Filter Synthesis Technique Research Articles

Novel filtering and diplexing linear tapered slot antenna with high-selectivity

In this article, a novel filtering and diplexing antenna using a linear tapered slot antenna (LTSA) are demonstrated. To begin, a highly-selective, second order bandpass filter is designed using generalized Chebyshev filter synthesis technique. Filtering and diplexing antennas are realized by co-designing the filter along with a wideband LTSA. The proposed filtering antenna exhibits 3.21% fractional bandwidth (FBW) over (4.29–4.43) GHz, high band-edge selectivity performance with 6 dBi flat in-band realized gain and stable end-fire radiation patterns with a low cross-polarization level of less than -30 dB. Further, a diplexing antenna with good bandpass filtering characteristics is also implemented. The design shows FBW of 3.32% (3.55–3.67) GHz and 3% (4.91–5.06) GHz and flat-radiation gain of 5.2 dBi and 5 dBi with sharp roll-off in Tx (lower) and Rx (upper) passbands, respectively. It also demonstrates good out-of-band suppression level of more than 20 dB, end-fire radiation patterns with cross-polarization lower than -27 dB and back-lobes lower than -14 dB for both the passbands. In order to validate their functionality, both the designs are fabricated and the experimental results correlate well with the simulated results.

A wideband omnidirectional planar filtenna for 5 GHz WLAN application

This paper presents a wideband planar filtenna based on the filter synthesis technique. The proposed filtenna consists of a third order hairpin line resonator filter coupled with an elliptical antenna. One arm of the last resonator of hairpin line resonator along with the extended feed arm of an antenna constitute an admittance inverter, which provides better integration between filter and antenna. The measured results show that the proposed filtenna exhibits a filtering response with impedance bandwidth of 26.5% (4.19–5.47 GHz), flat passband gain, good selectivity at band edges and omnidirectional radiation pattern well suited for WLAN application.

Compact RSFQ microwave pulse generator based on an integrated RF module for controlling superconducting qubits

An on-chip superconducting microwave pulse generator (MPG), incorporating rapid single-flux-quantum (RSFQ) logic gates and passive radio frequency (RF) components, is an energy-efficient solution for controlling superconducting quantum bits (qubits). Traditional RSFQ MPG designs, however, suffer from a large footprint as multiple RF components (including impedance matching networks, filters, etc.) are separately implemented one after another. In this Letter, we propose a compact on-chip MPG by introducing an integrated RF module. Using a generalized filter synthesis technique, the integrated RF module combines the functionalities of impedance matching and bandpass filtering as a single inductor-capacitor (LC) lumped network. Plenty of circuit elements can, thus, be saved, and the resultant LC network is applicable to both real and complex terminal impedance cases. For validation, a superconducting MPG adopting a fourth-order, 5 GHz centered, 100 MHz bandwidth integrated RF module is designed and fabricated, whose correct operations are confirmed through both simulation and measurement. These results raise the availability of controlling large-scale quantum systems by low-power superconductor technology in the future.

Microwave engineering filter synthesis technique for coupled ridge resonator filters.

Wavelength filters are among the most important building blocks required for integrated optical circuits. However, existing filter building blocks provide only basic functionality with limited options for controlling the filter function unless sophisticated filter design techniques are employed. Conversely, in the microwave regime, elegant and powerful filter synthesis techniques exist which use coupled resonators. As waveguide ring resonators have emerged, researchers in the optical domain have sought to translate these techniques but the multi-wavelength spacing required to couple optical ring resonator structures severely limits the types of filters that can be realized. In this paper we show how recently reported ridge resonance structures can be arranged as coupled resonators with very close spacing and thus can be harnessed to achieved many of the filter functionalities available in the field of microwave engineering. Our filter is comprised of multiple parallel ridges on a common silicon slab, with each resonator exhibiting a resonant frequency and quality factor which can be controlled through engineering the geometry of the ridge. It is thus possible to choose appropriate combinations of ridge geometries to satisfy the conditions required by filter synthesis prototype. We demonstrate through rigorous simulation how our approach can be used to achieve high order optical bandpass filters at 1.55 μm center wavelength with Butterworth or Chebychev responses and analyse the impact of non-ideal behaviours on filter performance.

Novel Wideband Microstrip Filtering Power Divider Using Multiple Resistors for Port Isolation

In this paper, a novel wideband filtering power divider with third-order quasi-Elliptic bandpass response is proposed. Its physical mechanism is revealed by the lumped-element equivalent circuit, such as how its transmission poles and zeros are formed. The design of the proposed filtering power divider can be simplified as its even-mode model can be synthesized by conventional filter synthesis technique, and then the initial structure parameters can be analytically determined. Owing to the fact that as many as three resistors are joined, high isolation can be achieved between two output ports. To demonstrate its good performance, an example was designed, fabricated, and measured, whose center frequency is 1.99 GHz and 3-dB fractional bandwidth is 43.7%. Moreover, as great as 34 and 28 dB out-of-band suppression can be achieved in the lower and upper stopbands, respectively. The isolation between two output ports is better than 20 dB for a wide frequency range.

