Fixed Center Frequency Research Articles

A Multiband Microwave Photonic Filter Based on a Strongly Coupled Microring Resonator With Adjustable Bandwidth

A bandwidth-tunable multiband microwave photonic filter (MPF) using a strongly coupled microring resonator (MRR) with optical phase modulation is demonstrated theoretically and experimentally. Two notches of the MRR adjacent to the optical carrier break the intrinsic balance of the phase-modulated signal and then two sub-MPFs are formed thanks to the conversion from phase modulation to intensity modulation (PM-IM). The frequency responses of the two sub-MPFs are superimposed to form a passband with a fixed center frequency. Due to the periodicity of the MRR transmission spectrum, multiple passbands separated by a certain spacing appear in the frequency domain and combine to form a multiband MPF, whose bandwidth can be adjusted by tuning the wavelength of the carrier. The tunable bandwidth and shape factors ranging from 0.73 GHz to 2.73 GHz and 5.06 to 1.38 are experimentally performed. The number of passbands can be reconfigured. The proposed multiband MPF has the potential to be employed in modern multi-standard wireless communication systems.

Reconfigurable Half-Mode SIW Antenna Using Uniaxial Field Programmable Microwave Substrate Structure

This communication presents the design and implementation of a beam steerable leaky wave antenna (LWA) based on integrated electronic devices (varactor diodes). The design uses a half-mode substrate-integrated waveguide (HMSIW) where the short-circuited wall or PEC boundary is realized with field programmable microwave substrate (FPMS)-based unit cells. By virtue of placing integrated varactor diodes in these unit cells, the wavenumber and the phase shift of the propagating signal can be controlled. This allows a beam steering of 25° for a fixed center frequency. Furthermore, control of the varactor bias voltages allows a fixed beam direction over a wide frequency bandwidth. An excellent agreement can be observed between the simulated and measured results, validating the first ever FPMS-based reconfigurable antenna design.

Design method of unidirectional wideband SH guided wave phased array magnetostrictive patch transducer

The existing meander coil type SH guided wave electromagnetic acoustic transducer (EMAT) has a fixed center frequency and narrow bandwidth, which cannot quantify the defect size by continuous frequency scanning. Therefore, this study proposes an array of wideband unidirectional SH guided wave magnetostrictive patch transducer and its control method for excitation of unidirectional SH guided waves at random frequencies over a wide frequency range. A narrow magnetostrictive patch and a linear coil are used for each array element to increase the bandwidth of a single element. By controlling the excitation delay and initial phase of each array element separately, the direction of the SH guided wave can be controlled, and its wavelength can be changed without replacing the coil. In addition, a mathematical model of the array sources of finite width is developed to excite unidirectional SH guided waves at different frequencies. Based on this model, the effects of the number, width and distance of the array element on the frequency response characteristics of the transducer array are analyzed. The experiments show that: The proposed transducer array can excite unidirectional SH guided waves of random frequency over a wide frequency range. The amplitude of the guided wave signal on the suppressed side is almost 0, while the signal on the non-suppressed side is significantly increased, leading to a significant improvement in the energy conversion efficiency. The frequency range can be selected by designing the width and distance of array elements, and the experimentally measured frequency response characteristics of the transducer array are highly consistent with the trend of the mathematical model results.

Reconfigurable Single-/Dual-Wideband Bandpass Filters Based on a Novel Topology

Based on a new topology, a series of single-/dual-wideband bandpass filters (SWB/DWB BPFs) with reconfigurable masses of properties are presented. The proposed design starts from a dual-wideband passive filtering structure, which owns five transmission zeros in the stopbands and three transmission poles in each passband. Then, three capacitors are employed as the tuning elements. By controlling these three capacitors, DWB BPFs with different reconfigurable properties, including three independently tunable passband edges, tunable center frequency of lower passband with fixed absolute bandwidth, tunable bandwidth of lower passband with fixed center frequency, and switchable lower passband, can be realized. In addition, SWB BPF with tunable bandwidth also can be achieved by varying the inserted capacitors. For verification, a prototype with different capacitors is designed and fabricated. As the measured and simulated results agree well with each other, a simple design approach of reconfigurable SWB/DWB BPFs can be verified.

