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This paper reports on the RF design and practical development of a non-reciprocal balanced bandpass filter (BPF) that exhibits a highly-selective quasi-elliptic response in the forward direction of propagation that is shaped by four transmission poles and two transmission zeros (TZs). By modulating some of the filterâ s resonators with phase-progressed AC signals, a non-reciprocal response is obtained in the differential mode. Its common-mode is also highly suppressed due to the incorporation of a balanced network that results in two additional TZs and resistive loss that are unique to the common-mode. The filter order can be increased by cascading additional resonators. For validation purposes, a microstrip prototype centered at 725 MHz was designed, manufactured, and measured. It showed a high isolation in the differential-mode reverse transmission of up to 62.1 dB. Moreover, the common-mode was suppressed by over 45 dB in a bandwidth greater than one octave.

A type of multilayer microstrip diplexer with highlyselectivewidebandfiltering channels is reported. Its closely-spaced fourth-order passbands are attributed to two circuit parts: (i) two third-order quasi-elliptic-type microstrip-to-microstrip wideband vertical transitions and (ii) a shunt two-stub dual-band bandpass filter (BPF) junction printed on the top layer. The two microstrip vertical transitions are developed by means of open-/short-circuitended microstrip lines and slotline stepped-impedance resonators (SIRs), respectively, and they correspond to the constituent lower and upper channels. The shunt dual-band BPF junction produces one additional transmission pole and one more pair of close-topassband transmission zeros (TZs) for each channel to further increase their filtering selectivity. The RF theoretical foundations and design procedure of the engineered broadband diplexer are detailed. For practical-validation purposes, a proof-of-concept prototype of two-layer fourth-order microstrip wideband diplexer is simulated, manufactured, and tested. Its measured lower and upper channels has two closely-spaced sharp-rejection passbands with center frequencies of 1.496 GHz and 2.759 GHz and 3-dB fractional bandwidths of 62.83% and 24.83%, respectively, while featuring power-isolation levels above 27.39 dB from 0.5 to 4 GHz., European Commission, Agencia Estatal de Investigación

A twin spiral-in–spiral-out (SISO) resonator has been proposed in the design of a compact ultra-narrowband high temperature superconducting filter. We systematically investigated the relationship between the coupling characteristics and the structure of the twin SISO resonator. Coupling strength and polarity can be effectively changed by adjusting the resonator structural ratio. This method of optimizing the ratio of the twin SISO resonator structure has an advantage of achieving stable and weak coupling, even if the resonator distance is relatively narrow, thereby promoting the miniaturization of the filter. Moreover, the three methods of optimizing ratio, distance, and staggering of adjacent resonators could be regarded as three degrees of freedom for adjusting the adjacent coupling to meet design needs. To demonstrate this method, we designed and fabricated a six-order superconducting filter with a fractional bandwidth of 0.18% at 2258 MHz based on the optimized twin SISO resonator. The resulting measurement shows a good agreement with the simulation.

IEEE A class of multi-resonant RF filtering stage that exhibits a multi-band bandpass filtering transfer function with embedded in-band notches is presented. It is derived from the application of a composed lowpass-to-multi-passband/multi-stopband frequency transformation that converts the normalized lowpass prototype into the proposed multi-passband/multi-embedded-notch filtering cell. Thus, when employed in higher-order filtering networks, high-selectivity multi-band bandpass-filter (BPF) counterparts with embedded in-band stopbands are synthesized. Furthermore, two different approaches for out-of-band transmission-zero (TZ) generation in these type of filters to achieve sharp-rejection characteristics into them are detailed. The operational foundations of the engineered multi-passband/multi-embedded-notch filtering stage are described, along with several illustrative first-to-multi-order theoretical design examples with/without stopband TZs. Moreover, for experimental-demonstration purposes, a proof-of-concept microstrip prototype of a third-order dual-band BPF with two and one embedded notches in its lower and upper transmission bands, respectively, is manufactured and characterized.

