Showing papers by "Dimitra Psychogiou published in 2018"

Balanced Symmetrical Quasi-Reflectionless Single-and Dual-Band Bandpass Planar Filters

Abstract: Microwave planar balanced single-/dual-band bandpass filters (BPFs) with symmetrical quasi-reflectionless differential-mode behavior are presented in this letter. They are made up of a direct single-/dual-band BPF branch with virtually short-ended stubs in differential-mode operation, whose input and output accesses are loaded with stub-loaded-type single-/dual-band bandstop filter (BSF) branches that are terminated with a resistor. These BSF branches exhibit a quasi-complementary transfer function with regard to the one of the BPF branch and absorb the differential-mode input-signal energy not transmitted by the filter to achieve quasi-reflectionless capabilities. The theoretical foundations of the proposed balanced quasi-absorptive single-/dual-band BPFs and synthesis examples are given. Furthermore, for experimental-demonstration purposes, microstrip prototypes of 3-GHz second-order single-band and 2.85/3.15-GHz first-order dual-band BPFs are manufactured and characterized.

Multi-Stub-Loaded Differential-Mode Planar Multiband Bandpass Filters

Abstract: A new type of RF $/$ microwave differential-mode planar multiband bandpass filters (BPFs) are presented. Each symmetrical half of the proposed balanced filtering architecture is composed of the in-series cascade of $K$ $N$ -stub-loaded cells through $K-1$ inter-connection transmission-line segments to synthesize a differential-mode transfer function with $N$ $K$ th-order passbands. Additional features of this balanced multiband BPF topology are as follows: 1) generation of transmission zeros at both sides of all differential-mode passbands; 2) high common-mode power-rejection levels within the differential-mode passband ranges; 3) scalability to any number of arbitrary-order differential-mode transmission bands; and 4) lack of electromagnetic couplings in its physical structure. The theoretical foundations of the engineered balanced filter approach, along with guidelines to design the differential-mode transfer function and to attain optimum in-band common-mode power-attenuation characteristics, are expounded. Furthermore, for experimental-demonstration purposes, a third-order triple-band microstrip prototype with differential-mode passbands that are located within the range 1.4–3 GHz is manufactured and characterized.

Split-Type Input-Reflectionless Multiband Filters

Abstract: 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.

RF Wide-Band Bandpass Filter With Dynamic In-Band Multi-Interference Suppression Capability

Abstract: 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.

Design and Optimization of Tunable Silicon-Integrated Evanescent-Mode Bandpass Filters

Abstract: This paper reports on the design and optimization of MEMS-tunable evanescent-mode cavity-based bandpass filters with continuously variable center frequency within an octave tuning range. The devised filters are manufactured using silicon-micromachining techniques that enable their actualization for frequencies located in the millimeter-wave (30–100 GHz) regime. An RF design methodology that takes into consideration all microfabrication-induced constrains—e.g., nonvertical wall profiles and finite MEMS deflection—enables high unloaded factor ( $Q_{u}$ ) and also minimizes bandwidth (BW) variation within the octave tuning range is reported. Furthermore, a new passively compensating package-integrated input/output feeding structure that enables optimal impedance matching over the entire tuning range is also presented. In order to evaluate the devised RF design methodology, a filter prototype was manufactured and measured at Ka-band. It exhibits a measured frequency tuning between 20 and 40 GHz (2:1 tuning range), relative BW between 1.9 and 4.7%, insertion loss between 3.1 and 1.1 dB, and input reflection below 15 dB. This paper also explores important tradeoffs between mechanical stability and insertion loss by comparing creep-resistant to pure-Au tuning diagrams.

