Tunable Bandwidth Research Articles

A Method of Tuning Frequency in S-Band Continuous-Wave Magnetron

An effective method of tuning the frequency of magnetron is studied in this article. The frequency-agile technique is based on changing the structure of the resonator by tuning elements. First, the working principle of this frequency-agile technique for changing an anode structure is proposed and simulation analysis suggested the good performance of this device. Next, a 3-D particle-in-cell simulation analysis is implemented to predict a frequency-adjustable magnetron with an output power of 2 kW, a mode separation of 50%, an efficiency of 67.7%, a bandwidth of 65 MHz, and a sinusoidal modulated signal. It was found in an experiment that our proposed prototype magnetron has a tunable bandwidth which meets with the simulation results. This effective method has a great potential for application in the frequency-agile magnetron.

On-Demand Storage and Retrieval of Microwave Photons Using a Superconducting Multiresonator Quantum Memory.

We realize on-demand storage and retrieval of weak coherent microwave photon pulses at the single-photon level. A superconducting multiresonator system which is composed of a set of frequency-tunable coplanar waveguide resonators is implemented as the quantum memory. By dynamically tuning the resonant frequencies of the resonators, we achieve tunable memory bandwidth from 10 to 55MHz, with well preserved phase coherence. We further demonstrate on-demand storage and retrieval of a time-bin flying qubit. This result opens up a prospect to integrate our chip-based quantum memory with the state-of-the-art superconducting quantum circuit technology for quantum information processing.

RF Co-Designed Bandpass Filter/Circulator With Tunable Center Frequency, Bandwidth, and Out-of-Band Isolation

This letter reports on a new type of miniaturized RF co-designed bandpass filter/circulator (BPFC). Miniaturization is achieved by: 1) capacitively loading a multi-mode ferrite-based disk resonator; 2) combining the function of an RF circulator and a bandpass filter (BPF) within the volume of a single microwave component; and 3) by tuning its transfer function. The proposed BPFC exhibits a quasi-elliptic power transmission response in the forward direction-passband in-between four transmission zeros (TZs)-and an all-stop response in the reverse one. Reconfigurability is achieved by tuning the capacitive loads of the ferrite disk and the mixed electromagnetic coupling elements in the RF input/output. For proof-of-concept validation purposes, an S-band tunable prototype was designed, built, and measured. It demonstrated multiple levels of tuning. These include the frequency tuning of 1.27:1, the bandwidth tuning of 1.73:1, the out-of-band isolation tuning, and intrinsic switching-off.

A General Variable Bandwidth Microring Filter for Lossless Bandwidth Tuning

We propose a general variable bandwidth filter of arbitrary even order based on the sum-difference microring filter architecture. The filter bandwidth can be varied by tuning only the resonant frequencies of the microrings and thus do not require additional controls other than those used to tune the filter center frequency. In addition, we show that there exists a bandwidth tuning range over which the filter exhibits no extra insertion loss and no degradation in the filter shape. We demonstrated a 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order variable bandwidth filter in Silicon-on-Insulator, achieving a bandwidth tuning range from 0.3 nm to 1.35 nm with a maximum in-band ripple of 3 dB. The proposed variable bandwidth filter could serve as a key element in elastic optical networks which can support variable data bandwidth allocation on demand.

Model detection and variable selection for mode varying coefficient model

Varying coefficient model is often used in statistical modeling since it is more flexible than the parametric model. However, model detection and variable selection of varying coefficient model are poorly understood in mode regression. Existing methods in the literature for these problems are often based on mean regression and quantile regression. In this paper, we propose a novel method to solve these problems for mode varying coefficient model based on the B-spline approximation and SCAD penalty. Moreover, we present a new algorithm to estimate the parameters of interest, and discuss the parameters selection for the tuning parameters and bandwidth. We also establish the asymptotic properties of estimated coefficients under some regular conditions. Finally, we illustrate the proposed method by some simulation studies and an empirical example.

Wideband switch enhanced by photonic crystal waveguide with graphene nanosheet heater

A compact wideband optical switch assisted by graphene nanosheet heater is demonstrated by shifting the bandedge of the photonic crystal waveguides (PhCWG) through current-induced heating. The high heating efficiency of graphene and the high light-matter interactions in slow-light PhCWG are combined to enhance the heating efficiency and extinction ratio. The extinction ratio is increased from 15 dB to 22 dB and the tuning bandwidth is up to 20 nm with only 28 K temperature change. Our measurements match well with simulation results, suggesting an effective way for CMOS compatible chip-scale integrated graphene microheater switch.

