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Based on the newly suggested wideband circularly polarized (CP) aperture-coupled magneto-electric dipole (MED), a millimeter-wave (mm-wave) frequency-scanned array (FSA) is proposed in this article. The MED is printed on two substrate layers. The electric dipole is two metal patches with perturbation structure, while the magnetic dipole is two rows of metal vias passing through the top substrate layer. The electric and magnetic dipoles, fed by a coupling slot, excite CP wave. By loading an arc-shaped vias row (AVR) at both ends of the magnetic dipole, the CP bandwidth with axial ratio (AR) less than 3 dB is extended to 40.9%. A new compact wideband transition from the rectangular waveguide (RWG) to the substrate integrated waveguide (SIW) is suggested as the feed structure for the CP FSA. A slow wave structure is etched on the ground of SIW to widen the beam scanning range. A 16-element array is designed and measured. The measured results show that the beam scanning range is 56° over 23–33 GHz band with a peak gain of 19.5 dBi. The CP mm-wave FSA has the advantages of wide scanning angle, low profile, and easy fabrication. [ABSTRACT FROM AUTHOR]

A low-cost, low-profile circularly polarized beam scanning patch array is presented. The patch array is fed by the coupling slots of parallel plate waveguide (PPW), which is excited by a substrate integrated waveguide-based plane wave line source generator. By suggesting a new impedance match method, the coupling slots and truncated patch array are combined for circularly polarized radiation. The beam scanning capability is achieved by the variable inclination method. In the PPW guiding wave layer, a circular plate is cut and separated from the main body of the PPW to make it rotatable around its axis. By rotating the assembly of the circular plate and the above patch layer, the phase difference between the adjacent radiation elements could be controlled. Thus, the circularly polarized beam scanning is realized. A Ku-band prototype array is fabricated and measured to verify the design. The measured peak gain is 19.6 dBi and the scanning range is ±40°, in which range the gain variation is below 2.7 dB and the axial ratio is less than 2.8 dB. [ABSTRACT FROM AUTHOR]

One of the key antenna requirements in many modern wireless systems for communications and sensing is wide-angle beam-scanning. The traditional method to achieve wide-angle beam-scanning is to employ mechanically controlled reflectors or lenses, which are bulky, heavy, and suffer from slow beam scanning speed. Other important limitations of mechanical scanning antennas include the lack of multi-beam scanning capability and the ability to conform with non-planar structures (conformal geometries), which are essential in a number of emerging systems requiring very low-profile antennas. An alternative technique is to employ electronically beam-scanning antennas using passive or active phased arrays. Main disadvantages of phased arrays are high complexity, high power consumption, and high cost due to a large number of radio frequency (RF) or microwave phase shifters and T/R modules required. The problems worsen for phased arrays at millimeter-wave, sub-THz, and THz frequencies, due to significant losses in phase shifters and feed networks at higher frequencies combined with lower efficiency of power amplifiers. The digital beamforming approach is even more costly and energy hungry due to the employment of large number of RF modules and digital devices , ,. [ABSTRACT FROM AUTHOR]

Low-profile wideband circularly polarized (CP) array antennas using integrated half-power quadrature power divider (HP-QPD) are presented. A novel HP-QPD is first proposed as an important design concept for CP radiation. Detailed analyses show that the proposed HP-QPD can have half-power CP radiation and the remaining half-power transmission with equal-magnitude but quadrature phase difference. Therefore, it can be utilized for designing a 1 $\times $ 2 CP array antenna. Compared to the traditionally designed single-feed or dual-feed CP counterparts, this 1 $\times $ 2 array antenna can have more than four times wider axial ratio (AR) bandwidth with three CP modes and a simple feed network. This 1 $\times $ 2 array antenna was then designed, fabricated, and measured for performance verification. Both measured and simulated results show that this array antenna can have a wide overlapped impedance and AR bandwidth of 7.9% with a thin dielectric thickness of $0.031\lambda _{0}$. The 1 $\times $ 2 array antenna was further extended to a 1 $\times $ 8 linear array antenna for high gain CP radiation. Measured results show that unidirectional and symmetrical radiation patterns are achieved with high peak realized gain of 15.4 dBic, low profile, and simple feed network. [ABSTRACT FROM AUTHOR]