Symmetrical Quasi-Reflectionless BSFs

Abstract: A type of symmetrical bandstop filters (BSFs) with quasi-reflectionless behavior is reported. The engineered BSF configuration is made up of a bandstop section with resistively terminated bandpass sections that are connected at its input/output accesses. These bandpass sections, which exhibit a nearly complementary transfer function with regard to the one of the bandstop section, dissipate the nontransmitted input-signal energy in their loads. The theoretical foundations of the first-order quasi-reflectionless BSF and synthesis examples are detailed. Its extrapolation to higher order and multiband BSFs is also shown. Furthermore, as experimental validation, a 2.35-GHz second-order microstrip prototype is developed and measured.

Coupling Matrix-Based Design of Fully Reconfigurable Differential/Balanced RF Filters

Abstract: This letter presents the coupling matrix design of differential/balanced RF filters They exhibit: i) a highly suppressed common mode that is obtained by multiple transmission zeros and resistively loaded poles and ii) a differential mode that exhibits a quasi-elliptic-type transfer function that can be tuned in frequency and bandwidth (BW) and can be intrinsically switched-off The filter’s reconfiguration properties are attained by only tuning the resonant frequencies of its constituent resonators Thus, it exhibits less in-band insertion loss than tunable differential architectures in which tuning of couplings is required For practical validation purposes, a microstrip prototype was manufactured and measured in the 14–19-GHz range with the following characteristics Differential mode: center-frequency tuning between 136 and 19 GHz (14:1), BW tuning between 43 and 270 MHz (63:1), and an intrinsically switched-off mode with isolation (IS) > 22 dB Common mode: 70%, 40-dB suppression BW and IS > 60 dB at the center frequency for all tunable states

Wide-band signal-interference duplexer with contiguous single/dual-band channels and its application to quasi-absorptive bandpass filters

Abstract: A type of wide-band signal-interference planar duplexer with single- and dual-band channels is presented. It exploits transversal-signal-interference-section-based channels with contiguous single- and dual-passband filtering transfer functions. Furthermore, by ending the dual-band channel in a reference-impedance resistor, a wide-band bandpass filter (BPF) with quasi-absorptive stopbands is realised. As experimental validation, microstrip prototypes of a duplexer and a two-stage quasi-absorptive BPF that operate in the 1.6–4.4 GHz range are built and tested.

Tunable reflectionless microstrip bandpass filters

Abstract: A class of frequency-reconfigurable reflectionless microstrip bandpass filters is reported. This RF/microwave device is based on a complementary-duplexer architecture made up of a bandpass-type and a bandstop-type channel with resistive termination. Whereas the bandpass channel defines the transmission profile of the overall filter, the input-signal energy that is not transmitted by this channel is absorbed by the bandstop branch. In this manner, a reflectionless behavior at the filter input is achieved. The theoretical foundations of the devised input-reflectionless bandpass filter and synthesis examples for single/multistage designs are presented. Furthermore, for experimental-validation purposes, a two-stage prototype that can be tuned within the 0.8–1.1-GHz range is manufactured and tested.

Multi-Band Bandpass and Bandstop RF Filtering Couplers With Dynamically-Controlled Bands

Abstract: This paper reports on multi-band bandpass and bandstop RF filtering four-port couplers with programmable bands in terms of center frequency and number of passbands/stopbands. They are based on four multi-resonant bandpass/bandstop-type modules that are inter-coupled by means of 90°/270°-long transmission lines. Each multi-resonant module is shaped by K in-parallel-cascaded resonators through impedance inverters. The center frequency of each band is controlled by the resonant frequency of each resonator and its bandwidth by the interconnecting impedance inverter. The proposed multi-band coupler with co-integrated spectrally adaptive filtering capability can be designed for symmetrically and asymmetrically located bands, passbands/stopbands with equal or unequal bandwidths, output signals with 0° or 180° phase difference, and equal or unequal power-division ratios at its output ports. For practical-validation purposes, microstrip prototypes of reconfigurable dual-band bandpass and bandstop filtering couplers have been designed, manufactured, and measured. They exhibit two bands that can be independently tuned in frequency and additionally merged to create a wider band within the frequency range between 1.3 and 1.8 GHz.

