Cutoff Bandwidth Research Articles

Reconfigurable millimeter-wave filters using CPW-based periodic structures with novel multiple-contact MEMS switches

In this paper, fully monolithic reconfigurable millimeter-wave filters are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass and band-pass filters were designed, fabricated, and tested. Three cascaded CPW-based periodic structures, with low-pass and band-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. By using the multiple-contact MEMS switches, the insertion loss can be reduced and the operating frequency ranges are extended to millimeter-waves with little increase of loss. Additionally, the number of the switching elements has been reduced and the bias-decoupling circuits are not required, resulting in a very small chip size. The measured results of the reconfigurable low-pass filter show the 3-dB cutoff frequency change from 67 to 28 GHz with very small change in the insertion loss from 0.32 to 0.27 dB. The center frequency of the reconfigurable band-pass filter is tuned from 55 to 20 GHz, and the measured 3-dB cutoff bandwidth changed from 32 to 12 GHz, while the average insertion loss changed from 1.27 to 1.61 dB. The chip size of the low-pass and band-pass filter including dc bias line is 1.2 mm /spl times/ 1.5 mm and 1.2 mm /spl times/ 4.5 mm, respectively.

Compact planar bandpass filter using multisection transformers

AbstractA novel design of multi‐section compact planar bandpass filter has been proposed. The filter uses two back to back three‐section Chebyshev impedance transformers with a coupling gap. The 15 mm by 15 mm filter resonates at 5.28 GHz and yields 6% 3 dB cutoff bandwidth. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 435–437, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20494

The effects of filtering and nonlinear amplification on the performance of DS-CDMA with OQPSK-type modulations

This paper investigates the effects of channel filtering and nonlinear amplification on the signal-to-noise ratio (SNR) performance of direct-sequence code-division multiple-access systems employing offset quadrature modulation formats with various chip waveforms. An average SNR analysis is developed and followed by numerical examples to illustrate relative performance merits among modulation formats, including offset quaternary phase-shift keying (OQPSK), minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and time-domain raised-cosine shaped QPSK (TDRC). The channel filtering considered is based on Butterworth-type filters with varying 3-dB cutoff bandwidth, and the nonlinear amplification is modeled by amplitude hard limiting. The results obtained show little SNR performance differences between the cases of filtering alone and combined filtering and hard limiting. It is also found that for tighter filtering (one-sided 3-dB bandwidth on the order of half the chip rate), all modulations have comparable performance, but that for wider filter bandwidth values, differences become more noticeable, with SFSK and TDRC slightly better than MSK (on the order of 0.5 dB) and clearly outperforming OQPSK (by up to 1.5 dB). On the other hand, examples with strictly bandlimited signals employing frequency-domain Nyquist raised cosine (FDRC) filtering with a rolloff factor varying from zero to one showed a clear degradation in performance (by about 1 dB) due to the introduction of hard limiting. These schemes were also outperformed by all of OQPSK, MSK, SFSK, and TDRC modulations when combined with strict brick wall filtering, with SNR differences ranging from 1 to 2 dB.

Application of Continuous Parameter Genetic Algorithm to the Problem of Synthesizing Bandpass Distributed Amplifiers

Summary Continuous parameter genetic algorithm (CPGA) is applied tosynthesis of monolithic GaAs FET bandpass distributed amplifiers for desired flat gain and maximum cutoff bandwidth. The results obtained by CPGA are compared with the results obtained by fuzzy genetic algorithm (FGA) and binary genetic algorithm (BGA).

Transverse resonance method for anaysing T-septum waveguides

A transverse resonance method for analysing rectangular T-septum waveguides is described. This method is based on a simple equivalent circuit model. Numerical results for cutoff wavelength and bandwidth characteristics are compared with available values in the literature.

