Cutoff Frequency Of Waveguide Research Articles

Power-modulated reconfigurable nonlinear plasmonic devices without DC power supply and feed circuit

High-power electromagnetic (EM) waves can directly modulate the parameters of nonlinear varactor diodes through the rectification and Kerr effects without relying on external sources. Based on this principle, we propose a power-modulated reconfigurable nonlinear device based on spoof surface plasmon polariton (SSPP) waveguide loaded by varactor diodes, without applying DC power supply or feed circuit. Increasing the input power level reduces the effective capacitance of the varactor diode, leading to a blueshift in the cutoff frequency of the SSPP waveguide. This feature can be employed to realize the switching on/off of the input signal depending on the signal power. On the other hand, the transmission state of a low-power signal can be controlled by inputting another independent high-power EM wave simultaneously. Increasing the power of the control wave will enable the low-power signal within a wider bandwidth switched from off to on states. Experimental results are presented to show the excellent performance of the power-modulated reconfigurable SSPP device. This method can reduce the system complexity and provide inspiration for reconfigurable all-passive multifunctional devices and systems.

Perfect splitting in rectangular-waveguide junctions for analog computing

It has recently been shown how computing operations such as high-speed switching, routing, and solving partial differential equations can be performed by exploiting perfect splitting of electromagnetic waves in networks of waveguides from microwaves to the optical regime. Here we propose a technique to achieve perfect splitting of electromagnetic waves using junctions of rectangular waveguides. The structure consists of air-filled rectangular waveguides interconnected at a junction. They are designed to have their cutoff frequency above the cutoff frequency of a further waveguides used as inputs. The proposed structure is studied theoretically with use of transmission-line models, and it is demonstrated that perfect splitting can occur at frequencies below the cutoff frequency of the interconnected waveguides (evanescent coupling). Numerical results are used to validate the designs, and it is demonstrated that the theoretical model fits the numerical data well. As examples of computing operations, it is shown how the proposed structure can be used to compare the amplitude of two incident signals (comparison operation) and also for routing of information to different output ports by exploiting the linear superposition of scattered waves excited at the junction of rectangular waveguides, opening new opportunities and possibilities for future exploration and exploitation of electromagnetic waves for high-speed computing. Published by the American Physical Society 2024

Single-Layer Evanescent Wave Absorbers in Rectangular Waveguides Based on Evanescent Mode Coupling and Attenuation

A microwave absorber for absorbing waves below the cutoff frequency of a rectangular waveguide (RWG) is proposed in this study. By loading an ideal lossy capacitive metasurface (LCMS) in the crosssection of an RWG close to the radiation source, the LCMS exhibits the ability to couple with and attenuate the waves below the cutoff frequency of the RWG, i.e., absorb the evanescent waves (EWs). The operating mechanism is analyzed with several parametric studies based on the momentum matching principle, and a systematic design procedure for a practical EW absorber is concluded. Three samples made of indium tin oxide thin films are designed, fabricated, and tested, and the experimental results agree well with the theoretical results. The maximum measured absorptance reaches up to 97%. Compared with conventional plane-wave absorbers with multilayer conductors, the proposed EW absorber only requires a single-layer conductor and has a distinct working mechanism, design principle, and application scenario. In the examples considered in this study, the samples can serve as the specific matching component for calibrating the RWG below the cutoff frequency. Notably, our EW absorption technique provides a feasible approach to suppress the electromagnetic interference dominated by the evanescent mode in the electrically small metallic cavity packages and near field of integrated circuits.

Ultrathin and Simple 3-D Rasorber Based on Ferrites With Embedded Epsilon-Near-Zero Waveguides

An ultrathin and simple three-dimensional (3-D) frequency-selective rasorber with a passband located between two absorption bands is proposed. The absorption bands are obtained by employing commercial magnetic materials in the absorption channel and the passband is realized using epsilon-near-zero tunneling waveguides. The attractively ultrathin and simple feature is achieved by utilizing tunneling effect at the cutoff frequency of metallic waveguides with arbitrary length, permitting the overall thickness shrink into the same as that of the absorber. A prototype with a thickness of only 0.108 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_c</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_c</i> is the free-space wavelength at the transmission frequency) is fabricated and measured, exhibiting a transmission band with −3 dB fractional bandwidth (FBW) of 35.7% and a minimum insertion loss of 1 dB, and an FBW of 135.6% for reflection coefficient less than −10 dB. The lumped-components-free and lithography-free features greatly facilitate the fabrication, which is promising in practical low-cost applications.