Frequency Selective Ferrite Circulators with Quasi-Elliptic Transmission Response

Abstract: This paper reports on a new class of miniaturized RF circulators with bandpass filtering capabilities. They are based on capacitively-loaded ferrite disk resonators that occupy a 64% smaller area than conventional RF circulator architectures. Frequency selectivity is achieved by introducing four transmission zeros (TZs) below and above the circulator passband. The spectral locations of the TZs are controlled by i) the position of the capacitive load on the ferrite-based disk and by ii) incorporating resonant-type external coupling elements to its input, output and isolated ports. In this manner, non-reciprocal quasi-elliptic type power transmission responses can be obtained, which eliminate the need for additional RF filtering elements in the RF front-end. For proof-of-concept validation, two microstrip prototypes are designed, built and measured at 2.5 GHz, achieving 2.2 and 1.4 dB minimum insertion loss, and 33.4 and 30 dB maximum isolation in the pass-band and are presented in this manuscript for the first time.

Tunable Multiband Bandpass-to-Bandstop RF Filters

Abstract: This paper reports on a new class of multiband band-pass-to-bandstop (BP-to-BS) tunable RF filters. The proposed $\mathbf{fi} -$ ter concept allows the simultaneous realization of multiband bandpass-and bandstop-type transfer functions that can be independently reconfigured in frequency and in number-through band merging-. Switching between the multiband bandpass-filter (BPF) and bandstop-filter (BSF) modes is achieved by changing the coupling path between the source and the load. In both modes, band reconfigurability is obtained by only tuning the resonant frequencies of the filter's resonators. The proposed spectrally-adaptive multiband BP-to-BS filter concept is presented by means of: i $)$ coupled-resonator synthesis through its coupling-matrix representation and of: ii) an experimental four-resonator microstrip $\mathbf{fil}-$ ter prototype (1-to-2 bands in the BPF mode and 1-to-4 bands in the BSF mode) that was designed and tested in the frequency range 0.9-1.6 GHz for proof-of-concept demonstration purposes.

Design-Oriented Modelling of Microstrip Ferrite Circulators

Abstract: A modeling approach for the design of microstrip ferrite circulators is presented and validated on several examples using the same commercially-available ferrite disk. A baseline narrowband 4.2S-GHz microstrip circulator is first demonstrated with a commercial 4.97-mm radius ferrite disk operated in saturation and below the ferromagnetic resonance. The non-uniform DC magnetic field distributions of a cylindrical permanent magnet is taken into accout by spatial discretization of the ferrite properties in full-wave simulations. Several design parameters are shown to affect the frequency response; the ferrite thickness relative the microstrip substrate thickness shifts the operating frequency, while external matching networks can increase the fractional bandwidth from 10% up 40%. Another degree of freedom is the applied DC magnetic field, which can be reduced to set the ferrite operation below the ferromagnetic resonance with significant miniaturization of the overall device, as demonstrated with a 1.6-GHz circulator designed with the same 4.97-mm radius ferrite disk, resulting in an almost factor of 3 reduction in linear electrical size.

Wide-passband filters with in-band tunable notches for agile multi-interference suppression in broad-band antenna systems

Abstract: Sharp-rejection and low-loss planar wide-band bandpass filters with embedded in-band frequency-agile notches, that are useful for dynamic multi-interference mitigation in broad-band antenna systems, are presented. The proposed RF filter concept consists of in-series-cascaded transversal signal-interference filtering cells with an embedded tunable quasi-absorptive-type notch in the transmission range of each of them. Each of these cells is made up of three signal-propagation paths in which one of them is reused by both filtering functionalities. This leads to smaller footprint as opposed to conventional solutions based on in-series cascades of separate filtering units. Furthermore, the in-band tunable notches can be spectrally merged so that the number of active rejection bands in the passband is dynamically controlled. For experimental-demonstration purposes, a 2-GHz two-stage microstrip prototype with two independently-tunable quasi-absorptive-type notches is developed and characterized.

