Showing papers on "Coplanar waveguide published in 2009"

Development of Low Profile Cavity Backed Crossed Slot Antennas for Planar Integration

Abstract: Single fed low profile cavity backed crossed slot antennas for dual frequency dual linear polarization and circular polarization applications are first presented in this paper. By employing the substrate integrated waveguide (SIW) technique in the antenna designs, the low profile backed cavity structure can be realized by using only a single layer of low cost printed circuit board (PCB) substrate. A single grounded coplanar waveguide (GCPW) is employed as the feeding element to excite the TE 120 and TE 210 modes in the SIW cavity. A crossed slot structure is used as the radiating element in order to radiate the desired dual linearly or circularly polarized wave. From the measurement results, it is seen that these novel antennas retain the advantages of conventional metallic cavity backed antennas, including high gain, high front-to-back ratio (FTBR), and low cross polarization level (CPL). Furthermore, the proposed antennas also possess the advantages of low profile, light weight, low fabrication cost, and easy integration with planar circuits.

Dynamical Casimir Effect in a Superconducting Coplanar Waveguide

Abstract: We investigate the dynamical Casimir effect in a coplanar waveguide (CPW) terminated by a superconducting quantum interference device (SQUID). Changing the magnetic flux through the SQUID parametrically modulates the boundary condition of the CPW, and thereby, its effective length. Effective boundary velocities comparable to the speed of light in the CPW result in broadband photon generation which is identical to the one calculated in the dynamical Casimir effect for a single oscillating mirror. We estimate the power of the radiation for realistic parameters and show that it is experimentally feasible to directly detect this nonclassical broadband radiation.

Open Complementary Split Ring Resonators (OCSRRs) and Their Application to Wideband CPW Band Pass Filters

Abstract: In this letter, open complementary split ring resonators (OCSRRs) are introduced for the first time. Such resonators are the dual counterparts of the open split ring resonators (OSRRs), introduced in 2004 by some of the authors, and consist on a pair of concentric hooks etched on a metal layer in opposite orientation. It is shown in the letter that OCSRRs can be modeled by means of an LC parallel resonant tank and that this particle roughly exhibits half the resonance frequency of the complementary split ring resonator (CSRR), hence being electrically very small. The interest of these resonators is illustrated through their application to a wideband coplanar waveguide band pass filter.

Development of a Novel UWB Vivaldi Antenna Array Using SIW Technology

Abstract: A compact Vivaldi antenna array printed on thick substrate and fed by a Substrate Integrated Waveguides (SIW) structure has been developed. The antenna array utilizes a compact SIW binary divider to significantly minimize the feed structure insertion losses. The low-loss SIW binary divider has a common novel Grounded Coplanar Waveguide (GCPW) feed to provide a wideband transition to the SIW and to sustain a good input match while preventing higher order modes excitation. The antenna array was designed, fabricated, and thoroughly investigated. Detailed simulations of the antenna and its feed, in addition to its relevant measurements, will be presented in this paper.

Compact coplanar waveguide-fed ultra-wideband monopole-like slot antenna

Abstract: A simple and compact coplanar waveguide (CPW)-fed ultra-wideband (UWB) monopole-like slot antenna is presented. The proposed antenna comprises a monopole-like slot and a CPW fork-shaped feeding structure, which is etched onto an FR4 printed circuit board (PCB) with an overall size of 26 mm x 29 mm x 1.5 mm. The simulation and experiment show that the proposed antenna achieves good impedance matching, consistent gain, stable radiation patterns and consistent group delay over an operating bandwidth of 2.7-12.4 GHz (128.5%). Furthermore, through adding two more grounded open-circuited stubs, the proposed antenna design features band-notched characteristic in the band of 5-6 GHz while maintaining the desirable performance over lower/upper UWB bands of 3.1-4.85 GHz/6.2-9.7 GHz.

Losses in coplanar waveguide resonators at millikelvin temperatures

Abstract: We study the loss rate for a set of lambda/2 coplanar waveguide resonators at millikelvin temperatures (20 mK - 900mK) and different applied powers (3E-19 W - 1E-12 W). The loss rate becomes power independent below a critical power. For a fixed power, the loss rate increases significantly with decreasing temperature. We show that this behavior can be caused by two-level systems in the surrounding dielectric materials. Interestingly, the influence of the two-level systems is of the same order of magnitude for the different material combinations. That leads to the assumption that the nature of these two-level systems is material independent.

