Multi-band Frequency Response Research Articles

Design of multivalued frequency response filters by using nonlinear feedback

This contribution introduces the design of multivalued multiband frequency response filters exploiting nonlinear feedback design techniques. The interest in this topic is related to the possibility of analysing in real-time sinusoidal signals unveiling whether their main frequency components increase or decrease along different complex paths and in fixed sets of windows. This can be done by using the effects of frequency hysteresis, peculiar characteristic of the proposed devices.

Multi-band microwave sensor based on Hilbert’s fractal for dielectric solid material characterization

A planar sensor designed using the fourth Hilbert fractal curve iteration for solid material characterization at multiple frequencies is reported in this paper. The fractal curve is self-similar with space-filling properties. The Hilbert fractal geometry is used to form a compact resonator, with a multiband frequency response where miniaturization is achieved since a large transmission line length is effectively confined in a limited area. The sensor provides five resonances in the frequency range from 0 to 5 GHz. The resonant frequencies are 0.56, 1.68, 2.72, 3.69 and 4.72 GHz, all used to measure the real permittivity of known samples with a sensitivity of 7, 20, 27, 43 and 50 MHz/permittivity, respectively. The sensor is used to measure dielectric samples with 20 × 20 mm2 areas with several thicknesses. Simulations and measurements demonstrate that the Hilbert fractal geometry can be used to design a multiband planar sensor for solid dielectric material characterization.

Asymmetric Transformer Design With Multiband Frequency Response for Simultaneous Power and Data Transfer

This article presents a novel approach to generate multiple passbands from an asymmetric two-coil transformer. The details of the asymmetry between the primary and secondary coils control the passbands’ location and bandwidth (BW). A cylindrical asymmetric connector was designed and prototyped. The S-parameters were measured with a vector network analyzer (VNA), which shows a very good match with the theoretical model up to the second passband frequency (10 MHz–1 GHz). The first passband is used for power transfer since the lower frequency is better for power transmission. The higher frequency of the second passband can be used to transmit high BW data. A carrier signal centered at the second passband frequency was used to modulate digital data at the transmitter side and demodulated at the receiver side. This connector can be used for transmitting only power, or only data, or both power and data simultaneously. We demonstrate 19 mW of power transfer and 100 Mb/s of data transfer simultaneously in a 5-mm-diameter and 7-mm high cylindrically coupled structure. To the best of our knowledge, it is the highest data rate demonstrated through a wireless power transfer link.

Codesign of High-Efficiency Power Amplifier and Ring-Resonator Filter Based on a Series of Continuous Modes and Even–Odd-Mode Analysis

A method enabling the codesign of a high-efficiency power amplifier (PA) and a ring-resonator microstrip bandpass filter is proposed in this paper. Even–odd-mode analysis and a series of continuous modes (SCMs) are combined to realize broadband or multiband impedance matching as well as the suppression of undesired signals. The proposed codesign method can achieve both broadband and multiband frequency responses, and the designed component is relatively easy to analyze and fabricate due to its microstrip structure. For verification, a broadband and triband PA-filter components are designed and fabricated separately. The first component operates across 0.8–3.2 GHz (120%) with 39.7–42.9-dBm maximum output power and 57%–74% drain efficiency (DE). The second component, which has three passbands, covers several commercial frequencies with a measured output power of 39.6–41.3 dBm and DE from 62% to 68%. When these two components are driven by a 20-MHz long-term evolution signal with a peak-to-average power ratio of 6.2 dB, adjacent channel leakage ratios from −26.4 to −33.8 dBc and from −29.4 to −33.1 dBc are measured, respectively.

Design and Realization of Variable Digital Filters for Software-Defined Radio Channelizers Using an Improved Coefficient Decimation Method

Variable digital filters (VDFs) are used in software-defined radio handsets for extraction of individual radio channels corresponding to multiple wireless communication standards. In this brief, we propose a VDF based on the improved coefficient decimation method. The proposed VDF provides variable low-pass, high-pass, bandpass, bandstop, and multiband frequency responses on the fly, using the same set of prototype filter coefficients. We present nonpipelined and pipelined implementation architectures for the proposed VDF, along with field-programmable gate array implementation results for multiple VDF designs. Analysis of the implementation results shows that the pipelined implementations achieve average reductions of 27.66%, 49.17%, and 25.59% in the number of occupied slices, dynamic power, and energy consumption, respectively, when compared with corresponding nonpipelined implementations. In addition, the proposed pipelined implementation architecture provides high operating frequencies that are independent of the prototype filter order across different VDF designs. An average maximum frequency of 157.89 MHz is obtained.

Design of compact multiband bandpass filter with suppression of second harmonic spurious by coupling gap reduction

In this paper, we describe a method to implement compact multiband bandpass filters with suppression of second harmonic frequency. This filter design approach is based on decreasing the coupling gap between adjacent resonators of a parallel-coupled-line bandpass filter in order to achieve both the desired multiband frequency response and the spurious suppression. We present the theoretical analysis of the proposed structure that consists of modeling the frequency dependence of the even- and odd-mode characteristic impedances as well as due to the different phase velocities of the parallel-coupled microstrip lines. As an example, a compact tri-band parallel-coupled-line bandpass filter with suppression of second harmonic frequency was implemented operating at 1.9/3.2/4.6 GHz to cover PCS1900, WiMAX, and C-band applications. A three-pole Chebyshev parallel-coupled microstrip bandpass filter was designed at a center frequency of 3.2 GHz and used as the basis to validate the gapping effect on the filter response which also achieves a narrower bandwidth for the second harmonic. Finally, the filter performance with minimized coupling gap is compared to a filter enhanced by the insertion of apertures in the ground plane. Generally speaking, good agreement was accomplished between simulated, calculated, and measured results.

