To screen out a particular band, or spread, or frequencies from a wider range of mixed signals, wireless-telecommunication systems use a band-pass filter that allows frequencies within a certain range to pass through, while rejecting frequencies that are outside the prescribed range. And with the advent of widespread mobile telephone system, the need for such screening with high selectiveness is felt more today than in the past. To meet this demand, the usage of Stepped Impedance Resonators (SIR) in filters has obviously gone up.

Against this backdrop, the authors, Jignesh Patoliya, Ved Vyas Dwivedi and Y P Kosta, of the first paper of the issue, "Miniaturized Modeling of a Quasi-Elliptic Tri-Band Pass Filter Using a Folded Tri-Section Stepped Impedance Resonator for Improved Performance", have designed and developed the SIR-based highly miniaturized triple band-pass quasi-elliptic microstrip filter, numerically simulated it and the electromagnetic responses obtained in the form of graphical results were analyzed. The authors opine that the results obtained are in general agreement with the standard published filter-requirements. The authors have found the rejection characteristics in the S_, C_ and X_ bands as well. The authors further claim that the size of the prototype filter circuit developed by them and its miniaturized volumetric dimensions are added advantages being at around 35 ´ 24 mm² and 666 mm³ respectively. Incidentally, the miniaturized volumetric dimensions are said to be less than 56% of the conventional stepped impedance resonator-based tri-section filter.

Moving away from filters to means of computing blocking in a loss network, we have, Jorma Jormakka, the author of the second paper, "A Combinatorial Method of Computing Blocking in a Loss Network with Non-Stationary Arrivals", who, treating an exchange in PSTNthough not a loss system but a combined loss and queuing systemas a loss system for dimensioning purposes, presents a blocking probability for a network where a loss system is fed by a number of exchanges or concentrators. He provides a way of computing good approximations of the blocking probability of a tree-shaped loss network with a non-stationary arrival processsuch as mass calls as appear in televoting and hot spots of certain application services in the internet. Such situations may also prevail in a military command and control system where services are concentrated in service hubs. According to the author, his method of approximation is mathematically sound, more accurate, computationally easier and hence better than the classical solution.

Switching from blocking system to microstrip antennas, we have the next paper, "Single Layer Rectangular Microstrip Array Antenna for X-Band Applications", from S L Mallikarjun and P M Hadalgi. Their study was carried out with 4-element rectangular microrstrip array antenna (4-RMSAA), 6-RMSAA and 10-RMSAA that where fed by a modified corporate feed network to increase the broad banding of the antennas array. The proposed antennas were designed using low cost glass epoxy material. The experimental results indicate that the band width of the 10-RMSAA was improved by 31.39% covering 9.14 to 12.54 GHz frequency range. The proposed antennas show an improvement in gain with broadside radiation pattern. It can also be used for X-band short-range microwave applications.

Moving to dual band microstrip antennas, we have, Kishan Singh, N M Sameena and S N Mulgi, the authors of the next paper, "Dual Band Microstrip Antennas", presenting a novel design of square microstrip antenna for dual band operation with magnitudes 6.58% of lower and 27.53% of upper band. This is achieved by doubling the thickness of substrate of conventional square microstrip antennas. The experimental results indicate that the enhancement of bandwidth does not affect the nature of broadside radiation characteristics. Their design and fabrication were also found to be simple.

Moving on to parametric spectral estimations, we have, K Nagi Reddy, S Narayana Reddy and A S R Reddy, the authors of the last paper, "Parametric Methods of Spectral Estimation of MST Radar Data", presenting the parametric spectral estimation techniques for MST radar back scattering of signals from the atmosphere. The algorithm designed by them estimates the spectrum of a complex stationary signal using harmonic methods. The results obtained using their MUSIC Algorithm, were found to provide better method for back scattering of signals with no side lobes and sharp peaks.

-- GRK Murty
Consulting Editor