A Novel Single-Cavity Dual Mode Substrate Integrated Waveguide Filter With Non-Resonating Node

Abstract: A single-cavity novel dual mode substrate integrated waveguide (SIW) filter with non-resonating node (NRN) is presented. The NRN is implemented by etching a coplanar waveguide on the top metal layer of SIW cavity. Under such circumstances, the filter occupies similar area in comparison with conventional two-pole SIW counterparts, but exhibits better frequency selectivity. The measured S-parameters of the realized filter agree well with the simulated ones, with its good performance predicted.

Broadband Circularly Polarized Slot Antenna Array Fed by Asymmetric CPW for L-Band Applications

Abstract: A novel broadband circularly polarized (CP) slot antenna array fed by asymmetric coplanar waveguide (CPW) with an inverted L-shaped strip for L-band applications is proposed. Broadband CP is obtained by an array composed of elliptically polarized elements using sequential rotation feed technique. Experimental results show that the VSWR les 1.5 impedance bandwidth and the 3-dB axial ratio bandwidth can be greatly raised to be as high as 52% (1.151.95 GHz) and 49% (1.151.9 GHz), respectively. The proposed antenna can provide a peak antenna gain of about 8 dBi at 1.5 GHz, with gain variations less than 1.5 dB for frequencies within the CP bandwidth. Good agreement is observed between simulation and measurement.

Low-loss ultra-wideband transition between conductor-backed coplanar waveguide and substrate integrated waveguide

Abstract: A novel transition between conductor-backed coplanar waveguide (CBCPW) and substrate integrated waveguide (SIW) is presented for microwave and millimeter-wave integrated circuit design. The proposed integrated transition that can provide simultaneous field and impedance matching, exhibits outstanding low-loss performances over an ultra-wideband range (entire Ka-band in our case). In this work, a generalized impedance inverter whose parameters are accurately extracted by the use of a numerical Thru-Reflection-Line (TRL) calibration technique is utilized to design the transition. Measured results for the fabricated transition in back-to-back configuration show that the insertion loss is better than 0.4 dB while the return loss is better than 20 dB over the entire Ka-band.

Applications of Open Split Ring Resonators and Open Complementary Split Ring Resonators to the Synthesis of Artificial Transmission Lines and Microwave Passive Components

Abstract: This paper is focused on the application of open split ring resonators (OSRRs) and their dual counterparts, open complementary split ring resonators (OCSRRs), to the synthesis of composite right/left-handed transmission lines, that is, artificial lines exhibiting backward wave propagation at low frequencies and forward wave propagation at high frequencies. Due to the small dimensions of these resonators, the resulting lines are very compact. Several artificial lines, with different electrical characteristics and topologies, are reported as illustrative examples. It is shown that these artificial lines can be applied to the synthesis of dual-band components and bandpass filters, and two prototype device examples are designed and fabricated in coplanar waveguide technology: a dual-band impedance inverter applied to a dual-band power divider, and an order-3 wide-band bandpass filter. Finally, it is also demonstrated that OSRRs and OCSRRs can be combined for the synthesis of band pass filters in microstrip technology. Since OSRRs and OCSRRs are described by means of series and shunt resonant tanks, respectively, and they are electrically small, their potential to the design of semi lumped planar microwave devices is very high.

CPW-Fed Stair-Shaped Slot Antennas With Circular Polarization

Abstract: The design is described of a coplanar-waveguide (CPW)-fed circularly polarized slot antenna. The slot antenna and the feeding structure are fabricated on the same plane of the substrate so that circuit process and position alignment could be simplified. By etching a longitudinal slot at a middle point of a stair-shaped slot and tuning geometrical parameters, two orthogonal electric fields with quadrature phase difference excite a circularly-polarized wave. A bandwidth of 31.2% (2.30-3.15 GHz) is achieved with an axial ratio < 3 dB and reflection coefficient < -10 dB. Details of the design procedure for the proposed antenna are described, and the results of the antenna performance are presented and discussed.

