Dual-band bandpass filters with high isolation using coupled lines

Two novel second-order dual-band bandpass filters (BPFs) with high isolation and high selectivity using coupled lines are realised with a T-shaped bandstop structure. The centre frequencies of the two dual-band BPFs can be adjusted to the desired values by changing the coupling coefficients and characteristic impedances of the two transmission paths. Two dual-band BPFs located at 1.87 and 2.53 GHz and 1.9 and 2.42 GHz are designed and fabricated for demonstration. Good agreements can be observed between simulated and measured performances.     

HIGH SELECTIVITY SC BANDPASS FILTERS WITH LESS CAPACITOR SPREAD

Two novel switched-capacitor(SC)bandpass filters using a single operational am-plifier(op amp)are presented.Optimal designs for minimizing capacitor spread are also given.Gain-bandwidth product(GB)effects of op amps on the proposed SC circuits are taken intoconsideration.Comparisons with the proposed circuits and the circuits given by the literatureshow that the new circuits require less chip area in monolithic integration and are less sensitiveto the GB effects.     

High-selectivity single-ended and balanced bandpass filters using ring resonators and coupled lines loaded with multiple stubs

High-selectivity single-ended and balanced bandpass filters (BPFs) using dual-mode ring resonators and coupled lines loaded with multiple stubs are proposed in this paper. With the help of the loaded short-circuited and open-circuited stubs, six deep transmission zeros (TZs) from 0 to 2f₀ (f₀: center frequency of the passband) can be realized in both of single-ended and balanced BPFs to improve the stopband suppressions. The functions of the loaded short/open stubs and calculated analysis of TZs’ positions have been presented. For further demonstration, two examples of single-ended BPF and balanced BPF with high common-mode suppression are designed and fabricated, whose center frequencies are both at 2.1 GHz. Their measured 3-dB fractional bandwidths are 23.7% and 24.7% (differential-mode), respectively. The simulated results and measurements of these two filters are in good agreement.     

Microstrip multistage coupled ring bandpass filters using spur-linefilters for harmonic suppression

Bandpass filters based on microstrip coupled ring resonators including spur-line filters to suppress higher harmonics have been investigated. Two topologies based on placing spur-line filters into or out of the coupled rings have been considered and compared. A harmonic suppression ratio >30 dB in a flat bandpass filter centred at 2.44 GHz is obtained placing spur-line filters into and out of the microstrip coupled rings     

Novel half-mode substrate integrated waveguide bandpass filters using semi-hexagonal resonators

In this paper, a novel bandpass filter is presented, designed, and implemented by using a triple mode semi-hexagonal Half-Mode Substrate Integrated Waveguide (HMSIW) cavity, which has the advantages of compact size, low insertion loss, and high selectivity in upper and lower passband. To realize a triple mode filter, the first resonant mode is shifted to near the next two modes using a via hole perturbation. Two microstrip open stubs connected to open edge of HMSIW resonator are introduced to generate two transmission zeros in the lower passband. The position of transmission zeros could be controlled by adjusting the coupling gap between the microstrip open stub resonators. By etching an E-shape slot on the top plate of HMSIW resonator, two other transmission zeros are produced in the upper passband. A wide-band planar six-pole bandpass filter, which has the advantages of wide bandwidth and small size, is also proposed and fabricated by cascading two triple mode resonators. Measured results indicate that 29% and 47% fractional bandwidth, as well as approximately 1 dB and 1.1 dB insertion loss, are achieved for the proposed filters. Measured results of all those filters agree well with the simulated results.     

Broadband bandpass filters using slotted resonators fed by interdigital coupled lines for improved upper stopband performances

This paper proposes new broadband microstrip bandpass filters based on slotted linear tapered-line resonator (SLTR) and slotted step impedance resonator (SSIR) structures for size reduction and improved stopband performances. A comprehensive treatment of slotted resonators and both ends of the resonator with interdigital coupled lines is described. The design concept is demonstrated by two filter examples including one with an SLTR and another one with an SSIR. These filters have not only compact size but also a wider upper stopband resulting from resonator bandstop characteristics. The simulated and experimental results of stopband performances are better than 15 dB for a frequency range up to 25 GHz.     

Dual-band bandpass filters using equal-length coupled-serial-shunted lines and Z-transform technique

A synthesizing method is presented to design and implement digital dual-band filters in the microwave frequency range. A dual-band filter consists of a bandstop filter and a wide-band bandpass filter in a cascade connection, wherein the transfer functions of both the bandpass filter and bandstop filter are expressed in the Z domain. The bandstop filter is implemented by using a coupled-serial-shunted line structure, while the wide-band bandpass filter is constructed by using a serial-shunted line configuration. In particular, the bandwidth of each passband of the dual-band filter is controllable by adjusting the characteristics of both the bandpass filter and bandstop filter. By neglecting the dispersion effect between microstrip lines of different widths over a wide bandwidth, a dual-band filter is realized in the form of microstrip lines and its frequency responses are measured to validate this method.     

