Variation Of Center Frequency Research Articles

Robust reconfigurable radiofrequency photonic filters based on a single silicon in-phase/quadrature modulator

Abstract Combining integrated photonics and radiofrequency (RF) signals in the optical domain can help overcome the limitations of traditional RF systems. However, it is challenging to achieve environmentally insensitive filtering in wireless communications using integration schemes. In this report, the performance of robust RF filters based on a single silicon in-phase/quadrature modulator with significantly improved temperature and optical carrier wavelength sensitivities, which were suppressed by more than three orders of magnitude compared with those of silicon resonators, was experimentally evaluated. Upconversion and the processing of signals were simultaneously realized on the modulator by setting the relative phases of the arms and the bias voltages. Moreover, the filters can be reconfigured as low-pass, high-pass, band-pass, or band-stop filters. From 25 to 75 °C, the center frequency variation was within 0.2 GHz. From 1500 to 1600 nm, the center frequency variation was within 2 GHz. The proposed scheme allows for filtering and reconfiguration without the use of optical processing modules such as resonators or delay lines, thus providing a novel approach to signal processing and a new robust filter for scenarios with dynamic environments.

A specialized partial discretized optimization algorithm for SLL suppression in FSS design

Side Lobe Level (SLL) suppression is a challenging but essential part of frequency selective surface (FSS) structural design. The SLL of the radiation pattern is a key parameter demonstrating the directional anti-interference ability and mainly depends on the geometry of the FSS. However, the correlation between SLL and FSS structural parameters is extremely complicated. A minor FSS structure change may result in a drastic diversion in the sidelobe’s direction or level, making the SLL the most difficult parameter to optimize. In this paper, an efficient optimization method specifically for SLL suppression is proposed. We discretized the edges of split square ring FSS structures by binary representation and generated new patterns based on the genetic algorithm. Optimization results showed that in the most optimal structure, the SLL was −23.41 dB, exhibiting a 5.17 dB reduction. Meanwhile, the center frequency variation was less than 2%. Moreover, the computation time cost was reduced by over 90% compared with that of the fully discretized pattern optimization method, showing that this novel method was truly effective in getting SLL suppressed FSS structures.

Multiple Narrowband Interferences Characterization, Detection and Mitigation Using Simplified Welch Algorithm and Notch Filtering

By increasing the demand for radio frequency (RF) and access of hackers and spoofers to low price hardware and software defined radios (SDR), radio frequency interference (RFI) became a more frequent and serious problem. In order to increase the security of satellite communication (Satcom) and guarantee the quality of service (QoS) of end users, it is crucial to detect the RFI in the desired bandwidth and protect the receiver with a proper mitigation mechanism. Digital narrowband signals are so sensitive into the interference and because of their special power spectrum shape, it is hard to detect and eliminate the RFI from their bandwidth. Thus, a proper detector requires a high precision and smooth estimation of input signal power spectral density (PSD). By utilizing the presented power spectrum by the simplified Welch method, this article proposes a solid and effective algorithm that can find all necessary interference parameters in the frequency domain while targeting practical implantation for the embedded system with minimum complexity. The proposed detector can detect several multi narrowband interferences and estimate their center frequency, bandwidth, power, start, and end of each interference individually. To remove multiple interferences, a chain of several infinite impulse response (IIR) notch filters with multiplexers is proposed. To minimize damage to the original signal, the bandwidth of each notch is adjusted in a way that maximizes the received signal to noise ratio (SNR) by the receiver. Multiple carrier wave interferences (MCWI) is utilized as a jamming attack to the Digital Video Broadcasting-Satellite-Second Generation (DVB-S2) receiver and performance of a new detector and mitigation system is investigated and validated in both simulation and practical tests. Based on the obtained results, the proposed detector can detect a weak power interference down to −25 dB and track a hopping frequency interference with center frequency variation speed up to 3 kHz. Bit error ratio (BER) performance shows 3 dB improvement by utilizing new adaptive mitigation scenario compared to non-adaptive one. Finally, the protected DVB-S2 can receive the data with SNR close to the normal situation while it is under the attack of the MCWI jammer.

Aplicación de metamateriales para estimar índices de refracción

Se presenta el desarrollo de un metamaterial para estimar el índice de refracción en líquidos. El metamaterial se desarrolló insertando celdas cilíndricas en el plano de tierra de una línea microcinta, cintas estas que forman una estructura de brecha de banda electromagnética (electromagnetic bandgap, EBG). Dentro de las celdas se depositaron líquidos con índices de refracción estimados en el laboratorio. Se evaluaron los parámetros de dispersión S21 y S11 mediante simulaciones electromagnéticas con modelos desarrollados, y de forma experimental, con prototipos fabricados. Se analizó la variación de la frecuencia central, el ancho de banda y el nivel de pérdidas por inserción de la brecha de frecuencias generada como respuesta a la variación del índice de refracción del material depositado dentro de las celdas. Los resultados obtenidos muestran que es posible estimar el índice de refracción de materiales monitoreando la frecuencia de resonancia o el nivel de pérdidas por inserción de la brecha generada. El metamaterial desarrollado es fácil de construir y su desempeño es adecuado en el rango de las microondas. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat.