Thermally Actuated Latching RF MEMS Switch and Its Characteristics

Abstract: Here, a new thermally actuated latching wideband RF microelectromechanical systems (MEMS) switch is presented. The switch employs two thermal actuators connected to two thin metal arms which serve as signal lines of coplanar waveguide switch. The actuators pull the thin arms sequentially, and latch the switch. The switch can be actuated on and off by using either short voltage or current pulses. Using a dielectric bridge (nitride) as an interface between the actuators and the thin arms, the RF circuitry is separated from DC actuators, allowing wide-band operation. The switch demonstrates an excellent wideband RF performance with an insertion loss of better than 0.3 dB up to 20 GHz and better than 0.8 dB up to 40 GHz. The return loss and isolation of the switch is better than 20 dB for the entire frequency band. The switch also has a very satisfactory repeatability with better than 0.1-dB variation in insertion loss and less than 1-dB variation in return loss and isolation at 30-dB level up to 6000 times switching cycles. The switch has been also successfully tested for RF power handling capability up to 40 dBm. The proposed switch has very simple RF structure which makes it an ideal candidate to be integrated in the form of more complex circuitry. An application of the proposed switch for a band selection network which is used in multiband transceivers has been presented here.

Design of a CMOS Tapered Cascaded Multistage Distributed Amplifier

Abstract: This paper presents the design and measurement of a distributed amplifier (DA) in a standard 90-nm CMOS process. To improve the gain and bandwidth (BW) of the DA, the use of an elevated coplanar waveguide line and also impedance tapering in the synthesized sections are proposed. The effects of elevation and shielding filaments on the impedance, loss, and effective dielectric constant of the transmission line are investigated and accompanied by measurements. A methodology for CMOS DA design is described that can take advantage of the multiple degrees of freedom in terms of device size, topology, and aspect ratio available in these processes. The fabricated tapered cascaded multistage DA achieves a 3-dB BW of 73.5 GHz with a passband gain of 14 dB. This results in a gain-BW product of 370 GHz. The realized 0-dB BW is 83.5 GHz and the input and output matchings stay better than -9 dB up to 77 and 94 GHz, respectively. The chip consumes an area of 1.5 mm times 1.15 mm, while drawing 70 mA from a 1.2-V supply.

High-frequency waveguide and phase shifter using same, radiator, electronic device which uses this phase shifter and radiator, antenna device, and electronic device equipped with same

Abstract: This high-frequency waveguide is formed by first/second conductors (22, 23) which are arranged facing each other with an interval of less than λ0/2 when the free space wavelength of the operating frequency of the high-frequency signal is λ0. In a waveguide-forming part between these first/second conductors (22, 23), a ridge (25) which protrudes from one toward the other of the first/second conductors (22, 23) and which is formed by extending along the waveguide-forming part is provided. Multiple columnar protrusions (24) with a height of λ0/4 are arranged with an interval of less than λ0/2 on at least one of the first/second conductors (22, 23) outside of the aforementioned waveguide-forming part and lateral to the ridge (25).

Multilayer Dual-Mode Dual-Bandpass Filter

Abstract: A dual-mode dual-bandpass filter for the U-NII bands is proposed and demonstrated. Its effective size reduction is achieved by using a multilayer configuration. The first and the third layers incorporate microstrip dual-mode bandpass filters with operating center-frequencies of f1 =5.2 GHz and f2 =5.8 GHz, respectively. The second layer is used as a common ground plane for both filters, which also serves as a decoupling interface. Capacitive coupling transition is used to connect both filters to I/O coplanar waveguide (CPW) ports. Single and dual-band passband filter prototypes are designed, fabricated, and measured in this work, thus validating the design principle. Designed topologies of single passband filters with center frequencies of 5.2 and 5.8 GHz exhibit an out-of-band rejection better than 40 dB with a 3 dB bandwidth of 5.8% and 6%, respectively. The proposed multilayer dual-passband response with center frequencies of 5.2 and 5.8 GHz provide band-to-band isolation better than 30 dB. Measured insertion losses are lower than 2.76 dB, with 3 dB bandwidth lower than 5%.

