Path Filters: A Class Of True In-Line Topologies With Transmission Zeros

International audienceIn this paper we present a comprehensive discussion of a new class of inline microwave filters with transmission zeros in the response, namely the path filters. The main features of this filters class are highlighted, and an original (synthesis-based) design approach is presented, relying on the derivation of suitable characteristic polynomials. In addition to the classical Generalized Chebyshev characteristic, two new characteristics are introduced (namely the Bounded Chebyshev and the Reduced Chebyshev), that allow improving the flexibility in the requirements assignment of path filters. A new method for the synthesis of the lowpass prototype is also introduced, that overcome the limitation in the classical synthesis based on the manipulation of the transversal prototype (whose synthesis may fail in case of path filters). Finally, the proposed approach for designing the class of considered filters has been validated by several examples that include the evaluation of the characteristic polynomials, the prototype synthesis and the dimensioning of the physical structures in waveguide technology

A True Inline Coaxial-Cavity Filter with Two Symmetric Zeros

This article has been presented at IEEE MTT-S International Microwave Symposium (IMS 2020), Atlanta, GA, USA, June 6–11, 2021.International audienceThis work deals with the design of true inline filters with two symmetric transmission zeros. A new filters category named "path filters" is introduced (including the considered filters), his general features are discussed and analyzed and a general method for the synthesis of the low-pass prototype network is proposed. To validate the proposed design approach, a coaxial-cavity filter with a true inline topology exhibiting two symmetrical transmission zeros has been designed and fabricated. The realized prototype shows a response in good agreement with the theory

Extended Path Filter Configurations

International audienceIn this work we introduce a method for increasing the maximum number of transmission zeros in the response of path filters. This recently introduced inline filter configuration allows for up to four transmission zeros on the imaginary axis. The solution proposed in this work, while maintaining the inline configuration, increases the number of transmission zeros up to N-1 (with N order of the filter). The novel concept allowing the additional zeros introduction is verified by means of the design of a waveguide filter of order 8 with 6 transmission zeros

Synthesis of duplexers with the common port matched at all frequencies

In this paper, we present a novel approach to the synthesis of duplexers with the antenna port matched at all frequencies without the use of 90° hybrids. The design is based on the synthesis of a three-port prototype network composed of coupled resonators, which models the duplexer in a normalized low-pass frequency domain. The polynomials characterizing this network are derived under the lossless assumption and imposing a particular condition on the polynomial determinant of the scattering matrix. Based on these polynomials, the synthesis of the canonical transversal prototype is performed. A new algorithm based on rotations of the coupling matrix is then introduced for the generation of new topologies, potentially more advantageous for the practical implementation. The proposed design approach is illustrated with several examples and by means of a test device, which has been designed and fabricated. The measurements have shown to be in excellent agreement with the expectations

A canonical prototype for coupled-resonator filters with frequency-dependent couplings

We present in this paper a novel canonical folded prototype circuit with some couplings varying linearly with the normalized frequency. The derivation of this prototype is based on a suitable transformation of an asymmetric lattice network, generated through a sequence of matrix rotations of the coupling matrix of the folded canonical prototype. It is shown that the lattice network is a generalization of the canonical cul-de-sac form, which is obtained when the reflection zeros are all imaginary. We have also verified that the cul-de-sac forms are possible only when the reflection zeros are all imaginary (or in para-conjugate pairs). The lattice network (or the one with frequency-dependent couplings) represents a possible alternative to the cul-de-sac forms in the synthesis of star-junction multiplexers, when the synthesized filters exhibits complex reflection zeros

Synthesis of Cross-Coupled Filters with Frequency-Dependent Couplings

This paper presents a novel synthesis technique for coupled-resonator filters with frequency-dependent couplings. Unlike the works so far appeared in the literature, the proposed technique is not based on the optimization of a network with assigned topology, but it consists in the explicit synthesis of a folded prototype with frequency-dependent transversal couplings. The proposed procedure starts with the synthesis of a new type of canonical prototype with frequency-invariant couplings (the asymmetric lattice); this prototype is then suitably transformed by means of scaling and rotations of coupling and capacitance matrices for obtaining the new configuration with frequency-dependent couplings. Concerning the asymmetric lattice prototype, we show how this canonical network degenerates, in a special case, into the cul-de-sac form; this happens when the assigned reflection zeros are imaginary (or in pairs with opposite real part). This also implies that cul-de-sac is admissible only when reflection zeros satisfy this condition. The novel synthesis approach is illustrated with several examples. A test diplexer employing filters with frequency-dependent couplings has been designed and fabricated for validating the novel synthesis approach