Synthesis Of Cross-coupled Filters Research Articles

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.

A Dual-TZ Extraction Technique for the Synthesis of Cross-Coupled Prototype Filters

This letter presents a novel circuital extraction possibility for filter prototypes including resonant and non-resonant nodes (NRNs). The proposed technique involves the extraction of a cross-inverter evaluated at infinity and a dangling resonator connected to an NRN at the same time. Therefore, two transmission zeros are extracted in one iteration step. This is an extension upon the results of the outstanding and original synthesis of cross-coupled filters proposed by S. Tamiazzo and G. Machiarella, providing different sets of configurations not considered by their methodology but within the same family of topologies. An example is shown in order to illustrate the proposed technique.

A Novel Method of Designing Cross-Coupled Filters Through Optimization

A novel method for the synthesis of cross-coupled filters through optimization is presented. Based on the relationship between zeros and poles of the characteristic function, an improved error function is proposed, which may increase the optimization algorithm efficiency and precision. Moreover, the full-wave EM simulation is used to find the relationship between the desired parameters and physical structure of the filter. Furthermore, a microstrip filter example is employed to illustrate the procedure and validity of the proposed method.