Quasi-Elliptic-Type Multiplexer Design Without Cross Coupling

Abstract: A method to design quasi-elliptic-type multiplexers without cross coupling in its channelizing bandpass filters is reported. It is based on the use of a multi-transmission-zero (TZ)/multipole filtering cell in the junction of the multiplexer channels. This filtering cell increases the orders of the multiplexer channels by one in relation to the isolated filters, whereas its TZs are shared by all channels. In this manner, an enhanced order sharp-rejection multiplexer can be synthesized. The operational foundations of the proposed quasi-elliptic-type multiplexer approach, which is general for symmetrical and asymmetrical arbitrary-order designs in any RF technology, are described under a coupling-matrix-based formalism. Moreover, for practical-validation purposes, a third-order microstrip duplexer prototype with channels centered at 2.15 and 2.65 GHz is manufactured and tested.

Mixed-Technology Quasi-Reflectionless Planar Bandpass Filters

Abstract: This paper reports on the RF design of mixed-technology quasi-reflectionless planar bandpass filters (BPFs). They are based on a hybrid integration scheme in which microstrip resonators are effectively combined with lumped-element ones for size compactness. By loading the input and output ports of a first-order BPF with first-order bandstop-filter (BSF) sections that exhibit complementary transfer function with regard to the BPF one, a symmetric quasi-reflectionless behaviour can be obtained at both accesses of the overall filter. The first-order quasi-absorptive BPF cell can be extended to higher-rejection realizations by cascading in series multiple first-order stages and merging their interconnecting BSF sections. For experimental-validation purposes, two quasi-absorptive BPF prototypes (one-and two-stage schemes, respectively) centred at 2 GHz were designed., manufactured., and measured. They exhibit return-loss (RL) levels higher than 10 dB over fractional bandwidths (FBW s) of 117% and 111%, respectively.

Input- Reflectionless Acoustic-Wave-Lumped- Element Resonator-Based Bandpass Filters

Abstract: This paper reports on an RF design methodology for acoustic-wave-resonator-(AWR)-based bandpass filters (BPFs) with input-reflectionless behavior in both their passband and stopband regions. The proposed concept is based on acoustic-wave-lumped-element resonators (AWLRs) that are incorporated in se-ries-cascaded reflectionless stages (RLSs). Each RLS comprises a first-order bandpass section-shaped by three impedance inverters and one AWLR-and a first-order resistively-terminated bandstop section-shaped by two impedance inverters and one AWLR-that are designed to exhibit complementary transfer functions. In this manner, an input-reflectionless behavior can be obtained both at the passband and stopband regions of the filter. In addition, the use of AWLRs in the RLSs facilitates the realization of high-quality-factor $(\mathcal{\pmb{Q}} > \pmb{10,000})$ quasi-elliptic-type transfer functions with fractional bandwidths (FBWs) that are wider than the electromechanical coupling coefficient $\pmb{(k_{t^{2}})}$ of its constituent AWRs. For proof-of-concept validation purposes, one- and two-state prototypes were manufactured, and measured at 418 MHz using commercially-available surface-acoustic-wave resonators.

Bandwidth design of ferrite-based circulators

Abstract: This paper reports on the RF design of planar ferrite-based RF circulators with bandwidth control through the height of the ferrite-puck and the DC magnetic biasing. The analysis is performed with the aid of a commercially-available finite-element solver for a design frequency of 3.9 GHz. The study reveals that by varying the ratio of ferrite height to substrate height within the circulator cavity from 0.1 to 1, the 1-dB bandwidth varies between 5 and 36.2%. While conventional RF circulators are designed for a fill factor equal to 1, this study shows that maximum bandwidth is obtained for a fill factor of 0.82.

