V. Makios

The complex‐dielectric constant of sea ice at frequencies in the range 0.1–40 GHz

A comprehensive and unique set of measurements of the complex‐dielectric constant of sea ice, performed at several frequencies in the range 0.1–7.5 GHz, is described. In addition, a brief survey of previously published results is given and a set of dielectric models describing the complex‐dielectric behavior of sea ice, over the frequency range 0.1–40 GHz, is discussed.

Dielectric properties of fresh and sea ice at 10 and 35 GHz

A free‐space and in‐waveguide dielectric constant measurement facility at 10 and 35 GHz is described. Results are presented for the dielectric constant and loss of both fresh and sea ice at these frequencies, and are interpreted in terms of a dielectric model of sea ice. Suggestions are made for possible improvements in the model and the measurement technique.

Analysis of a modified Sierpinski gasket monopole antenna printed on dual band wireless devices

The traditional Sierpinski gasket monopole antenna is well known for its multiband behavior, but it cannot be printed on the circuit board of a portable wireless device due to the limited space availability. In this paper a modified Sierpinski gasket monopole antenna is presented that possesses a small physical size, high efficiency and the ability to allocate both the 2.4 and 5.2 GHz Industrial Scientific and Medical bands without the need of a matching network. The modified element respects the multiband behavior of the gasket since the input impedance characteristics of the upper bands maintain their symmetry. Several modification techniques are proposed making the monopole very flexible in terms of band allocation and fine-tuning. The dimensions of the ground plane are also proven to play a significant role on the operational bandwidth of the antenna system.

A Microstrip and Stripline Crossover Structure (Letters)

A microstrip or stripline four-port structure which allows two signal paths to physically cross over while maintaining high isolation is described in this letter.

A NOVEL METHOD FOR DETERMINING THE OPTIMUM SIZE OF STAND-ALONE PHOTOVOLTAIC SYSTEMS

Abstract A method is presented to select the optimum tilt angle, photovoltaic array area and battery storage capacity of stand-alone photovoltaic systems. This method uses monthly average meteorological data and easily acquirable system parameters in order to determine possible photovoltaic system sizes, capable of supplying any given monthly average hourly load profile. The optimum system selected is that with the minimum life-cycle cost while ensuring a desired reliability level. In the life-cycle cost computations a battery-life model has been used to determine the number of battery bank replacements. The reliability criterion used is the loss-of-energy probability. The method can be implemented on a personal computer and is applied to an illustrative example, where the optimum system size proposed by this methodology is compared with that of a newly installed system on a Greek island.

Equivalent Circuits of Microstrip Impedance Discontinuities and Launchers

Experimental results obtained indicate that an excess phase shift is the most pronounced high-frequency parasitic effect resulting from a microstrip quarter-wave transformer impedance discontinuity. An empirically derived design-oriented model describing the dominant parasitic reactance associated with a microstrip impedance discontinuity at X-band frequencies is described. A description is also given of the dominant parasitic reactance associated with a number of commercially available coaxial-to-microstrip launchers.

A new efficient access protocol for integrating multimedia services in the home environment

This paper presents a new dynamically adaptable medium access method that can be applied to home networks in order to create a distributed environment for multimedia and data processing services. The method uses a mechanism that detects silent periods in voice transmissions and dynamically adapts the bandwidth allocation between isochronous and asynchronous traffic.

A reduced size fractal rectangular curve patch antenna

A novel fractal rectangular curve microstrip antenna is investigated as an efficient scheme of miniaturization. Based on simulation results the element possesses good size reduction ability without compromising significantly on the antennas bandwidth and efficiency. The radiation patterns between the conventional quarter wavelength patch and the shorted fractal element are similar, concluding that the latter can be used to replace the former. Moreover, the novel geometry has several degrees of freedom that can be used to either reduce further the size of the antenna or keep the bandwidth to a satisfactory level. The novel geometry was also considered for production of circular polarization and exhibited very good results.

Ground plane effect on the performance of a printed Minkowski monopole antenna

This paper concentrates on a printed Minkowski monopole antenna that uses the ground plane as an active part of the radiating system. The effect of the antennas placement on the input impedance characteristics of the antenna-ground system is initially investigated and a method to fine tune the system in its worst case is proposed. The influence of the ground plane dimensions on the resonant frequency, bandwidth and input resistance are also examined.

Transverse CO2 laser action at several atmospheres

Laser action has been achieved at pressures up to 6 atm. by applying 200kV pulses from a Marx generator of 20–50 ns-duration to a mixture of CO2:N2:He = 8:7:85. Peak powers in excess of 20MW were measured at the optimum pressure of 4 atm.