In this article, an ultrathin frequency selective rasorber (FSR) based on electromagnetic composite absorption is proposed. At first, a subwavelength unit (SLU) for electromagnetic composite absorption is designed and its mechanism is discussed under the excitation of electric field ($E$ -field) and magnetic field ($H$ -field) of incident electromagnetic waves separately. Next, a single layer ultrathin frequency selective absorber (UFSA) is constructed by eight SLUs, which are arranged by mirror symmetry and 90° rotation symmetry. Then, two UFSAs are designed, which work at different frequencies. The proposed ultrathin FSR, which is constructed by simply stacking two UFSAs, has a transmission band (2.09–2.69 GHz) and two absorption bands (two absorptive peaks above 90% at 2.05 and 2.78 GHz) on both sides of the transmission band. Importantly, compared to the traditional FSR, the profile of the FSR is low and $0.039\lambda _{c}$. Finally, to verify the design and analysis, the proposed FSR was fabricated and measured. A good agreement between the results of the experiment and simulation can be obtained accordingly. [ABSTRACT FROM AUTHOR]

A dual-polarized filtering antenna with steep cut-off and compact size is developed for base-station applications. In this design, four controllable radiation nulls are obtained by utilizing split rings, slotted T-shaped branches, a single-stub tuner, and a parasitic loop. Split rings are first used as the dipole arms to obtain the first radiation null at upper out-of-band. Four T-shaped branches working as DGS are printed under the crossed dipoles to achieve the second radiation null. The connected outer conductors of the differential feed structure acting as a single-stub tuner can provide the third radiation null to further enhance the upper band rejection. Finally, a parasitic loop is incorporated around the split rings, and the out-of-band rejection of the lower band is further enhanced by the fourth radiation null. More importantly, the impedance bandwidth of the antenna can be expended with two newly introduced resonant modes. As a result, a compact filtering antenna with a wide operational bandwidth of 1.7–3.01 GHz (56%) is realized for $\vert \text{S}_{dd11}\vert < -15$ dB with the isolation higher than 38 dB. The out-of-band suppression is higher than 18.4 dB in 3.1–4.5 GHz and more than 47 dB in 0.8–1.1 GHz. [ABSTRACT FROM AUTHOR]

A wideband differentially-fed slot antenna is presented for millimeter-wave (mmWave) applications. A novel method of using stepped corner-shaped slot is first utilized to establish the wideband circularly polarized (CP) radiation. In the configuration of corner-shaped slot, two wide open slots at the ends are utilized for effective orthogonal radiation, while the narrow slot at the center is utilized for power transmission and quadrature phase delay. An equivalent circuit is given to illustrate the inner working principle for CP radiation. In addition, square cuts are etched on the four corners of the radiating patches to further increase the axial ratio (AR) and impedance bandwidth. Based on this design concept, the antenna element was first designed and fabricated for performance verification. Then, a $1\times $ 4 linear array with beam-scanning performance and a $4\times $ 4 planar array with high gain and stable radiation were designed and fabricated. Both the simulated and measured results show that the $1\times $ 4 linear array and $4\times $ 4 planar array can have the wide overlapped impedance and AR bandwidths of 30.6% and 33.6% with a thickness of $0.16\lambda _{0}$ , respectively. The advantages of compact size and wide bandwidth make the presented antenna a good candidate for mmWave applications. [ABSTRACT FROM AUTHOR]

A novel aperture-coupled patch rectenna backed by a substrate integrated waveguide (SIW) cavity operated at 35 GHz for millimeter-wave power transmission (MMPT) with high conversion efficiency is presented in this article. A four-element SIW patch array with a harmonic suppression function based on the barbell-type defect ground structure (DGS) is proposed as the receiving antenna; thus, the low-pass filter in the rectifying circuit can be omitted. The Schottky diode is parallel-mounted in the rectifying circuit, which has a measured rectifying efficiency of 61.2% with a $500~\Omega $ load when the received power is 100 mW. The maximum conversion efficiency of the rectenna element is 60.9% when the received power is 79.4 mW. Additionally, 4–8-and 16-element rectenna arrays are also investigated to obtain high direct current power. When the power density is 9.2 mW/cm2, the conversion efficiencies of the rectenna element, $2\times2$ array, $2\times4$ array and $2\times8$ array are 50.5%, 44.1%, 41.9%, 38.9%, respectively. The measured conversion efficiency of the $2\times8$ rectenna array at 35 GHz is 49.2% when the input power is 1259 mW. The low profile and easy integration of the studied rectenna will make it easy to expand its use to large-scale arrays for high-power MMPT applications. [ABSTRACT FROM AUTHOR]