Comprehensive Performance Evaluation of Computationally Efficient Discrete Fourier Transforms for Frequency Estimation

In this paper, the design of frequency-locked loop (FLL) is proposed based on computationally efficient discrete Fourier transform (DFT) structures. In recent years, the DFT structures are evolved as sliding DFT (SDFT), modulated SDFT, hopping DFT (HDFT), modulated HDFT, and sliding-windowed infinite Fourier transform. Considering their tuned filter characteristics, an attempt has been made to obtain a solution for the instantaneous frequency estimation problem of the input signal under varying center frequency condition. In each DFT structure, the $k$ th bin in-phase and quadrature components are separated for instantaneous signal extraction. The feedback loop is designed around these DFT structures, and it was observed that the frequency responses exhibit flat magnitude and phase interestingly when compared with the open-loop structures. Hence, an adaptive sampling frequency adjustment scheme is proposed for these structures as FLL to estimate the instantaneous frequency of the input signal for the wide variation in center frequency. These FLLs with different DFT structures are tested for dynamic performance and wide operating range. The proposed FLLs are implemented in field-programmable gate array (FPGA), and the experimental investigations have been carried out for frequency estimation. Further experimental investigations on these FLLs as a system on chip were carried out with area and power analysis.

Process optimization and device variation of Mg-doped ZnO FBARs

Thin film bulk acoustic resonator (FBAR) plays a very important role in radio frequency (RF) filters used in cell phone and other wireless systems. Although FBAR is commercialized, the design/process interactions on the frequency response variation in FBAR device are still lacking. Design and fabrication are two crucial aspects affecting FBAR device performance. In this report, various solidly mounted resonators (SMR) were designed, fabricated and analyzed to study wafer-level site-to-site RF variation on design and fabrication process. As a key process step for SMR FBAR, the optimization process of Mg-doped ZnO piezoelectric thin film deposition was studied by varying thin film sputtering conditions using various sputtering targets and by post annealing treatment after the deposition. The quality of this crucial layer was verified by XRD on its (0 0 2) crystallization and wafer-level FBAR RF characterization. FBAR devices with high quality were fabricated with an excellent resonant behavior near 2 GHz and a maximum return loss of −15 to 25 dB. Quality factor Q ranges from 400 to 800, with a coupling coefficient keff2 of 1.5–3%. Wafer-level and wafer-to-wafer variation of central frequency are within 1.8–2.1 GHz. Computer simulation verified that this frequency variation correlates to the piezoelectric film variation of 1.6–1.9 μm. Process control on this piezoelectric thin film is essential to maintaining the resonator frequency-controlled value when building duplexer RF circuits. The dependency of RF performance on FBAR size, density and orientation is not obvious, compared to that of the wafer-level FBAR device variation on fabrication process. Regarding to the Mg-doping effect in MgxZn1-xO piezoelectric film, the amount of Mg in MgxZn1-xO film during the sputtering process must be properly controlled within 30% to keep the piezoelectric quality. The average acoustic speed of the Mg-doped ZnO film is 6870 m/s with the estimated range of 5760–7980 m/s, which is better than that of pure ZnO film (6330 m/s).

High-Resolution Dielectric Sensor Based on Injection-Locked Oscillators

The structure of a high-resolution microwave material sensor is presented based on the injection locking phenomenon. For a sample under test, the variation of center frequency and lock range of the oscillator with respect to a reference sample are measured to indicate the resonance frequency and quality factor of the resonator. A low power level and low phase noise injection locking can significantly reduce the lock range of the oscillator. Therefore, even small variations in the loop filter of the oscillator change the response and can be determined with a high sensitivity. The unknown sample is characterized based on the measured center frequency and quality factor of the resonator. An output power control (OPC) system increases the dynamic range of the sensor with respect to the dielectric constant of samples. Moreover, a method of material detection in the microwave frequency is proposed based on data from the OPC to eliminate the frequency analyzer from the system for Internet of Things (IoT) applications. As an example for validation, a 1-GHz sensor is fabricated and the measurement results are presented.

