Sharp Frequency Response Research Articles

A Microstrip Low-Pass Filter Design Using a Modified Radial Resonator in the Application of Aircraft Distance Measurement Equipment

In this paper, the application of microstrip technology is investigated in low-pass filters. A cascade microstrip low-pass filter with a sharp frequency response and a good cut-off bandwidth is presented using a modified radial resonator. The advantages of this proposed filter include minor losses in the transit band as well as the desired return. This filter design shows consistency when compared with the results of simulation and model performance. A comparison between the parameter values of this filter and previous structures indicates that it is desirable. The proposed filter can be used in modern communication systems such as aircraft distance measurement equipment (DME) antenna.

Glide-Symmetric Acoustic Waveguides for Extreme Sensing and Isolation

Glide symmetry offers new degrees of freedom to engineer the properties of periodic structures, and thus it has been exploited in various electromagnetic structures. However, so far there has been little exploration on the impact that glide symmetry can offer in the field of acoustics. In this paper, we explore glide-symmetric acoustic waveguides, highlighting their dispersion characteristics and guiding properties and demonstrating opportunities in the context of acoustic devices. Here we analytically derive their dispersive features applying a semi-analytical mode matching technique. We then demonstrate how the unusual dispersion properties of glide-symmetric acoustic waveguides can be used to achieve very sharp frequency responses. Based on these results, we propose a sensing platform for liquid analytes that exhibits large sensitivity and linearity. Furthermore, by introducing fluid motion, we leverage these responses to design an acoustic isolator based on acoustic Mach-Zehnder interferometry, whose design is more favorable in terms of footprint and complexity in comparison to other acoustic nonreciprocal devices that do not rely on glide symmetry.

Compact wide stopband microstrip diplexer with flat channels for WiMAX and wireless applications

This study presents a compact wide stopband microstrip diplexer which is designed based on a novel resonator structure. This novel resonator consists of a main hairpin cell loaded by a smaller hairpin and T-shaped cells. The presented diplexer operates at 3.46 and 4.75 GHz for IEEE 802.16 worldwide interoperability for microwave access (WiMAX) and IEEE802.11a Wireless LAN applications, respectively. The main advantages of the proposed diplexer are its flat channels, two wide bandwidths, attenuated harmonics, low insertion losses better than 0.18 dB, several transmission zeros and sharp frequency response. From first up to fifth harmonics of the proposed diplexer are well attenuated with the maximum harmonic level -20 dB. Meanwhile, the simulation results show that the presented design can suppress harmonics up to 44 GHz. In other words, the harmonics from the 1st up to 12th are suppressed. The group delay at both channels is lower than 1.1 ns, which is good for a microstrip diplexer. This good performance is obtained, while the overall area of the designed diplexer is only 0.037 λ g 2 . Based on the comparison results, the proposed diplexer has a compact size, the minimum group delay and a wide stopband rejection. The proposed diplexer is fabricated and measured. Both simulation and measurement results are in good agreement.

Analysis and Design of Reflectarray Antennas Based on Delay Lines: A Filter Perspective

The analysis and design of reflectarray (RA) antennas based in delay lines is introduced for the first time from a filter perspective. To this purpose, each unit-cell of the RA is considered as a network composed of two ports, one being the delay line and the other one the free-space. This approach allows to borrow the coupling matrix formalism from filter theory and apply it to design unit-cells exhibiting broadband operation together with very sharp frequency responses. The concept is demonstrated with the aid of planar printed unit-cells coupled to substrate integrated waveguides (SIWs) through slots, a configuration that offers significant advantages to shape its frequency response while providing relatively low loss. With the aim of validation, a third order filter structure integrated in SIW-based unit-cells has been experimentally tested using the waveguide simulator technique, at a center frequency of 9 GHz. Measurements demonstrate a high-quality linear phase variation and range, and large frequency selectivity together with broadband response for the element of about 18%. The experimental results show the feasibility of this approach for the design of broadband reflectarray antennas exhibiting sharp gain responses. To illustrate the concept, a medium size reflectarray has been theoretically designed using the proposed unit cell at 9 GHz, showing a directive beam with 35.8 dB gain, sharp gain selectivity over 18 dB, and confirms the wide band operation with 20.3% bandwidth for a 3 dB gain variation.