Tunable Input-Quasi-Reflectionless Multiplexers

Abstract: A class of frequency-tunable planar multiplexer with quasi-reflectionless behavior at its input port for modern RF wireless-communications transceivers is presented. To attain the input quasi-absorptive characteristic in a Kth-order N-channel realization, an additional Kth-order N-band multi-stopband channel terminated in a reference-impedance resistor is added. Each Kth-order stopband in this N-band bandstop channel exhibits a nearly-complementary frequency profile with regard to the one of a counterpart bandpass channel. Thus, the input-signal energy not transmitted by the bandpass channels in their stopband regions is dissipated in the resistor of the nearly-complementary multi-band bandstop branch. The theoretical operational principles and coupling-matrix-based design equations for the first-order input-quasi-reflectionless multiplexer stage are detailed. Furthermore, for experimental-validation purposes, a first-order microstrip duplexer prototype that can be tuned in the 0.85–1.15-GHz range is manufactured and characterized.

Multi-band reflectionless filtering impedance transformers

Abstract: A type of double-functionality filtering impedance transformer with multi-band and input-reflectionless capabilities is presented. It exploits a multi-passband filtering/impedance-transformation channel loaded with a complementary resistively-terminated multi-bandstop branch at its input node that dissipates the input-signal energy in the stopband regions of the former. This multi-band/multi-operational circuit approach could result in insertion-loss and circuit-size advantages when employed in complete RF front-end chains by relaxing the need for isolators or attenuators for inter-block matching. A coupling-matrix-based formulation for its design and theoretical examples of first-order dual-band and second-order triple-band realizations are provided. Furthermore, for experimental-demonstration purposes, a 1.9/2.1-GHz dual-band microstrip prototype is built and tested.

Constant In-Band Group-Delay Acoustic-Wave-Lumped-Element-Resonator-Based Bandpass Filters and Diplexers

Abstract: The RF design of acoustic-wave (AW)-resonator-based bandpass filters (BPFs) with constant in-band group delay ( $\tau _{g}$ ) and analog transfer-function reconfigurability is presented. The proposed filter concept is based on $N$ identical acoustic-wave-lumped-element resonators (AWLRs) that are electromagnetically coupled through impedance inverters and result in quasi-elliptic-type transfer functions shaped by $N$ poles and $2N$ transmission zeros (TZs). Unlike conventional ladder- or lattice-type AW-resonator filter configurations, they facilitate: 1) flat in-band $\tau _{g}$ that does not depend on the electromechanical coupling coefficient ( $k_{t}^{2}$ ) of its constituent AW resonators and does not require the incorporation of lossy elements; 2) passbands with fractional bandwidths (FBWs) that can exceed $k_{t}^{2}$ ; and 3) continuous analog-type FBW tuning. The operating principles of the devised concept are presented through two different filter architectures that, respectively, present advantages in terms of size and FBW tuning and are subsequently extended to the design of RF diplexers. They are experimentally verified through the following prototypes: 1) a three-pole/six-TZ BPF that is centered at 418 MHz and exhibits bandwidth (BW) of 0.3 MHz, minimum in-band insertion loss of 2.1 dB (i.e., effective quality factor $Q_{\mathrm {eff}}$ of 9000), and in-band $\tau _{g}$ between $1.78 \pm 0.02~ \mu \text{s}$ ; 2) a two-pole/four-TZ BPF with 2.4:1 BW tuning ratio, flat $\tau _{g}$ , and $Q_{\mathrm {eff}}> 9000$ ; and 3) a flat $\tau _{g}$ diplexer with two transmission bands centered at 418 and 433.9 MHz.

