A.J.B. de Oliveira

A smart antenna system for remote supervision

This paper presents a switched smart antenna system, designed to provide a reliable communication between a Center for Integrated Operation of a distributor of electric power and automation devices such as electrical switches remotely controlled. The smart antenna system is controlled by an electronic device which sets de direction of the main lobe of an antenna array to the automation device. Network of power distribution automation devices are used as switches, remotely controlled and su- pervised by a Center for Integrated Operation (COI, from Portuguese Centro de Operacao Integrado). The communication between the COI and the automation devices can be performed by various forms of media such as dial-up, cellular, satellite and radio link in the UHF band. In the case of UHF radio link, the system consists of a base station that communicates with all devices in the area, focuses the information and sends it to the COI. The base station is usually located at a substation of the electricity Distribution Company, and devices on poles. At the base station, an antenna array of collinear dipoles is used which produces an omnidirectional radiation pattern with gain of about 6 dBi. The distance,terrain, vegetation and buildings in the path between the devices and the base can disrupt radio communication, leaving these devices in shadow regions. An increase in signal intensity would be sufficient to overcome various obstacles and reestablish communication path, eliminating the shadow regions. This could be achieved by the omnidirectional dipole array, but at the expenses of a great number of dipoles which in the end would be unpractical. This paper describes a smart antenna switched system installed at the base station that focuses the main lobe towards the automation device with a higher gain than the one of the original system. This would reestablish communication and also would be able to spread the communi- cation with more devices to be installed for further expansion. As far as the authors are concerned, no similar application of a smart antenna array has been reported yet.

Coupled microstrip comblines filters: Research Articles

This paper presents recent advances in the areas of modeling, design, and fabrication of microwave filters for space applications. A fast and accurate hybrid analysis method, combining boundary integral resonant mode expansion (BI-RME) and integral equation (IE) techniques, is described. Several filters used in satellite payloads have been successfully designed, manufactured, and measured.

Measuring the dielectric properties of granular and liquid materials in the microwave range

This paper presents a technique to enhance accuracy in the measurement of dielectric constant of granular and liquid non-magnetic materials in the microwave range. The S-parameter method is used with the aid of an expression developed for S/sub 21/ which takes into account the existence of the plugs.This paper presents a technique to enhance accuracy in the measurement of dielectric constant of granular and liquid non-magnetic materials in the microwave range. The S-parameter method is used with the aid of an expression developed for S/sub 21/ which takes into account the existence of the plugs.

Improving measurements of granular and liquid materials permittivities in the microwave range

This paper describes a technique to improve the accuracy in measurements of dielectric constants of liquids and granular materials. Two pieces of low loss dielectric material (plugs) are placed inside a waveguide to house the sample under measurement. The expression for the S/sub 21/ transmission parameter is derived here to take into account the multiple reflections within the plugs. The S-parameter method is employed in combination with Newtons complex iterative method to solve a nonlinear system of equations. Comparative numerical results are produced.This paper describes a technique to improve the accuracy in measurements of dielectric constants of liquids and granular materials. Two pieces of low loss dielectric material (plugs) are placed inside a waveguide to house the sample under measurement. The expression for the S/sub 21/ transmission parameter is derived here to take into account the multiple reflections within the plugs. The S-parameter method is employed in combination with Newtons complex iterative method to solve a nonlinear system of equations. Comparative numerical results are produced.

A single six-port reflectometer measures the scattering parameters of two-port microwave devices

A single six-port reflectometer configuration is proposed to measure the four scattering parameters of two-port microwave devices. In order to determine the transmission coefficients, only one calibration standard and three measurements are required to complete the calibration procedure. Furthermore, s/sub 12/ and s/sub 21/ can be measured without reversing the device under test.

Measuring complex permittivity with the six-port technique

This paper presents a novel circuit to measure the complex dielectric constant /spl epsi/* based on the six-port principle. Its most attractive feature resides in the fact that calibration procedure avoids liquids or granulated material of known permittivities as calibration standards. Instead, conventional loads (short-circuits) are used. The method works for low and high-loss materials. Computer simulations results are here presented for fat (high losses).

A new method of measuring the dielectric constant of liquids and granular materials up to the L-band in the microwave region

This paper describes a new method of measuring the complex relative permittivity /spl epsiv/* of low-loss liquids and granulated materials up to the L-band in the microwave range, based on the six-port technique. The novel feature of this method is the determination of /spl epsiv/* directly from the intersection of three circles in the complex /spl epsiv/*-plane. Furthermore, neither liquids nor granulated materials are used as calibration standards; instead, a matched load and nine adjustable short circuits are employed as standards. The ambiguity usually found in several reported methods is completely eliminated by the already consolidated six-port technique. Results of computer simulations are presented and discussed.

The six-port reflectometer: choosing a calibration method

This paper presents a discussion on four known and frequently employed six-port reflectometer calibration procedures, namely the ones by Glenn Engen (1978), Ghannouchi et al. (1988), Sunil Judah (1985) and Cong-Zhen Qian (1985). The desired features usually sought in a calibration method, like accuracy, ease of calibration and low cost, among others, are discussed for each method above. The procedure introduced by Engen can lead to the determination of the scattering parameters of microwave devices from power measurements only, without the complex circuitry of the heterodyne network analyzer.

Switched smart antenna system for SCADA telesupervision and telecontrol systems

This paper presents the conception and simulation results of a switched smart antenna array to be used for a reliable communication between a Distributor of Electricity and its automation devices such as remotely supervised and controlled electrical switches. The smart antenna system controls the direction of the radiation main lobe, increasing the transmitted power density, which allows the establishment of communication with devices located in shadow regions. This prevents new repeater stations to be installed for the same purpose. Also laboratory tests with Beamforming Controller Circuit are here reported.

Measuring the scattering parameters of microwave devices

A complete six-port network analyser is proposed that makes use of a single reflectometer. The proposed configuration employes a precision attenuator which dispenses with connections and disconnections with calibration standards, needs no inversion of the two-port device under test for measuring the transmission parameters and as its main feature, avoids the use of switches which are always present in the traditional configurations described in the literature. Its calibration and measurement procedures are also described.A complete six-port network analyser is proposed that makes use of a single reflectometer. The proposed configuration employes a precision attenuator which dispenses with connections and disconnections with calibration standards, needs no inversion of the two-port device under test for measuring the transmission parameters and as its main feature, avoids the use of switches which are always present in the traditional configurations described in the literature. Its calibration and measurement procedures are also described.