Design and implementation of sharp edge FIR filters using hybrid differential evolution particle swarm optimization

The filter is an important building block of modern communication and electronic systems. Based on well-defined bandwidth, it extracts the desired portion of the spectrum when the raw input signal is applied. Efficacy of filtering depends on the preciseness of bandwidth to avoid co-channel interference and signal loss. In addition, it must provide higher stopband attenuation and passband attenuation very close to unity with a tolerable quantity of pass/stop band ripple. Design/implementation of sharp edge modern FIR filter is structured as a multi-objective, constrained, complex, and highly nonlinear (hence multimodal) error minimization challenge. Hence, this work proposes a novel objective (normalized error fitness) function and a robust hybrid algorithm for the effective searching of the optimal filter coefficients for providing excellent sharp edge frequency response during the filtering action. Most popular particle swarm optimization (PSO) and differential evolution (DE) algorithm are effectively combined together to frame the proposed hybrid DE-PSO algorithm for enhancing the exploration and exploitation abilities of it. The proposed hybrid algorithm is validated using twelve different benchmark functions. Through simulations, the qualitative performance of the proposed approach is compared with the conventional PSO, DE, real-coded genetic algorithm and the Parks–McClellan method.

Digital Nonlinear Metasurface with Customizable Nonreciprocity

AbstractRecently, investigation of metasurface has been extended to nonreciprocity through breaking time‐reversal symmetry. Among a number of magnetless strategies, nonlinearity is an important nonreciprocal principle amenable to the metasurface. As passive analog‐based devices, most of the existing nonlinear nonreciprocal metasurfaces are inherently characterized by the relatively unchangeable performance, sharp frequency response, and hysteresis loops. Here, an analog–digital–analog mechanism is proposed to realize the nonlinear nonreciprocity, which provides a digitally reconfigurable solution for a family of nonreciprocal performance within a shared hardware architecture. This concept is validated by a metasurface prototype with the integration of a digital module at microwave frequencies. Based on the proposed mechanism, the properties can be customized as demanded, ranging from a normal reciprocal response to a variety of nonreciprocal functions, including electromagnetic (EM) diode and EM unidirectional limiting functions, which have been experimentally demonstrated with direction reversibility and threshold tunability. The proposed metasurface is also underpinned by the nonhysteretic performance and wide operating bandwidth, thereby potentially making it an inexpensive and stable candidate for advanced manipulations of EM waves.

Fundamental bounds on the operation of Fano nonlinear isolators

Nonlinear isolators have attracted significant attention for their ability to break reciprocity and provide isolation without the need of an external bias. A popular approach for the design of such devices is based on Fano resonators, which, due to their sharp frequency response, can lead to very large isolation for moderate input intensities. Here, we show that, independent of their specific implementation, these devices are subject to fundamental bounds on the transmission coefficient in the forward direction versus their quality factor, input power, and nonreciprocal intensity range. Our analysis quantifies a general tradeoff between forward transmission and these metrics, stemming directly from time-reversal symmetry, and that unitary transmission is only possible for vanishing nonreciprocity. Our results also shed light on the operation of resonant nonlinear isolators, reveal their fundamental limitations, and provide indications on how it is possible to design nonlinear isolators with optimal performance.

Compact Microstrip Low-pass Filter with Wide Stop-band Using P-Shaped Resonator

This paper, a compact lowpass filter (LPF) with an Elliptic function response using P-shaped resonators is presented. The LPF with simple structure results in the low insertion loss less than 0.1 dB and high return loss better than 20 dB, in the passband. The proposed filter with a -3 dB cutoff frequency of 2.61 GHz is fabricated and measured. The measured results show that the proposed LPF has significant advantages such as a wide stopband from 2.9 GHz to 17.3 GHz with the suppression level better than -20 dB, and it has an acceptable sharp frequency response in the transition band. The measurement results are in good agreement with the simulation results.

Adaptive Time-Frequency Analysis for Noise Reduction in an Audio Filter Bank With Low Delay

In this paper, an adaptive time-frequency analysis scheme is proposed along with a synthesis scheme using an asymmetric window. The proposed scheme is suitable for audio noise reduction with a low delay in the range of 0 to 4 ms. The main novelty of the paper is the adaptive analysis scheme that can adapt to the incoming signal independently in both time and frequency by employing a complex filter on a DFT modulated filter bank. A number of adaptive time-frequency schemes are described that are suitable for low delay and low computational complexity. The adaptive time-frequency scheme is used for the computation of noise reduction gain factors, which are then adopted in a nonadaptive analysis/synthesis scheme. The synthesis scheme uses an asymmetric window to achieve a good tradeoff between low delay and a sharp frequency response. Examples are given of the adaptive analysis and measurements of the synthesis scheme are given to show that the filter bank has a gain dependent nonlinear phase response. Finally, a noise reduction task is performed that shows good performance compared to reference implementations in terms of segmental SNR and PESQ.