Cut-off and Bandwidth Characteristics of Inhomogeneous Rectangular Waveguide with Two Double Ridges

The dispersion relation of the hybrid modes of a rectangular waveguide with two arbitrarily placed asymmetric double ridges and the five gap and trough regions filled with dielectrics of different permittivities has been determined using the Ritz-Galerkin technique. At cut-off the general characteristic equation splits into two decoupled eigenvalue equations the solutions of which yield the H- and E-type cut-off wavelengths. Some typical numerical data on the cut-off wavelength and bandwidth of the dominant hybrid modes of nine different symmetric inhomogeneous ridged structures loaded with one dielectric are presented to illustrate their characteristics. The dispersion characteristics of a particular configuration, similar to fin-lines with thick fins, are also determined and compared with the published data.

Variable cut-off digital ladder filters

This paper presents a now class of transformations whose implementation to doubly terminated LC ladder filters results in variable cut-off frequency digital filters. It is shown that using this transformation and the concept of generalized delay, from a given prototype ladder structure, we can construct low-pass, high-pass, band-pass and band-stop filters with variable cut-off frequency and bandwidth. Thu resulting variable filters are canonical in the sense that a minimum number of multipliers in the prototype filter need to be adjusted. Two examples are worked out to illustrate the application of this method.

Polar Geometry Waveguides by Finite-Element Methods

For waveguides whose geometries are described as coordinate surfaces in circular polar coordinates, a finite-element method is used to derive base matrices over a triangular element in the polar geometry. These matrices are used to solve,mode problems in circular, sector, double-ridged circular, and spiral waveguides. The discussion is mainly in terms of cutoff frequency, bandwidth, and convergence.

High Speed Tensile Testing of Fibers

The requirements placed on the stress recording device of a tensile tester (usually a stress-transducer and recorder) become more stringent as the time to complete the test decreases. Untess these requirements are met, the difference between the true stress- strain curve and the indicated stress-strain curve becomes so large as to make the latter meaningless. In this paper, the response of a stress-strain tester to the forces arising in testing a sample having a linear stress-strain curve is examined theoretically. An equation is derived which gives the indicated stress in terms of the true stress, the strain, the rate of strain, the resonance frequency and damping of the stress-transducer, and the upper and lower cut-off frequencies or bandwidth of the amplifier-recorder system. Wave effects, however, are not considered. This equation has been solved for a variety of conditions using a small scale digital computer. Indicated stress-strain curves are presented showing their increased deviation from the true stress-strain curve as the rate of testing is increased, as the resonance frequency is lowered. or as the bandwidth is decreased. These results show that certain minimum requirements involving the ratio of the rate of strain to the resonance frequency, damping. and upper and lower cut-off frequencies must be met for accurate indication of stress. As each requirement fails to be met, certain characteristic faults in the recorded stress-strain curve appear. The principles developed above were put to use in designing and constructing a simple stress-strain tester capable of true stress recording at a strain rate of 104 % min.. using a 5-in. gauge length. This tester is described and data taken on textile fibers at 1, 102, and 105 % min. strain rates presented by way of example. The structural basis of fiber behavior at different experimental time-scales is discussed briefty.

Bandwidth Limitations in Equalizers and Transistor Output Circuits

The attenuation-integral theorem shows that a limit exists to the power gain times bandwidth product when an ideal current generator drives a network having a finite capacitance in shunt with the input. This paper derives a comparable theorem which includes both capacitance and device behavior like the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> -cutoff effect in transistors. The result of the theorem is the familiar <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pi/(2RC)</tex> when <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> cutoff can be ignored. The result depends upon both capacitance and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\alpha</tex> cutoff in general. The analysis is somewhat different from the classical method and hence can be considered to provide an alternate derivation of the attenuation-integral theorem. The results can also be interpreted to indicate the limitations of general amplitude equalization by means of a single network driven from a current source. Specific nonminimum-phase networks suitable for equalizing output networks when the (transistor) current source behaves as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\delta/(p + \delta)</tex> are the subject of the second half of this paper. Both networks and convenient design relations are given, as well as a specific example which increases <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\delta</tex> -cutoff bandwidth by a factor of 10.