This communication proposes a novel compact multiple-input multiple-output (MIMO) antenna with low mutual coupling based on a 2 × 2 dual-polarized half-mode substrate integrated waveguide (HMSIW). The antenna is printed on a single-layer substrate to provide a low profile and ease of integration with planar circuits. The proposed HMSIW antenna element operates in TE110 mode and can be orthogonally arranged with two slots on the ground between the antenna elements, resulting in low mutual coupling. The edge-to-edge element space is only 0.033λ0 (λ0 is the free-space wavelength). A new miniaturized decoupling structure of neutralization lines is proposed to further reduce the mutual coupling by −10 dB in comparison with the ground slot structure. The 2 × 2 MIMO antenna was fabricated and implemented to verify the design. The simulated and measured results were in good agreement. The measured impedance bandwidth of |S11| less than −10 dB ranges from 5.025 to 5.135 GHz, and the peak gain is 5.6 dBi on the broadside at the center frequency of 5.08 GHz. The mutual coupling levels between the orthogonal and the parallel antenna elements are −45 and −36 dB, respectively. The envelope correlation coefficient is lower than 0.003 across the operating bandwidth. The overall size of the antenna is only 1.08λ0 × 1.08λ0 × 0.025λ0, making the antenna a suitable candidate for upcoming fifth-generation MIMO systems. [ABSTRACT FROM AUTHOR]

This article presents a new design of a differentially fed substrate integrated planar antenna array with dual-polarization. Compared with the traditional dual-polarized antenna arrays, the proposed array antenna has the advantages of simple configuration, high cross-polarization discrimination (XPD), and high gain. The 2 × 2-element subarray design with a via-loaded crossover structure is used, which reduces the complexity of the array antenna. The operation bandwidth is improved by generating three resonances in the subarray. An 8 × 8 antenna array is designed, prototyped, and tested to exemplify its potential applications in large dual-polarized antenna arrays. A planar orthomode transducer is used to achieve differential excitation for the antenna array. The measured results show that the proposed antenna array has an impedance bandwidth of 19.2–20.7 GHz for |S11|< −10 dB and port isolation higher than 20 dB. The array antenna exhibits a high XPD of 43 dB and a flat gain of about 22.2 dBi within the bandwidth. [ABSTRACT FROM AUTHOR]

This article presents a novel dual slant polarized antenna for millimeter-wave (mmWave) base stations. Compared with the traditional slant polarized mmWave antennas, the proposed antenna offers the advantages of high cross-polarization discrimination (XPD), good aperture efficiency, simple structure, and low profile. The corner-fed substrate integrated waveguide (SIW) cavity is adopted to improve the port isolation and XPD of this slot-coupled antenna. Four corner-truncated patches connected by a thin cross strip are placed over the SIW cavity to increase the operation bandwidth. Then, a $2\times 8$ antenna array is designed to exemplify the antenna element performance. To improve the impedance matching, a shorted patch is introduced in designing the series feeding network and the power divider. The experimental results show that the 2 dB-down gain bandwidth of the proposed antenna array reaches 6.0% and the port isolation is better than 20 dB. The gain and XPD of the antenna array measure 16.7 dBi and 25 dB at the center frequency, respectively. [ABSTRACT FROM AUTHOR]

To speed up the design process of antenna arrays, a new multibranch artificial neural network (ANN) modeling technique is proposed and applied to tackle the inverse problem of antenna array directivity estimation. In the inverse modeling of an antenna array, the model inputs are electromagnetic parameters, whereas geometrical or physical parameters are set as the outputs. Due to the nonuniqueness of the inverse problem, it is difficult to directly use ANN for inverse modeling. We are trying to solve this problem utilizing monotonicity. The directional derivatives of the corresponding forward problem are calculated and the derivatives are utilized to determine the monotonicity of training data. Based on the monotonicity, the training data are divided into several groups, which are, respectively, used for training parallel branches of ANN. In this way, valid outputs can be provided without the forward model. Three dipole antenna arrays are utilized as examples to verify the efficiency of the proposed technique. [ABSTRACT FROM AUTHOR]

