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In electronic warfare systems, the optimization of the adaptive antenna array’s parameters toward achieving a certain null or maximum at specific directions could consume a long time. This may be crucial especially when a quick reaction is required before the spatial situation changes. In this work, a novel technique based on the Schelkunoff theory of incorporating nulls into the array factor (AF) expression is presented. It is shown that by introducing these nulls in the AF, the number of unknown array coefficients to be optimized is reduced. Hence, the optimization processing time is considerably decreased compared to the conventional all parameters technique, without impairing other radiation pattern characteristics such as the beamwidth or the side lobe level.

A simple solution is presented for identifying the phase fraction and flow rate of a petroleum carrying pipeline with three-phase stratified smooth and wavy flow. The proposed method mounts a set of semicylindrical electrodes on the internal surface of the Plexiglas pipe to monitor the total capacitance and resistance of the three-phase contents. The phase fractions are determined by relating these electrical properties with the phase angles associated with the interface between water, oil, and gas phases of the mixture. To calculate the flow rate, measured capacitances from two sets of electrodes with known separation distance are cross-correlated to determine time delay. Calculated and measured results demonstrated close agreement. The percentage error exhibited by the proposed inclined capacitive plate technique is calculated and compared with published values.

Phased or parasitic array antennas with complex feed mechanism are widely used to realize beam scanning. This letter presents a simple magnetized ferrite-loaded circular waveguide antenna with three-dimensional (3-D) scan characteristics. Professional software is used to optimize the dimension and biasing requirement of the antenna. The required magnetizing fields (H 0 ) are tabulated to realize 60° of maximum beam scan in elevation plane for eight different azimuth regions covering 360°. A prototype of the high-power waveguide antenna is fabricated to experimentally verify some of the simulated scan characteristics. Using LTCC technique, embedding the biasing coils within the ferrite cylinder can considerably reduce the H 0 values needed for 3-D beam scan.

A new technique based on the analogy between the transfer function of the digital filter used in Sigma-Delta modulation and the target array factor of an antenna array is attempted. The technique is based on optimizing the array factor within the finite angle of the main lobe using direct power minimization outside this lobe. The method achieves better results when compared to a number of optimization techniques available in the literature. Some of the theoretical results are simulated using FEKO commercial software with results compared well to the theoretical findings.

Summary The paper presents a novel design for data transmission Nyquist filter with controlled bandwidth and almost flat time response at the sampling time. The controlled bandwidth criterion is very important in high speed digital data transmission, while the flat response at the sampling time makes the pulse maximally immune to small timing offset (jittering) at the sampling instant, hence reducing the channel bit error rate.

The problem of microwave filters design using non-uniform transmission line is tackled based on a global solution of the overall filter characteristics rather than localized characteristics. This technique simplifies the design process by significantly reducing the numerical efforts. A bandstop filter is designed using the proposed technique and optimized using genetic algorithm. The experimental results are presented and compared with the predicted response of the S-band filter. Good agreement is found between the predicted and the experimental results. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:310–312, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25749

A simple solution to the problem of designing a Nyquist pulse shape with maximum energy within any particular period in the signal impulse response is presented. Such design is important in minimizing timing error at the sampling time in the receiver. Further, the problem of controlling the frequency response pattern of the pulse to conform with specific requirements is solved and an example of emphasizing the high frequency contents is given.

An expression in the form of a series expansion for the error span recovery for variable length codes is presented. Numerical results for both the error span recovery and its standard deviation show complete agreement with those obtained via the complex exact functions. The expression is simple and can be applied to any model where the exact expression is prohibitively complicated.

A simple recurrence formula for computing the impulse response coefficients of the Sinc/sup N/ FIR made of a cascade of N Sinc filters each of length M is presented. The formula allows for a much lower mathematical operation compared to the previously published format and thus leads to a faster execution time and simpler circuitry.

A new Nyquist pulse shape is used to shape a 16-QAM pulse train under the effect of frequency-selective fading as well as AWGN. A simulation process is set up for the newly shaped pulse as well as the standard raised cosine. Results of the simulation show that the new design achieves better BER and results in superior system signature compared to the raised-cosine design.

The design of a linear phase Nyquist filter is introduced. The technique is based on setting a target function with a strictly linear phase and attempting to approximate the filter transfer function to the target function using the least-mean-square method. Further, the analysis is extended to cover the practical case of a pulse response rather than the impulse response. In all cases excellent results have been obtained, which compare favourably with other results available in the literature.

Application of the reciprocity theorem leads to a variational expression for the propagation constant of the fields inside shielded microstrip-like transmission lines. The resulting equation involves both the propagation constant and the tangential fields at the air-dielectric interface. Using the Rayleigh-Ritz optimization technique, both the propagation constant and the fields are completely determined. The calculated results of the propagation constant compare well with other available data. Moreover, the field solution obtained is presented in the form of a polarization ratio relating the axial to the transverse electric field. Results cover both low and high frequencies, and the technique proves valid at both frequency ranges. The method may be extended to other configurations of planar striplines by proper adjustment of the integration limits.

The electromagnetic problem of an infinite, axially slotted coaxial cable is solved. The monofilar and bifilar eigenmodes are obtained with good accuracy and previous conflicting results are discussed. Further, a field solution satisfying the proper boundary conditions is obtained and shown to be essentially azimuthal. >

The use of unequal spacing between taps in fractionally-spaced equalisers is proposed. This achieves a good performance, comparable to that of the conventional FSE, and a reasonable complexity, comparable to that of the synchronous equaliser. When applied to PAM and QAM systems, the new equaliser gives satisfactory results.

A reduced mathematical formulation of the problem of optimum design of a linear phase Nyquist filter is introduced. The method makes use of the even symmetry inherent in the filter design which leads to an eigenvalue problem with a matrix size one quarter of that of the original formulation, resulting in a considerable CPU time saving and greater numerical accuracy.