Reconfigurable Bandpass Filter With Wide-Range Bandwidth and Frequency Control

In this brief, a novel reconfigurable bandpass filter with adjustable center frequency and wide bandwidth reconfiguration is presented. The proposed bandpass filter is formed by cascading tunable high-pass (HP) and low-pass (LP) filter sections directly. Both the operating frequency and bandwidth of the reconfigurable bandpass filter can be reconfigured independently by tuning the frequencies of the band edges, which are controlled by the cut-off frequency of the HP and LP filter sections. Finally, the proposed filter is designed, fabricated and measured for validation purposes. The measured results demonstrate that the bandwidth can be tuned from 180 MHz to 1390 MHz at the fixed center frequency with tuning ratio up to 7.8:1. Center-frequency agility is also verified with different constant absolute bandwidth of 400 MHz, 600 MHz, and 800 MHz The measured results show that proposed filter possesses the advantages of simple implementation, wide bandwidth tuning range, wide frequency tuning range, and compact size.

Demonstration of Reconfigurable BPFs with Wide Tuning Bandwidth Range Using 3λ/4 Open- and λ/2 Short- Ended Stubs

In this paper, two implementations of reconfigurable bandwidth bandpass filters (BPFs) are demonstrated both operating at a fixed center frequency of 2.4 GHz. The proposed reconfigurable bandwidth filters are based on a square ring resonator loaded with λg/4 open-ended stubs that are permanently connected to the ring and converted to either 3λg/4 open-ended stubs or λg/2 short-ended stubs by means of positive-intrinsic-negative(PIN) diodes to implement two reconfigurable bandwidth states for each case. Due to the symmetrical nature of the design, even- and odd-mode analysis is used to derive the closed-form to describe the reconfigurable filters’ behavior. The switching between narrowband and wideband is achieved using PIN diodes. In the first implementation (λg/4 open-ended stubs to 3λg/4 open-ended stubs), a reconfigurable bandwidth bandpass filter is proposed where additional out-of-band transmission zeros are generated by integrating a λg/2 open-ended stub at the input port. In the second implementation (λg/4 open-ended stubs to λg/2 short-ended stubs), further improvement in the upper stopband is achieved by utilizing a pair of parallel coupled lines (PCLs) as feeding lines and a pair of λg/4 high impedance short-ended stubs implemented at the input and output ports. To verify the validity of the simulated results, the prototypes of the proposed reconfigurable filters were fabricated. For the first case, measured insertion loss is less than 1.8 dB with a switchable 3-dB fractional bandwidth (FBW) range from 28% to 54%. The measured results for the second case exhibit a low insertion loss of less than 1 dB and a 3-dB fractional bandwidth that can be switched from 34% to 75%, while the center frequency is kept constant at 2.4 GHz in both cases.

Design of Notched-Wideband Bandpass Filters With Reconfigurable Bandwidth Based on Terminated Cross-Shaped Resonators

In this paper, a series of novel reconfigurable-bandwidth notched-wideband bandpass filters (NWB BPFs) with controllable notch bands are proposed. The proposed filters start from a passive filtering structure, which is formed by a terminated cross-shaped resonator (TCSR) with a pair of parallel-coupled lines and two open-ended stubs. Theoretical analysis finds that the filter bandwidth can be independently controlled by the TCSR, while the center frequencies and bandwidth of notch bands are mainly controlled by the rest parts. According to this, a BPF with controllable notch bands can be designed. To achieve the reconfigurable-bandwidth NWB BPFs with controllable notch band, whose bandwidth and center frequency can be maintained unchanged under different work states, two PIN diodes and a varactor are employed. By controlling the work states of PIN diodes, three bandwidth states can be achieved with fixed center frequency. By controlling the applied voltage on the varactor, other NWB BPF with independently tunable lower passband edge can be realized. For verification, three prototypes are designed and measured. The measured results agree well with the theoretical analysis and simulated ones, verifying a simple and effective design approach of reconfigurable-bandwidth NWB BPFs.

