High-order single-ended and balanced wideband bandpass filters (BPFs) with quasi-elliptic-type (QET) responses are reported. Firstly, a fifth-order wideband BPF based on a two-layer ...microstrip-to-microstrip vertical transition with two shunt open-circuit-ended two-section microstrip stubs at the input and output ports, respectively, is designed. Compared to a typical third-order vertical transition, two more transmission poles (TPs) along with a pair of close-to-passband transmission zeros (TZs) are attained. Next, an application to design a ninth-order QET balanced wideband BPF using a vertical transition is carried out. Owing to the used slotline resonator, an intrinsic common-mode (CM) suppression capability is obtained for it. The RF operational and design principles of these BPF devices are detailed by means of their relevant transmission-line-(TL)-based equivalent circuits. For experimental-validation purposes, two microstrip prototypes corresponding to a 3-GHz fifth-order wideband BPF and a 2-GHz ninth-order balanced wideband BPF are developed and tested. The measured single-ended and balanced BPF circuits feature sharp-rejection QET responses with two close-to-passband TZs and stopband-power-attenuation levels above 27.3 dB and 43.66 dB, respectively. The measured CM suppression levels for the balanced BPF device are higher than 34.59 dB from DC to 5 GHz.
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.
A class of input reflectionless dual-behavior resonator (DBR)-based bandpass filters (BPFs) with reconfigurable center frequency, bandwidth, out-of-band attenuation, and intrinsic switching-off ...capabilities is reported. They exploit a complementary-duplexer approach, in which the resistively terminated bandstop-filter (BSF) channel dissipates the RF input signal energy that is not transmitted by the main BPF channel in its out-of-band region. Spectral reconfiguration is realized through the synchronous tuning of the counterpart resonators in the DBR-based BPF and BSF channels-i.e., without variable couplings-which results in a dynamic transmission-zero (TZ) reallocation process. The theoretical analysis of the first-order section and design examples for higher order schemes are presented. Furthermore, for experimental-validation purposes, a microstrip prototype that can be tuned within the frequency range 1.3-2 GHz is manufactured and characterized.
A new series of multifunctional reconfigurable bandpass filters (BPFs) and their analytical synthesis design are presented in this paper. They feature frequency-adaptive characteristics in both their ...passbands and notched bands, as well as switchable-notched-band capability. Their basic filter architecture is discussed and modeled in a progressive manner. The initial circuit consists of a second-order Chebyshev-type filter to which two stubs are added to increase filtering selectivity through transmission-zero (TZ) creation. Subsequently, to produce an embedded notched band, stubs acting as band-stop structures are also inserted at the input-output terminals. The multifunctional properties of this filter scheme are analyzed attending to the resonance frequencies of the introduced stubs. When these resonance frequencies are tuned while keeping a constant spacing between them, a center-frequency reconfiguration with constant bandwidth is achieved; when the resonance frequency of the notched band is shifted to the TZ positions, the notched band is switched-off. The described filter synthesis methodology is based on the constant and frequency-mapping technique, where the dual-mapping functions are controlled to obtain reconfigurable/switchable properties from a low-pass prototype. For experimental-validation purposes, two reconfigurable lumped-element filter prototypes using the proposed synthesis technique are designed, manufactured, and tested. One exhibits a simple reconfigurable passband, whereas the other one adds a controllable/switchable embedded notched band that results in a quasi-elliptic-type dual-passband response. When compared to some related prior-art designs, these filters have the advantages of explicit design process, quantified analysis, and multifunctional responses.
Two classes of RF/microwave planar quad‐band bandpass filters (BPFs) that simultaneously exploit transversal signal‐interference and multi‐passband‐splitting mechanisms are reported. The first ...approach makes use of a triple‐band bandpass transversal filtering section (TFS) composed of two in‐parallel stepped‐impedance coupled‐line signal‐propagation paths. By inserting an open‐ended stub at the input and output terminals of this TFS, its middle passband is divided into two sub‐bands to attain an overall quad‐passband filtering response. The second configuration employs a dual‐passband TFS based on a coupled‐line directional coupler with open‐ended stubs at its direct and coupled ports. By loading such TFS with a replica of it at the direct and coupled ports of its coupler, the two passbands are split into four sub‐bands to obtain the quad‐band functionality. The RF operational foundations of these quad‐band BPFs, along with single‐ and multi‐stage design examples featuring sharp‐rejection four‐passband filtering responses with transmission zeros (TZs), are detailed. Moreover, for experimental‐demonstration purposes, two microstrip prototypes are developed and tested. Besides, as a further application, a two‐layer balanced‐circuit version with ultra‐broad common‐mode (CM) suppression of the constituent triple‐passband TFS of the first prototype is built and measured.
Two classes of RF/microwave planar quad‐band bandpass filters (BPFs) that simultaneously exploit transversal signal‐interference and multi‐passband‐splitting mechanisms are reported or for experimental–demonstration purposes, two microstrip prototypes are developed and tested. Besides, as a further application, a two‐layer balanced‐circuit version with ultra‐broad common‐mode (CM) suppression of the constituent triple‐passband TFS of the first prototype is built and measured.