Ultra-wide stopband waveguide bandpass filter based on out-of-band staggered tuning coupling technology

ABSTRACT A design method of greatly widening the stopband of waveguide bandpass filter is proposed in this paper. The parasitic passband of the filter mainly comes from the high-order oscillation mode of the resonant unit. Based on the theory of capacitance loading shortening of the transmission line and the transmission characteristics of each mode in the resonant cavity, a pair of transverse one-dimensional uniform capacitive diaphragms are placed in the center of the resonant cavity to shorten the resonant cavity and suppress the high-order modes. By changing the width of the waveguide and the height of the waveguide on the distribution of out-of-band transmission poles, the out-of-band transmission poles of each resonator can be staggered, which destroys or weakens the high-order oscillation coupling transmission conditions between the resonant units of the filter and further expands the stopband width of the filter. The results show that the length of the X-band waveguide bandpass filter (center frequency 9.5 GHz, bandwidth 400 MHz) is reduced by 54%, and the 40 dB stopband rejection bandwidth is 5.7 times the cutoff frequency of the transmission waveguide, compared with the prototype half-wavelength direct-coupled filter of the conventional Chebyshev filter.

Multipactor suppression via asymmetric grooves in S-band waveguide

To investigate multipactor, we designed a testbed for S-band frequencies with geometries akin to the standard WR-284 waveguide geometry. Narrowing the waveguide height from WR-284 dimensions to 5.5 mm for a suitable frequency-gap product left the waveguide cutoff frequency unaffected and the RF signal propagating in the dominant TE10 mode. A coaxial magnetron provides the test input power at 2.85 GHz with a peak power output of 4 MW and a 3.5 μs pulse width, and an RF solid-state source using gallium nitride high-electron-mobility transistors delivers a pulse width of 100 μs with a test input power of 2 kW for comparison of threshold power. Local (electron multiplier tube) and global (phase/power) diagnostic methods are implemented to detect multipactor within the test setup. At power levels tested (MW) and a 5.5 mm gap, low multipactor orders (N = 1) are observed. Prior numerical studies demonstrated that structures with grooves in the waveguide broadside wall reduced multipactor susceptibility. Such grooves run along the direction of propagation to avoid continuous impedance mismatching. The efficacy of this mitigation technique was experimentally evaluated. Differences over a smooth broadside wall are noticeable, however limited.

Ultra-Compact Dual-Band Half-Mode substrate integrated waveguide filter and filtering power divider based on metamaterial concept

In this paper, a novel dual-band (DB) half-mode substrate integrated waveguide (HMSIW) filter and three novel equal/unequal DB HMSIW filtering power dividers (FPDs) based on the metamaterial concept with ultra-compact dimensions are proposed. The working principle of the proposed configurations is based on the theory of evanescent-mode propagation. Based on the metamaterial concept, a novel compact metamaterial unit cell with double negative permittivities by combining two different types of metamaterial unit cells has been introduced. By loading the proposed metamaterial unit cell with dual negative effective permittivities at different frequencies on the HMSIW surface, two forward passbands have been generated, independently. These two passbands are located below the waveguide cut-off frequency of the dominant mode in the HMSIW structure, which have been designed for WiMAX and WLAN applications. The resonance frequencies of each metamaterial unit cells can be arbitrarily regulated. Accordingly, by resizing the dimensions of each unit cells, the center frequencies of the introduced unit cell could be separately controlled. Four different techniques have been utilized to reduce the size of the proposed devices, which are the evanescent mode technique, HMSIW technique, meander technique, and fractal technique. To illustrate the performance of the proposed structures, the designed dual-band filters (DBFs), and equal DB FPD have been fabricated and measured. A reasonable agreement between simulated and measured results has been achieved. The total size of the proposed HMSIW DBF and FPD is about 0.10 λg × 0.10 λg. The proposed devices have many advantages in terms of compact size, low insertion loss, high selectivity, easy integration with the other planar circuits, and flexible bandwidth allocations.

Nonlinear absorption of high-power microwave pulses in a plasma filled waveguide

We observe complete absorption of an ∼1.2 GW, 0.5 ns, 25.6 GHz high power microwave pulse propagating in a plasma-filled waveguide when the plasma density dependent waveguide cutoff frequency is close to the pulse frequency. Some of the plasma electrons are ejected to the walls, leaving in the waveguide an uncompensated ion charge which forms a potential well where the remaining electrons oscillate in the pulse field. Due to the decreased group velocity of the wave, these trapped electrons have sufficient time to collide with ions, while their regular oscillatory motion becomes chaotic and thermal. Almost all the energy of the electromagnetic pulse is transferred to the kinetic energy of the electrons. This mechanism of absorption is absent when the pulse power is low, and a potential well does not form in the waveguide.