A Frequency Reconfigurable Antenna based on Few Layer Graphene

In this paper, a frequency reconfigurable antenna was presented. This antenna is made up of a square loop and a microstrip line with a gap, in which the few layer graphene (FLG) sheet is located to achieve frequency reconfigurable. FLG is likes a lumped resistor with resistance. And the surface impedance can be adjusted by applying a direct current bias voltage, which obtains two work modes that imitate switch. Additionally, the experimental evidence show the proposed frequency reconfigurable antenna can provide a tunable bandwidth.

Quantum dot membrane external-cavity surface-emitting laser at 1.5 μm

A membrane external-cavity surface-emitting laser (MECSEL) with an InAs/InP quantum dot (QD) based gain region is demonstrated. The pumping scheme employs a 90° off-axis parabolic mirror to focus the diode laser pump beam to a nearly circular pump spot. With this pump arrangement, the QD MECSEL with SiC heat spreaders produced 320 mW output power at room temperature with direct emission in the near-infrared at 1.5 μm. We report a record value of 86 nm for the tuning range at this wavelength region, owing to a broad QD gain bandwidth and wide tunability in MECSELs.

Antenna-integrated silicon–plasmonic graphene sub-terahertz emitter

Photo-mixing with its advantages of ultra-large bandwidth and precise tunability has emerged as an important technique for terahertz (THz) wave generation. Recently, graphene photodetectors exhibiting a large bandwidth are expected to further boost the development of integrated THz emitters. Here, we fabricate a sub-THz emitter based on a large-bandwidth silicon–plasmonic graphene (SPG) photodetector integrated with a broadband rounded bow-tie THz antenna. The SPG sub-THz emitter is experimentally demonstrated to emit sub-THz waves with a radiation spectrum from 50 to 300 GHz. A maximum sub-THz emission power of 5.4 nW is obtained at 145 GHz with only 3 mW input light power. The SPG sub-THz emitter can be fabricated by a CMOS-compatible process, which offers enormous opportunities for its use in a variety of THz applications.

A microstrip bandpass filter with tunable bandwidth and center frequency

AbstractThis paper presents a bandwidth and center frequency tunable bandpass filter with wide tuning range. The proposed filter employs two cascade cross‐shaped resonators. The cross‐shaped resonator can generate two independent tunable transmission zeros by introducing two microwave varactors. The center frequency and bandwidth can be tuned by adjusting the DC bias voltages applied to the varactors. For demonstration, a filter example was designed, fabricated and measured. The tuning 3‐dB bandwidth from 20% to 30% is achieved when the center frequency is tuned from 3.5 to 5 GHz. Meanwhile the insertion loss is less than 4 dB with a high selectivity. The size of the filter is 0.32λg × 0.36λg where λg is the guided‐wavelength at the center frequency.

Reconfigurable diplexer using hybrid couplers and perturbed TE012 cavities

AbstractA continuously tunable Ku-band waveguide diplexer is proposed in this paper. This diplexer is based on a hybrid coupler topology and is composed of an input filter centered at 11.9 GHz with a 200 MHz bandwidth, a pair of ladder-type hybrid couplers, and a pair of tunable filters. This diplexer can provide two bandpass channels (channels 1 and 2) that can continuously go from a state where the bandwidths of channels 1 and 2 are maximum (up to 140 MHz) and minimum (down to 40 MHz), respectively, to another configuration where the bandwidth of channel 1 is the largest and the bandwidth of channel 2 is the narrowest. We propose a tunable filter based on TE012 mode circular cavities that are perturbed by low-loss dielectric inserts to obtain such performance. The resonant frequency of these cavities can be continuously tuned between 11.8 and 12 GHz due to the linear movement of the dielectric perturber. The design process for these components is presented and a breadboard device has been manufactured and measured to prove the concept. Different measured configurations of the diplexer are demonstrated, showing that the 200 MHz operating bandpass between 11.8 and 12 GHz can be efficiently separated into two tunable channels. The measured bandwidth of channels 1 and 2 in the manufactured diplexer can be tuned from 135 to 40 MHz (and vice versa) while maintaining an average guard band between the channels of approximately 26 ± 7 MHz. The obtained bandwidth tuning ratios are 3.2 for the highest channel and 3.1 for the lowest channel.

Compact bandwidth tunable IF filters for reconfigurable converters

AbstractThis paper aims to present some outcomes from a European Space Agency (ESA) Technology Research Programme (TRP) project on R&amp;D of new design techniques, concepts, and filtering configurations for tunable IF (intermediate frequency) filters with a compact footprint, wide bandwidth tuning range (covering from 49 to 478 MHz at f0 = 1 GHz) as well as equivalent high-Q performance (i.e. low insertion loss variation and high selectivity by using low-Q resonators). In order to obtain a wide tuning range, the proposed filtering configuration utilizes a new tuning technique that only necessitates control of coupling values with simple DC control circuits, without the need of tuning the electrical length of resonators to avoid deviating the center frequency. Furthermore, in order to achieve the equivalent high-Q performance, a novel lossy technique by using a centrally resistor-loaded half-wavelength resonator is adopted. For the proof of concept, a six-pole prototype filter is designed, fabricated, and tested.