Tuning of Multiple Parameters With a BIST System

This paper presents a low-power built-in self-test system to compensate for mismatch and variations in CMOS IC. The system is designed and compiled on a low-power field programmable analog array (FPAA) fabricated on a 350-nm CMOS process. A second-order bandpass filter is used as a device under test. A set of 12 parallel filter banks are compiled on three different FPAA chips and compensated for local mismatch and variations in the bias current, and mismatch in parasitic and routing capacitances. The bandpass filters are biased in subthreshold regime and the system of 12 parallel filter banks consumes a power of $7.072~\mu \text{W}$ . The proposed tuning algorithm reduces variation in center frequency to 5.07% compared with a variation of 10.16% when they are not tuned, variation in quality factor to 8.52% from 13.86%, and variation in the gain at the center frequency to 3.83% from 21.04%. These values are deviation of the parameters from its mean for the data taken from three different FPAA chips fabricated on the same wafer.

A Power-Line Interference Canceler Based on Sliding DFT Phase Locking Scheme for ECG Signals

A power-line interference (PLI) removal method is proposed based on a previously published sliding discrete Fourier transform (SDFT) phase locking scheme (PLL), which extracts the nonstationary sinusoids from the electrocardiogram (ECG) signal. The proposed PLI canceler consists of SDFT PLL as a vital element, which can track the variation in center frequency of the PLI either 50 or 60 Hz. The PLI canceler involves the adaptive sampling frequency control in which the sampling frequency of SDFT filter is adaptively adjusted according to the center frequency variation of the interference. Since the in-phase and quadrature components of SDFT filter can provide instantaneous sinusoidal and cosinusoidal interference signals, the SDFT PLL is capable of tracking amplitude, phase, and frequency of the interference. Additional resonators of different bin indices are augmented with SDFT PLL to handle the dominant odd harmonics of PLI. Furthermore, the SDFT PLL is cascaded with another SDFT bin to eliminate the baseline wander present in the real-time ECG signal. The adaptive PLI canceler based on SDFT PLL offers the tracking capability of variant PLI, attenuation of 40 dB, less acquisition time of 0.2 s for a variant PLI of ±5 Hz, removal of dominant odd harmonics, and baseline wander with expense of sampling frequency. Experimental results prove the efficacy of the proposed method in nonstationary sinusoidal interference extraction. Experimental investigation on SDFT PLL using field programmable gate array demonstrates the feasibility of digital implementation of the proposed algorithm.

Multiband center-frequency estimation for robust speckle tracking applications

Speckle tracking is widely used for the detection and estimation of minute tissue motion and deformation with applications in elastography, shear-wave imaging, thermography, etc. The center frequency of the echo data within the tracking window is an important parameter in the estimation of the tissue displacement. Local variations in this quantity due to echo mixtures (specular and speckle components) may produce a bias in the estimation of tissue displacement using correlation-based speckle tracking methods. We present a new algorithm for estimation and tacking of the center frequency variation in pulse-echo ultrasound as a quantitative tissue property and for robust speckle tracking applications. The algorithm employs multiband analysis in the determination of echo mixtures as a preprocessing step before the estimation of the center frequency map. This estimate, in turn, is used to improve the robustness of the displacement map produced by the correlation-based speckle tracking. The performance of the algorithm is demonstrated in two speckle tracking applications of interest in medical ultrasound: (1) ultrasound thermography and (2) vascular wall imaging.

Miniaturized Superconducting K-Band Bandpass Filter

A novel high-temperature superconducting (HTS) microstrip K-band filter is designed, fabricated, and measured. The Chebyshev filter has five poles and is designed for the center frequency of 20.45 GHz with a percentage bandwidth of 2.5%. The proposed miniaturized resonator minimizes the unwanted coupling between nonadjacent resonators, which is typically pronounced at high frequencies. The layout is patterned on a 0.5-mm-thick MgO substrate. The dimension of the fabricated filter is 7.5 mm × 3 mm. The filter employs a via-less Coplanar Waveguide to microstrip transition and the layout is configured to allow ease of adjusting and tuning. The filter with via-less Coplanar Waveguide input/output pads is measured in an RF cryogenic probe station at 77 and 4 K to investigate variation of center frequency with operating temperatures. Simulation and measured results of the filter show a spurious-free response up to 35 GHz.

Ultrasound Diagnostic Flow Imaging with Coded Excitation

Diagnostic ultrasound flow imaging is performed with coded excitation pulses. Due to the use of frequency coded excitation pulses, flow information may suffer from spatial misregistration and estimate errors. Spatial position shift in flow data is offset for alignment with B-mode or other imaging. The flow estimates are compensated for the imaging center frequency variation with depth. The wide bandwidth information available due to coded excitation may allow anti-aliasing by estimating velocities from two frequency bands.