Design and experimental verification of compact dual-band SIW power dividers with arbitrary power division

Abstract This paper communicates the design and experimental validation of dual-band SIW power dividers (single-stage and double-stage) with arbitrary power division. The dual-band power dividers are developed for WiMAX (3.5 GHz) and WLAN (5 GHz) applications. The proposed SIW power dividers are realized by a rectangular cavity, two rows of metallic-vias and one pair of unequal complementary split-ring resonators (CSRRs). Two resonating frequencies are produced below the waveguide cut-off frequency due to the unequal CSRRs etched-out on the top-surface of the cavity, which results in size reduction. To realize arbitrary power division, two output-ports are configured asymmetric with respect to input-port. The power division is varied by altering the distance between the two output-ports. Finally, two compact dual-frequency power dividers (single-stage and double-stage) working at 3.5 and 5 GHz are designed and validated through fabrication and measurement. The fabricated prototype exhibits dual-band operation, compact size (0.027 λ g 2 ${\lambda }_{g}^{2}$ ), good magnitude imbalance, return loss and isolation.

Ultra-Wideband and Compact Terahertz Planar Load Based on Spoof Surface Plasmon Polaritons With Nickel

In this brief, an ultra-wideband and compact planar terahertz matching load based on spoof surface plasmon polaritons (SPPs) is proposed. As a result of subwavelength field confinement and huge metallic loss near the cutoff frequency of SPP waveguides, a tapering SPP structure with nickel (Ni) can terminate the circuit with quasi- 50 Ω impedance. The Ni-SPP structure can absorb most of the propagating electromagnetic wave as a matching load. The voltage standing wave ratio (VSWR) of this proposed Ni-SPP load, with half a wavelength in length at 250 GHz, is below 1.2 from 150 GHz to 1000 GHz. In order to demonstrate its feasibility in terahertz circuits, this SPP load is then applied in a conventional two-way power divider working from 220 to 325 GHz. The simulated and experimental results show that it has performance similar to that of an ideal load, indicating that the proposed SPP load could have lots of potential applications in terahertz planar multiple-port circuits.

Compact dual mode X-band SIW bandpass filter with wide spurious suppression using split square ring slot resonator

PurposeThis paper aims to design a dual mode X-band substrate integrated waveguide (SIW) bandpass filter in the conventional SIW structure. A pair of back-to-back square and split ring resonator is introduced in the single-layer SIW bandpass filter. The various coupling configurations of SIW bandpass filter using split square ring slot resonator is designed to obtain dual resonant mode in the passband. It is shown that the measured results agree with the simulated results to meet compact size, lower the transmission coefficient, better reflection coefficient, sharp sideband rejection and minimal group delay.Design/methodology/approachA spurious suppression of wideband response is suppressed using an open stub in the transmission line. The width and length of the stub are tuned to suppress the wideband spurs in the stopband. The measured 3 dB bandwidth is from 8.76 to 14.24 GHz with a fractional bandwidth of 48.04% at a center frequency of 11.63 GHz, 12.59 GHz. The structure is analyzed using the equivalent circuit model, and the simulated analysis is based on an advanced design system software.FindingsThis paper discusses the characteristics of resonator below the waveguide cut-off frequency with their working principles and applications. Considering the difficulties in combining the resonators with a metallic waveguide, a new guided wave structure – the SIW is designed, which is synthesized on a planar substrate with linear periodic arrays of metallized via based on the printed circuit board.Originality/valueThis study has investigated the wave propagation problem of the SIW loaded by square ring slot-loaded resonator. The electric dipole nature of the resonator has been used to achieve a forward passband in a waveguide environment. The proposed filters have numerous advantages such as high-quality factor, low insertion loss, easy to integrate with the other planar circuits and, most importantly, compact size.

Passband broadening of sub-wavelength resonator-based glide-symmetric SIW filters

Here, we discuss the virtues of glide symmetry for designing low-frequency band-pass periodic filters in substrate integrated waveguide (SIW) technology based on complementary split-ring resonators (CSRRs). Conventional (non-glide) versions of these filters have a narrow passband, due to the fact that this band is below the cutoff frequency of the background waveguide. When glide symmetry is added to the filter configuration, the low-frequency passband is significantly widened, as well as the first stopband. The dispersion properties of both conventional and glide-symmetric periodically loaded waveguides are analyzed and compared with commercial software and an equivalent circuit model. Finally, two prototypes of the proposed glide-symmetric structure have been designed and built, illustrating the potential of this technique to widen the passband and reduce insertion losses of conventional sub-wavelength CSRR-loaded SIW filters.