Application of direct synthesis techniques to customize filters with complex frequency response

SummaryRecently, direct synthesis techniques (DSTs) have been presented for filter synthesis. Unlike conventional synthesis techniques, DSTs derive the filtering polynomials of the filters to be synthesized directly in their own frequency domain. These filtering polynomials are real coefficient so that they might find applications in various fields. Furthermore, DSTs might be used to customize filters with a more complex frequency response, such as asymmetric frequency response or multi‐band frequency response. In this paper, DSTs are compared with some well‐known filter synthesis techniques. Then, the application of DSTs in the design of lumped‐element LC filters, distributed‐element filters, active RC filters, and infinite impulse response digital filters with complex frequency response is discussed. Some examples are presented for demonstration. Copyright © 2015 John Wiley & Sons, Ltd.

Comb transmission filters defined by phase-shifted superstructure Bragg gratings

We present a design method and numerical results describing the construction of distributed feedback grating filters that support discrete combs of transmission resonances. These filter designs define open superstructure grating resonators with transmission channels that can be placed at predetermined frequencies, such as those defined by the wavelength division multiplexing grid or by a secondary frequency comb source. Focusing on a specific example with 40 GHz channel spacing, we optimize an active structure that defines three low-threshold lasing modes. How our design approach relates to filter synthesis techniques based on cascaded grating resonators is also discussed.

Erratum: Power Divider with Arbitrary Power Ratio and Arbitrary Ripple Level Using Filter Synthesis Techniques

ABSTRACTOriginally published Microwave Opt Technol Lett 55:1819–1820, 2013; © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2524, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27945 (Original article DOI 10.1002/mop.27722)

Power Divider with Arbitrary Power Ratio and Arbitrary Ripple Level Using Filter Synthesis Techniques

Originally published Microwave Opt Technol Lett 55:1819–1820, 2013; © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2524, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27945 (Original article DOI 10.1002/mop.27722)

Miniature on-chip bandpass power divider with equal-ripple response and wide upper stopband

In this study, a miniature bandpass power divider based on capacitive-loaded multicoupled line is proposed, which features equal-ripple insertion loss, return loss and isolation responses. Owing to the employment of capacitive-loaded transmission line resonators, it can achieve very compact size and wide upper stopband. The proposed bandpass power divider can be designed according to the conventional filter synthesis techniques, and is suitable for on-chip implementation. Specifically, a bandpass power divider with a centre frequency f0 of 5.5 GHz, 18.2% fractional bandwidth, and third-order equal-ripple response is designed and implemented using the commercial GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The circuit size without pads is 0.87 mm×0.95 mm, and the electrical size is only 0.057 λg×0.062 λg at f0. The in-band insertion loss is less than 6 dB with a minimum insertion loss of 5.12 dB. The in-band return loss is better than 10 dB, and the isolation is better than 15 dB. In addition, a wide 30-dB upper stopband up to 57 GHz is achieved.

Lossy microwave filter synthesis technique

An easy and straightforward technique for the synthesis of lossy coupled-resonator filters is presented. A lossy filter designed by attachment of attenuators is transformed into a realisable lossy filter through linear operations of its admittance matrix and optimisations. This technique can synthesise lossy symmetric filters, asymmetric filters and different loss level filters.

Advanced Filter Synthesis

Until the early 1970s, nearly all filter synthesis techniques were based on the extraction of electrical elements (lumped capacitors and inductors, transmission line lengths) from the polynomials that represented the filter's electrical performance in mathematical terms. This was perfectly adequate for the technologies and applications that were available at the time, and many important contributions were made to the art of advanced filter transfer and reflection polynomial generation, and then their conversion to electrical component values corresponding to the filter technologies that were available at this time [1]-[13].

Overlap-Save and Overlap-Add Filters: Optimal Design and Comparison

Overlap-save (OLS) and overlap-add (OLA) are two techniques widely used in digital filtering. In traditional OLS and OLA implementations, the system is compelled to be time-invariant and conventional filter synthesis techniques are used for designing the block filter. In this paper, based on the OLS and the OLA structures, we develop a fast algorithm for designing the optimal OLS and OLA block filters using a quadratic criterion. Comparing OLA to OLS optimal design, we demonstrate that, as in classical design approaches, they show no difference when the filters are time-invariant. However, when aliasing is not zero, although the global aliasing is the same, its components with respect to frequency are different. This conclusion is supported by simulation results, and a comparison between the optimal approach and some other standard approaches is also provided.