UHF-band bandpass filters with fully-reconfigurable transfer function

Abstract: This paper presents a lumped-element bandpass filter (BPF) with multiple levels of transfer-function tunability including bandwidth (BW), center frequency, and intrinsic RF switching. The reported filter is based on a cascaded-resonator structure that exhibits three poles and two transmission zeros (TZs). Transfer-function reconfigurability is achieved by only tuning the filter's resonators via variable capacitors which results in less in-band insertion-loss (IL) variation and better linearity than in conventional filter schemes in which coupling controllability is required. For practical-validation purposes, a lumped-element BPF prototype was designed, built, and measured in the UHF band. It exhibits center-frequency tunability of 1.63:1, BW tunability of 7.3:1 and minimum in-band IL in the range 1.26–3.96 dB.

Multi-Band Acoustic-Wave-Lumped-Element Resonator-Based Bandstop Filters with Continuously Tunable Stopband Bandwidths

Abstract: A new class of multi-band acoustic-wave-Iumped-ele-ment-resonator (AWLR)-based bandstop filters (BSFs) is reported. It is based on $N$ multi-resonant A WLRs-shaped by $K$ AWLRs and 2K inverters-that are connected to an all-pass network and result in $\pmb{K\ N^{th}}$ order rejection bands. The proposed concept allows the realization of multiple rejection bands with the following characteristics: i) fractional bandwidths (FBWs) larger than the electromechanical coupling coefficient $\pmb{k_{t}^{\ 2}}$ of its constituent acoustic-wave resonators, ii) continuously variable and inde-pendently-controlled FBWs, iii) intrinsically-switched stopbands, and iv) an all pass state. For proof-of-concept validation purposes a dual-band prototype was designed, built, and tested. It exhibits two stopbands centered at 418 and 433 MHz that can be continu-ously-tuned in FBW (up to 7.7:1 tuning range) and in number.

A design approach for monolithically integrated broadband circulators

Abstract: A design approach for self-biased monolithic microwave integrated circulators using a commercial computational electromagnetic code is presented. The nano-magnetic self-biased material is included in a microwave gallium nitride (GaN) on silicon carbide (SiC) integrated circuit process allowing for the design and realization of microstrip-type circulators. Simulated design performance showing >30% bandwidth, insertion loss of approximately 2.5 dB, and isolation greater than 9.3 dB from 16 to 23 GHz is compared between two commercial computational electromagnetic (EM) solvers.

Planar RF Duplexer with Multiple Levels of Transfer-Function Reconfigurability

Abstract: This paper reports on the RF design of planar RF duplexers with unprecedented levels of transfer-function adaptivity. These reconfiguration capabilities include center-frequency tuning, bandwidth (BW) tuning, and intrinsic RF switching-off. The proposed RF duplexer concept is based on the connection of two three-pole/two-transmission-zero (TZ) bandpass filters (BPFs) that exhibit fully-reconfigurable quasi-elliptic-type transfer functions, so that they can be exploited for the independent control of its transmit and receive channels. For experimental-validation purposes, a microstrip RF duplexer prototype was designed, manufactured, and measured in the 1.4-2 GHz band. Its channels show center-frequency tuning ratio of 1.3:1, BW tuning ratio of 5:1, and can be intrinsically switched-off in an independent way.

Linear Time-Invariant Behavioral Digital Models of Frequency-Periodic RF/Microwave Filters

Abstract: Analog RF/microwave passive filters are traditionally realized by means of electromagnetically-coupled-resonator circuit networks. Nevertheless, alternative design techniques can be exploited to synthesize advanced filtering transfer functions, such as those based on signal-interference principles and generalized stub-loaded-circuit approaches. Contrary to the filtering responses that are synthesized through conventional coupling-matrix-based procedures, the theoretical power transmission parameters of these filtering circuits are usually frequency periodic. Hence, they can be directly matched with the frequency response of an associated digital model. In this paper, this behavioral methodology is applied to the design of novel linear time-invariant digital systems with transfer functions that are inspired by frequency-periodic analog RF/microwave passive filters. Specifically, the coefficients corresponding to the two following synthesis examples are extracted and presented: i) signal-interference quasi-elliptic-type bandpass filter with in-band linear-phase profile and ii) stub-loaded-based dual-passband filter with multiple transmission zeros (TZs). Furthermore, the properties of their associated analog-inspired linear time-invariant digital systems are discussed.