Super compact dual-band substrate integrated waveguide filters and filtering power dividers based on evanescent-mode technique

AbstractThis paper proposes a series of novel super compact dual-band substrate integrated waveguide (SIW) filters and filtering power dividers (FPDs) using two new compact metamaterial unit-cells. The proposed unit-cells, called COCSRRs, consist of a complementary split-ring resonator (CSRR) and an open CSRR (OCSRR). The working principle of the proposed filters and FPDs is based on the evanescent-mode technique.Based on the theory of evanescent mode, an additional passband below the waveguide cut-off can be achieved by etching the electric dipoles on the metal surface of the SIW structure. The CSRR and OCSRR unit-cells, behave as electric dipoles when excited by an axial electric field and are able to generate a forward-wave passband region below the cut-off frequency of the SIW configuration. Therefore, the proposed COCSRR unit-cells can be interpreted in term of electric dipoles, which can generate two forward-wave passbands below the cut-off frequency of the SIW structure. Although, the center frequencies of each passband can be independently controlled by changing the dimensions of the CSRR and OCSRR sections in the proposed COCSRR unit-cells. Accordingly, by loading the proposed COCSRR unit-cells on the waveguide surface, two arbitrary passbands below the waveguide cut-off frequency are achieved for WLANs and WiMAX applications. The designed SIW filters and FPD are fabricated and measured. Good agreement is observed between the simulated and measured results of the proposed filters and FPD. The proposed dual-band filters and FPD have many benefits like compact size, high selectivity, tunable passband frequencies, and easy integration with other planar technologies.

A tunable high-Q millimeter wave cavity for hybrid circuit and cavity QED experiments

The millimeter wave (mm-wave) frequency band provides exciting prospects for quantum science and devices since many high-fidelity quantum emitters, including Rydberg atoms, molecules, and silicon vacancies, exhibit resonances near 100 GHz. High-Q resonators at these frequencies would give access to strong interactions between emitters and single photons, leading to rich and unexplored quantum phenomena at temperatures above 1 K. We report a 3D mm-wave cavity with a measured single-photon internal quality factor of 3×107 and mode volume of 0.14×λ3 at 98.2 GHz, sufficient to reach strong coupling in a Rydberg cavity quantum electrodynamics system. An in situ piezotunability of 18 MHz facilitates coupling to specific atomic transitions. Our unique, seamless, and optically accessible resonator design is enabled by the realization that intersections of 3D waveguides support tightly confined bound states below the waveguide cutoff frequency. Harnessing the features of our cavity design, we realize a hybrid mm-wave and optical cavity, designed for interconversion and entanglement of mm-wave and optical photons using Rydberg atoms.

Characterization of Metamaterial Slow-Wave Structure Loaded With Complementary Electric Split-Ring Resonators

We proposed an all-metal metamaterial slow-wave structure (MSWS) that consists of a circular waveguide periodically loaded with complementary electric split-ring resonators (CeSRRs). We set up an equivalent circuit theoretical model of MSWS and analyzed its high-frequency characteristics. Also, based on the surface current distribution on the CeSRR obtained by using the eigenmode solver in the CST Microwave Studio, a method of calculating the resonant frequency of the CeSRR was proposed. Furthermore, an MSWS with RF coupling port was designed, simulated, fabricated, and experimentally characterized. The dispersion characteristics of MSWS obtained by interpreting the experimental transmission characteristics agreed well with those predicted by theory as well as simulation. Based on the results of simulation and experiment, a concept of “resonance-coupling” was proposed for the passband of MSWS for frequencies below the cutoff frequency of an empty circular waveguide. The role of the slot-line in the CeSRR in influencing the performance of MSWS was also analyzed. The proposed MSWS has wide potential applications in vacuum electron devices, such as backward-wave oscillator and extended interaction klystron.