Variation-Aware Low-Power Synthesis Methodology for Fixed-Point FIR Filters

In this paper, we present a novel finite-impulse response (FIR) filter synthesis technique that allows for aggressive voltage scaling by exploiting the fact that all filter coefficients are not equally important to obtain a ldquoreasonably accuraterdquo filter response. Our technique implements a level-constrained common-subexpression-elimination algorithm, where we can constrain the number of adder levels (ALs) required to compute each of the coefficient outputs. By specifying a tighter constraint (in terms of the number of adders in the critical path) on the important coefficients, we ensure that the later computational steps compute only the less important coefficient outputs. In case of delay variations due to voltage scaling and/or process variations, only the less important outputs are affected, resulting in graceful degradation of filter quality. The proposed architecture, therefore, lends itself to aggressive voltage scaling for low-power dissipation even under process parameter variations. Under extreme process variation and supply voltage scaling (0.8 V), filters implemented in the predictive technology model (PTM) 70 nm technology show an average power savings of 25%-30% with minor degradation in filter response in terms of normalized passband/stopband ripple (0.02 at a scaled voltage of 0.8 V compared with 0.005 at a nominal supply).

Equivalent circuit modeling of coupled resonator filters

Using the stacked crystal filter (SCF) concept, a coupled resonator filter (CRF) can be interpreted as a device in which 2 piezoresonators are stacked on top of each other in such a way that a certain degree of acoustic interaction occurs. The work presented in this paper reports a novel all-electrical model for the CRF. The model associates acoustical coupling with an equivalent electrical coupling between resonators. The resulting equivalent circuit makes it possible to apply classical filter synthesis techniques directly based on the coupling control between resonators. It complements with a synthesis approach the analysis approach of the Mason model.

Microstrip multiplexer with compact in‐line feed structure

AbstractA microstrip multiplexer circuit using a compact in‐line feed structure is presented and experimentally demonstrated. The multiplexer consists of four edge‐coupled microstrip bandpass filters that are independently designed using any filter synthesis technique. The bandpass filters are interconnected in a sequential manner using specific lengths of transmission line that isolate the filters from one another at the center frequency of their passbands. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3128–3130, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22945

Analytical Diagnosis and Tuning of Narrowband Multicoupled Resonator Filters

A novel analytical filter diagnosis technique based on the partial fraction expansions of admittance matrix is proposed in this paper. The technique is applicable to computer-aided filter tuning of a general Chebyshev filter. The key issue in the proposed technique is the extension of the realizability conditions to the asynchronously tuned filters for removing the phase-loading effect. Using this analytical diagnosis technique, the inherent dispersion effects of the resonators and coupling elements are compensated by removable stray couplings in the diagnosed filter models. The filter topology that can be handled by this technique is only limited by the availability of the exact filter synthesis technique with which the filter to be diagnosed is designed

Synthesis of canonical topology microwave filters using Householder's transformations

The general even-mode coupling matrix, which contains all possible couplings of a microwave filter can be synthesised with well established filter synthesis technique. Presented is a simple but efficient method to annihilate unwanted couplings to realise canonical topology microwave filters using Householder's transformations. Furthermore, this method can be easily adopted into filter design software to synthesise canonical topology microwave filters.

Optimal Design of Transform-Based Block Digital Filters Using a Quadratic Criterion

Block digital filtering is a powerful tool to reduce the computational complexity of digital filtering systems. However, due to their block structure, block digital filters (BDFs) are time-varying linear systems, hence, their design is not easy. The most widely spread approaches to BDF design consist of constraining the BDF to be time-invariant (by restricting the design process to a specific subset of possible solutions) and then using conventional filter synthesis techniques. In this paper, we do not restrict the design process, and we propose a simple and optimal matrix-oriented approach to optimize the BDF coefficients. Furthermore, the proposed approach takes profit of the structure of transform-based BDFs to considerably reduce the computational complexity and memory requirements of the design process. Experimental results confirm that as expected, the obtained global distortion is lower than the distortion obtained with a traditional technique such as overlap-save.

A filter synthesis technique applied to the design of multistage broad-band microwave amplifiers

A method for designing multistage broad-band amplifiers based upon well-known filter synthesis techniques is presented. Common all-pole low-pass approximations are used to synthesize prototype amplifier circuits that may be scaled in frequency and impedance. All-pass filters introduced at the first stage are shown to improve input match while maintaining circuit performance less 6 dB gain. A theoretical comparison is made with the distributed amplifier and the cascaded single-stage distributed amplifier. Theoretically, a larger gain-bandwidth product is achieved using the synthesis technique. A proof-of-concept Butterworth low-pass two-stage amplifier was designed, simulated, and measured and achieved a flat gain performance of 1-4 GHz with a power gain of 14.5/spl plusmn/1 dB close to the predicted 1-4.2 GHz, 15/spl plusmn/1 dB.