This work presents the design techniques to synthesize a class of compact inline quasi-elliptic-type waveguide cavity bandpass filters based on novel nonlinear frequency-variant couplings (NFVCs). ...These highly dispersive frequency-variant couplings (FVCs) are realized by means of a pair of partial-height posts that are placed at the junctions between every two cavity resonators. Each NFVC produces a transmission pole in between a pair of independently adjustable transmission zeros (TZs). Although the pole is added to the overall filtering function to augment its order, the TZs can be placed at each side of the filter passband to attain sharp rejection capability and increase the stopband attenuation levels. To synthesize these filters, two coupling-routing-diagram (CRD) approaches for the NFVC are presented that either consider: 1) an arbitrary FVC (AFVC) or 2) two resonating nodes interacting with a zero-susceptance nonresonating node through constant inverters. An equivalent lumped-element circuit model associated with both CRD approaches is provided. It is demonstrated that both CRD models can be exploited for the theoretical synthesis of this type of filter, whereas the equivalent lumped-element circuit model can provide a deeper insight into the systematic dimensioning of the posts. For experimental validation purposes, three design examples are synthesized, and 10-GHz proof-of-concept filter prototypes of two of them are EM-simulated, fabricated, and characterized. The measured results agree well with the simulations and the design theory, thus verifying the concept of inline waveguide cavity filters with TZs using NFVCs.
A class of RF multi-functional bandpass filter with multiple frequency-reconfigurable rejected bands that are embedded into its broad transmission frequency range is reported. This filter concept ...exploits an original tunable multi-band quasi-bandstop section as constituent block. In this manner, unprecedented levels of spectral adaptivity are obtained for its in-band notches. Among them: 1) independent control of center frequency and rejection level; 2) notch-combination capability to conform wider rejected bands and make their number dynamically selectable; and 3) generation of dual-band bandpass responses with adjustable bandwidth and inter-band transmission zeros. This results in controllable in-band stopbands with reconfigurable bandwidth, attenuation level, and filtering-profile type. The devised filter architecture, which is appropriate for dynamic multi-interference mitigation in broad-band RF receivers, is scalable to any number of arbitrary-order in-band notches. For proof-of-concept purposes, a UHF-band microstrip prototype with up to two tunable in-band second-order stopbands is manufactured and measured.
Surface acoustic wave (SAW)-based bandpass filters (BPFs) with symmetrical quasi-reflectionless characteristics and continuously tunable bandwidth (BW) are reported. They are based on ...in-series-cascaded symmetrical quasi-reflectionless acoustic-wave (AW)-lumped-element resonator (AWLR)-based networks whose input and output ports are connected to resistively terminated AWLR-based bandstop filter (BSF) sections. The proposed concept is presented through the coupling routing diagram (CRD) formalism that allows their design using coupled-resonator-based synthesis. It is shown that by incorporating variable reactance elements in their BPF sections, continuous-type BW tuning can be realized. In addition, the fractional BW (FBW) of the filter can be designed to be wider than the electromechanical coupling coefficient <inline-formula> <tex-math notation="LaTeX">k_{t}^{2} </tex-math></inline-formula> of its SAW resonators. This allows enhanced-FBW passbands to be obtained. For proof-of-concept validation, two prototypes were designed and measured. They include a single-stage prototype with 1.9:1 continuously tunable BW and a static two-stage with effective quality factor > 6500, FBW of <inline-formula> <tex-math notation="LaTeX">1.2k_{t}^{2} </tex-math></inline-formula>, and return loss >15 dB throughout its passband and stopband ranges.
A class of RF low-pass filters (LPFs) simultaneously featuring flat-in-band-group-delay and input-quasi-reflectionless characteristics is reported for the first time. By means of a multilayered ...complementary-diplexer-based topology, a single-ended input-quasi-reflectionless LPF with in-band quasi-flat group-delay response and multiple out-of-band transmission zeros (TZs) is first conceived. It consists of the combination of single-pole LPF units with resistively terminated microstrip-to-microstrip vertical slotline transitions (MS-to-MS VSTs). Subsequently, intrinsic common-mode-(CM)-signal suppression for its balanced counterpart is realized through in-series cascading two single-ended LPF stages with a coplanar stripline (CPS) section. As a result, a balanced LPF possessing differential-mode (DM) in-band quasi-constant group-delay response, DM input-quasi-absorptive behavior, and intrinsic CM suppression is obtained. Furthermore, to increase DM selectivity and out-of-band attenuation levels along with CM suppression levels, a higher rejection balanced LPF composed of multiple cascaded single-ended LPF units and CPS sections is also devised. The RF operating principles of the engineered single-ended and balanced LPF circuits are detailed. Three demonstrative prototypes-i.e., one single-ended and two balanced LPF circuits-are manufactured and characterized for practical validation purposes. For the higher rejection balanced LPF prototype, eye-diagram tests are also carried out to verify the quality/integrity of the transmitted DM signal in the time domain.
This paper addresses the exploitation of signal-interference concepts for the realization of single/multi-frequency Wilkinson-type filtering power dividers in planar/lumped-element technologies. By ...embedding transversal signal-interference filtering sections into the arms of conventional Wilkinson-type power-divider topologies, RF/microwave power-distribution actions with intrinsic mono/multi-band bandpass filtering capabilities can be obtained. Analytical equations and rules for the theoretical synthesis of this dual-function device are derived. The generalization of the approach to multi-stage schemes for enhanced-performance designs or for the shaping of frequency-asymmetrical responses is also discussed. Furthermore, for practical demonstration, three prototypes are developed and characterized. They are a microstrip quad-band circuit for the 1-5 GHz range, a dual-band lumped-element device for the band of 0.2-0.6 GHz, and a new type of two-branch channelized active bandpass filter at 3 GHz that makes use of single-band versions of this dual-behavior component as signal-division/combination blocks.
PDF
