Slavko Rupčić

Moment method analysis of circular-cylindrical array of waveguide elements covered with a radome

We have developed a moment method program that analyzes arrays of waveguide elements on circular-cylindrical surfaces. The presence of a radome is rigorously taken into account by using the Greens function of a multilayer circular cylindrical structure. Special attention is given to numerical treatment of the Greens function when analyzing cylindrical antennas of large radii. The calculated results are compared with the measured S-parameters of the array with 54 waveguide elements. The agreement between measured and calculated results is very good.

Generalized background noise modeling in power line communication

As power line communications show hostile properties for communication signal transmission (noise, multi path propagation...) there is a need for a model that adequately describes noise phenomena in power line communication networks in order to speed up the development of PLC systems. This paper introduces a background and narrowband noise model based on measured data. The data measured was captured with a spectrum analyzer in the 0-20 MHz frequency range. Further the measured data are statistically processed and the results are used for a computer simulation model of background and narrowband noise.

Theoretical and experimental study of spherical arrays

The spectral-domain approach to the analysis of the spherical antenna arrays is studied in the paper. The main advantage of transforming the original problem in the spectral domain is that the original three-dimensional problem is reduced to a spectrum of one-dimensional problems. Therefore, the Greens functions needed for applying the moment method, as well as the elements of the moment method matrix, can be determined in the spectral domain. The main disadvantage lies in numerical problems appearing when the structures with large radii are analyzed. In order to avoid numerical problems a modified vector-Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. The abilities of the method are demonstrated on the analysis of the microstrip patch antennas and waveguide antennas mounted on the spherical supporting structure.

Walsh function synthesis of the combined multiple shift-keyed modulated signals

Introduction of redundancy in modulation of shift-keyed signals by combining phase, frequency and/or amplitude information elements, can increase their detection probability. To make receiving side measurements for evaluation of detection probability and spectral occupancy penalty it is necessary to build a flexible, but simple for realization, modulator by which all combinations of the shift-keyed signals can be easily synthesized. The paper introduces the Walsh function based generator for synthesis of the combined multiple shift-keyed signals: M/sub P/-PSK/M/sub F/-FSK, M/sub P/-PSK/M/sub P/-ASK, PSK/M/sub A/-ASK, and M/sub F/-PSK/M/sub A/-FSK/M/sub A/-ASK. The proposed generation technique is chosen because the generator can be realized digitally in the small ROM-less PLD with a small number of components outside of the chip. The core of the generator is synthesis of the sine-wave carrier by Walsh functions. This synthesized carrier is modulated by a digital signal, producing single or combined shift-keyed modulated signals. Frequency modulation is achieved by a change of input clock frequency, discrete phase shifts are synthesized within a generator by the special shift-functions set, and discrete amplitude elements are obtained from the attached gain control amplifier. The generator is realized digitally in low complexity PLD, with a D/A conversion weighted resistor network and gain control amplifier outside of the chip. The paper presents oscillograms and power spectrum for the two combined multiple shift-keyed modulated signals.

Soybean Straw, Corn Stover and Sunflower Stalk as Possible Substrates for Biogas Production in Croatia: A Review

Biomass availability is one of the key factors for biogas production in the future. Current status and possibility of utilization of harvest residues (soybean straw, corn stover and sunflower stalk) in Croatia for biogas production was given. In the last few decades, different pretreatment methods have been developed for degradation of different lignocellulosic biomass, but many of them are environmentally unfriendly and sometimes very expensive. More research and development is necessary to conduct in order to find both, economically and environmentally friendly pretreatment methods. This paper provides a review on mechanical, physical and biological methods used for different lignocellulose material pretreatment. Harvest residues are usually left in the field, but with the pretreatment process improvement, along with the soil protection they could be used for the production of huge amounts of energy in the future.

Analysis of hexagonal and square TLM air-vent models against incident plane wave direction

This paper analyzes the impact of an incident plane wave direction on the shielding effectiveness of a metal enclosure with hexagonal or square air-vents. The analysis is conducted based on the compact TLM air-vent model for hexagonal and square perforations, for small azimuth and elevation angles of the incident plane wave. It is shown that even at low elevation and azimuth angles, significantly different characteristics of shielding effectiveness (SE) can be obtained. This is due to the fact that the higher resonant modes occur inside the enclosure.

Ultra-wideband systems with orthogonal coded differential TR receiver

This paper presents coded differential TR (cDTR) receiver that transmits extra bit by mapping information in K different orthogonal codes. The performance of the coded DTR is analyzed and compared with the conventional DTR. Throughout the analysis, the performance of receivers in terms of bit error probability (BEP), data rate and receiver complexity are assessed. The results show that coded DTR is able to outperform conventional DTR receiver in terms of data rate maintaining the same BEP. Additionally, the receiver hardware complexity issue is discussed

Agent Based Architecture for Pricing the Services in Dynamic User/Network Environment

The main goals of Internet service providers are to maximize profit and maintain a negotiated quality of service. However, achieving these objectives could become very complex if we know that Internet service users might during the session become highly dynamic and proactive. This connotes changes in user profile or network provider/s profile caused by high level of user mobility or variable level of user demands. This paper proposes a new pricing architecture for serving the highly dynamic customers in context of dynamic user/network environment. The most convenient concept that could comprise highly adaptive and proactive architecture is agent based architecture. The proposed agent based architecture places in context some basic parameters that will enable objective and transparent assessment of the costs for the service those Internet users receive while dynamically change QoS demands and cost profile.