High-Q Slow-Wave Coplanar Transmission Lines on 0.35 $\mu$ m CMOS Process

Abstract: In this letter, experimental results and trends for shielded coplanar waveguide transmission lines (S-CPW) implemented in a 0.35 μm CMOS technology are provided. Because of the introduction of floating strips below the CPW transmission line, high effective dielectric permittivity and quality factor are obtained. Three different geometries of S-CPW transmission lines are characterized. For the best geometry, the measured effective dielectric permittivity reaches 48, leading to a very high slow-wave factor and high miniaturization. In addition, measurements demonstrate a quality factor ranging from 20 to 40 between 10 and 40 GHz, demonstrating state-of-the-art results for transmission lines realized in a low-cost CMOS standard technology.

A 300 GHz mHEMT amplifier module

Abstract: In this paper, we present the development of an H-band (220 – 325 GHz) submillimeter-wave monolithic integrated circuit (S-MMIC) amplifier module for use in next generation active and passive high-resolution imaging systems operating around 300 GHz. Therefore, a variety of compact amplifier circuits has been realized by using an advanced 35 nm InAlAs/InGaAs based depletion-type metamorphic high electron mobility transistor (mHEMT) technology in combination with grounded coplanar waveguide (GCPW) circuit topology. A single-stage cascode design achieved a small-signal gain of 5.6 dB at 300 GHz and a linear gain of more than 5 dB between 258 and 308 GHz. Additionally, a four-stage amplifier S-MMIC based on conventional devices in common-source configuration was realized, demonstrating a maximum gain of 15.6 dB at 276 GHz and a linear gain of more than 12 dB over the frequency range from 264 to 300 GHz. Finally, mounting and packaging of the monolithic amplifier chips into H-band waveguide modules was accomplished with only minor reduction in circuit performance.

Characterization of Parylene-N as Flexible Substrate and Passivation Layer for Microwave and Millimeter-Wave Integrated Circuits

Abstract: Investigation of Parylene-N (Pa-N) as a flexible substrate, multilayer dielectric material, and passivation layer for microwave and millimeter-wave integrated circuits is presented. For the first time, the electrical properties of Parylene-N have been characterized up to 60 GHz using various microstrip ring resonators and transmission lines. As a flexible substrate, Parylene-N measures a nearly invariant relative dielectric constant (epsivr) of 2.35-2.4, and a loss tangent (tan delta) of lower than 0.0006 for frequencies up to 60 GHz. Because of the above properties, as a passivation layer, Parylene-N causes insignificant modifications to the properties of underlying passive and active structures. Measurement of coplanar waveguide transmission lines before and after passivation reveals that a 5-mum Parylene-N barely changes the insertion loss (below measurement accuracy) while a 10-mum-thick Parylene-N layer increases the insertion loss by only 0.007 dB/mm (below measurement error) at 40 GHz. Ring resonators before and after a 5 or 10 mum passivation show a frequency shift of less than 0.05% or 1.51%, respectively, up to 40 GHz. The influence of Parylene-N passivation on the RF performance of GaAs MESFETs is also found to be negligible. Finally, humidity studies with dew point sensors reveal that with a 10- mum-thick passivation at 25degC and 100% relative humidity, the MTTF is about 481.6 days. In summary, the results indicate that Parylene-N is an excellent and promising material for application at microwave and millimeter-wave frequencies.

A Micromachined Inline-Type Wideband Microwave Power Sensor Based on GaAs MMIC Technology

Abstract: Wideband 8-12-GHz inline-type microwave power sensors that are based on measuring the microwave power coupled from the coplanar waveguide line by a microelectromechanical systems membrane are presented. In this method, the signal is available during the power detection. In order to obtain the low reflection losses and insertion losses, as well as the wideband response of the power sensor, an impedance match structure and a compensating capacitance are proposed. The fabrication of the power sensor is compatible with the GaAs monolithic microwave integrated circuit (MMIC) process. The experimental results show that the sensor has reflection losses better than 20 dB and insertion losses less than 0.45 dB up to 12 GHz. A sensitivity of more than 30 muV/mW and a resolution of 0.2 mW are obtained at the 10-GHz frequency.

