Signal-interference single- and multiband bandpass-type transversal filtering sections (TFSs) with input- and two-port low-reflection (LR) behavior are reported. These LR TFSs consist of the ...following three parts: 1) a reflective-type TFS shaped by two in-parallel unequal length transmission line segments; 2) a lossy open-ended stub shunted at the input or both at the input and output nodes of the building reflective-type TFS for the input- and two-port-LR TFS cases, respectively; and 3) input/output power-matching transmission line sections. In this manner, the stopband RF-signal energy that is not transmitted by the reflective-type TFS is dissipated by the resistor(s) of the lossy open-ended stub(s) instead of being reflected back to the source. This allows LR capabilities to be obtained in the overall modified TFSs. The operational principles of the proposed input- and two-port-LR TFSs, along with theoretical design examples and their comparison, are presented. Moreover, multi-TFS-stage LR bandpass filters (BPFs) are shown. They are based on the in-series cascade of several LR TFSs to enlarge the bandwidth and power rejection levels of the stopbands while keeping their LR nature. For experimental validation purposes, microstrip prototypes of a three-TFS-stage BPF with broadened input-LR stopbands and a quintuple-band input-LR TFS are developed and characterized.
A differential single-port switched-RC N-path filter with band-pass characteristic is proposed. The switching frequency defines the center frequency, while the RC-time and duty cycle of the clock ...define the bandwidth. This allows for high-Q highly tunable filters which can for instance be useful for cognitive radio. Using a linear periodically time-variant (LPTV) model, exact expressions for the filter transfer function are derived. The behavior of the circuit including non-idealities such as maximum rejection, spectral aliasing, noise and effects due to mismatch in the paths is modeled and verified via measurements. A simple RLC equivalent circuit is provided, modeling bandwidth, quality factor and insertion loss of the filter. A 4-path architecture is realized in 65 nm CMOS. An off-chip transformer acts as a balun, improves filter-Q and realizes impedance matching. The differential architecture reduces clock-leakage and suppresses selectivity around even harmonics of the clock. The filter has a constant -3 dB bandwidth of 35 MHz and can be tuned from 100 MHz up to 1 GHz. Over the whole band, IIP3 is better than 14 dBm, P 1dB =2 dBm and the noise figure is 3-5 dB, while the power dissipation increases from 2 mW to 16 mW (only clocking power).
This brief reports on the electromagnetic (EM) design and the practical development of frequency-reconfigurable quasi-reflectionless bandpass filters (BPFs) using substrate integrated coaxial (SIC) ...resonators. The filter concept is based on in-series-cascaded quasi-reflectionless stages that are shaped by a first-order bandpass section and two resistively-terminated first-order bandstop sections. For the first time, we explore the realization of these filters using tunable SIC resonators that exhibit high quality factor (<inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula>) and can be widely tuned with commercially-available linear piezoelectric actuators. Synthesized examples alongside various EM design and practical integration aspects are discussed in detail. The concept is experimentally validated at S-band through the manufacturing and testing of two reconfigurable (one-stage and two-stage) prototypes.
An original RF design approach for the realization of fully reconfigurable planar multiband bandstop filters (BSFs) is reported. The engineered RF filtering topology allows independent control of its ...stopbands in terms of center frequency and bandwidth. It exploits the in-series cascade of K spectrally agile N-notch filtering cells that are connected through K - 1 static impedance inverters to realize an N-band filtering transfer function with Kth-order stopbands. Each of these multinotch cells is formed by N tunable resonators-center-frequency control-that interact with the same nonresonating node by means of different variable couplings-bandwidth control. Additional features of this tune-all multiband BSF architecture when compared with related prior-art devices are: 1) scalability to the synthesis of an arbitrary number of stopbands; 2) notch-spectral-merging capability into wider eliminated bands of the same order, which equivalently allows the intrinsic control, i.e., without RF switches, of the amount of active rejected bands; and 3) smaller physical size. The coupling-matrix modeling of the conceived multiband BSF scheme is presented. Moreover, its cointegration with other RF analog-processing actions in multifunctional components, such as bandpass filtering and power division, is investigated. For experimental-validation purposes, three UHF-band mechanically reconfigurable microstrip prototypes are developed and tested. They correspond to a dual-notch filter, a wideband bandpass filter with embedded notches in its tunable passband, and a Wilkinson-type power divider with inserted stopbands for dynamic multi-interference mitigation.
A varactor-based tunable bandstop filter has been proposed in this letter. The proposed filter is based on a dual-mode circuit developed by introducing inductive and capacitive couplings into a notch ...filter. The frequency tunability is achieved by using varactor diodes instead of the lumped capacitors in the circuit. Next, the equivalent circuit model has been implemented in planar microstrip technology using thin inductive traces and varactor diodes. The fabricated filter prototype shows a continuous center frequency tuning range of 0.66-0.99 GHz with a compact size of <inline-formula> <tex-math notation="LaTeX">0.12\lambda _{g} \times 0.16\lambda _{g} </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">\lambda _{g} </tex-math></inline-formula> is the guided wavelength at the middle frequency of the tuning range.
