L. Accatino

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.

Hybrid circuit-full-wave computer-aided design of a manifold multiplexers without tuning elements

A hybrid procedure is introduced for computer-aided design (CAD) of manifold multiplexers without tuning elements. The procedure is based on: (1) a standard initial design with a simple network prototype; (2) a hybrid optimization with the multiplexer manifold rigorously described by a full-wave model and filters still described in terms of their network prototype; and (3) a final full-wave optimization of the entire structure. The proposed approach drastically reduces computer time while making it feasible to perform a very accurate full-wave optimization which in turn allows the avoidance of using tuning elements. An example illustrates and validates the CAD procedure.

A New Dielectric-Loaded Dual-Mode Cavity for Mobile Communications Filters

A new dielectric loaded cavity structure for dual-mode filters suitable for cellular-radio base stations is presented. The cavity exhibits high unloaded Q-factor, wide spurious-free operating window and possibility of tight coupling either to input or between the dual-mode resonances. Experimental results, on a four-pole filter with an asymmetric transmission zero, confirm the validity of the proposed resonator for realizing transmit filters for UMTS cellular-radio base stations.

Dual-mode filters with grooved dielectric resonators for cellular-radio base stations

Dual-mode filters for cellular-radio base-stations require resonators with high unloaded Q-factor, wide spurious-free operating window and possibility of high coupling values either to input or between resonators. These features are obtained by employing a new cavity resonator loaded by a grooved ceramic disk. The groove, which may increase up to a full air gap, allows the insertion of probes and tuning/coupling screws where the field is stronger. Experimental results of an eight-pole transmit filter show the suitability of the proposed resonator for realizing cellular-radio base stations filters.

CAD of multipactor-free waveguide components for communication satellites

Power handling capabilities of satellite waveguide components are limited by multipactor discharge which, so far, has received scarce attention in terms of a model for design purposes. We describe a procedure, based on the knowledge of the field distribution inside the considered component, for calculating the minimum power above which the multipactor risk becomes significant. It is shown that the proposed technique allows to avoid over-restrictive specifications and is useful for quantitative evaluation of multipaction prevention techniques. Experimental results and examples confirm the procedure validity.

Dual-mode filters with grooved/splitted dielectric resonators for cellular-radio base stations

Dual-mode filters for cellular-radio base stations require resonators with a high unloaded Q-factor, a wide spurious-free operating window and the possibility of high coupling values either to input or between resonators. These features are obtained by employing a cavity resonator loaded by grooved/split ceramic disks, which allows insertion of probes and/or tuning/coupling screws where the field is highly concentrated. In this paper, cavity resonator behavior, intercavity couplings, and filter computer-aided tuning are discussed in detail. Experimental results of an eight-pole transmit filter confirm the suitability of the proposed resonator for realizing cellular-radio base stations filters for UNITS and IMT-2000 applications.

CAD of Waveguide Butler Matrices Including Mechanical and Thermal Constraints

Modern CAD tools make feasible to perform an integrated design of microwave networks that accounts also for mechanical and thermal constraints. In this contribution we examine the application of such design approach to Butler matrices, frequently employed in advanced satellite antennas. By using the proposed technique it is shown that Butler matrices implemented in nonstandard waveguide and with compensated bends in order to reduce size and weight can successfully rival microstrip implementations at X-band and pave the way to sophisticated antenna designs at Ka-band.

Suspended-grooved dielectric resonators for high Q, dual-mode, mobile communications filters

A new suspended and grooved dielectric resonator configuration is used for realizing high unloaded Q-factor, wide spurious-free operating window and tight coupling either to input or between dual-mode resonances. The latter couplings are obtained by inserting probes inside the dielectric resonator groove. This approach allows significant values of coupling/tuning to be obtained while metallic contacts with the dielectric resonator are avoided. Experimental results, on a three-pole filter with an asymmetric transmission zero, confirm the validity of the proposed resonator for realizing transmit filters for UMTS cellular-radio base stations.

A stable and efficient admittance method for the analysis of complex waveguide circuits

The generalised admittance method is a rigorous approach for the analysis of waveguide circuits. Unfortunately, it presents the risk of ill-conditioning, especially when very complex structures are analyzed with a considerably high number of modes. In this paper, the concept of adjacence graph is proposed to solve this problem. By applying the latter strategy, the linear system representing the core of the analysis is partitioned into many independent anti well-conditioned subsystems, thus improving the numerical stability of the approach, and its efficiency. Results are given referred to a real industrial case, a complex E/H-plane filter, whose analysis could not be performed via a standard admittance method when a very high number of modes were considered. With the present approach, the ill-conditioning is avoided, and a speed-up of about 12 times is achieved.