A compact beam-scanning flat antenna array with high gain based on the substrate- integrated waveguide (SIW) is presented in this article. The radiation elements are the continuous transverse stub (CTS) constructed by SIW, which are arrayed on the substrate. The SIW-CTS array has a 4 dB higher gain than the traditional CTS array with the metal parallel plate waveguide and the theoretical explanation is analyzed. A new compact corporate-feed network consisting of an SIW-horn and a flat lens is also proposed. The flat lens could convert the cylindrical wavefront generated by the feed probe and the SIW-horn to a planar wavefront for feeding the CTS array. The Taylor distribution of the feed level made the array has a low sidelobe and high gain. The beam scanning of the array could be realized by simply moving the small SIW-horn along the line across the focal point. An eight-element array is designed, simulated, and fabricated to verify the design. The measured results show that the scanning range is from −35° to 35° with the highest gain of being 20.6 dBi and the sidelobe level of −25.2 dB at the broadside. [ABSTRACT FROM AUTHOR]

A hybrid metasurface (HMS) is proposed to form a low-profile wideband antenna array. The antenna element is an array of $4\,\,\times4$ square metal patches and fed by a $50~\Omega $ microstrip line through an H-shaped coupling slot on the ground plane. Only are the edge patches of HMS antenna element grounded by shorting pins for the suppression of surface waves and cross-polarization levels as well as the enhancement of the gain. With the HMS antenna element, a compact $2\times 2$ array with an overall size of $1.58\lambda _{0} \times 1.58\lambda _{0} \times 0.068\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at 5.0 GHz) is designed, where the adjacent elements share the edge patches of the elements. The measurement shows the impedance bandwidth of 28% (4.41–5.85 GHz) for $\vert \text{S}_{11}\vert \le -10$ dB is obtained, and the boresight gain is greater than 8.4 dBi across the operating band, covering both fifth-generation (5G) sub 6 GHz and WiFi bands. [ABSTRACT FROM AUTHOR]

A hybrid topology optimization (HTO) method is utilized to optimize the isolation structure of a multiple-input multiple-output (MIMO) antenna. The HTO method, in which the scalar isotropic material with penalization (SIMP) and the level set method (LSM) are integrated, is based on the gradient optimization method with fast convergence speed. It combines the advantages of strong topology-searching ability of SIMP and smooth structure boundary of LSM. The proposed HTO method is adopted to optimize the isolation structure for good impedance matching, high isolation and high polarization purity of the MIMO antenna simultaneously. By setting the optimization structure as a symmetric one, the number of optimization variables is reduced by half. The optimization is validated by the full-wave simulation and the measurement. At the expected frequency of 5.8 GHz, the measured mutual coupling between the MIMO antenna elements with a center-to-center distance of $0.25\lambda _{0}$ is reduced by more than 24 dB, and the cross-polarization ratio reaches more than 27 dB. Furthermore, the reason for the isolation improvement is analyzed as well. [ABSTRACT FROM AUTHOR]

A cylindrical phased array (CPA) for quasi-full-space wide-angle scanning is presented. The quasi-full-space scanning is achieved by combining a pattern reconfigurable technique with a subarray scanning method. The pattern reconfigurable technique achieves wide-angle scanning in the elevation plane of the cylindrical carrier, while the subarray scanning ensures omnidirectional coverage in the azimuth plane of the cylindrical carrier by employing the CPA circumferential elements. Furthermore, a covariance matrix adaptation evolution strategy (CMA-ES) is used to optimize the quasi-full-space scanning performance. The proposed approach provides superior performance of sidelobe level (SLL < −6.1 dB), particularly small gain fluctuation (±0.75 dB) when scanning from −88°to +88° in the elevation plane of the cylindrical carrier, and smooth omnidirectional coverage with a gain fluctuation of only ±0.1 dB in the azimuth plane of the cylindrical carrier. The array supporting structure, including the control circuits, feed lines, p-i-n diode switches, and the radiating magnetic current elements are fabricated on or underneath the metallic ground plane. [ABSTRACT FROM AUTHOR]

