Luciano Accatino

Elliptical cavity resonators for dual-mode narrow-band filters

A novel cavity resonator with elliptical cross-section is proposed in order to realize dual-mode narrowband filters without tuning and coupling elements. No discontinuities are required inside the cavities hence significantly enhancing the unloaded Q, the ability to operate with higher power levels, and the ease of manufacturing. Dual-mode coupling is generated by the step discontinuity between the input rectangular waveguide and an inclined elliptical waveguide; a rigorous full-wave electromagnetic model for this discontinuity has been developed. Proper choice of the ellipticity and of the inclination angle allows us to obtain the desired coupling and tuning actions. Representative prototypes of elliptical cavities exhibiting various degrees of coupling have been carefully measured; the favorable comparison between experimental and theoretical results proves the accuracy of the model and its applicability for narrowband X/Ku band filters.

Full-wave design and optimization of circular waveguide polarizers with elliptical irises

We describe the design and optimization of a new polarizer structure realized in circular waveguide with insertion of elliptical irises. The device is compact, showing a considerable reduction in size and weight when compared to previously known realizations. It requires manufacturing by milling techniques only and, since it is composed entirely by waveguides with separable cross sections, it is also well suited for electromagnetic modeling. Measured and theoretical results for a polarizer with a 90/spl deg//spl plusmn/1/spl deg/ differential phase shift and a return loss better than 35 dB for both polarizations over the operating frequency band confirm the validity of the proposed design.

Design of coupling irises between circular cavities by modal analysis

Single and dual iris coupling between circular waveguide cavities is studied using a rigorous mode-matching approach. Single, dual, and triple mode coupling irises are considered. It is seen that triple mode coupling can be achieved and controlled employing only a dual iris configuration. The analysis is performed by means of the generalized S-matrix technique; frequency dependence and finite thickness are accurately taken into account, and extensions to other types of coupling, i.e., coupling to an external input waveguide are straightforward. Measured results on dual and triple mode irises show close agreement with computations. >

A four-pole dual mode elliptic filter realized in circular cavity without screws

A 4-pole filter displaying an elliptic type response and implemented in circular cavity without tuning screws is presented. The cavity employs a novel arrangement, consisting of the insertion of a short length of inclined rectangular waveguide in the middle of the cavity body, in order to obtain the desired coupling and tuning actions. A full-wave model of the complete filter has been developed and specialized pretuning techniques are used. The measured response of a breadboard channel filter operating at Ku-Band shows good agreement with computed data and proves the proposed approach to be valid and viable.

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.

Elliptical cavity resonators for dual-mode narrowband filters

A novel cavity resonator with elliptical cross-section is proposed in order to realize dual-mode narrowband filters without tuning and coupling elements. No discontinuities are required inside the cavities hence significantly enhancing the unloaded Q, the ability to operate with higher power levels, and the ease of manufacturing. Dual-mode coupling is generated by the step discontinuity between the input rectangular waveguide and an inclined elliptical waveguide; a rigorous full-wave electromagnetic model for this discontinuity has been developed. Proper choice of the ellipticity and of the inclination angle allows us to obtain the desired coupling and tuning actions. Representative prototypes of elliptical cavities exhibiting various degrees of coupling have been carefully measured; the favorable comparison between experimental and theoretical results proves the accuracy of the model and its applicability for narrowband X/Ku band filters.

Modal Analysis of Curved Waveguides

A rigorous modal analysis of continuously curved waveguides both below and above cutoff is given. This analysis is a basic tool for modelling discontinuities involving curved waveguides and promises to be particularly valuable in the design of BFNs (Beam Forming Networks). As a typical application the modal scattering matrix of the junction between a straight and a curved guide is derived. Computed results compare favourably with experiment.

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.

Multipaction analysis and power handling evaluation in waveguide components for satellite antenna applications

A reliable model for calculating the power causing a multipactor discharge inside waveguide components for antenna feed systems has been developed and tested. Predicted results are in good agreement with dedicated measurements carried out on a diplexer prototype. The proposed technique represents a very useful design tool for the evaluation of power handling capability of antenna feed components for space application.

An elliptical cavity for triple-mode filters

An empty cavity resonator with elliptical cross-section is proposed for realizing triple-mode narrowband filters. Triple-mode coupling is generated by the step discontinuity between the input rectangular waveguide and an inclined-displaced elliptical waveguide resonator. Proper choice of ellipticity, inclination angle, and displacement of the cavity with respect to input iris, allows one to control generation of the three resonant modes inside the cavity. Representative prototypes of elliptical cavities exhibiting various degrees of coupling have been carefully measured proving the accuracy of the model and its applicability for narrowband X/Ku band filter design. The full-wave analysis of a complete 6-pole triple-mode filter demonstrates the capability of generating elliptical responses with finite transmission zeros.