Review of saw devices and their signal processing applications in space communications

An increasing number of advanced signal processing techniques are being investigated in satellite communications systems as the ground and space segments require more and more sophisticated, light-weight, low-power-consumption and cost-effective equipment. RF signal processing techniques based on surface acoustic wave (SAW) devices can be suitably exploited in these systems, constituting a valid alternative to digital baseband processing. This paper aims at presenting the most recent applications of SAW devices to RF signal processing in satellite communication systems. They span the frequency range from about 10 MHz to 10 GHz. Interaction of SAWs with laser beams is also illustrated.     

New topology for implementing bandpass,bandstop and allpass filters with CFAs

In this brief, a new filter topology based on current feedback amplifiers is presented and compared with its operational amplifier counterpart. The circuits arising from the new topology have the important advantage that access to the Z node of the current feedback amplifier is not required, as is the case with many existing current feedback amplifier filter circuits. The operation and requirements for each of the filters are described. Theoretical results and circuit limitations are discussed and verified with experimental results. In one experiment a bandpass filter with a calculated Q and centre frequency of 20 and 158.53 kHz, respectively was built using the OPA2607 dual CFAs IC. Measured results yielded a Q of 20.153 at a centre frequency of 148.62 kHz showing close agreement with theory.     

A chip-on-board packaged bandpass filter using cross-coupled topological optimised hairpin resonators for X-band radar application

Devices that are compact in design and fabrication continue to draw attention for specific applications that require high performance. A compact elliptic bandpass filter using a cross-coupled topological structure with a hairpin resonator optimised for radar applications is presented in this paper. This work presents the design theory and corresponding semiconductor fabrication processes and describes the chip-on-board packaging method in detail. The proposed design of the bandpass filter can not only reduce the size of the device and result in good RF performance, but the accurate semiconductor fabrication process can also ensure high performance further. In addition, the presented chip-on-board packaging method can greatly enhance the reliability and long-term stability of a microwave device, which rarely introduces RF characteristic interference. The simulated, bare-chip measured and final chip-on-board measured results agreed well, which validated the correctness of the proposed approach.     

第三代卫星移动通信发展前景分析

主要论述第 3代卫星移动通信的现状、发展前景、市场定位策略、尚待研究开发的技术。经济和信息全球化给第 3代卫星移动通信的发展提供了良好的机遇 ,同时 ,陆地移动通信网的迅猛发展向第 3代卫星移动通信提出了严重的挑战。因而 ,第 3代卫星移动通信既有美好的发展前景 ,也会遇到种种困难。     

Nonlinear order statistic filters for image filtering and edge detection

A novel class of nonlinear filters for image processing is proposed. This class is a combination of nonlinear mean and order statistic filters. Median, homomorphic, α-trimmed mean, nonlinear mean, order statistic, and linear filters can be considered as special cases of this class. The properties of these filters in the presence of different kinds of noise are investigated. It is shown that these filters can be used for the reduction of additive white noise, signal-dependent noise, and impulse noise. It is also shown that they preserve edges better than linear filters. Such filters can successfully be used as edge detectors, by appropriate adjustment of some of their parameters. Edge information can be used as an input to these filters to perform in an adaptive manner, changing their behaviour near the edges of an image. It is finally shown that many of the filters proposed have a reasonable (and in certain cases small) computational complexity.     

Novel coplanar-waveguide bandpass filters using loaded air-bridge enhanced capacitors and broadside-coupled transition structures for wideband spurious suppression

Novel inline coplanar-waveguide (CPW) bandpass filters composed of quarter-wavelength stepped-impedance resonators are proposed, using loaded air-bridge enhanced capacitors and broadside-coupled microstrip-to-CPW transition structures for both wideband spurious suppression and size miniaturization. First, by suitably designing the loaded capacitor implemented by enhancing the air bridges printed over the CPW structure and the resonator parameters, the lower order spurious passbands of the proposed filter may effectively be suppressed. Next, by adopting the broadside-coupled microstrip-to-CPW transitions as the fed structures to provide required input and output coupling capacitances and high attenuation level in the upper stopband, the filter with suppressed higher order spurious responses may be achieved. In this study, two second- and fourth-order inline bandpass filters with wide rejection band are implemented and thoughtfully examined. Specifically, the proposed second-order filter has its stopband extended up to 13.3f/sub 0/, where f/sub 0/ stands for the passband center frequency, and the fourth-order filter even possesses better stopband up to 19.04f/sub 0/ with a satisfactory rejection greater than 30 dB.     