Sharp Skirt Dual-Mode Bandpass Filter with Overlay Plate to Control Upper Passband Edge

This paper presents design and analytical model for Sharp Skirt Dual-Mode Bandpass Filter for RF receivers. Proposed filter is designed using open stub loaded H shaped resonator. Based on analytical model insertion loss S21 and return loss S11 for proposed filter are demonstrated. Inductive Overlaying plate is proposed to control upper passband edge of proposed filter to improve frequency selectivity with fixed center frequency. The proposed filter has sharp frequency selective range from 5.1GHz to 9.2GHz. With overlay plate, frequency selective range is tuned to 5.1GHz-8.6GHz. Without overlaying plate the proposed filter has return loss greater than 10dB and insertion loss of 0.7dB. Lower and upper passband edges are at 5.1GHz and 9.2GHz with attenuation level of 52dB and 54dB respectively. With overlaying plate, the filter has same S 11 and S 21 parameters, but upper passband edge is shifted from 9.2GHz to 8.6GHz.

Metamaterial absorber with independently tunable amplitude and frequency in the terahertz regime.

A tunable metamaterial absorber is proposed in the terahertz regime. The amplitude and center frequency of the absorber can be tuned independently. Owing to the effective combination of graphene and strontium titanate (STO) in one metamaterial structure, the tunable properties of the amplitude and center frequency are implemented. The amplitude can be tuned by adjusting the chemical potential of graphene sheet, and center frequency can get a shift through temperature changes in the STO material. In a full-wave numerical simulation, the amplitude of the absorber can be tuned from approximately 100% to 35% with a fixed center frequency when chemical potential varies from 0.7 eV to 0.0 eV. The center frequency of the absorber can shift from 0.43 THz to 0.3 THz when temperature changes from 400 K to 200 K. The complex surface impedance of the graphene and permittivity of STO material in this research range are thoroughly examined, and the independently tunable mechanism of the absorber is explored by elucidating the electric field distribution. The influence of the oblique incidence of electromagnetic wave to the absorber is studied. The absorber can be scalable to the infrared and visible frequencies and demonstrates promising application on tunable sensors, filters, and photovoltaic devices.

A fully reconfigurable bandpass-to-bandpass-with-embedded-stopband filter with an ultra-wide 0.09–1.41 GHz bandwidth tuning range

AbstractA varactor-based fully reconfigurable microstrip bandpass-to-bandpass-with-embedded-stopband filter is presented in this paper. This filter offers wide center frequency and bandwidth tuning flexibility under both bandpass mode and bandpass-with-embedded-stopband mode. The entire tuning ability is based on multiple mode resonator theory and external quality factor tuning structure for bandpass mode and the introduction of transmission zeros (TZs) for bandpass-with-embedded-stopband mode. Under the bandpass mode, the center frequency tuning range is 0.96–1.45 GHz and the bandwidth can be tuned from 0.09 to 1.41 GHz with a fixed center frequency at 1.22 GHz. Under bandpass-with-embedded-stopband mode, the center frequency and bandwidth can be tuned from 0.94 to 1.61 GHz and 0.2–0.33 GHz, respectively. Good agreements are shown between simulated and measured results.

A fully reconfigurable bandpass‐to‐notch filter with wide bandwidth tuning range based on external quality factor tuning and multiple‐mode resonator

AbstractA fully reconfigurable microstrip bandpass‐to‐notch filter based on varactors is presented in this article. This filter offers wide center frequency and bandwidth tuning flexibility under bandpass mode and wide notch tuning range under notch mode. The entire tuning ability is based on multiple‐mode resonator (MMR) theory and tunable external quality factor for bandpass mode and the introduction of transmission zero (TZ) for notch mode. Under the bandpass mode, the center frequency tuning range is 0.9 to 1.42 GHz, and the bandwidth can be tuned from 0.09 to 1.44 GHz at a fixed center frequency 1.28 GHz. Under notch mode, the notch can be tuned from 0.98 to 2.02GHz. Good agreement can be observed between simulated and measured results.

