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 a novel multiband RF filtering concept and a compact low-loss integration scheme for coaxial resonator-based multiband bandpass filters (BPFs). Size compactness is achieved by: 1) vertically stacking its constituent resonators, so that the available 3-D volume is optimally occupied; 2) the use of subwavelength capacitively loaded coaxial resonators; and 3) monolithic integration enabled by stereolithography apparatus (SLA) additive manufacturing (AM). A unique coupling routing diagram (CRD) is proposed and implemented with capacitively loaded coaxial resonators that allow to independently control the passband and stopband frequencies and facilitate both symmetric and asymmetric responses. A dual-band and triple-band BPFs operating at sub-6 GHz were designed, manufactured, and tested demonstrating highly miniaturized form factors and passbands with in-band insertion loss (IL) < 0.2–0.3 dB, i.e., $Q_{\mathrm {eff}}$ : 640–1030.

https://ieeexplore.ieee.org/ielx7/9944983/10004777/10081334.pdf

Vertically Integrated Coaxial Resonator-Based Multiband Bandpass Filters Using SLA 3-D Printing

This article reports on the RF design and practical development of active MMIC single-band, multi-band, and tunable bandpass filters (BPFs) with lossless and nonreciprocal transfer functions. They are based on series-cascaded lumped-element frequency-selective cells that are coupled with MMIC-based FETs. The FETs introduce gain and counteract the loss of the lossy elements. Furthermore, due to their unilateral behavior, nonreciprocal transfer functions can be obtained. This allows for an RF codesigned filtering isolator functionality to be created within a single RF component. By cascading multiple frequency-selective cells, both single-band and multi-band transfer functions with and without transmission zeros (TZs) can be realized. The basic operating principles of the MMIC concept are first described through parametric studies on different types of frequency-selective cells. These are followed by tunable and higher selectivity design methodologies. For practical demonstration purposes, four MMIC prototypes were designed, built, and measured using a commercially available GaAs process. They include a three-cell frequency-tunable BPF, two dual-band BPFs, and a quasi-elliptic BPF.

GaAs MMIC Nonreciprocal Single-Band, Multi-Band, and Tunable Bandpass Filters

This paper presents a microfluidically reconfigurable metasurface for polarization switching. A 5 × 5 unit cells metasurface array acts as a superstrate layer on the top of a circularly polarized antenna. The square split ring resonator with cross-shaped microfluidic channels can be reconfigured by pneumatically injecting or removing liquid metal alloy into 3D printed channels in two orthogonal directions. The incoming circular polarized (CP) wave can be either converted into a linearly polarized (LP) wave or transmitted without any effect as a CP wave. The simulated return loss plots for CP-CP and CP-LP conversion exhibit good impedance matching from 4.5 – 4.9 GHz, which represents a fractional bandwidth (FBW) of 8.5%. The far-field realized peak gain for both states remains greater than 6 dBi. The common bandwidth of CP-CP and CP-LP conversion is 4.5 –4.7 GHz resulting in FBW of 4.3%. The proposed metasurface antenna can be used in MIMO systems and biomedical applications to reduce polarization mismatches and multipath fading.

Polarization Agility Using A Microfluidically Reconfigurable Metasurface

A class of multi-band bandpass filters (BPFs) based on glass-integrated multi-resonant cells (MRCs) are reported. Each MRC comprises multiple in-parallel connected series-type resonators that create passbands in-between transmission zeros (TZs)—located at the resonators’ resonance. The MRCs can be combined in multi-stage configurations to create high-order multi-band transfer functions or used in the RF input and output ports of a conventional transversal multi-band BPF to enhance its selectivity by adding poles and TZs without increasing its size. A compact integration concept using high-Q 3D integrated-passive devices (IPDs) is used for the realization of sub-6-GHz multi-band BPFs. For practical validation purposes: (1) a tri-band BPF with passbands centred at 1.58, 2.07, 2.83 Hz and fractional bandwidths (FBWs): 10.9, 9.06, 10% respectively and in-band insertion loss (IL) between 2 and 2.8 dB and (2) a dual-band BPF with passbands centred at 2 and 2.9 GHz with FBW 14.9% and 16.14% we manufactured and tested. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/ell2.12781

Multi‐band glass‐integrated bandpass filters for new radio (NR) communications

MMIC co-designed RF components exhibiting the collocated RF signal processing actions of a dual-band bandpass filter and an RF isolator (DBPFI) are presented. They are based on in-parallel cascaded bandpass filters/isolators that operate at two different frequencies and two multi-resonant cells that are added in the RF input and RF output to increase the selectivity and the out-of-band isolation of the DBPFI through six added transmission zeros. For proof-of-concept demonstration purposes, a DBPFI prototype was designed and manufactured using a commercially available GaAs MMIC process. It exhibited the following RF-measured characteristics: center frequencies: 8.14 GHz and 10.8 GHz, 3-dB fractional bandwidth (FBW): 11.1% and 16.4%, |S21|: −3.7 dB and −8.8 dB, isolation >36.6 dB and 16.5 dB, IP1dB: 11.8 dBm and 12.8 dBm, IIP3: 18.2 dBm and 16.5 dBm, and OIP3: 14.2 dBm and 6.7 dBm, respectively, at the lower and the upper band. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/ell2.12780

Dimitra Psychogiou

Papers

Vertically Integrated Coaxial Resonator-Based Multiband Bandpass Filters Using SLA 3-D Printing

GaAs MMIC Nonreciprocal Single-Band, Multi-Band, and Tunable Bandpass Filters

Polarization Agility Using A Microfluidically Reconfigurable Metasurface

Multi‐band glass‐integrated bandpass filters for new radio (NR) communications

On‐chip GaAs‐based dual‐band bandpass filters/isolators (DBPFIs)