Microstrip conical-beam antennas are designed by the topology optimization of metallic patches combining the discrete optimization of vias. The antennas are designed to be angular-periodic structures with eight identical sectors, which makes the rotational symmetric radiation pattern more easily to be achieved and the optimization problem much easier to be solved. A restarting technique is introduced for the circular polarization design case, where the high cross-polarization discrimination (XPD) is hard to be realized. By increasing the weight of cross-polarization penalization function after the optimization restarts, much higher XPD is achieved compared to that of the antennas optimized with fixed subobjective weighting factors. By this method, two conical-beam antennas, which are linearly polarized and left-handed circularly polarized antennas, respectively, are designed. Simulated and measured results show that the antennas have expected conical shape radiation patterns, good matching, and high polarization purities. [ABSTRACT FROM PUBLISHER]

In this paper, we present a transverse electric (TE)-polarized Bessel-beam antenna in the microwave range based on a leaky radial waveguide. According to the dispersion equation, an inductive sheet over a ground plane is needed. To achieve the inductive sheet, a grid structure printed on a dielectric substrate is designed. Besides, the radial waveguide is coaxially fed with a quasi-loop shaped structure to excite TE mode. The proposed antenna is investigated by simulation and measurement. In the measurement, a small loop is used to probe near magnetic field, and accurate measured magnetic intensity profiles are presented. The measurements show that TE-polarized Bessel beams can be launched within the nondiffractive range of 145 mm ( 2.803\lambda 0 ) at 5.8 GHz. [ABSTRACT FROM AUTHOR]

A two-port pattern reconfigurable three-layered Yagi-Uda patch antenna with ±45° dual-polarization characteristic is presented. A driven patch (DP) and two large parasitic patches (LPPs) are printed on the top side of the middle layer, and the middle and bottom layers share a common metal ground. Two microstrip feedlines printed orthogonally on the bottom side of the bottom layer are used to feed the DP through two H-shaped slots etched in the ground. The LPPs are connected to/disconnected from the ground controlled by switches. By adjusting the connection states of the LPPs, one wide-beam mode and three narrow-beam modes can be obtained in both polarizations. A small parasitic patch is printed on the top side of the top layer to improve the pattern coherence of the two polarizations. This antenna is studied by both simulation and measurement. The measured common bandwidth of the four modes in both polarizations is 3.32–3.51 GHz, and the isolations between two polarizations in all the modes are higher than 20 dB. The low-profile antenna is very suitable for microbase-station applications. [ABSTRACT FROM PUBLISHER]

A novel method of achieving a single-feed circularly polarized (CP) microstrip antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented. The CP characteristics are generated by employing a resonator to excite the two orthogonal modes of the patch via two coupling paths and the required 90° phase difference is achieved by using the different orders of the two paths. The presented method, instead of conventional methods that power dividers and phase delay lines are usually required, not only significantly enhances the bandwidths of the antenna but also results in a compact feed, reduced loss and high gain. Based on this method, a dual-band shared-aperture CP array antenna is implemented for $C$ -/ $X$ -band satellite communications. The antenna aperture includes a $2 \times 2$ array at $C$ -band and a $4 \times 4$ array at $X$ -band. To accommodate the $C$ - $X$ -band elements into the same aperture while achieving a good isolation between them, the $C$ -band circular patches are etched at the four corners. The measured results agree well with the simulations, showing a wide impedance bandwidth of 21% and 21.2% at $C$ -band and $X$ -band, respectively. The $C$ -band and $X$ -band 3 dB AR bandwidths are 13.2% and 12.8%. The array also exhibits a high aperture efficiency of over 55%, low sidelobe ( $C$ -band: −12.5 dB and $X$ -band: −15 dB), and high gain ( $C$ -band: 14.5 dBic and $X$ -band: 17.5 dBic). [ABSTRACT FROM PUBLISHER]