A Non-Contact-Type RF MEMS Switch for 24-GHz Radar Applications

Abstract: This paper presents the design, fabrication, and measurement results for a novel non-contact-type radio-frequency (RF) microelectromechanical systems switch for 24-GHz radar applications. The proposed switches are free from unavoidable microwelding and stiction problems in other contact types, which in turn guarantee high reliability and long lifetime. The developed switch is a capacitive shunt type using a variation of the capacitance between the signal line and ground lines. The capacitance is precisely regulated by comb-drive actuators. This concept is simple, but the design requires a large and precise mechanical motion. In addition, for a low-loss switch structure, an air bridge with a large air gap is required. Therefore, the selective silicon-on-insulator process, based on the sacrificial bulk micromachining process, is designed for this switch fabrication. First, large insulating supports are fabricated 60 ?m below the wafer surface, and then, the RF switch is fabricated on these insulating supports. The measured actuation voltage is 25 V, and the actuation stroke is 25 ?m. The switching times are 8 ms in the off to the on state and 200 ?s in the on to the off state. In the RF characteristic measurements, the insertion loss without the long coplanar waveguide line loss is 0.29 dB and the isolation is 30.1 dB at 24 GHz. The bandwidth is relatively narrow, and the isolation is 25 dB or better in the range of 23.5-29 GHz. The reliability test for the switch was performed 109 times with 18-mW RF power. We observed no mechanical failure or RF performance degradation. A power handling capacity of 0.9 W with a hot-switch condition was achieved.

Compact Modeling and Comparative Analysis of Silicon-Chip Slow-Wave Transmission Lines With Slotted Bottom Metal Ground Planes

Abstract: A compact modeling approach for silicon-chip slow-wave transmission lines with slotted bottom metal ground planes is studied and its limitations are presented. The modeling approach facilitates the calculation of the slow-wave transmission line parameters based upon the corresponding coplanar and grounded coplanar transmission-line parameters. The described analysis method is used for a comparative study of the slow-wave structures versus their coplanar and grounded coplanar reference structures. Floating bottom shield slow-wave transmission lines are then compared with their grounded bottom shield counterparts. The theoretical results are supported by electromagnetic simulations and by measurements up to 30 and 50 GHz.

Compact Dual-Band Hybrid Dielectric Resonator Antenna With Radiating Slot

Abstract: A miniature independent dual-band hybrid dielectric resonator antenna (DRA) fed by a coplanar waveguide (CPW) inductive slot is proposed. In this configuration, the CPW inductive slot performs the functions of an effective radiator and the feeding structure of the DR. By optimizing the structure parameters, the hybrid structure resonates at two different frequencies independently. One is from the DRA with the broadside patterns and the other from the inductive slot with the dipole-like patterns. In order to determine the performance of varying design parameters on bandwidth and resonance frequency, parametric study is carried out using simulation software HFSS and experimental results. The measured and simulated results show excellent agreement.

Ultrawideband (UWB) Antennas With Multiresonant Split-Ring Loops

Abstract: Novel ultrawideband (UWB) antennas with multiresonant split-ring loops and with coplanar waveguide (CPW) feed are presented in this communication. Dual concentric microstrip split-ring loops with different geometrical ground planes have been analyzed and compared. UWB antennas are designed, of which the dimension of each split-ring loop varies proportionally to the arithmetic progression sequence. The dimensions of the rectangular ground planes and the split-ring loops are tuned for achieving a very wide bandwidth. A tapered transmission line is adopted to improve the return loss performance in the required band. Measurement results show that the proposed UWB antennas have a wide bandwidth from 2 to 20 GHz, and the measured return losses are less than -10 dB in this band combined with relative stable radiation characteristics.

GaN MMIC amplifiers for W-band transceivers

Abstract: This paper presents W-band monolithic microwave integrated circuit (MMIC) amplifiers with grounded coplanar waveguide (GCPW) in 0.12µm GaN HEMT technology. A fabricated four-stage low-noise amplifier (LNA) exhibited a record gain of 23 dB at 76.5 GHz and a first reported noise figure (NF) of 3.8 dB at 80 GHz for any W-band GaN MMIC. Another MMIC power amplifier (PA) delivered an output power of 25.4 dBm at 76.5 GHz with continuous wave (CW) operation. To our knowledge, this is the first demonstration of GaN LNA as well as GaN MMICs with GCPW in the W-band. In addition, a practical design technique to prevent instability of the W-band MMIC is described.

