Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

A class of frequency-reconfigurable input-reflectionless/absorptive RF/microwave filters is presented. They consist of tunable complementary-duplexer architectures that are composed of a main and an auxiliary channel with opposite filtering transfer functions. By loading the auxiliary channel with a reference-impedance resistor and by taking the output node of the main channel as the output terminal of the overall circuit, a filtering network of the same type of the main channel with theoretically perfect input-reflectionless behavior at all frequencies can be realized. This technique can be applied to design spectrally agile completely input-reflectionless filters with any kind of transfer function, such as low-pass, high-pass, and single/multiband bandpass/bandstop filters. The theoretical analysis of the first-order absorptive bandpass/bandstop filtering sections based on a coupling-matrix formulation is detailed. Furthermore, the synthesis of high-selectivity reflectionless filters either by cascading multiple first-order cells or using high-order channels in a single complementary duplexer is also described. For practical-demonstration purposes, frequency-tunable lumped-element and microstrip prototypes are manufactured and characterized. They correspond to first- and second-order bandpass/bandstop filters. In addition, their in-series cascade connection is used to implement a bandpass filter with spectrally controllable passband and out-of-band notches.

Reflectionless Adaptive RF Filters: Bandpass, Bandstop, and Cascade Designs

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.

Single/multi-band Wilkinson-type power dividers with embedded transversal filtering sections and application to channelized filters

In this paper, a balanced-to-unbalanced microstrip power divider based on branch lines with several stubs and one resistor is proposed. The functions of power dividing, frequency selectivity, isolation between output ports, and common-mode suppression can be realized at the same time. The even–odd-mode equivalent circuits combining with the standard S-parameters and the mixed-mode S-parameters are adopted to derive the analytical equations at the center frequency. One or two transmission zeros can be achieved to enhance the out-of-band suppression. The center frequency, bandwidth, isolation, common-mode suppression, and the frequencies of transmission zeros can be controlled by the design procedure. To verify the theoretical prediction, two fabricated prototypes are designed and compared. One gets 7.7% 1-dB bandwidth with 0.6-dB insertion loss and one transmission zero. The other gets 1-dB bandwidth of 5% with 0.7-dB insertion loss and two transmission zeros. The isolation and common-mode suppression for both prototypes are better than 15 and 20 dB within the whole passband, respectively.

A Balanced-to-Unbalanced Microstrip Power Divider With Filtering Function

In this work, we present first-order antisymmetric (A1) mode resonators in 128° Y-cut lithium niobate (LiNbO3) thin films with electromechanical coupling coefficients ( $k^{2}$ ) as large as 46.4%, exceeding the state-of-the-art. The achievable $k^{2}$ of A1 in LiNbO3 substrates of different orientations is first explored, showing X-axis direction in 128° Y-cut LiNbO3 among the optimal combinations. Subsequently, A1 resonators with spurious mode mitigation are designed and fabricated. In addition to the large $k^{2}$ , the implemented devices show a maximum quality factor ( $Q$ ) of 598 at 3.2 GHz. Upon further optimization, the reported platform can potentially deliver a wideband acoustic-only filtering solution in 5G New Radio. [2020–0003]

/pdf/a1-resonators-in-128-y-cut-lithium-niobate-with-7qzey9qrsr.pdf

A1 Resonators in 128° Y-cut Lithium Niobate with Electromechanical Coupling of 46.4%

This letter reports on the RF design and practical development of miniaturized substrate-integrated-(SI)-coaxial-resonator-based bandstop filters (BSFs). Size compactness is achieved through the use of double-resonant coaxial resonators that are shaped by two coupled capacitively loaded posts within the volume of a circular cavity. The operating principles of the double-resonant SI-coaxial-resonator-based BSF concept are demonstrated by means of coupled-resonator diagrams and synthesized examples of both single-stage and multi-stage higher order BSF configurations. For proof-of-concept validation, various single- and two-stage coaxial-resonator-based BSF prototypes were designed, manufactured, and measured at $S$ -band.