A Compact Wideband SIW Bandpass Filter with Wide Stopband and High Selectivity

A novel method to design a wideband substrate integrated waveguide (SIW) bandpass filter (BPF) with compact size, wide stopband and high selectivity is presented. In this method some unique electromagnetic band-gap (EBG) cells are periodically etched on the top layer of SIW to realize a wide passband propagating below the equivalent waveguide cutoff frequency. By changing the configuration of EBG cells, undesired harmonics in upper stopband can be suppressed and a wideband BPF with wide stopband can be obtained. By symmetrically loading two complementary split ring resonators (CSRRs) on the tapered gradient lines of the input/output ports, a transmission zero near the passband can be introduced, and it makes the frequency selectivity of upper sideband improve significantly. As a verification, a wideband SIW BPF with a 3.02 GHz absolute bandwidth (ABW) and a 64.7% fractional bandwidth (FBW) centered at 4.67 GHz is designed, simulated, manufactured, and measured. The results of the experiment and simulation are in good agreement.

A new design of substrate integrated waveguide diplexer using complementary split ring resonators

Design method for achieving the acceptable electrical responses (isolation and impedance matching) of a mixer in two-close frequency with substrate integrated waveguide (SIW) is presented. SIW diplexer with complementary split ring resonators and an open stub is proposed. The SIW loaded diplexer is operated below the cutoff frequency of the equivalent waveguide for SIW; therefore, the size of the structure is compacted. Input and output ports matching are realized in the light of open microstrip stub. The diplexer with optimum dimensions is designed and fabricated. The measurement results verified the design procedures. They also show that operation frequencies are very close together, and also the proposed structure is suitable for long term evolution frequency bands.

Waveguide Dispersion Tailoring by Using Embedded Impedance Surfaces

The capability to tailor the dispersion and the cutoff frequency of waveguides is of importance, as these essential parameters govern the operating frequency range and the waveguide dimension. Here, we propose the concept of substrate-integrated impedance surface (SIIS) that enables arbitrary control of propagation characteristics of closed-shape waveguides. Specifically, we develop a theoretical framework for the simplest form of SIIS constituted by a one-dimensional array of blind vias, which is equivalent to a homogenized surface capacitance embedded in the waveguide. We theoretically and experimentally demonstrate that loading a substrate-integrated waveguide (SIW) with a capacitive SIIS can effectively reduce its cutoff frequency, regardless of the transverse dimension of the SIW. In addition, a SIIS-loaded SIW exhibits several intriguing phenomena, such as the slow-wave guiding properties and the local field concentration. This SIIS-loading technique may open up new possibilities for miniaturization of various waveguide-based components and for enhancement of their uses in microwave sensing and nonlinear functions.

Effects of rf magnetic field on upstream dielectric multipactor

A theoretic model of upstream dielectric multipactor in TEM microwaves, taking both the rf electric field and rf magnetic field into account, is proposed. In this theory, the growth rate of the window multipactor is predicted. The multipactor is approximately independent of the rf frequency, and much more serious than Kishek’s model (1998 Phys. Rev. Lett. 80 193) in the regions of weak dc electric fields and strong rf electric fields. Then, an electromagnetic Particle-In-Cell method is carried out to simulate the multipactor in TEM microwaves. Simulation results show a good agreement with the theoretical results. Furthermore, the lower boundary of multipactor is derived analytically, while there is no upper boundary any more. Finally, a gradually transition between Kishek’s model and our model is found by examining microwaves of TE modes. It is found that the upper boundary reappears when the rf frequency of TE modes trends to the cutoff frequency of waveguide.

Selective Attenuation of Lightning‐Generated Whistlers at Extralow Frequencies: DEMETER Spacecraft Observations

AbstractFrequency‐time spectrograms measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft (2004–2010, altitude about 700 km) at frequencies below 20 kHz sometimes contain lightning‐generated whistlers whose intensity is significantly reduced at specific frequencies. The frequencies of the reduced intensity vary smoothly over the event duration, forming apparent curves in frequency‐time spectrograms. Events at frequencies higher than the Earth‐ionosphere waveguide cutoff frequency were explained by the interference of the first few waveguide modes of lightning‐generated spherics propagating therein (Záhlava et al., 2015, https://doi.org/10.1002/2015JA021607. Here we present an analysis of events observed at frequencies lower than about 1 kHz. Altogether, we analyze 263 events identified at the times when DEMETER operated in the burst mode. The vast majority of the events (95%) took place during the nighttime, and they occurred more frequently during spring/autumn than during winter/summer. We present an overview of event properties. Moreover, measurements of all six electromagnetic field components performed by DEMETER allow us to perform a detailed wave analysis. It is shown that the emissions propagate with high wave normal angles inclined toward the Earth. We suggest that the events might be due to the wave propagation in the ionospheric waveguide formed around the refractive index maximum at the altitude of about 105 km.