Accurate synthesis of inline prototype filters using cascadedtriplet and quadruplet sections

A general method for designing low-pass prototype networks with cascade inline topology is presented. The generalized Chebyshev characteristic is imposed, allowing an equiripple response in the passband and transmission zeros arbitrarily displaced in the complex plane (symmetry with respect to the imaginary axis is, however, required). A computationally efficient method is employed for evaluating reflection and transmission polynomials, given the transmission zeros; then, the synthesis of a starting coupling matrix is performed using one of the methods available in the literature. The desired inline topology is then assembled by cascading elementary building blocks (triplets and/or quadruplets), following specific rules which assure the feasibility of the structure; finally, the synthesis is performed by applying a multiple similarity transform to the starting coupling matrix (the set of rotation angles is determined by means of an efficient and fast optimization procedure). Examples are reported which validate the proposed synthesis procedure     

Synthesis of inline filters with arbitrarily placed attenuation poles by using nonresonating nodes

A general and direct synthesis technique of pseudoelliptic inline filters with arbitrarily placed attenuation poles (APs) (transmission zeros) at real frequencies is presented. The APs are brought about and independently controlled by dedicated resonators, which are coupled to nonresonating nodes. Simple rules to properly determine the phases of the reflection coefficients at the input and output are given. To reduce the effect of roundoff errors, especially for higher order filters, the extraction of the elements of the network is performed from the input and output simultaneously. Multiplicity and scaling properties of the solutions are discussed. Synthesis examples are presented to demonstrate the soundness of the procedure. Theoretical results are compared with measurement to demonstrate the validity of the presented theory.     

Robust Formulations of the Cauchy Method Suitable for Microwave Duplexers Modeling

It is well known that a Vandermonde matrix generates an ill-conditioned system matrix when applied with finite numerical precision. This deficiency affects the Cauchy method by restricting its application to only lower order systems. This paper presents innovative, accurate, and robust formulations of the Cauchy method to rectify this limitation and make the Cauchy method suitable for the extraction of a high-order microwave duplexer polynomial model. The techniques employed are: the change of polynomial basis into the Krylov subspace and the precondition technique, both acting on the system matrix of the classic Cauchy method formulation. A novel formulation using the QR algorithm on the two characteristic functions of the duplexer and a suitable combination of the QR method and the precondition technique are then presented. Each of these procedures has been successfully verified by numerical application examples     

Multiple Methods for Determining Stability of Attenuating MTBE Groundwater Plume

A gasoline release site at the Dept. of Defense Housing Facility (DODHF) in Novato, Calif., resulted in dissolved methyl tertiary-butyl ether (MTBE) in a shallow, thin, heterogeneous aquifer. Multiple methods were used to evaluate the stability of the MTBE plume, including concentration versus time plots, isoconcentration contour maps, total dissolved MTBE mass and center of mass (COM) estimates, total plume extent changes, and parametric and nonparametric statistical techniques. The COM evaluation revealed a small upgradient shift in COM relative to both total plume extent and total MTBE mass reduction over the period examined. The total mass removal received substantial contributions from both the southern and northern portions of the plume, and the only removal mechanisms active in the northern plume were natural attenuation mechanisms. The results indicate that there exists at DODHF Novato a dissolved MTBE plume at the approximate balancing point between groundwater advection, which is carrying MTBE downgradient, and natural attenuation processes including aerobic biodegradation, which are reducing MTBE concentrations at about the same rate.     

An original approach to the design of bandpass cavity filters withmultiple couplings

A novel approach to the design of general cavity filters with each cavity coupled to an arbitrary number of other cavities is presented. This approach is based on a suitable characterization of the filter structure which does not require one to model separately the cavities (resonators) and the coupling elements. Suitably defined equivalent admittances are associated with each cavity allowing one to design the filter structure once the parameters of a suitable low-pass prototype are given; an efficient procedure for the synthesis of such a prototype with equiripple passband response is also presented which allows one to arbitrarily prescribe transmission zeros placed in the complex plane (even asymmetrically). The described design approach is particularly convenient when the filter structure does not allow a simple modeling of the resonators and coupling elements separately. This is the case of slot-coupled cavity filters and of filter structures based on arrays of coupled transmission lines. It is also shown that the simplified design approach often adopted in the past, where only two coupled cavities at a time are considered, can produce large errors even in the case of filters with all attenuation poles at infinity (i.e., two couplings per cavity)     

Synthesis of an in-line prototype filter with two transmission zeros without cross couplings

This letter describes a method for synthesizing a general in-line prototype filter presenting one or two transmission zeros without using cross couplings; the basic topology is constituted by resonators coupled through inverters, with input and/or output taken at the second and/or last but one resonators. In this case, the first and last resonators, tuned at frequencies in the stopband, produce two zeros in the transfer function. It is shown that, even if it is not possible to exactly synthesize this structure with extracted poles techniques, an approximated design procedure can be derived; the procedure is based on the synthesis of a low pass prototype with multiple couplings starting from source and/or load, followed by suitable network transformations. This design technique can be easily implemented in case of classical combline or interdigital filters.     

A formulation of the Cauchy method suitable for the synthesis of lossless circuit models of microwave filters from lossy measurements

In this letter, a novel formulation of the Cauchy method is presented, to be employed in the extraction of circuit models from measured(lossy) response of microwave filters. In particular, it is shown how to generate,from lossy measurements, the characteristic polynomials which allow synthesis of a lossless low-pass prototype (and the evaluation of the coupling matrix). To this purpose, suitable constraints are introduced in order to have the transmission zeros generated with the Cauchy method strictly compatible with the low pass synthesis requirements (pure imaginary or complex pair with opposite real part). The application of the proposed method has been verified employing measurements from a test filter for GSM base stations. This method can find application in computer-aided tuning procedures.     

De‐embedding response of filters from diplexer measurements

In this article, we present two methods to de‐embed the filters' responses from a diplexer whose junction is known. A weak identification problem is here described by means of a dual‐state junction and can be applied for general diagnosis of prototype diplexers. A strong identification problem based on rationality of the filters is also introduced here and is suited for a real‐time tuning process. This technique is based on a polynomial approximation derived analytically from the algebraic structure of the diplexer's response. Additional unknown delays violating the rational assumption can be moreover detected and estimated. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Improved feed network for group-type unidirectional transducers

In the letter we propose a phasing and matching network for group-type unidirectional transducers (GT-UDTs) which takes into account the electroacoustic interactions between the two phases of the GT-UDT. In comparison with analogous feed circuits from the literature, this network represents an improvement as far as the reduction of the residual fluctuations in the passband frequency response of a GT-UDT device is concerned.