/pdf/compact-substrate-integrated-bandstop-filters-using-double-1azuak7roi.pdf

Compact Substrate-Integrated Bandstop Filters Using Double-Resonant Coaxial Resonators

In this article, we demonstrate a method for codesign of filtering matching networks for power amplifiers (PAs) with the desired frequency response, improved efficiency, and reduced footprint. The microwave transistor operates with high efficiency with a specific complex-impedance load, and this requires the development of a theory for filter matching network design with arbitrary complex-impedance ports. The formulation is first developed and then applied to a simple second-order filter and a fourth-order filter with cross couplings and transmission zeros and verified in the experiment. A single-stage high-efficiency 4.7-GHz, 4-W hybrid GaN filter-PA (FPA) within a sub-6-GHz 5G band is designed, built, and characterized. The port impedances are determined by load– and source–pull for an efficiency–power tradeoff. The measured performance shows a gain of 15 dB, PAE = 55% with 9% fractional bandwidth, and 10-dB rejection at 4.5 and 5 GHz. Comparison with a cascaded PA-filter circuit shows a 25% lower loss with the same rejection and a reduced footprint with the same rejection. A GaAs monolithic microwave integrated circuit (MMIC) FPA at 28 GHz (millimeter-wave 5G FR2 band) is also designed and measured with a second-order output matching filter, demonstrating 8-dB gain, 200 mW of output power, and PAE = 30% with a rejection of 8 dB at 26.5 and 29.6 GHz.

Power Amplifiers With Frequency-Selective Matching Networks

This letter reports on a compact, low-cost, and low-loss monolithic integration concept for additively manufactured coaxial-resonator-based bandpass filters (BPFs). Size compactness and low weight are achieved by vertically stacking capacitively loaded coaxial resonators and by monolithic integration that eliminates the need for assembly screws or fixtures. Furthermore, the proposed vertical integration concept allows for: 1) flexible cross couplings to be realized enabling highly selective transfer functions through transmission zero (TZ) generation and 2) for fairly complex geometries to be manufactured using low-cost stereolithography apparatus (SLA). For proof-of-concept demonstration purposes, a two-pole BPF with fractional bandwidth (FBW) of 8.5% and a three-pole/one-TZ BPF with FBW 6.2% at 3.8 GHz were designed, SLA-manufactured, and measured. They exhibited low levels of insertion loss (IL) ( 1833, and wide spurious-free operation.

A Monolithic Vertical Integration Concept for Compact Coaxial-Resonator-Based Bandpass Filters Using Additive Manufacturing

This paper focuses on the design of surface-acoustic-wave-(SAW)-based bandpass filters (BPFs) with enhanced fractional bandwidth (FBW) and constant in-band group delay (τ g ). They are based on a hybrid RF-design approach in which high-quality-factor (Q) SAW resonators are effectively combined with low-Q lumped elements (LEs). Contrary to conventional ladder-or lattice-type filter architectures, the devised configuration enables passbands that can simultaneously achieve: i) flat in-band τ g , ii) FBWs that are larger than the electromechanical coupling coefficient (kt2) of its constituent substrate, and iii) Qs of the order of a thousand. In order to validate the proposed filter design approach, a two-pole/four-transmission-zero (TZ) prototype has been designed, manufactured, and measured. It exhibited passband bandwidth of 0.45 MHz, FBW of 1.4kt2, minimum in-band insertion loss of 1.5 dB, effective Q of 8,000, in-band return loss of 23 dB, and an average τ Β of 0.86 ps.

SAW-based bandpass filters with flat in-band group delay and enhanced fractional bandwidth

A class of negative-group-delay (NGD) bandstop-filter (BSF) circuits with input-reflectionless behavior are presented. By absorbing the non-transmitted RF-input-signal energy in their circuit volume, they cancel the undesired RF-power reflections that can adversely affect preceding active stages. They are based on a lossy complementary-duplexer approach, in which the lossy BSF channel is used as NGD circuit and its lossy resistively-terminated bandpass-filter-(BPF)-channel counterpart dissipates the non-transmitted RF signal power. The theoretical analysis of the basic input-reflectionless first-order NGD stage and illustrative design examples are presented. In-series-cascaded multi-stage NGD realizations to increase the NGD flatness are also explored. Furthermore, for experimental-validation purposes, a two-stage microstrip prototype with center-frequency reconfiguration and controllable NGD pattern within the spectral range 1.55–2.1 GHz is manufactured and characterized.

Dimitra Psychogiou

Papers

Compact Substrate-Integrated Bandstop Filters Using Double-Resonant Coaxial Resonators

Power Amplifiers With Frequency-Selective Matching Networks

A Monolithic Vertical Integration Concept for Compact Coaxial-Resonator-Based Bandpass Filters Using Additive Manufacturing

SAW-based bandpass filters with flat in-band group delay and enhanced fractional bandwidth

Input-Reflectionless Negative-Group-Delay Bandstop-Filter Networks Based on Lossy Complementary Duplexers