Design concepts for broadband antenna arrays with constant half-power beamwidth

Abstract: This paper reports on the design of broadband antenna arrays with constant half-power beamwidth (HPBW). The proposed concept is based on non-uniformly spaced and non-uniformly-fed radiating elements using frequency-selective feeding networks. As opposed to conventional feeding schemes, it facilitates the realization of constant HPBW within two octaves of bandwidth. For proof-of-concept demonstration purposes, the radiation characteristics of a five-element array are studied for frequencies between 1–4 GHz. The proposed frequency-selective feeding scheme allows for HPBW of 45°±2° and HPBW variation of 9.3 % to be obtained within the entire 1–4 GHz range.

Switched-bandwidth SAW-based bandpass filters with flat group delay

Abstract: Tunable surface-acoustic-wave-(SAW)-based bandpass filters (BPFs) with flat in-band group delay (Tg) and variable passband bandwidth (BW) are reported. They are based on N hybrid acoustic-wavelumped-element-resonator (AWLR) modules shaped by one lumpedelement resonator and K RF-switched SAW resonators that are arranged in a Gaussian-type source-to-load impedance-inverter network. Fractional bandwidth (FBW) tuning is achieved by reconfiguring the number of SAW resonators within the AWLR modules. Major advantages of the proposed filter concept when compared to conventional SAW BPFs are as follows: (i) they do not depend on the electromechanical coupling coefficient (k t 2 ) of the SAW resonators - FBW>k t 2 can be realised -, (ii) they do not require lossy elements or SAW resonators with different frequencies, and (iii) they can be tuned. For experimental-validation purposes, a 433.9 MHz two-pole/fourtransmission-zero prototype was built and measured. It exhibited flatin-band-T g passbands with discretely-tunable BW between 0.18 and 0.45 MHz (i.e. 2.5:1 tuning ratio).

Co-simulations of DC magnetic bias fields and RF performance for microwave ferrite circulators

Abstract: This paper presents finite element co-simulations for DC magnetic field and microwave non-reciprocal performance of ferrite circulators. Permanent magnets provide a DC bias field, but need to be large for a uniform magnetic field distribution inside the ferrite material. Additionally, the ferrite effective permeability is a nonlinear function of magnetic bias. Smaller magnets give a non-uniform bias field distribution, which can be taken into account in the full-wave simulations. To demonstrate the effect of this nonuniform bias, a commercial ferrite material from Skyworks (TT105) is chosen for a circulator design around 3.9 GHz assuming first a uniform DC magnetic field that saturates the ferrite. A small commercial rare-earth permanent magnet is then simulated to obtain the nonuniform static magnetic field in the ferrite, and resulting HFSS simulations show that the effects of nonuniform bias field on circulator performance can be predicted using a combination of analysis methods.

Behavioural digital modelling of lossy frequency-periodic microwave passive filters

Abstract: The theoretically synthesised power transmission response of several classes of RF/microwave passive filters is frequency periodic. Examples of these filters include those exploiting signal-interference techniques as well as those consisting of stub-loaded circuit networks. A behavioural z -plane digital modelling of these ideally synthesised frequency-periodic high-frequency filters has been recently proposed. It led to innovative explanations for commonly observed spurious resonant peaks and circuit redundancies in suboptimal designs. This work reports on a novel behavioural discrete-time modelling methodology for frequency-periodic microwave lossy filters. It considers for the first time the effect of high-frequency losses by introducing a σ parameter on the originally lossless transfer function. For practical-validation purposes, the manufacturing and characterisation of a new type of generalised stub-loaded-based extended-upper-stopband bandpass filter along with its lossy digital modelling are shown.