Comment on "an overview of three-dimensional frequency-selective structures" [letter to the editor

In the above paper (published in the IEEE Antennas and Propagation Magazine, 56, 3, June 2014, pp. 43-67), it was stated that the single-layer two-dimensional (2-D) frequency-selective surface (FSS) with dipole, ring, or square-loop elements exhibits a poor filtering response, and fails to meet the performance requirements of practical applications. On the contrary, various single-screen two-dimensional frequency-selective surfaces [1-6] were described with a sharp transition from in-band to out-of-band characteristics, which was also insensitive to the angle of incidence. Specifically, Holloway, et al. [1] presented the single-screen two-dimensional frequency-selective surface with split-ring resonator (SRR) elements, as depicted in Figure 1, having a sharp transition frequency response and nearly incident-angle-independent behavior up to 60°. Figure 2 shows the quasi-optical grids with a sharp transition performance and similar split-ring resonator elements printed on a one-mil thick Kapton sheet [2]. Finally, Figures 3a-3e illustrate the superior filtering performance of the single thin-screen two-dimensional frequency-selective surfaces with the fractal-type elements [3-6]. These low-mass, -cost, and -volume two-dimensional frequency-selective surfaces can be readily mounted in front of a large antenna aperture for a myriad applications in advanced and multifunctional radar or communication systems.

A cascaded microwave photonic filter based on a low-coherence infinite-impulse-response filter

A cascaded filter combining active and passive filters is proposed. The active filter acts as a low-coherence infinite-impulse-response (IIR) filter and achieves a sharp frequency response. The low-coherence IIR filter is realized by employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE) spectrum of the semiconductor optical amplifier (SOA). The passive filter is an n-section unbalance Mach-Zehnder (UMZ) structure, which is used to increase free spectral range (FSR) and Q factor further. The low-coherence IIR filter cascaded with one section of UMZ passive filter is experimentally demonstrated, and a Q factor of 1268 is obtained.

Microstrip dual-band bandstop filter to suppress DGS, DMB, GPS, UTMTS, WCDMA, WIBRO, and WLAN bands

In this article, a new microstrip dual-band bandstop filter (DSBF) is proposed. By combining coupled three-line microstrip structures, single transmission lines, and coupled open-end stubs, a DSBF with high-rejection levels and sharp frequency responses in the stopbands is found. The proposed DSBF is optimized to suppress DGS, DMB, GPS, UTMTS, WCDMA, WIBRO, and WLAN bands. The insertion loss in the two stopbands is >20 dB from 1.52 to 2.77 GHz and from 4.88 to 5.8 GHz. Four transmission zeros are realized at 1.7, 2.7, 5.1, and 5.8 GHz. Moreover, return loss of passband between the first and second stopbands is excellent. The proposed DSBF is simulated (by ADS simulator) and fabricated on a substrate with a thickness of 0.635 mm and a relative dielectric of 10.2. Here is an excellent agreement between simulation and measurement results. The overall size of the DSBF is 17.538 × 14.4 mm2. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:854–856, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26684

Microstrip lowpass filter with high and wide rejection band

A miniaturised lowpass filter with sharp roll-off and wide stopband using radial split ring resonator loaded by folded polygon patches is proposed. Multiple transmission zeros by different resonator due to different attenuation poles in the stopband region is created. A wide stopband and sharp frequency response are obtained in the stopband region. The proposed filter has 3 dB cut off frequency at 1.76 GHz, and the stopband region with the attenuation level better than −23 dB is extended from 2.06 up to 18.83 GHz. The roll-off rate of the proposed filter is 94.9 dB/GHz and, finally, the proposed filter has a high figure of merit equal to 27292.

Compact Microstrip Low-Pass Filter with wide stopband using symmetrical U-shaped resonator

This paper peresents a novel Microstrip Low-Pass Filter (LPF) using a simple symmetrical U-shaped resonator. In this work, a 5.45GHz LPF is developed. The experimental results show that in comparison with other LPFs, it has a wide stopband with high attenuation in the stopband and acceptable sharp frequency response. The insertion-loss is less than 0.1dB and the rejection band over -20dB covers 6.05GHz to 37.35GHz. The measured and simulated results are in good agreement.

Dual mode wideband band-pass filter with notched band for communication system

This paper presents a planar microstrip wideband dual mode Band-Pass Filter (BPF) from 2 GHz to 3.4 GHz with a notched band at 2.62 GHz. The dual mode band-pass filter consists of a ring resonator with two quarter-wavelength open-circuited stubs at Φ =90° and Φ =0°, respectively. A square perturbation stub has been put at the corner of the ring resonator to increase the narrow stopbands and improve the performance of selectivity. By using a parallel-coupled feed line, a narrow notched band is introduced at the required frequency and its Fractional BandWidth (FBW) is about 5%. The proposed filter has a narrow notched band and a wide pass-band with a sharp cutoff frequency characteristic, the attenuation rate for the sharp cutoff frequency responses is 297.17 dB/GHz (calculated from 1.959 GHz with −34.43 dB to 2.065 GHz with −2.93 dB) and 228.10 dB/GHz (calculated from 3.395 GHz with −2.873 dB to 3.507 GHz with −28.42 dB). This filter has the advantages of good insertion loss in both operating bands and two rejections of greater than 16 dB in the range of 1.59 GHz to 1.99 GHz and 3.49 GHz to 3.98 GHz. Having been presented in this article, the measurement results agree well with the simulation results, which validates our idea.