Despite the increasing importance and critical needs, reconfigurable radio frequency (RF) multiband filters are currently underdeveloped even both RF electronics and photonics technologies are being ...explored. Although RF multiband filters with large numbers of simultaneous passbands and wide frequency tuning range are extremely desired, achieving such functionality is extremely challenging. In this paper, a photonics-based highly tunable and reconfigurable RF multiband filter is proposed through the combination of a special designed tunable Mach-Zehnder interferometer and a reconfigurable Lyot loop filter. Both the passband frequencies and the number of simultaneous passbands are adjustable, that one or multiple passbands are continuously tuned over a 20 GHz frequency range, and the number of simultaneous passbands is reconfigurable from zero to seven. As a result, the proposed RF multiband filter can be configured with various passband combinations through the same setup, providing exceptional operation flexibility. Furthermore, broadband operation and excellent filter selectivity are obtained, with sharp passband profiles and over 35-dB sidelobe suppression.
In this paper, a fully tunable bandpass filter (BPF) with three states of filtering (single passband state, dual passband state and all-off state) is proposed, the proposed fully tunable BPF is ...cascaded by a tunable low pass filter section (LP) and a tunable high pass filter section(HP). By introducing a switchable dual-mode notch in the passband, the proposed BPF is capable of operating in single, dual passband and all-off state, demonstrating high flexibility in working mode. Tunable LP and HP filters with 7-order generalized Chebyshev response are designed to improve the roll-off rate and out-of-band rejection level of the BPF. The measured results show that the bandwidth of the BPF can be tuned from 0.21GHz to 2.26GHz (10.8:1), and the center frequency can be tuned from 2.9GHz to 4.6GHz with constant absolute bandwidth of 1GHz. Besides, high rejection level of out-of-band is realized in all working mode. The high flexibility in working mode makes the proposed fully tunable BPF very attractive in carrier aggregation scenarios.
As an essential part in technologies for energy storage systems (ESSs) or renewable energy systems (RESs), grid‐connected inverters need power passive filters to meet grid regulations. As typical ...passive filters, L filter and LCL filter are employed. Although LCL filter is more cost‐effective than L filter, a design of LCL filter is more complicated than L filter. LCL filter has three filter elements: inverter‐side inductor, grid‐side inductor, and filter capacitor. To design the three elements for LCL filter, three or more simultaneous equations should be required, which means that three or more design target should exist. Since conventional design methods for LCL filter do not suggest clear targets and do follow try & error method which cannot be matched exactly with design targets, the conventional methods cannot be optimal design. In this study, a filter inductance ratio to minimise total filter inductance, a filter admittance to meet grid regulation and characteristic impedance for low current stress of switch stack are suggested as design goals. Optimal design equation is proposed to meet the three design goals. The proposed method can solve unique filter elements for LCL filter without iterative try & error. The design method is evaluated through simulation and experiment.
This article reports on the RF design and implementation of monolithic microwave integrated circuit (MMIC) bandpass filters (BPFs) with broadband symmetric quasi-reflectionless characteristics. They ...are based on in-series cascaded quasi-reflectionless stages that comprise one bandpass (BP) and two resistively terminated bandstop (BS) sections with approximately complementary transfer functions. This allows the resistors to absorb the reflected RF signal energy, and a quasi-reflectionless behavior is obtained at both the input and output ports of the BPF. The frequency selectivity of the BPF can be increased by: 1) introducing out-of-band transmission zeros (TZs) through inductive, capacitive, or resonant source-to-load couplings and/or by 2) increasing the number of stages in the overall filter. An on-chip integration scheme with minimum number of components is proposed using the commercially available PIH-110 GaAs MMIC process from WIN Semiconductors. Three prototypes were designed, manufactured, and measured at X-band. They demonstrated ultra-compact physical size and ultrawide >9:1 quasi-reflectionless characteristics.
This paper presents a novel multiband waveguide filter model employing cylindrical resonators arranged horizontally and vertically in Olympic and parallel topologies, respectively. The proposed model ...has the advantages of reduced footprint and the ability to realise more complex filtering functions. 3 <inline-formula> <tex-math notation="LaTeX">^{\mathrm{ rd}} </tex-math></inline-formula> order dual-band, triple-band, quad-band and 5 <inline-formula> <tex-math notation="LaTeX">^{\mathrm{ th}} </tex-math></inline-formula> order dual-band filters in Ku -band were designed to validate the proposed model. Design flexibility in terms of reconfigurability of centre frequencies and bandwidths is demonstrated with dual-band filter examples. The design strategy is presented and validated with a triple-band filter example. For experimental validation of the proposed model, Selective Laser Melting, a metal Additive Manufacturing technique, was used to fabricate triple-band filter prototypes in copper. Since this model has a complex internal structure, 3-D printing allowed us to avoid complicated assembly and manufacture filters in one piece. The measured results of the four prototypes show a good agreement with the simulations and adequate repeatability.
PDF
