Stefano Sirci

Compact CPW-Fed Combline Filter in Substrate Integrated Waveguide Technology

In this letter, the design and experimental results of compact low loss combline filters, based on the extension of the classical coaxial waveguide resonator to Substrate Integrated Waveguide (SIW) technology, are succesfully demonstrated. A three-pole 5% FBW Chebyshev filter has been designed, fabricated and measured. The fabricated device shows an excellent agreement with simulated results. These structures keep the low-cost fabrication scheme of single-layer PCB processing, while requiring less than half the area compared to a conventional SIW design.

Substrate Integrated Waveguide Diplexer Based on Circular Triplet Combline Filters

The design of substrate integrated waveguide (SIW) diplexers, based on combline triplet sections with transmission zeros (TZs) placed below and above the passband, is presented. In order to control the location of the TZs, positive and negative couplings are conveniently provided. A highly compact implementation based on circular substrate integrated coaxial resonators is proposed. An X-band diplexer with channel center frequencies at 9.5 and 10.5 GHz and absolute bandwidths of 400 MHz is designed. The structure shows important advantages in terms of size reduction, while keeping good insertion losses as well as high rejection and isolation levels.

Design and Multiphysics Analysis of Direct and Cross-Coupled SIW Combline Filters Using Electric and Magnetic Couplings

In this paper, combline substrate integrated waveguide (SIW) filters using electric and magnetic couplings are thoroughly studied. Thus, a negative coupling scheme consisting on an open-ended coplanar probe is proposed and analyzed in detail. Several in-line 3-pole filters at C-band are designed, manufactured and measured showing how the presented approach can be used for implementing direct couplings while enabling an important size reduction and improved spurious-free band compared to conventional magnetic irises. A fully-packaged quasi-elliptic 4-pole filter is also designed at 5.75 GHz showing how the negative coupling structure can be used for introducing transmission zeros by means of cross-couplings between non-adjacent resonators. Finally, average and peak power handling capabilities of these filters have been also analyzed from a multiphysics point of view. Measured results validate the theoretical predictions confirming that combline SIW filters can handle significant levels of continuous and peak power, providing at the same time easy integration, compact size and advanced filtering responses.

Compact SMD packaged tunable filter based on substrate integrated coaxial resonators

A surface mountable tunable SIW filter based on coupled coaxial resonators is presented in this paper. A CPW vertical transition is designed in order to provide input/output access to the device. Biasing components are also integrated in the same substrate and accessed through castellated via holes. The proposed filter presents a very compact size and constant fractional bandwidth. Measured results including the effect of the vertical transition show low insertion losses while keeping a constant fractional bandwidth along the tuning range.

Quasi-elliptic filter based on SIW combline resonators using a coplanar line cross-coupling

In this paper, a novel electric coupling for Substrate Integrated Waveguide (SIW) bandpass filter is proposed, designed and applied in combline SIW structure. The electric coupling is obtained by means of an open-ended coplanar transmission line which couples combline SIW resonators. The proposed coupling structure can introduce mixed electric and magnetic coupling thus helping to enhance the filter selectivity. To prove the concept, a quasi-elliptic cross-coupled 4-pole SIW filter is designed including transmission zeros (TZs) at both sides of the pass-band. The filter is centred at 5.75 GHz with absolute bandwidth of 114 MHz (2%). The TZs are set at 5.63 GHz and 5.87 GHz. The measured results confirm the performances of the proposed structure, showing the advantages of wider upper stop-band, higher compactness and easy integration with planar structures.

Compact SIW filter with asymmetric frequency response for C-band wireless applications

In this paper, the design of a low-loss compact filter with asymmetric response for 5.15-5.35 GHz wireless local area network (WLAN) applications is presented. The proposed filter implements a cross-coupled trisection topology that enables to conveniently add a transmission zero at the upper-side in order to reject strong interferers that could come from the close UNII-2e and UNII-3 bands (i.e. between 5.47-5.825 GHz). The filter is based on capacitively loaded circular coaxial resonators embedded into a dielectric material following a substrate integrated waveguide (SIW) approach. The designed filter shows good electromagnetic performance in terms of losses and out-of-band rejection while greatly reducing the device size.

Compact Dual-Mode Substrate Integrated Waveguide Coaxial Cavity for Bandpass Filter Design

This letter proposes a new compact filtering building block. It consists of two via holes embedded into a substrate integrated waveguide (SIW) cavity connected to capacitive metal patches at the top layer. This topology provides two coaxial modes performing a doublet filtering configuration. The proposed dual-mode SIW coaxial cavity is studied in detail and guidelines for the filter design are given. As will be shown, the proposed building block presents a high degree of design flexibility, which allows for the design of multiple kind of bandpass filter (BPF) responses, including both narrow- and wide-band BPFs along with transmission zero generation. As a verification, several filters are designed and implemented at 8 GHz.

Practical considerations on the design and optimization of substrate integrated coaxial filters

A practical approach for the design and optimization of substrate integrated coaxial filters is presented in this work. The technique is based on the electromagnetic optimization of the 3D filter by using a circuit-level model of the structure. As an example, a 6-pole filter with quasi-elliptic response and tight requirements in terms of group delay flatness has been designed, manufactured and measured. The proposed approach can be used on any cross-coupled substrate integrated coaxial filters and can help to minimize the computational effort and number of design iterations required for satisfying stringent filter specifications.

Compact bandpass filters based on a new substrate integrated waveguide coaxial cavity

In this paper a new approach for the design of very compact bandpass filters (BPFs) with transmission zero generation is proposed. The proposed filters are based on a dual mode substrate integrated waveguide (SIW) coaxial cavity. This filtering building block provides two coaxial modes performing a doublet filtering configuration. The proposed dual-mode SIW coaxial cavity is studied in detail and guidelines for the filter design are given. As will be shown, the proposed building block presents a high degree of design flexibility, which allows for the design of multiple kind of bandpass filter responses, including both narrow- and wide-band bandpass filters along with TZ generation. Two proof-of-concept filters are implemented and tested: a wide-band BPF with a fractional bandwidth of 20% centered at 8 GHz, and a quasi-elliptic type narrow-band BPF formed by cascading two dual-mode SIW coaxial cavities.