We illustrate the principles of digital quadrature detection and call attention to its various benefits (ghost-free spectra and high immunity to low-frequency interference) and its intrinsic capability of generating data sets with different aliasing behaviors. A function describing the filtering efficiency is introduced, and the digital filters of our detector are compared with their analog counterparts of conventional nuclear magnetic resonance spectrometers. With an appropriate analog-to-digital converter (ADC), our digital detector has a dynamic range which is essentially limited by the analog noise, and increases when the spectral bandwidth is reduced. These nearly ideal performances are achieved through dithering, which randomizes the quantization error and oversampling, which reduces the quantization noise in the band of interest. We introduce a ‘‘figure of merit’’ for AD converters which estimates the noise performances of ADCs, and allows to compare products which achieve different compromises between speed and accuracy. The distortions due to the nonlinearities of the ADCs are analyzed through simulations. We find that the majority of the spurious signals (i.e., the errors other than noise) occur outside the band of interest, and are disposed through digital filtering. An unexpected result of the simulation is that, in some circumstances (e.g., large-scale narrowband dithering), an increase in the number of bits of the ADC may actually reduce the distortion-free dynamic range. In Sec. VIII we analyze practical problems like the role of the aperture jitter and the selection of the sampling frequency.

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A novel microstrip low‐pass filter utilizing defected ground structure (DGS) units is presented in this article. A DGS unit is simulated with different physical dimensions in order to show variation of attenuation pole and cut‐off frequency. Next, a low‐pass filter using proposed DGS unit is designed. A method for determining dimensions of microstrip structure and DGS units is proposed. Influence of dimensions of the microstrip structure on filter characteristics is investigated and simulated. Filters of various orders are simulated as well. Selected filter is simulated and experimentally verified. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 10–13, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22982

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This article deals with novel microstrip low-pass filter (LPF) design method using defected ground structure (DGS). The DGS allows significant length reduction of inductive microstrip lines, thus overall filter dimensions are reduced. Chebyshev prototype filter design is described and conversion from lumped network structure to microstrip structure with DGS resonators is shown. For given passband ripple and cutoff frequency, a 7th order filter design is described. S-parameters of proposed LPF are simulated and theoretical results are compared with measurement. ABSTRACT: This letter presents a compact triple-band bandpass filter using pseudointerdigital trisection stepped impedance resonators (SIR).By tuning the impedance ratio and physical length of trisection SIRs, the BPF has good triple-band performances at 1.57-/2.45-/5.25-GHz and high isolation among the three passbands. It is shown that the tripleband bandpass filter has a small size in comparison of previous works. Good agreement is shown between the simulated and measured results.