B. Piovano

CAD and optimization of compact ortho-mode transducers

We describe a new, efficient, computer-aided optimization technique for compact ortho-mode transducers (OMT). As an example, we refer to the full-wave design of an OMT operating in the 17-18.5 GHz frequency band; this design has been entirely carried out at computer level and demonstrates a significant advantage in terms of development times and no need of post manufacturing adjustments. The very satisfactory agreement between experimental and theoretical results further confirms the validity of the proposed technique.

CAD and Optimization of Compact Wide-band Septum Polarizers

We describe a computer-aided optimization technique for the efficient and reliable design of compact wide-band waveguide septum polarizers (WSP). Wide-band performance is obtained by a global optimization which considers not only the septum section but also several step discontinuities placed before the ridge-to-rectangular bifurcation and the square-to-circular discontinuity. The proposed technique mnakes use of a dynamical optimization procedure which has been tested by designing several WSP operating in different frequency bands. In this work two examples are reported, one operating at Ku band and a very wideband prototype (3.4-4.2 GHz) operating in the C band. The component design, entirely carried out at computer level, has demonstrated significant advantages in terms of development times and no need of post manufacturing adjustments. The very satisfactory agreement between experimental and theoretical results further confirm the validity of the proposed technique.

Multiport power amplifiers for mobile-radio systems using microstrip Butler matrices

A multiport power amplifier (MPA) is an amplifying system consisting of two networks, a power divider and a combiner, connected by an array of identical amplifiers. In this case both the divider and the combiner are Butler matrices (designed to operate over the 1.7-1.9 GHz band). A signal entering one port of the input matrix is divided in equal parts, phased, and amplified by all the amplifiers and then recombined by the combining matrix at the output port corresponding to that particular input port. In this way the failure of one of the amplifiers no longer causes the total loss of a beam or carrier. Furthermore, for coping with traffic variations its possible to properly apportion the available RF power among the various beams simply making small adjustments of the low level input signals. Finally, being a signal divided into equal parts by the input matrix, lower power amplifiers operating in linear region are required and intermodulation products can be kept very low. The paper describes the design and implementation of various order Butler matrices and MPAs with thick film microstrip technology for cellular DCS 1800 base stations.<<ETX>>

Reduction in size and weight of waveguide beam forming networks for satellite applications

The reduction in size and weight of beam forming networks (BFNs) used in contoured and reconfigurable beam antennas for satellite applications, is a main objective of the whole antenna design. This objective is achieved by including in the BFN branchguide couplers with 6 or 8 ports instead of all 4-port branchguide couplers as in previous prototypes. A very good electrical performance is maintained following an approach based on the electromagnetic characterization of these multiport devices and on the BFN design entirely performed at the computer level.

High performance microstrip networks for multibeam and reconfigurable operation in mobile-radio systems

This paper presents the development of high performance multiport hybrid networks based on the Butler matrix concept in thick film microstrip technology to provide the multibeam and reconfigurable operation of antennas of DCS 1800 (ground mobile) base stations. This work was performed to meet the increasing demand for mobile communications that calls for the use of advanced components to improve the electrical performance and reduce the size of transceivers, in view of the integration of ground and satellite communication equipments. In what follows a survey of the various applications of these multiport networks is presented. Furthermore, the possibility of increasing the operation flexibility suggested the use of specific components able to carry out a close control of the phase. With regard to this fact, innovating types of phase-shifters, providing a very accurate slope equalization of the phase over a specified frequency band, were developed. All designs were performed using CAD Libra (software by Eesof) to operate over the 1.7-1.9 GHz band and prototypes were manufactured on Rogers RT6006 and RT5880 Duroid substrates. Finally, the microstrip technology used for DCS applications at 1.8 GHz can easily be transferred to satellite mobile systems at 1.6 GHz and to cellular based PCN (2-2.5 GHz band).

Advanced computer design for a high performance compact ortho-mode transducer

We present a compact-size, high-performance, single-branched ortho-mode transducer (OMT), operating in the 17-18.5 GHz frequency band designed and optimized entirely at the computer level. We have used an hybrid approach which employs both the mode-matching technique (generalized scattering matrix) and an integral equation approach (admittance type representations). This hybrid approach not only provide increased confidence with the computed response by checking the results obtained with the two different techniques, but also allows the designer to optimize part of the structure with one technique and part with the other, thus enhancing flexibility, efficiency and reliability of the final design. The OMT has been designed, fabricated, measured and, due to its very satisfactory performance, subsequently included in a compact range in order to test the transmit and receive circuitry of satellites operating within the specified frequency band.

Evolution of microstrip components for mobile communication systems

This paper present the development of advanced components to minimize the size and improve the reliability and performance of transceivers of mobile systems. In particular, multiport hybrid networks based on the Butler matrix concept and an innovating type of phase-shifters, able to provide a very accurate phase equalization over a wide frequency band, are shown. The technology used is the thick film microstrip and the applications are the antennas of cellular DCS 1800 (ground mobile), in view of the integration of ground and satellite communication equipment. A Butler matrix can advantageously be used as a key element of multiport power amplifiers (MPAs) and as a transmit combining network in place of other solutions employing filters or couplers. Prototypes of these components, designed using Libra software (by Eesof) to operate over the 1.7-1.9 GHz band, were manufactured on Rogers RT6006 and RT5880 Duroid substrates. It is to be noticed that the microstrip technology used for DCS applications at 1.8 GHz can easily be transferred to satellite mobile systems at 1.6 GHz and to cellular based PCN (2-2.5 GHz Band).<<ETX>>

Analysis and Design of Circular Waveguide Polarizers with Elliptical Irises

A new design of a polarizer realized in circular waveguide with the insertion of short lengths of guide with elliptical cross-section is introduced. The new structure, that requires a manufacturing by milling techniques only, compares favourably with circular waveguide implementations, since it is composed only by waveguides with separable cross-section, hence producing a definite advantage in electromagnetic modeling. With respect to previously known solutions using square waveguide sections it has the intrinsic advantage of avoiding the rectangular-to-circular transition when the component is used, as customary, with a circular feed. Measured and theoretical results for a polarizer with a 90° ± 1° differential phase shift over the operating 7.75-8.55 GHz band show a very good agreement.

A Hierarchical Optimization Procedure for CAD of Antenna Waveguide Components

Modern CAD tools for antenna waveguide components design require the introduction of optimization strategies in order to reduce both the computer effort and the overall complexity of the optimization task. We introduce a hierarchical optimization procedure which breaks down the overall problem in a sequence of simpler tasks, hence also reducing the parameter space dimensions and avoiding local minima traps. Examples of manufactured components illustrate the methodology and confirm the quality of the electrical performances obtained via the suggested optimization procedure.

A General Software Tool for the Accurate Design of Narrow and Wide Band Orthomode Transducers

OrthoMode Transducers (OMTs) play a fundamental role in the implementation of antennas for dual polarization transceivers and their design is critical for achieving good performances. We describe an efficient electromagnetic simulator for the Computer Aided Design (CAD) and Optimization of OMTs which employs two different types of full-wave electromagnetic analysis (i.e. the generalized scattering matrix and the generalized admittance matrix) and a topological optimization of the overall OMT structure. This design tool has been successfully employed in the realization of several OMTs for various satellite applications. Favorable measured and computed electrical performances of all breadboards prove the great flexibility and accuracy of the proposed design tool.