Linear and Nonlinear Characteristics of a Low-Voltage Gyrotron Backward-Wave Oscillator in the Subterahertz Range

Gyrotrons operating at low voltage are highly attractive for subterahertz applications because such an operation can greatly reduce the size and cost of gyrotron systems. Among the oscillator versions of gyrotrons, the gyrotron backward-wave oscillator (gyro-BWO) features continuous frequency tuning in a broadband. This study investigates the characteristics of the beam-wave interaction in a low-voltage gyro-BWO in the subterahertz wave range. Operation at lower voltages has the advantage of a broader frequency tuning range and the suppression of negative $k_{z}$ competing modes. The phenomenon of a sharp increase in the start-oscillation current near the lower limit of the operating voltage is investigated. In addition to the linear characteristics, the dependence of the efficiency and tuning bandwidth on voltage is analyzed. The potential performance of a low-voltage gyro-BWO is predicted using the existing beam parameters: beam voltage of 2 kV, beam current of 0.2 A with a velocity ratio of 1.0, and axial velocity spread of 20%. Although the gyro-BWO operating at 2 kV exhibits the problem of low efficiency (an efficiency of 5.6%), it has a broad frequency tuning range of 3.0 GHz. The efficiency can be enhanced to 15% (a peak power of 60 W) by tapering the waveguide radius. Possible competing modes in low-voltage operation are considered and a stability analysis reveals stable operation.

A Cascaded Tunable Wide Stop Band Frequency Selective Surface with High Roll-off Band Edge

A Cascaded Tunable Wide Stop Band Frequency Selective Surface with High Roll-off Band Edge

Optically switchable broadband metasurface absorber based on square ring shaped photoconductive silicon for terahertz waves

We numerically demonstrate an optically switchable broadband metasurface absorber (MSA) structure based on planar patterned photoconductive silicon (Si) in terahertz (THz) region. The designed MSA is composed of planar-square-ring-shaped (PSRS) structure photoconductive Si array placed over a ground-plane separated by a dielectric substrate. The electric conductivity of the PSRS Si array can be controlled through the external optical pump beam. Through adjusting the electrical conductivity of the Si array, the structure can realize a switching absorption from 2.8% to 99.9%, and the relative bandwidth of the continuous absorption of 90% is tuned from 16.2% to 86.4%. Thus, the corresponding modulation depth of the proposed structure is up to 97.2%, and frequency tuning bandwidth of the continuous absorption of 90% is about 81.25%. The broadband stronger absorption of the structure mainly originates from the excitation of the fundamental dipolar mode. In addition, this design is polarization-independent and wide angles for both incident transverse electric (TE) and transverse magnetic (TM) waves. The Fabry-Pérot interference theory is used to analyze the operation mechanism of the structure, and the theoretical results agrees well with simulations. Furthermore, the broadband absorption properties can be adjusted by varying the geometric parameters of the structure. Due to its excellent optically switchable response, the proposed structure may find potential applications in dynamic functional THz devices, such as modulators, switches, reflector and absorber.

Multi-Band LFM Signal With Unidentical Bandwidths Subjected to Optical Injection in a DFB Laser

This letter demonstrates a tunable multi-band linear frequency modulation (LFM) signal with improved and unidentical bandwidths subjected to optical injection in a distributed-feedback (DFB) laser. In the proposed scheme, an optical beam is divided into two paths, one modulating with a baseband LFM signal and another with a power-varying signal. The basic principle of the proposed scheme is the optical beating of the carrier-suppressed $\pm 1^{\text {st}}$ sidebands in one path and the red-shifted emission mode of the DFB laser after optical injection in another path. In the experiment, the generated three LFM signals have the bandwidths of 11.5 GHz (from 23.0 to 34.5 GHz), 7.5 GHz (from 15.0 to 22.5 GHz), and 4 GHz (from 8.0 to 12.0 GHz) in one period of $1~\mu $ s. Moreover, we analyze the effect of the injected beam’s frequency and power on the bandwidth tunability of the generated LFM signals.