Design of a circularly polarized reconfigurable reflectarray antenna (RRA) at X band is presented. The RRA element employs concentric dual split rings, and can be mechanically rotated to obtain continuous 360° phase coverage with negligible element loss. A prototype with 15\times15 manually rotated elements is first computed, simulated, and measured. Full-wave simulations show that the gain of the beam focused in ( \theta =20^{\circ } , \varphi = 0^{\circ } ) direction is 25.8 dB and the 1-dB gain bandwidth is over 28.6%. The measured results show that the beam at ( \theta = 20^\circ , \varphi = 0^\circ ) direction achieves the maximum gain of 25.6 dB, corresponding to an aperture efficiency of 51.8%. The beam-steering capability of the RRA is measured within ±60° angular range, and well-defined scanned beams are obtained with maximum scan loss of 3.7 dB. The versatile beam-forming capability of the RRA is also verified by synthesizing a square shaped beam and a cosecant shaped beam. Another micromotor-controlled prototype with 756 elements on an octagonal aperture is fabricated and its measured radiation performance validates the feasibility of the proposed design as well. [ABSTRACT FROM PUBLISHER]

A beam scanning flat antenna array with the frequency that covers about the whole X-/Ku-band is proposed in this communication. The radiation element is the continuous transverse stub (CTS) constituted by the substrate integrated waveguide (SIW). The feed structure is an SIW parabolic reflector fed by a linear source with a metallic post, which exhibits a good impedance matching characteristics within a broad bandwidth. The beam steering direction is tunable with the frequency increasing within the operation band. The design principles of the SIW-based CTS array and the feed structure are explained in detail. One 16-element array is simulated, designed, and fabricated. The measurement results show that the antenna has a scanning angle range from 52.2° to −16.8° with the 3-dB gain from 8.5 to 14.1 GHz. At the center frequency of 12 GHz, it achieves a maximum gain of 18.1 dBi with an array size of 11.7\lambda 0\times 1.28\lambda 0 , while the first sidelobe level is −11.4 dB and the 3-dB beamwidth is 6.5°. [ABSTRACT FROM PUBLISHER]

A broadband polarization reconfigurable rectenna is proposed, which can operate in three polarization modes. The receiving antenna of the rectenna is a polarization reconfigurable planar monopole antenna. By installing switches on the feeding network, the antenna can switch to receive electromagnetic (EM) waves with different polarizations, including linear polarization (LP), right-hand and left-hand circular polarizations (RHCP/LHCP). To achieve stable conversion efficiency of the rectenna (\etar) in all the modes within a wide frequency band, a tunable matching network is inserted between the rectifying circuit and the antenna. The measured \etar changes from 23.8% to 31.9% in the LP mode within 5.1–5.8 GHz and from 22.7% to 24.5% in the CP modes over 5.8–6 GHz. Compared to rectennas with conventional broadband matching network, the proposed rectenna exhibits more stable conversion efficiency. [ABSTRACT FROM PUBLISHER]

A wide-beam antenna and a planar phased array with wide-angle scanning performance based on image theory are proposed. To solve the wide-angle scanning problem, a summative evaluation of basic types of carrier-based antennas is given and the antenna types available for wide-angle scanning arrays or end-fire arrays are pointed out. Afterward, a wide-angle scanning array with an artificial magnetic conductor (AMC) ground is proposed. The main beam direction of the array can scan from - \mathbf 89^\circ \;\mathbf to\;\mathbf 90^\circ in the H-plane with a gain fluctuation less than 3 dB and the scanning 3-dB beamwidth can cover a range from - \mathbf 105^\circ \;\mathbf to\;\mathbf 105^\circ . An excellent wide-angle scanning performance from the broadside direction to the end-fire direction can be obtained by the proposed method, which can be used to guide the design of wide-angle scanning arrays. [ABSTRACT FROM PUBLISHER]

A novel design of a two-port printed microstrip rectenna with compact structure for communication systems is presented. An aperture-coupled dual polarization patch antenna is utilized as the receiving antenna. The vertical feed port receives the microwave energy and transfers it to the rectifying circuit for dc power generation, while the horizontal feed port is used for data communication, with high isolation between the two ports. This patch antenna includes harmonic suppression functionality, which is essential for high microwave—direct current (mw-dc) conversion efficiency. A co-simulation procedure using HFSS and ADS for the analysis of the rectenna and the rectifying circuit design is used. This design assumes low input power for the rectifying circuit to comply with safety standards. A mw-dc conversion efficient of 63% is measured with a 900 \Omega load, 5.78 GHz operation frequency, and 25 mW receiving power. For the communication port, the measured reflection coefficient is -18 dB at 6.1 GHz center frequency, the gain is 7.0 dBi, and the cross polarization in the broadside direction is -15 dB. [ABSTRACT FROM PUBLISHER]