High Speed FPGA-based implementations of Delayed-LMS filters

A variation of the least means squares (LMS) algorithm, called the delayed LMS (DLMS) algorithm is an ideally suited to achieve highly pipelined, adaptive digital filter implementations. The paper presents an efficient method of determining the delays in the DLMS filter and then transferring these delays using retiming in order to achieve fully pipelined circuit architectures for FPGA implementation. The method has been used to derive a series of retimed delayed LMS (RDLMS) architectures, which considerable reduce the number of delays and convergence time and give superior performance in terms of throughput rate when compared to previous work. Three circuit architectures and three hardware shared versions are presented which have been implemented using the Virtex-II FPGA technology resulting in a throughout rate of 182 Msample/s.

Signal-to-Noise Ratio Analysis for Nonlinear N-ary Phase Filters

The problem of recognising targets in non-overlapping clutter using nonlinear N-ary phase filters is addressed. Using mathematical analysis, expressions were derived for an N-ary phase filter and the intensity variance of an optical correlator output. The N-ary phase filter was shown to consist of an infinite sum of harmonic terms whose periodicity was determined by N. For the intensity variance, it was found that under certain conditions the variance was minimised due to a hitherto undiscovered phase quadrature effect. Comparison showed that optimal real filters produced greater SNR values than the continuous phase versions as a consequence of this effect.

Compact ridged-waveguide bandpass filters and diplexers

A ridged-waveguide diplexer incorporating integrated compact ridged-waveguide filters and a ridged-waveguide T-junction is presented. The compact size of the filter is achieved by integrating of bandpass periodic filter, and a low-pass structure is used in order to suppress spurious responses. Simulation using the mode-matching method has been carried out for ridge-waveguide filters and T junctions and the results are presented. The measured results are in good agreement with the simulated results. (C) 2004 Wiley Periodicals, Inc.

Novel periodically loaded E-plane filters

Novel E-plane waveguide filters with periodically loaded resonators are proposed. The proposed filters make use of the slow wave effect in order to achieve improved stopband performance and size reduction of roughly 50% without introducing any complexity in the fabrication process. Numerical and experimental results are presented to validate the argument.

Design of asymmetrical RF and microwave bandpass filters by computer optimization

This paper presents an optimization-based approach to the design of asymmetrical filter structures having the maximum number of return- or insertion-loss ripples in the passband such as those based upon Chebyshev function prototypes. The proposed approach. has the following advantages over the general purpose optimization techniques adopted previously such as: less frequency sampling is required, optimization is carried out with respect to the Chebyshev (or minimax) criterion, the problem of local minima does not arise, and optimization is usually only required for the passband. When implemented around an accurate circuit simulation, the method can be used to include all the effects of discontinuities, junctions, fringing, etc. to reduce the amount of tuning required in the final filter. The design of asymmetrical ridged-waveguide bandpass filters is considered as an example. Measurements on a fabricated filter confirm the accuracy of the design procedure.