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Usual measurement techniques determine amplitudes and phases of signals at the ports of a device and in the far field of an antenna. They do not show what happens within the device or close to the antenna, how signals travel along lines and across junctions, sometimes disappearing mysteriously at some ports, and which edges of an antenna actively contribute to radiation.
A six-port junction is used to perform demodulation of PSK signals directly at RF frequencies. The proposed direct phase demodulator is capable of demodulating various digital modulations such as BPSK, QPSK, etc. The hardware imperfections are readily eliminated by software. Due to the absence of the frequency conversion stages the receiver becomes very simple. Measurements have been performed at...
Intensive investigations of the millimeter waves spectrum are stimulated by the requirements of large bandwidth adapted to the high bit rate of the future wireless LAN. This paper deals with experimental results obtained for the narrowband and wideband indoor radio channels at 37.2 GHz. CW results are obtained using two kinds of transmission antennas, omnidirectional and directional Under LOS condition,...
This paper focuses on the design of an indoor broadband radio system at 29 GHz with some emphasis on the effect of antennas on the availability of the system, for various cell sizes. The system has a maximum information bit rate of 155 Mb/sec and a maximum receiver noise figure of 8 dB. Channel measurements with antenna diversity were carried out during an earlier stage of the project at 2L6 GHz and...
Modeling propagation in urban areas is fundamental for microcellular network design. The main difficulty in developing deterministic models is that propagation areas are both large in size and complex in shape. In this study, we focus on the power transmission characteristics of the wave propagation process and we divide the process into basic elements according to the geometrical characteristics...
This paper is concerned with the applicability of polarization diversity with switch and stay combining to indoor communication systems [1][3] in order to reduce the effect of the excessively deep fades that affect the signal envelope. Measurements made at 900 MHz in a large room and a long corridorare reported. It is generally accepted that for coefficient correlation ρ ≤ 0.7 an improvement in the...
The use of handheld transmitter-receiver units by the military, commercial users and others has proliferated in the last ten years. This paper presents calculations that indicate with reasonable accuracy that these units, although excluded from ANSI C95.1-1982 protection guidelines, may be a radiation hazard. The transmitters generate between one and five watts of radio frequency power, operate on...
In recent years, the investigation of inverse scattering problems in the area of microwave imaging has been performed mainly by applying iterative algorithms. The method based on me Born approximation [1] and the method using a Newton-type iterative algorithm [2] are two typical iterative methods currently being employed. An improved technique based on the equivalent current reconstruction has been...
Numerical results presented recently show that the stochastic inversion method is one of the promising spatial domain methods for reconstructing dielectric permittivities, especially in a noise contaminated environment [1],[2]. The stochastic inversion algorithm is developed based on statistical considerations, with the generated reconstructions and the noise modelled in terms of stochastic or random...
The design and measurements of a Bootlace lens feed for an auxiliary sidelobe canceller array are discussed in this paper. The sidelobe canceller is an array of 8 pyramidal horns, each fed by a phase-matched low noise receiver, as shown in Fig. 1. These active elements are connected to the output or array ports of the lens. The Rotman variation of the Bootlace lens, depicted in Fig. 2, is implemented...
Generally, an Adaptative Antenna System (AAS) controls the beam shape and steering. AAS's tasks are essentially to find the direction of an emitter and to reduce sidelobe levels of the antenna pattern in the direction of interferences. AAS finds application in radars [1] and in mobile or wireless indoor communications [2]. The AAS contains coherent receivers giving relative phase and magnitude and...
This paper outlines the development of a new type of digital adaptive-array algorithm for interference cancellation. It is fast in the sense that it requires only order-of-N computations per iteration and converges in a substantially fixed number of iterations (proportional to N) regardless of the signal scenario or geometry of the N-element array. The need for such algorithms arises in dynamic signal...
As telecommunications and radar systems are increasingly being designed to operate at higher and higher frequencies in the millimetre wave band, antenna designers have looked arrays, with feed networks based in microwave integrated circuit (MIC) technology, to meet the antenna requirements of these systems. Most of the research and design into arrays for millimetre wave applications has focused on...
In this paper, we report the results of our experimental investigations on microstrip-fed series dielectric resonator arrays. The antennas have been fed by proximity coupling between the microstrip line and the dielectric resonator. The performance of three and twelve element arrays is discussed.
A cellular phone is a portable radio that radiates 0.6 watt from an antenna located very close to the operator's head. Concern has been expressed as to whether a cellular phone is capable of inducing damaging field strengths inside the user's head. This paper reviews the application of electromagnetic modelling techniques using the finite-difference time-domain(FDTD) method to this problem. The construction...
Computer modeling and numerical techniques provide valuable results in the area of bioelectromagnetics. In this paper, advantages and limitations of three numerical techniques, namely the method of moments (MoM), the finite-difference time domain method (FDTD) and the spherical wave expansion functions are addressed and discussed. Examples of the results obtained with the FDTD for the interaction...
The knowledge of induced currents in the human body from exposure to various sources of power line frequency magnetic field is important in the assessment of potential health hazards. This paper briefly outlines methods of computations of magnetic fields from sources such as high-voltage transmission lines or other line current-carrying conductors, and from small appliances. To compute the induced...
The impedance method, which is a circuit representation of the finite difference method for quasi-static problems is applied to model induced electric fields and currents in biological cells exposed to 60 Hz magnetic fields. Two simplified representations of actual preparations used in laboratory studies are considered. These are: low and high density suspension of cells in a conductive medium. and...
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