Benito Gimeno Martínez

Fast automated design of waveguide filters using aggressive space mapping with a new segmentation strategy and a hybrid optimization algorithm

Waveguide filters are key elements present in many microwave and millimeter-wave communication systems. In recent times, ever-increasing efforts are being devoted to the development of automated computer-aided design (CAD) tools of such devices. In this paper, a novel CAD tool based on modal analysis methods, which improves the efficiency and robustness of the classical aggressive space-mapping technique, is presented for those purposes. The use of a new segmentation strategy and the hybridization of a specific combination of several well-known optimization algorithms is proposed. The CAD tool has been successfully validated with the practical design of several H-plane coupled cavity filters in a rectangular waveguide for space and communication applications. A filter prototype for local multipoint distribution systems operating at Ka-band, and two tunable H-plane filters with tuning posts operating at 11 and 13 GHz, have been successfully designed, manufactured, and measured.

Fast S-domain modeling of rectangular waveguides with radially symmetric metal insets

This paper describes the application of the boundary integral-resonant-mode expansion (BI-RME) method to the modeling of rectangular waveguides with metal insets. It extends to more complicated radially symmetric insets, a method recently introduced by the authors, for the simple case of a cylindric post. In this extension, a self-consistent new theory is presented, which fully exploits the peculiarities of the considered class of structures, thus straightforwardly leading to the system equations. The efficiency of the BI-RME method, already demonstrated in the wide-band modeling of arbitrarily shaped waveguide components, is further enhanced in the particular application considered in this paper because the currents on the waveguide walls are not involved in the calculation. For this reason, the method-of-moments discretization of the field equations leads to a mathematical model of order much smaller than in the general BI-RME approach and in other boundary integral methods. Due to the state-space formulation of this model, a wide-band representation of the generalized admittance matrix of the structure is easily found in the form of a pole expansion in the S-domain by the calculation of a reasonably small number of eigensolutions of a matrix eigenvalue problem. The method is very fast and reliable, and permits the realization of a very efficient software, well suited for inclusion in computer-aided design tools for microwave circuit design. Some examples show the efficiency of the method, including the application to multiple and slanting insets and to the modeling of an evanescent-mode filter.

Study of the Multipactor Effect in Bandpass Wedge-Shaped Waveguide Filters

Recently developed high-power radio-frequency discharges prediction tools have suggested that wedge-shaped waveguides are more resistent to multipactor effects than the equivalent rectangular waveguides. As a result of several research activities performed in cooperation with the European Space Research and Technology Centre of the European Space Agency, a filter structure based on wedge-shaped cavities is designed and manufactured, thus proving the previous theoretical results with a passive device widely used in the output (high-power) stage of satellite payloads. Experimental results are presented that confirm the developed prediction models. Finally, a discussion of advantages and potential limitations of this new filter topology is included, and further improvements for this waveguide topology are also suggested.

FULL-WAVE ANALYSIS AND DESIGN OF BROADBAND TURNSTILE JUNCTIONS

The e-cient design of broadband turnstile junctions compensated with piled-up cylindrical metallic posts is discussed in this contribution. Very high relative bandwidths can be obtained, while maintaining the diameter of the input circular access port lower than the width of the rectangular waveguide ports, thus reducing the number of excited higher order circular waveguide modes. A novel full-wave analysis tool has also been implemented in order to reduce the CPU efiort related to the complete design process.

Efficient Analysis and Design of Compensated Turnstile Junctions Using Advanced Modal Techniques

In this work, the e-cient analysis and design of optimised turnstile junctions showing low re∞ection coe-cient is investigated. For this purpose, a rigorous multimodal analysis of compensated junctions is developed, which is based on the computationally e-cient 3-D Boundary Integral-Resonant Mode Expansion (3-D BI-RME) technique. The electrical performance of the standard

Optimized Multipactor-Resistant Wedge-Shaped Waveguide Bandpass Filters

Wedge-shaped waveguides present a certain advantage with respect to rectangular waveguides regarding their resistance to multipactor discharges. In this paper, the optimal configuration for the wedge geometry is investigated based on theoretical results, on a precise multipactor prediction tool, and on previous experience. In addition, design rules are presented, which allow us to achieve for wedge-shaped filters electrical performances comparable to the ones of rectangular waveguide filters, while at the same time improving the multipactor-free power range. As a proof of concept, two three-pole bandpass filters with equivalent electrical characteristic of 150-MHz bandwidth, centered at 12 GHz (Ku band), and the same

Multipactor RF Breakdown in Coaxial Transmission Lines With Digitally Modulated Signals

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Thermal desorption gas chromatography with mass spectrometry study of outgassing from polymethacrylimide foam (Rohacell

factor have been designed, manufactured, and tested. The first design is based on conventional rectangular waveguide technology, while the second one has non-parallel broadside walls (wedge-shaped cross section). The multipactor power threshold and RF performance of the filters have been measured in order to validate the improvements achievable employing wedge-shaped resonators.

Practical Design of Filters Using EBG Waveguides Periodically Loaded with Metal Ridges

The aim of this paper is the study of the RF multipactor breakdown in coaxial transmission lines excited by a single carrier with a digitally modulated signal. Employing an in-house developed code, numerical simulations are performed to determine the RF multipactor voltage threshold for several digitally modulated signals under different modulations schemes: quadrature phase-shift keying, 16-quadrature amplitude modulation, 16-amplitude and phase-shift keying, and 32-amplitude and phase-shift keying. Moreover, a coarse method based on the envelope integration to determine the RF multipactor voltage threshold when involving arbitrary digital modulations is also presented. These results are also compared with the “20-gap-crossing” rule used in the space standard document ECSS-E20-1A. In order to validate the theoretical results, a test campaign was performed for realistic modulated signals, finding good agreement between theoretical predictions and experimental data.

Wideband generalized admittance matrix representation for the analysis and design of waveguide filters with coaxial excitation

Polymethacrylimide foams are used as light structural materials in outer-space devices; however, the foam closed cells contain volatile compounds that are outgassed even at low temperatures. These compounds ignite as plasmas under outer-space radiation and the intense radio-frequency fields used in communications. Since plasmas may cause spacecraft fatal events, the conditions in which they are ignited should be investigated. Therefore, qualitative and quantitative knowledge about polymethacrylimide foam outgassing should be established. Using thermogravimetric analysis, weight losses reached 3% at ca. 200°C. Thermal desorption gas chromatography with mass spectrometry detection was used to study the offgassed compounds. Using successive 4 min heating cycles at 125°C, each one corresponding to an injection, significant amounts of nitrogen (25.3%), water (2.6%), isobutylene (11.3%), tert-butanol (2.9%), 1-propanol (11.9%), hexane (25.3%), propyl methacrylate (1.4%), higher hydrocarbons (11.3%), fatty acids (2.2%) and their esters (1.3%), and other compounds were outgassed. Other compounds were observed during the main stage of thermal destruction (220-280°C). A similar study at 175°C revealed the extreme difficulty in fully outgassing polar compounds from polymethacrylimide foams by baking and showed the different compositions of the offgassed atmosphere that can be expected in the long term.