A novel dual-band tunable notch filter with controllable center frequencies and bandwidths

This article proposes a new dual-band tunable bandstop filter. This tunable filter is composed of two separate parts, the transmission line, and coupled stubs that each connect to three varactors. The center frequency and bandwidth in each band can be controlled individually. Moreover, the LC equivalent circuit of the proposed filter is calculated, and the results are simulated. In the proposed filter, the simulations show that the first stopband can be tuned in a frequency range from 1.2 to 1.9 GHz with 10-dB absolute bandwidth 310 ± 30 MHz, whereas the second stopband varies from 2.5 to 3.3 GHz with the 10-dB absolute bandwidth 720 ± 20 MHz. These two stopbands can also be tuned independently. Furthermore, the bandwidth of each fixed center frequency can be changed easily. The fabricated proposed filter validates the simulation results. The compact filter has an effective size of 9 × 27.5 mm2.

Reconfigurable Bandwidth Bandpass Filter With Enhanced Out-of-Band Rejection Using $\pi $ -Section-Loaded Ring Resonator

A novel ring resonator bandpass filter with reconfigurable bandwidth with central frequency at 2.4 GHz is demonstrated. Theoretical analysis for computing the resonant frequencies is shown, and the design approach of implementing $\pi $ -section stubs connected to the ring to obtain the bandwidth reconfigurability is explained. The use of reconfigurable $\pi $ -section allows the alteration of the stub’s effective width and therefore the filter’s bandwidth reconfigurability. p-i-n diodes are used as switching elements to achieve the narrowband/wideband response. Coupled line sections are used for suppressing the higher modes by generating out-of-band transmission zeros, resulting in a significantly enhanced out-of-band rejection. Measurements indicate that the 3-dB fractional bandwidth can be switched from 58.5% to 75% at a fixed center frequency of 2.4 GHz with an insertion loss better than 1.1 dB. Moreover, the −20-dB stopband performance is extended to $2.7f_{0}$ .

Hierarchical-Table-Based Model for All-Digital RF Transmitters

Transmitters based on nonlinear radio-frequency (RF) modulators and switched-mode power amplifiers are systems that, at least theoretically, can provide high linearity and energy-efficient generation of RF signals at the same time. However, the nonlinear memory-affected behavior remains an issue hindering practical applications. This paper shows that it is possible to model the nonlinear memory of such circuits based on time-domain observations and how to use this information in computationally efficient time-domain RF circuit models. In contrast to other works, this model covers the full bandwidth of the active device (dc–10 GHz) and it uses hierarchical data structuring to adaptively find a compact model without prior knowledge of the circuit’s memory depth. The data for this work were gained from a laboratory setup, designed to be used as an LTE transmitter for a signal bandwidth of 20 MHz at a fixed center frequency of 2.5 GHz.

Neglect of bandwidth of odontocetes echolocation clicks biases propagation loss and single hydrophone population estimates

Passive acoustic monitoring with a single hydrophone has been suggested as a cost-effective method to monitor population density of echolocating marine mammals, by estimating the distance at which the hydrophone is able to distinguish the echolocation clicks from the background. To avoid a bias in the estimated population density, this method relies on an unbiased estimate of the propagation loss (PL). It is common practice to estimate PL at the center frequency of a broadband echolocation click and to assume this narrowband PL applies also to the broadband click. For a typical situation this narrowband approximation overestimates PL, underestimates the detection range and consequently overestimates the population density by an amount that for fixed center frequency increases with increasing pulse bandwidth and sonar figure of merit. We investigate the detection process for different marine mammal species and assess the magnitude of error on the estimated density due to various simplifying assumptions. Our main purposes are to quantify and, where possible and needed, correct the bias in the population density estimate for selected species and detectors due to use of the narrowband approximation, and to understand the factors affecting the magnitude of this bias to enable extrapolation to other species and detectors.

Neglect of bandwidth of Odontocetes echo location clicks biases propagation loss and single hydrophone population estimates

Passive acoustic monitoring with a single hydrophone has been suggested as a cost-effective method to monitor population density of echolocating marine mammals, by estimating the distance at which the hydrophone is able to intercept the echolocation clicks and distinguish these from the background. To avoid a bias in the estimated population density, this method relies on an unbiased estimate of the detection range and therefore of the propagation loss (PL). When applying this method, it is common practice to estimate PL at the center frequency of a broadband echolocation click and to assume this narrowband PL applies also to the broadband click. For a typical situation this narrowband approximation overestimates PL, underestimates the detection range and consequently overestimates the population density by an amount that for fixed center frequency increases with increasing pulse bandwidth and sonar figure of merit.