Design and Analysis of Ultra Wideband GaN Dual-Gate HEMT Low-Noise Amplifiers

Abstract: In this paper, we present three ultra wide bandwidth low-noise amplifiers (LNAs) using dual-gate AlGaN/GaN HEMT devices. The single-stage, resistive feedback amplifiers target two different frequency bands: two LNAs operate in 0.3-4 GHz and one LNA is in 1.2-18 GHz. All three LNAs are capable of better than 13:1 bandwidth. The first low frequency amplifier uses a microstrip design and achieves 17.7 dB flat gain between 300 MHz-3 GHz, and 1.2 dB minimum noise figure around 1.3 GHz. The second 0.3-4 GHz LNA uses coplanar waveguide transmission lines and demonstrates 18 dB flat gain and 1.5 dB noise figure between 2 and 5 GHz. The high frequency microstrip-type LNA shows an average of 13 dB gain and between 2-3 dB noise figure across the band. The robust LNAs can be operated under various bias voltages while similar gain and noise figure performance are maintained.

Noise in NbTiN, Al, and Ta Superconducting Resonators on Silicon and Sapphire Substrates

Abstract: We present measurements of the frequency noise and resonance frequency temperature dependence in planar superconducting resonators on both silicon and sapphire substrates. We show, by covering the resonators with sputtered SiOx layers of different thicknesses, that the temperature dependence of the resonance frequency scales linearly with thickness, whereas the observed increase in noise is independent of thickness. The frequency noise decreases when increasing the width of the coplanar waveguide in NbTiN on hydrogen passivated silicon devices, most effectively by widening the gap. We find up to an order of magnitude more noise when using sapphire instead of silicon as substrate. The complete set of data points towards the noise being strongly affected by superconductor-dielectric interfaces.

A CPW-fed broadband circularly-polarized square slot antenna with E-shaped slits in ground plane

Abstract: A new broadband circularly polarized (CP) square slot antenna with coplanar waveguide (CPW) fed is proposed. E-shaped slits in opposite corners of ground plane are designed to obtain an excellent CP bandwidth. The bandwidth with an axial ratio (AR) of less than 3 dB can be tuned by varying the length of a tuning-stub which is the middle of the E-shaped slit. Measured results show that the 3 dB AR bandwidth is larger than 32.8% relative to the centre frequency of 2165 MHz and the impedance bandwidth is as large as 54.8% with VSWR ≤2.

Compact Ultra-Wideband Conductor-Backed Coplanar Waveguide Bandpass Filter With a Dual Band-Notched Response

Abstract: This work presents a novel ultra-wideband (UWB) bandpass filter (BPF) based on a conductor-backed coplanar waveguide structure with tunable transmission zeros. The symmetrical UWB BPF, which consists of the broadside-coupled transitions and the stub resonators in double-layer configuration, achieves a UWB bandwidth with transmission zeros. For characterizing this structure, the equivalent-circuit model is established to realize a four-pole response with two transmission zeros located close to the passband edges. To eliminate the interference of the coexisting wireless local area network (WLAN) within the UWB spectrum, two slotlines are symmetrically arranged on the ground plane of UWB BPF to generate the band-notched frequencies at 5.2 and 5.8 GHz simultaneously. The proposed UWB BPFs have the advantages of compact size, low insertion loss, good selectivity, and flat group delay. All results obtained from the equivalent-circuit model and the full-wave simulation are verified by measurements.

Surface Plasmon Coplanar Waveguides: Mode Characteristics and Mode Conversion Losses

Abstract: We investigate characteristics of modes supported by a surface plasmon (SP) coplanar waveguide (CPW) and contrast them against those of SP gap waveguide (GW) mode. We illustrate that the SP CPW can yield higher mode confinement versus the SP GW. In addition, we analyze 90deg bend structures to investigate mode conversion losses associated with discontinuities and we further propose a modified SP CPW to alleviate these losses.

Small printed CPW-fed triangular monopole antenna for ultra-wideband applications

Abstract: A novel small size coplanar waveguide (CPW)-fed monopole antenna with wide bandwidth and small group delay variation is proposed for ultra-wideband (UWB) applications. It consists of a triangular patch with a pair of wide stubs on the lower sides thereof and linearly tapered coplanar ground planes. The measured return loss of the fabricated antenna is better than −10 dB from 2.9 to 13.2 GHz. The radiation pattern is nearly omni-directional and the variation of the measured group delay between two proposed antennas is less than 0.94 ns over the entire UWB band. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1180–1182, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24278