An approach for the realization of radiofrequency (RF)/microwave balanced filters with simultaneous differential-mode (DM) and common-mode (CM) two-port-reflectionless behavior for bandpass, ...quasi-bandstop, and dual-passband applications is reported. These RF filtering components exploit as basic constituent circuit block a type of two-layer broadband magic-T, in which its two-side/coplanar arms are designed as the balanced feeding ports at the top layer. Specifically, two replicas of this wideband magic-T on a microstrip-to-slotline transition are back-to-back connected between their <inline-formula> <tex-math notation="LaTeX"> {\Delta } </tex-math></inline-formula> terminals by means of a double-complementary-diplexer-based single-ended low-reflection filtering unit inserted at the bottom layer. In addition, their <inline-formula> <tex-math notation="LaTeX"> {\Sigma } </tex-math></inline-formula> accesses are loaded with a resistor to perform the CM RF-power-absorption functionality. Thus, balanced symmetrical-absorptive RF filtering devices for both the DM and CM operations are developed. Such distinctive feature makes this family of microwave filters unique since most of related prior-art balanced filters mainly focused on obtaining the RF-power-absorption property only for the DM or the CM. The theoretical operational foundations and RF design principles of the engineered class of balanced filters with double DM and CM symmetrical-absorptive capabilities are described. Furthermore, their two-layer implementations exemplified in second- and fourth-order bandpass filters (BPFs), a second-order quasi-bandstop filter (BSF), and a second-order dual-band BPF are presented. For experimental-validation purposes, three different prototypes centered around 2 GHz corresponding to single-band BPF and quasi-BSF devices, as well as a dual-band BPF circuit with passbands located at 1.75 and 2.25 GHz, are manufactured and tested. For all these prototypes, 10-dB-referred DM and CM two-port-RF-power-absorption relative spectral ranges larger than 3:1 are measured. Their expected RF filtering functionalities and highly suppressed CM transmission at all frequencies are also verified.
Split-type multiband bandpass filters (BPFs) and bandstop filters (BSFs) with input-reflectionless capabilities are reported in this letter. In the multiband BPF case, they consist of a duplexing ...network with a split-type multiband BPF channel-main channel-and its complementary resistively terminated multiband BSF channel-auxiliary channel-that absorbs the input-signal energy that is not transmitted by the overall filter. The multiband BSF counterpart is obtained from the latter by interchanging the roles of the main and auxiliary channels. The operational foundations, theoretical design rules, and synthesis examples of the devised split-type input-reflectionless multiband filters under a coupling-matrix-based formulation are described. Furthermore, for practical validation purposes, two microstrip prototypes corresponding to 3.85-/4.55-GHz second-order dual-band BPF and BSF circuits are constructed and measured.
In recent years, there is an increased use of passive filters in both transmission and distribution systems due to the proliferation of power electronic devices. However, the problem of filter design ...has not been well addressed in the past and one example is the application of high-pass filters in a filter package. Three types of HP filters are widely used to mitigate multiple harmonics, i.e., 2 nd HP filter, 3 rd HP filter and C-type filter. There is still a lack of research to clearly reveal the characteristics of each filter, which makes it difficult for the designer to select the optimal filter topology under different circumstances. The main goal of this paper is to solve the problem of how to select a proper configuration among three HP filter candidates for a given harmonic problem. Unlike the conventional optimization-based filter studies, this paper investigates three HP filters in an analytical way. As a result, the paper provides a deep insight into the inherent characteristics of the filter and the conclusions drawn in the paper are universal; thus can be used in different applications, ranging from low voltage levels to high voltage levels. The research results lead to a recommended application scope of each HP filter, which is very useful to guide the design of filter packages and help designers to evaluate the design results.
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.
The direct synthesis of a family of digital-filter-based RF analog circuits with transmission zeros (TZs) and constant-group-delay behavior is reported. The adopted RF circuit consists of a ...transversal filtering network composed of transmission-line segments that are connected through a multi-way power divider and combiner at its input and output terminals, respectively. The synthesis procedure starts by obtaining the coefficients of a finite-impulse-response (FIR) digital filter of interest and finalizes with the determination of the electrical parameters of the RF circuit. In particular, designs corresponding to Dolph-Chebyshev windows are addressed in this brief. For experimental-demonstration purposes, two 5-GHz proof-of-concept microstrip prototypes of a symmetrical-quasi-reflectionless bandpass filter (BPF) with Dolph-Chebyshev-type response and the in-series cascade connection of two replicas of it are designed, manufactured, and tested.