A New Fault Diagnosis Method of Adaptive Demodulated Resonance Technique Based on Wavelet Packet in Multi-Information Domains

Fault information is incomplete while using a single information domain fault feature parameters to construct fault feature vector, and demodulated resonance technique have to predetermine resonant frequency and fixed center frequency also has its shortcomings , in order to solve these problems, a new fault diagnosis method is proposed of adaptive demodulated resonance technique based on wavelet packet in multi-information domains. The fault feature vector extracted from multi- information domains is described, signal processing flow of envelope demodulation based on denoising and filtering of wavelet packet is analyzed, the fault diagnosis method of adaptive demodulated resonance technique based on wavelet packet is given, and the method is applied to fault diagnosis of axial piston hydraulic pump. Experiment results show that multi-domain feature vector increases the completeness of the fault information, it is able to obtain good diagnosis effect, and the new fault diagnosis method is able to identify known and unknown faults resonance frequency automatically, the frequency range is narrow, the rate of diagnosis is high.

Bandpass Filter With Tunable Bandwidth Using Quadruple-Mode Stub-Loaded Resonator

In this letter, a novel quadruple-mode resonator bandpass filter (BPF) with tunable bandwidth is proposed. By using two types of microwave varactors to tune the resonant frequencies and transmission zeros (TZs), the high-side edge of the passband and low-side edge of the passband can be separately varied. Therefore, the bandwidth could be tunable with reasonable adjust of the values of varactors. Theoretical expressions have been derived for the resonant frequencies and the TZs. The measured results of the BPF show that the fractional bandwidth can be tuned from 22% to 34% at a fixed centre frequency 2.0 GHz with a return loss better than dB. The tested results show good agreement with simulated results.

Analysis and design of a 1.8–2.7 GHz tunable 8-band TDD LTE receiver front-end

This paper describes the analysis and design of a 0.13 μm CMOS tunable receiver front-end that supports 8 TDD LTE bands, covering the 1.8–2.7 GHz frequency band and supporting the 5/10/15/20 MHz bandwidth and QPSK/16QAM/64QAM modulation schemes. The novel zero-IF receiver core consists of a tunable narrowband variable gain low-noise amplifier (LNA), a current commutating passive down-conversion mixer with a 2nd order low pass trans-impedance amplifier, an LO divider, a rough gain step variable gain pre-amplifier, a tunable 4th order Chebyshev channel select active-RC low pass filter with cutoff frequency calibration circuit and a fine gain step variable gain amplifier. The LNA can be tuned by reconfiguring the output parallel LC tank to the responding frequency band, eliminating the fixed center frequency multiple LNA array for a multi-mode receiver. The large various gain range and bandwidth of the analog baseband can also be tuned by digital configuration to satisfy the specification requirement of various bandwidth and modulation schemes. The test chip is implemented in an SMIC 0.13 μm 1P8M CMOS process. The full receiver achieves 4.6 dB NF, −14.5 dBm out of band IIP3, 30–94 dB gain range and consumes 54 mA with a 1.2 V power supply.

Scintillation statistics of broadband acoustic transmissions in the Gulf of Maine.

Broadband acoustic transmissions from a vertical source array in the 300–1200 Hz frequency range of 1 s duration, with source‐receiver separations ranging from 2 to 20 km measured in the Gulf of Maine, are analyzed. The received signal intensity is shown to follow the gamma distribution, implying that the field has been fully saturated by independent multimodal propagation contributions. The gamma distribution depends on the mean intensity and the number of independent statistical fluctuations of the received signal. The standard deviations of the received broadband signal intensities are found to be a function of center frequencies and bandwidths. For a fixed center frequency, the standard deviation decreases with increasing bandwidth, implying that there are more independent fluctuations in larger bandwidth signals. The measured scintillation statistics are verified with a range‐dependent numerical Monte‐Carlo propagation model incorporating linear internal wave fluctuations in the random waveguide. Further analysis with the model indicates the range‐dependence of broadband signal intensity standard deviations, which increase rapidly from deterministic at the source location to a maximum at roughly 3‐km range and decay gradually afterward. The standard deviation of a short‐duration monotonic signal remains constant at between 5 and 6 dB after a 3‐km range since it contains only one independent fluctuation.