Flexible Low Complexity Uniform and Nonuniform Digital Filter Banks With High Frequency Resolution for Multistandard Radios

Multistandard radios typically employ digital filter banks (FBs) for channelization of wideband input signals consisting of multiple radio channels corresponding to different wireless communication standards. In this paper, we propose a new design technique to obtain uniform as well as nonuniform digital FBs for multistandard channelization. In the proposed FB design technique, the improved coefficient decimation method (ICDM) is used to obtain different low-pass, high-pass, and multiband frequency responses using a single low-pass prototype filter. These frequency responses are algebraically operated upon using appropriate spectral subtraction, complementary filter response operation, and frequency response masking operations to obtain the desired sub-bands in the FB. With the help of suitable design examples, we show that our FB is a low complexity and flexible alternative to the other digital FBs in the literature, in both uniform and nonuniform channelization scenarios. The proposed ICDM-based FB is shown to be able to achieve a higher number of distinctly located sub-bands with twice the center frequency resolution when compared with the discrete Fourier transform-based FB (DFTFB) and the conventional coefficient decimation method-based FB (CDFB). For a uniform channelization design example for wireless communications, implementation results show that the proposed ICDM-based FB achieves 70.92% and 15.49% reductions in resource utilizations and 58.72% and 23.13% reductions in power consumptions when compared with the DFTFB and CDFB respectively. Also, for a nonuniform channelization design example for wireless communications, the proposed ICDM-based FB shows an 11.46% reduction in multiplication complexity when compared with the CDFB.

Simple, Compact, and Multiband Frequency Selective Surfaces Using Dissimilar Sierpinski Fractal Elements

This paper presents a design methodology for frequency selective surfaces (FSSs) using metallic patches with dissimilar Sierpinski fractal elements. The transmission properties of the spatial filters are investigated for FSS structures composed of two alternately integrated dissimilar Sierpinski fractal elements, corresponding to fractal levelsk=1, 2, and 3. Two FSS prototypes are fabricated and measured in the range from 2 to 12 GHz to validate the proposed fractal designs. The FSSs with dissimilar Sierpinski fractal patch elements are printed on RT/Duroid 6202 high frequency laminate. The experimental characterization of the FSS prototypes is accomplished through two different measurement setups composed of commercial horns and elliptical monopole microstrip antennas. The obtained results confirm the compactness and multiband performance of the proposed FSS geometries, caused by the integration of dissimilar fractal element. In addition, the proposed FSSs exhibited frequency tuning ability on the multiband frequency responses. Agreement between simulated and measured results is reported.

Low complexity flexible filter banks for uniform and non-uniform channelisation in software radios using coefficient decimation

A new approach to implement computationally efficient reconfigurable filter banks (FBs) is presented. If the coefficients of a finite impulse response filter are decimated by M, that is, if every Mth coefficient of the filter is kept unchanged and remaining coefficients are replaced by zeros, a multi-band frequency response will be obtained. The frequency response of the decimated filter will have bands with centre frequencies at 2πk/M, where k is an integer ranging from 0 to M−1. If these multi-band frequency responses are subtracted from each other or selectively masked using inherently low complex wide transition-band masking filters, different low-pass, high-pass, band-pass and band-stop frequency bands are obtained. The resulting FB, whose bands’ centre frequencies are located at integer multiples of 2π/M, is a low complexity alternative to the well-known uniform discrete Fourier transform FBs (DFTFBs). It is shown that the channeliser based on the proposed FB does not require any DFT for its implementation unlike a DFTFB. It is also shown that the proposed FB is more flexible and easily reconfigurable than the DFTFB. Furthermore, the proposed FB is able to receive channels of multiple standards simultaneously, whereas separate FBs would be required for simultaneous reception of multi-standard channels in a DFTFB-based receiver. This is achieved through a second stage of coefficient decimation. Implementation result shows that the proposed FB offers an area reduction of 41% and improvement in the speed of 50.8% over DFTFBs.

Ultrasonic waveguide with square wave surface grating

The effect of spatial harmonics of a square-wave surface grating on the multiband frequency response of ultrasonic SH waves in an elastic plate is investigated. Stopbands are found to occur under simultaneous occurrence of first-order and higher-order Bragg resonances together with co-directional and/or contra-directional mode coupling conditions. The odd harmonic nature of the structure causes stopbands to appear above the cutoff frequencies of the odd-numbered modes. The attenuation within stopbands is found to be greatest when all propagating modes are coupled and reflected. The simultaneous resonance conditions for higher order stopbands must contain at least one co-directional mode coupling condition. The analysis is performed according to the multiple scales scheme, leading to the derivation of coupled mode equations, which are solved numerically using the fundamental matrix method.

Stub loaded multi-band slotted rectangular microstrip antennas

The multi-band rectangular microstrip antennas (MSAs) realised by placing an open-circuit stub on the edges of the patch and by cutting resonant slots inside the patch are proposed. The multi-port network models for these multi-band rectangular MSAs are also proposed which helps in analysing the voltage distributions at various frequencies. Also the multi-band frequency response of these configurations is experimentally verified.

Multiband least squares FIR filter design

This paper gives two methods for the least squares approximation design of FIR digital filters. They both allow multiple pass and stop bands and arbitrary transition bands, all with explicit control of band edges. The first method is as simple to use as a window method. This design method builds up an optimal multiband frequency response by sequentially adding and subtracting optimal lowpass filters with transition bands. However, it assumes the ideal response has spline transition functions and does not allow error weighting. The second method allows different weights in the multiple passbands, stopbands and transition bands but it requires numerical solution of simultaneous equations which may be ill-conditioned. These methods compliment the Parks-McClellan algorithm which minimizes the Chebyshev error.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>