In this work, a family of frequency-variant reactive coupling (FVRCAFVC) networks is introduced and discussed as new building blocks for the synthesis of coupled-resonator bandpass filters with real ...or complex transmission zeros (TZs). The FVRCAFVC is a type of nonideal frequency-dependent inverter that has nonzero elements on the diagonal of the impedance matrix, along with a nonlinear frequency-variation profile of its transimpedance parameter. The distinctive feature of these new FVRCsAFVC is that they can be modeled with a simple bridged-T network consisting of four reactive elements. Such FVRCsAFVCs can introduce one pole and up to two TZs-so that they are referred to as double-zero single-pole (DZSP) networks. DZSP networks allow the pole to be located above, below, or in-between the TZs. Depending on the choice of the elements in the bridged-T circuit, the position of the TZs and the pole can be controlled independently. The coupling matrix for filters with DZSP networks can be found by solving an inverse-structured nonlinear eigenvalue problem (ISNEVP). Examples of possible implementations of DZSP couplingAFVC networks are provided for both lumped and quasi-lumped-element circuits, as well as for transmission-line-based and waveguide technologies. The application of DZSP coupling networks to the design of microwave bandpass filters with generalized Chebyshev-type characteristics is illustrated by means of the synthesis of three microstrips and two waveguide coupled-resonator bandpass filters. The waveguide filters are verified through electromagnetic (EM) simulations and the microstrip filters are manufactured and characterized for proof-of-concept demonstration purposes, showing a fairly close agreement between EM simulations and measurements.
An RF input-quasi-reflectionless bandpass filter (BPF) with reconfigurable center frequency and constant absolute bandwidth (ABW) is presented. The proposed BPF is based on a tunable ...complementary-diplexer architecture, which is made up of a main bandpass-type channel and an auxiliary channel with nearly-complementary bandstop-type filtering response that are synchronously reconfigured in frequency. The auxiliary channel is terminated by a resistor to absorb the RF power reflected by the main channel within its out-of-band region. In this manner, input-quasi-reflectionless capability is obtained. As an original technique, the constant ABW is attained in this overall BPF across the tuning range by means of the compensation of the bandwidth variations between its two channels. Subsequently, as a further application of this filter design concept, an RF frequency-adaptive Wilkinson-type power divider (PD) with constant-ABW filtering response and input-quasi-reflectionless behavior is reported. A single resistively-terminated bandstop-type branch is connected at the input port of the filtering PD to absorb the non-transmitted RF-input-signal energy. For validation purposes, a varactor-tuned frequency-reconfigurable input-quasi-absorptive BPF and a 3-dB filtering PD with constant-ABW are built and measured.
In this article, a novel design method for rectangular waveguide filters intended for fabrication using direct metal additive manufacturing (AM) is proposed. The synthesized filters will feature a ...smooth profile that allows us to fabricate them orienting the filter propagation axis in the vertical building direction, achieving an optimum configuration for direct metal AM fabrication. The novel design method is valid for any all-pole transfer function, which is initially implemented with a commensurate-line distributed unit element prototype. The impulse response of that initial prototype is then properly interpolated to obtain the target response for a smooth-profiled filter with similar length and profile excursion. Finally, the target impulse response just generated is implemented in the rectangular waveguide technology employing a novel inverse scattering synthesis technique that relies on the coupled-mode theory to model the electromagnetic behavior of the waveguide filter. The novel inverse scattering synthesis technique is general and also valid for the case of filters with very high rejection levels, which is of great relevance in rectangular waveguide technology. A Ku-band low-pass filter with stringent satellite specifications is designed using the proposed method, fabricated by means of a direct metal AM technique, and measured with a vector network analyzer. A very good agreement is achieved between the simulated and measured results, fulfilling the required specifications and demonstrating the feasibility and performance of the novel design method.
In this paper, two simple structures, i.e., coupled line and T-shaped microstrip structures, are used to construct four types of quasi-reflectionless (QR) filters, including single-and two-port QR ...bandpass filters (BPFs) and bandstop filters (BSFs). First, the characteristics of the coupled line and T-shaped microstrip structures are analyzed in details using each two electrical parameters. Then, the single-port QR BPF and BSF are designed using duplexer architectures formed by these two simple structures. Subsequently, the two-port QR BPF and BSF are constructed through loading an additional absorption channel near the output port based on the architectures of single-port QR filters. The relations between the fractional bandwidth (FBW) of each type of QR filters and 3-dB FBWs of the two simple structures are provided, which give a guidance of the QR filter design with desired specifications. Moreover, a brief design procedure for the proposed QR filters is summarized. Finally, to validate the feasibility of the proposed approach, two proof-of-concept microstrip prototypes of the two-port QR filters are fabricated, whose simulations and measurements agree well with each other. This work will facilitate the design of QR filters with different desired specifications and simplify their design procedures.
In this brief, a class of microstrip bandpass filters (BPFs) with quasi-reflectionless behavior on both input and output ports is presented. A single-port reflectionless BPF is proposed by shunt ...connecting one bandstop filter cell namely one-cell. This one-cell single-port reflectionless BPF is made up of a high impedance transmission line as a series band-pass filter section and a shunt-connected band-stop section with resistively terminated. In the operation passband, the bandpass filter section is used to transmit spectral energy, while the bandstop section is regarded as an open circuit. Besides, the out-of-band energy is absorbed by resistively component in the bandstop filter section. In order to achieve better out-of-band reflectionless characteristic, a two-cell two-port reflectionless BPF is constructed by shunt connecting two cells at input/output ports and one series bandpass filter section in the center. In addition, a three-cell reflectionless BPF is designed to further verify the improvement of out-of-band performance. Finally, two-cell and three-cell two-port reflectionless BPFs are fabricated and tested to verify the design concept. The measured results of these two reflectionless BPFs are in good agreement with the simulation ones.
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