Frequency controlled intelligent standalone RF sensor system for dispersive material testing

An artificial neural network (ANN) based frequency controlled automated RF sensor system for the characterization of dispersive liquids is presented. The frequency of the designed structure is electronically controlled by varying the applied reverse-biased voltage to the complementary split ring resonator (CSRR) attached varactor diode. A hybrid modelling approach has mainly been devised to account for the effects of biasing circuitry and the parasitic elements. The designed RF sensor can provide a relatively higher tuning bandwidth (800 MHz) for applied DC biasing voltage of 0–25 V. The proposed sensor system employs an artificially intelligent feed-forward neural network architecture, which is trained by the Levenberg–Marquardt training algorithm for the complex permittivity estimation in the designated frequency band with reasonable accuracy. It employs the Bayesian Regularization for better input–output correlation and system performance. The ANN based characterization algorithm is integrated with a graphical user interface (GUI) and implemented using MATLAB.

High-order and tunable balanced bandpass filters using mixed technology resonators

AbstractThis paper reports on high-order balanced bandpass filters (BPFs) that are continuously tunable in terms of frequency and bandwidth and can be intrinsically switched-off. They use a hybrid integration scheme based on two different types of capacitively loaded resonators—ceramic coaxial and microstrip—that reduce the filter size, enhance its out-of-band selectivity and common-mode suppression, and allow for multiple levels of transfer function tuning. High selectivity is obtained in the differential mode due to the high number of poles and transmission zeros present. The common mode is highly suppressed through the introduction of additional transmission zeros and resistively loaded resonators. Furthermore, the use of ceramic coaxial resonators results in supplementary transmission zeros that are used to lower the out-of-band transmission in the differential mode. Multiple levels of tuning are obtained by reconfiguring only the frequency of the BPF's resonators. For experimental validation, a tunable mixed-technology microstrip prototype was manufactured and measured at S-band. It exhibited frequency tuning between 2.22 and 2.94 GHz, bandwidth tuning between 104 and 268 MHz, and an intrinsically switched-off mode with isolation &gt;50 dB in the differential mode. For all states, the common mode was suppressed by at least 35 dB at the center frequency and within a wide range.

Novel Reconfigurable Full-Metal Cavity-Backed Slot Antennas Using Movable Metal Posts

Novel design concept of reconfigurable full-metal cavity-backed slot antennas (CBSAs) using movable metal posts is proposed in this article. It is found that the cavity mode with purely directional electric field is only affected by the metal post to be placed in parallel to its electric field. Thus, two orthogonal cavity modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> can be perturbed by two respective metal posts so as to independently tune the resonant frequencies of these two modes. Electromagnetic energy of the cavity modes can be radiated out through the slots on the top wall of the cavity. In this context, reconfigurable slot antennas with different functionalities, such as single-band, dual-band, dual-mode wideband, the tunable frequency with constant bandwidth, and tunable bandwidth with constant frequency, are thus constituted to demonstrate its attractive design feasibility. The frequency-reconfigurable cavity-back slot antenna with movable metal posts is proposed for the first time. The utilization of the metal posts allows us to achieve a continuous frequency tuning property, while the full-metal structure of the proposed antenna holds a high power-handling capacity and a high radiation efficiency. In final, a prototype of the dual-mode wideband slot antenna is designed, fabricated, and tested to reveal its total efficiency higher than 88% and stable radiation pattern over the tuning band. Good agreement between the measured and the simulated results well validates the presented design concept.

State-resolved rotational distributions and collision dynamics of CO molecules made in a tunable optical centrifuge.

State-resolved distributions and collision dynamics of optically centrifuged CO molecules with orientated angular momentum are investigated by probing the CO J = 29-80 rotational levels using high-resolution transient IR absorption spectroscopy. An optical centrifuge with tunable bandwidth is used to control the extent of rotational excitation in the sample. The rotational distributions are inverted with a maximum population in J = 62. Rotational levels with J > 62 have populations that correlate with the intensity profile of the optical trap. The full bandwidth trap excites CO up to the J = 80 level, while J = 67 is the highest level observed in the reduced bandwidth trap. Polarization-sensitive transient spectroscopy shows that the initial orientational anisotropy is r = 0.8 for levels with J ≥ 55, while anisotropy values are near r = 0.4 for levels with J < 50. The rotational distribution for J > 50 is broadened slightly by collisions, consistent with small |ΔJ| propensity rules for rotational energy transfer. Doppler-broadened line profiles show that the J = 60-80 levels have translational temperatures near Ttrans = 300 K and that these temperatures remain constant for as much as 24 gas kinetic collisions. Doppler linewidths for levels with J < 60 are broadened by non-resonant rotation-to-translation energy transfer. Kinetic analysis of transient signals shows that collisions with thermal bath molecules are the predominant relaxation pathway.