multiband compact couplers. On one hand, design of such components is difficult because of multiple objectives (achieving equal power split and good matching and port isolation for all frequency bands of interest). On the other hand, because of well-defined shapes of the S-parameter responses for this class of components, feature-based optimization seems to be well suited to control multiple figures of interest as demonstrated in this work. Two-level EM modeling is used for further design cost reduction. More importantly, we develop a procedure for automated determination of the low-fidelity EM model coarseness that allows us to find the fastest possible model that still ensures sufficient correlation with its high-fidelity counterpart, which is critical for robustness of the optimization process. Our approach is illustrated using two dual-band compact couplers. Experimental validation is also provided.

Electrode structure of a compact microwave driven capacitively coupled atomic beam source

A compact magnetic field free atomic beam source was designed, assembled and tested the performance to produce hydrogen and nitrogen atoms. A forced air-cooled solid-state microwave power supply at 2.45 GHz frequency drives the source up to 100 W through a coaxial transmission cable coupled to a triple stub tuner for realizing a proper matching condition to the discharge load. The discharge structure of the source affected the range of operation pressure, and the pressure was reduced by four orders of magnitude through improving the electrode geometry to enhance the local electric field intensity. Optical emission spectra of the produced plasmas indicate production of hydrogen and nitrogen atoms, while the flux intensity of excited nitrogen atoms monitored by a surface ionization type detector showed the signal level close to a source developed for molecular beam epitaxy applications with 500 W RF power.

Resonant frequency of 30°–60°–90° triangular dielectric resonator at fundamental mode

Theoretical and experimental investigations on 30°–60°–90° Triangular Dielectric Resonator (TDR) are presented here for TMz and TEz modes for the first time. Approximate expressions for eigenfunction and eigenvalue are given here. Fundamental TM101z mode is explored in detail. A qualitative explanation of decrease in effective dimensions from actual physical dimensions is explained here with help of internal electric field. Approximate curve fitted graphical solution is given here to predict the resonant frequency for 10⩽εr⩽100 where εr is relative permittivity of the TDR. Four 30°–60°–90° TDRs are fabricated and tested. It is found that our theory is in excellent agreement with experimental data and data obtained using 3D EM simulator. It is found that for a given resonant frequency, height of TDR and εr, 30°–60°–90° TDR takes just half volume compared to equilateral TDR. Mathematical explanation is also given here to justify this fact. Therefore, our theory on 30°–60°–90° TDR will help to design compact microwave resonator. It is also believed that our theory can be applied to investigate 30°–60°–90° triangular shaped circulators, oscillators, filters, dielectric resonator antennas etc.