스텝 Perturbation의 영향에 따른 주기적 스텝 임피던스 링 공진기의 해석 및 이중 모드 대역 통과 필터의 적용

Dual-mode bandpass filter was designed by using periodic stepped impedance ring resonator with step perturbation. The periodic stepped impedance ring resonator has the effects of size reduction and harmonic suppression by changing characteristic impedance ratio. The perturbation for dual-mode generation was also easily controlled by characteristic impedance ratio, and the variation of dual-mode resonant frequencies and attenuation pole frequencies were analyzed by the effect of step perturbation. Chip capacitors were used for input/output coupling, and the variation of center frequency by the coupling capacitance and step perturbation was also considered. From the results, two types of 2 GHz dual-mode bandpass filter were fabricated in size of , those have different attenuation poles and bandwidths. The measured results of proposed bandpass filters showed a good agreement with the calculated estimations, and those have insertion loss of 2.52, 0.52 dB and 3 dB bandwidth of 4.03, 15.02 %, respectively.

Correction for nonstationarity and window broadening in Doppler spectrum estimation

The width of the time-varying spectrum of signals from the pulsed Doppler ultrasonic blood flow detector is overestimated as a result of window and nonstationarity broadening when analyzed using the conventional short-term Fourier transform (STFT). By deriving the broadening function width from a consideration of signal phase variation arising from the deterministic spectral center-frequency variation during each window, the increase In the root-mean-squared (RMS) spectral width can be calculated and the spectral width estimation corrected. Using this procedure on simulated Doppler signals of known characteristics, a significant reduction in spectral width estimation error can be demonstrated.

Effect of trial-by-trial variation in center frequency on detection of interaural temporal and intensitive differences in bands of noise.

Sensitivity to interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) was measured as a function of duration in conditions where the center frequency (CF) of the stimuli was constant and, separately, in conditions where the CF of the stimuli was varied on a trial-by-trial basis. Stimuli were bands of noise centered at either 300, 1200, 2400, or 4800 Hz with the bandwidth of the noise being 40% of their CF. The largest effects of shortening duration and varying center CF of the stimuli were degradations of sensitivity to ITDs for stimuli centered at 2400 or 4800 Hz. Overall, the data confirm and extend previous findings which indicate that ITDs and IIDs are processed separately within the central nervous system.

Adaptive digital notch filter design on the unit circle for the removal of powerline noise from biomedical signals

This paper investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz, three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared (CLMS) algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal.

A comparison of Ku‐band Doppler measurements at 20° incidence with predictions from a time‐dependent scattering model

The analysis of coherent Ku‐band radar data measured from the Chesapeake Bay Light Tower as part of the SAXON Experiment in September‐October 1988 is discussed. We concentrate on a 20‐min data segment collected at an incidence angle of 20° for both V‐V and H‐H polarization. Average Doppler spectra are estimated for each second of the data. These Doppler spectra show a large variation in center frequency and relative power due to the influence of the longwave surface on the backscattered field. The basic assumptions and approximations used in the formulation of a time‐dependent scattering model are briefly presented, and concurrent measurements of the longwave surface spectrum at the tower are input into this model in order to calculate the expected mean Doppler spectra. These calculated spectra show very good agreement with the measurements. Implications of the measurements and calculations concerning future experiments and refinements to the model are also discussed.

A high-Q temperature insensitive bandpass filter using the operational amplifier pole

A bandpass filter using only two resistors and two operational amplifiers is suggested. The circuit has a Q equal to the ratio of the ressistors. While Q and gain are insensitive to temperature variations, the variations in center frequency is minimized uing a compensation scheme.

Investigation of Microstrip Applications for Varactor-Tuned UHF Tuners

The use of microstrip with varactor diodes to construct a UHF tuner for commercial television receivers is a marked departure from previous exploitations of microstrip. Usually, it has been used for network elements in broadband applications with fixed center frequency. Such applications are diametrically opposed to the conditions in UHF receivers, where fractional bandwidths less than 5% are required over nearly an octave variation of center frequency. The scope of this paper is a discussion of the most fundamental problems associated with microstrip in varactor-tuned UHF tuners. These problems are as follows: 1. Determination of parametric relationships 2. Delineation of device limitations 3. Formation of an approach to preselection

Transistorized 2-24 channel carrier telegraph equipment

The transistorized 2×24-channel carrier telegraph equipment consists of two FM (frequency modulation) type 24-channel systems in a bay, as recommended by the CCITT (International Telegraph and Telephone Consultative Committee). Taking account of the major weakness of the transistor circuit and of the center frequency variation of the FM system caused by temperature rise, the various parts and circuits have been specially designed, including, for example, the use of afc (automatic frequency control), electronic relay, and special circuits for the oscillator and discriminator. This paper describes these features and characteristics.