Automated defect detection in uniform and structured fabrics using Gabor filters and PCA

This paper describes an algorithm for texture defect detection in uniform and structured fabrics, which has been tested on the TILDA image database. The proposed approach is structured in a feature extraction phase, which relies on a complex symmetric Gabor filter bank and Principal Component Analysis (PCA), and on a defect identification phase, which is based on the Euclidean norm of features and on the comparison with fabric type specific parameters. Our analysis is performed on a patch basis, instead of considering single pixels. The performance has been evaluated with uniformly textured fabrics and fabrics with visible texture and grid-like structures, using as reference defect locations identified by human observers. The results show that our algorithm outperforms previous approaches in most cases, achieving a detection rate of 98.8% and a false alarm rate as low as 0.20–0.37%, whereas for heavily structured yarns misdetection rate can be as low as 5%.     

All-optical filter for simultaneous implementation of microwave bandpass and notch responses based on semiconductor optical amplifier

An all-optical filter structure to simultaneously implement microwave bandpass and notch filter is proposed and experimentally demonstrated. The structure is based on a recirculating delay line (RDL) loop consisting of a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter and a 10:90 coupler. The converted signal is generated in a wavelength conversion process based on cross-gain modulation of amplified spontaneous emission in the SOA. The converted signal circulating in RDL loop realizes a negative bandpass response. The negative bandpass filter and a broadband allpass filter are synthesized to achieve a notch filter with flat passband which can excise interference with minimal impact on the wanted signal.     

All-inkjet-printed low-pass filters with adjustable cutoff frequency consisting of resistors,inductors and transistors for sensor applications

Low-cost and flexible first and second order low-pass filters with adjustable cutoff frequency were designed and printed by inkjet printing technology. The all-inkjet-printed low-pass filters were characterized and an adjustable cutoff frequency feature in form of an inkjet-printed organic thin-film transistors (OTFTs) was added to the filters for application-oriented fine-tuning. The applicability of these small circuits was evaluated by signal filtering for sensor applications. As a result, low-pass filters with an adjustable cutoff frequency ranging from 82 Hz to 740 Hz were obtained, demonstrating their suitability in signal filtering and their promising applicability for tactile sensing characterized by low frequency signals.     

A 0.5-V, 2-nW, 55-dB DR,fourth-order bandpass filter using single branch biquads: An efficient design for FoM enhancement

A compact nano-power fourth-order bandpass filter operating from a 0.5 V supply, with an adjustable center frequency ranging from 125 Hz to 16 kHz, is presented. The filter is constituted from cascadable second-order circuit cells that are realized by a network of three transistors and two capacitors comprising only one branch of bias current. The measurement results of the filter fabricated in a 0.18-μm CMOS IC process indicate that, for a 1 kHz center frequency, a dynamic range of 55 dB is obtained from 2 nW power consumption. These results lead to best figure of merit achieved when compared to other existing designs to date.     

Joint angular and spectral estimation technique using nonlinear Kalman filters for cognitive radio

The joint estimation of direction of arrivals (DOA) and carrier frequencies of band-limited source signals is considered in this paper. A novel technique based on nonlinear Kalman filters is proposed for this joint angular and spectral estimation problem for cognitive radio (CR). Since sampling a wideband spectrum at Nyquist rate increases the analog-to-digital converter (ADC) requirements, we propose executing Kalman filter algorithm over a spatial state space model. Thus, one time sample is required and hardware complexity is reduced. Two types of nonlinear Kalman filters, extended Kalman filter (EKF) and unscented Kalman filter (UKF), are proposed. We consider their sub-optimal performance and show how to control their convergence. However, the proposed algorithms can detect a number of source signals limited to the number of elements in employing arrays.     

Design and nonlinearity compensation of Fabry-Perot type tunable optical filters for dynamic strain sensing systems

The collected spectrum of the fiber Bragg grating （FBG） and the loss of the detected optical power are discussed with respect to the 3-dB bandwidth of a Fabry-Perot （F-P） type tunable optical filter （TOF）, respectively. And the optimized parameters of the TOF are obtained consequently. It is demonstrated that the relationship between the transmission wave- length of the TOF and its drive voltage is nonlinear. A new method to compensate the nonlinearity of the TOF is proposed. The linear sweeping of the transmission wavelength of the TOF is achieved through modifying the drive voltage using interpolation algorithm. It is observed that the average error and the maximum error of the transmission wavelength are reduced sharply under linear fit. The dynamic strain sensing is realized by use of a reference FBG and moving averaging algorithm in this system.