A MULTI-BAND MEANDERED SLOTTED-GROUNDPLANE RESONATOR AND ITS APPLICATION OF LOW-PASS FILTER

A slotted-ground-plane meandered-slot resonator with multi-resonance characteristics and a compact lowpass fllter (LPF) by using the resonator are demonstrated in this paper. The meandered slot provides a wideband resonator with low insertion loss and very sharp cutofi frequency response. Unlike conventional design of cascading bandstop slotted-ground-plane resonators in the literature, the introduced LPF is presented, which consists of a modifled-meander slot in the ground plane, a spurred C-like slot, and a uniform microstrip transmission line with constant characteristics impedance. Two rectangular-head slots, giving an increase in the inductance, are added at the two terminals of the meandered slot for purpose of frequency reduction. An arm aperture is embedded to form another resonant path so that an additional transmission zero could be generated. In order to increase rejection capability, the slot width of one section of the meandered-slot resonator is widened. Meanwhile, a C-like slot with a spur slit is also etched inside the meandered slot to improve rejection performance. The measured insertion loss at a passband is below 0.7dB, and the rejection band over 20dB is from 2.9 to 12.0GHz.

On Two-Channel Filter Banks With Directional Vanishing Moments

The contourlet transform was proposed to address the limited directional resolution of the separable wavelet transform. One way to guarantee good approximation behavior is to let the directional filters in the contourlet filter bank have sharp frequency response. This requires filters with large support size. We seek to isolate the key filter property that ensures good approximation. In this direction, we propose filters with directional vanishing moments (DVM). These filters, we show, annihilate information along a given direction. We study two-channel filter banks with DVM filters. We provide conditions under which the design of DVM filter banks is possible. A complete characterization of the product filter is, thus, obtained. We propose a design framework that avoids 2-D factorization using the mapping technique. The filters designed, when used in the contourlet transform, exhibit nonlinear approximation comparable to the conventional filters while being shorter and, therefore, providing better visual quality with less ringing artifacts. Furthermore, experiments show that the proposed filters outperform the conventional ones in image approximation and denoising.

Zero-pinning the Bernstein polynomial: a simple design technique for orthonormal wavelets

A novel technique is presented for designing finite impulse response orthonormal wavelet filters. The filters are obtained from the spectral factorization of an appropriately designed parametric Bernstein polynomial. We show that by strategically "pinning" some of the zeros of the polynomial, the nonnegativity requirement on the polynomial, which is mandatory for orthonormal filter design, can be easily achieved. Filters with a high number of vanishing moments and sharper frequency response (but lower vanishing moments) than the maximally flat Daubechies filters can be easily designed. The technique is simple as it only involves solving linear equations yet is versatile as filters with different characteristics can be obtained with ease.

A novel method for designing FIR digital filters with nonuniform frequency samples

A new method of designing FIR digital filters using nonuniform frequency samples is presented. There is no restriction on the phase to be linear. The method is based on a Newton-type polynomial interpolating on the unit circle of the complex plane. Attractive features of the proposed method are the applicability to unequally spaced samples, the recursive and semipermanent computation of filter parameters, the capability of obtaining short transition bands or sharp cut-off frequency responses, and the design of efficient algorithms for real-time applications. In the serial case, when the next sample appears, the design parameters are evaluated only by updating the old ones with correction terms that could be used as indicators for convergence, approximation, or filter reduction. The method can be extended to m-D filter design, DFT calculation, design of parallel algorithms, etc. >

High-temperature superconductor antennas: Utilization of low rf losses and of nonlinear effects

The low radio frequency (r.f.) losses in epitaxial HTS thin films allow the realization of novel antenna structures which have to be excluded in conventional antenna techniques with normal conductors because of the highly reduced radiation efficiency. Thus, the design of miniaturized but nevertheless highly efficient antennas down to a lower limit determined by both the required order of radiation pattern and the frequency bandwidth becomes possible. For a bandwidth of more than about 1%, a considerable margin for a size reduction below the “critical size” is restricted to the case of electrically small antennas and of superdirective antennas with a relatively low order of the radiation pattern, e.g. antennas with a beam of less than 15 dB maximum gain. If the size approaches the lower limit, the antennas show a sharp bandpass frequency response. This is demonstrated by means of experimental results for a novel HTS meander antenna. These bandpass characteristics can be utilized in compact multiport antenna systems in order to decouple subantennas for adjacent frequency bands. Besides the low losses in HTS's, their nonlinear properties can be used in order to realize current-controlled HTS switches for antenna systems.