A class of quasi-elliptic-type planar bandpass filters (BPFs) with electronically controllable bandwidth between narrow-band and ultra-wideband states and enhanced passband flatness is reported. It consists of the in-series cascade of replicas of an adaptive BPF stage that exhibits three in-band poles and two transmission zeros (TZs). In this manner, BPF transfer functions with 3K poles and multiple TZs-between two K-multiplicity and 2K one-multiplicity TZs-without cross-coupling can be synthesized with a K-stage BPF architecture. Bandwidth reconfiguration is performed through the spectrally agile allocation of these TZs. Passband flattening for all the states is accomplished through the adjustment of the BPF in-band return-loss profile by tuning the external admittance inverters and those between BPF stages. The aforementioned procedures for bandwidth control and passband flattening are theoretically demonstrated with the coupling-routing diagram formalism. Furthermore, a mechanism to avoid the appearance of out-of-band spurious peaks due to the multi-stage in-series-cascade process in the associated transmission line-based BPF implementation is described. For experimental-validation purposes, a 1-GHz sixth-order varactor-tuned BPF microstrip prototype with measured flattened 1-dB referred passband-width states going from 46 to 482 MHz-measured bandwidth tuning ratio of 11.5:1-is developed and characterized. Measurements for various temperature conditions and their in situ compensation are also shown.

In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept.

[EN] A procedure for improving the stopband response of planar bandpass filters is presented in this letter. The technique is based on the introduction of transmission zeros by using lumpedelement bisected-pi sections at the filter input/output. As an example, a 3¿pole 10% FBW bandpass filter with Chebyshev response centered at 1 GHz, based on strongly loaded combline microstrip resonators has been designed, manufactured and measured. The proposed solution can be used on any planar topology in order to improve the stopband performance with a negligible additional footprint., This work was supported in part by MINECO (Spanish Government) under project TEC2013-48036-C3-3-R and TEC2013-47037-C5-1-R.

The timestep of the Finite-Difference Time-Domain method (FDTD) is constrained by the stability limit known as the Courant-Friedrichs-Lewy (CFL) condition. This limit can make FDTD simulations quite time consuming for structures containing small geometrical details. Several methods have been proposed in the literature to extend the CFL limit, including implicit FDTD methods and filtering techniques. In this paper, we propose a novel approach which combines model order reduction and a perturbation algorithm to accelerate FDTD simulations beyond the CFL barrier. We compare the proposed algorithm against existing implicit and explicit CFL extension techniques, demonstrating increased accuracy and performance on a large number of test cases, including resonant cavities, a waveguide structure, a focusing metascreen and a microstrip filter.

In this article we reviewed the implicit space mapping concept. We illustrated it using a simple tapped-line microstrip filter example. We demonstrated the robustness of our approach by performing an accurate design of a microstrip hairpin filter. A detailed and easy-to-follow design optimization procedure was provided and the Agilent ADS implementation of the algorithm was described. A good electromagnetically validated design in Sonnet em was obtained in a few fine model simulations. Implicit space mapping is a simple approach to combine a circuit-theory based CAD model and an EM simulator model to achieve fast and accurate optimal design and modeling.

There have been difficulties in realizing wideband coupled-line filters with microstrip technology due to tight couplings demanded at input and output ports. To solve the problem, a realization method using high-impedance short-circuited stubs is proposed. To verify it, a coupled-line microstrip filter with more than 65% bandwidth is fabricated at 3 GHz and measured. Measured results are in good agreement with prediction, showing that the measured return and insertion losses are better than 18 and 0.85 dB, respectively, within more than 65% bandwidth.

We propose, for the first time, neural space-mapping (NSM) optimization for electromagnetic based design. NSM optimization exploits our space-mapping (SM)-based neuromodeling techniques to efficiently approximate the mapping. A novel procedure that does not require troublesome parameter extraction to predict the next point is proposed. The initial mapping is established by performing upfront fine-model analyses at a reduced number of base points. Coarse-model sensitivities are exploited to select those base points. Huber optimization is used to train, without testing points, simple SM-based neuromodels at each NSM iteration. The technique is illustrated by a high-temperature superconducting quarter-wave parallel coupled-line microstrip filter and a bandstop microstrip filter with quarter-wave resonant open stubs.

This letter introduces a DGS slot with an interdigital shape. The resonant frequency of the slot can be easily controlled by changing the length of the metal fingers, without changing the area taken by the structure. Using this slot, two quasi-elliptic low-pass filters were designed, fabricated and tested. The filters have a cut-off frequency of about 3 GHz.

An innovative computer-aided design (CAD) technique for efficient and accurate microstrip filter design is presented in this paper. The technique utilizes full-wave electromagnetic (EM) simulation for the individual circuit elements, while interactions between nonadjacent elements are emulated by introducing circuit components to form extra signal paths. Designs can be accomplished with the accuracy of complete circuit EM simulation while keeping the computational efforts at a cascading simulation level which is crucial for design optimization. The technique has clear physical interpretations and is easy to implement. The authors have successfully applied this technique to design several microstrip filters. Very good filter performance was achieved with good correlation between predicted and measured results.