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Item type:Publication, Access status: with files , Advancing 60-GHz SISO radar: additively manufactured leaky wave antenna with enhanced beam steeringIn this work, a waveguide-based leaky wave antenna (LWA) for beam scanning operation at 60GHz is presented, fabricated, and experimentally investigated. It employs a slotted radiator in a rectangular waveguide, achieves a beam squint of 76° with 5.5-GHz bandwidth, offering enhanced angular resolution. The antenna employs dual feeding, thereby virtually doubling the bandwidth, which permits more beam scan angle per employed physical bandwidth in radar systems for precise angle estimation. The antenna was fabricated using SLA 3-D printing and subsequently silver-coated, enabling efficient production of complex 3-D antenna geometries. As expected, printing inaccuracies and metallization processes influence the antenna gain and beam squint. However, these effects can not only be reduced but even fully eliminated through targeted optimization of the manufacturing process, as demonstrated in this article. By combining application-specific antenna design with optimized fabrication techniques, best-in-class performance can be achieved despite the constraints of additive manufacturing. Compared with previous works, the antenna presented herein offers a unique combination of a large squint angle, high-operating frequency, and practical manufacturability. By combining the beam squint with dual feeding, a balance between high-range resolution and precise angle estimation is achieved in radar applications.Publicationtype: Journal Article30 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Analysis of the radar channel and its variability in vital-sign sensing applicationsIn millimeter-wave (mmWave) radar-based vital-sign sensing, the radar sensor usually operates in the radiative near field of the target, which is the human body. Therefore, in contrast to far-field conditions, scattering cannot be quantified by a target-inherent radar cross section (RCS) as it strongly depends on the relative position and directivity of the radar antenna. To investigate the resulting consequences for the application, this article examines the radar channel transfer function, i.e., the ratio between the power waves feeding and being received by the antenna, with particular focus on its variability due to changes of the relative antenna position. The analysis is supported by a physical-optics-based simulation model tailored to practical circumstances. Measurements at 24 GHz and 61 GHz using antennas with different directivities and a human-like mannequin as a target confirm the simulative predictions. The radar channel suffers from significant variations, e.g., displacing the antenna by less than 1mm can cause a 30-dB receive power drop. A statistical analysis comprehensively evaluates the radar channel variability and clarifies the challenges for the application that stem from target near-field effects.Publicationtype: Journal Article146 33 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Near-field scattering phenomena in monostatic radar applications derived from physical opticsIn the context of radar, this article examines phenomena that occur in conditions where the physical extent of the target cannot be considered negligible compared to the range and, thus, far-field assumptions are violated. Based on physical optics principles, a transfer function of the radar channel between the antenna input and output power wave is derived for a monostatic configuration. The effects are studied using a circular metallic disk as an exemplary target. Exact and approximative expressions for the transfer function are derived incorporating the influence of the antenna radiation characteristic in addition. Measurements with targets of different sizes performed with horn as well as open-ended waveguide antennas at 24 and 61 GHz validate the phenomena of receive power level fading and nonlinear phase distortion.Publicationtype: Journal Article71 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Antenna Phase Center Determination Using a Six-Port-Based Direction-of-Arrival Detector(2023-05-01); ; This article presents a novel technique to determine the antenna phase center. It relies on measuring the direction of arrival of the radiated field. Therefore, no access of the measurement equipment to the antenna under test is required. A direction-of-arrival detector is implemented that performs phase difference measurements in two orthogonal planes. Six-port interferometers are used for this purpose. By considering phase differences, the proposed method is robust against phase disturbances, which may occur at the feed of the antenna under test, e.g., due to flexible cables or rotary joints. Besides, impairments stemming from reflections in the measurement environment are addressed. Measurements of a K-band horn and a patch antenna in an anechoic chamber validate the approach. A single phase center is determined for each principle plane as well as for the three-dimensional main beam. In addition, the phase center locus is retrieved.Publicationtype: Journal Article112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A dual-polarized SIW lens antenna array for Rx-/Tx-integration at K/Ka-bandThe terminal antenna with dual circular polarization reported here operates around 20GHz and 30GHz, i.e., in the down- and uplink frequency bands of current satellite communication systems. The passive array, this work focuses on, integrates the receive and the transmit paths (Rx/Tx) in a single aperture. This approach is shown to be advantageous compared to classical solutions with two separate antennas. The modules, the array consists of, are formed by a stack of eight linear sub-arrays which themselves are composed of an alternating series of four Tx-only and four combined Rx/Tx end-fire antenna elements. The resulting brick architecture provides enough real estate for the future implementation of phased array electronics. The array is implemented in substrate integrated waveguide (SIW) technology. For improved matching, it is covered with a periodically shaped dielectric lens. A technique is proposed to mitigate cross-polarization in the pointing direction. A module is realized using standard technologies. The relevant array parameters are measured. The module patterns are synthesized from the individual element responses. They confirm the simulated results and, in particular, a bandwidth of more than 2.5GHz for both Rx and Tx.Publicationtype: Journal Article57 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Glide-Symmetric Lens Antenna in Gap Waveguide Technology(2020-04); ; ; ; In this article, we propose a wideband fully metallic impedance-matching horn lens antenna based on glide symmetry realized in the gap waveguide technology. A multiple iterative method is adopted, which overcomes the limitation of large phase deviations at the interface of traditional lens antennas, thus increases the directivity as a result. Moreover, the glide-symmetric configurations of inner metallic pins within the gap waveguide are employed to construct the artificial dielectric lens, with the advantage of the ultralow dispersion, which is especially helpful to broaden the working bandwidth and improve the lens performance. The antenna is fed by a stepped double-ridged gap waveguide which can easily excite the antenna working in a wideband. To reduce the undesired reflections at the antenna aperture, the antenna is ended with a tapered structure as an impedance transition. A prototype of the horn lens antenna is manufactured and measured, showing a broad operation bandwidth from 12 to 18.5 GHz with S11 less than -10 dB. The antenna can be further extended to the millimeter band due to the low losses of the gap waveguide at high frequencies and the iterative method can also be applied to other types of lens antenna designs.Publicationtype: Journal Article90 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dual-Polarized Phased Array with End-Fire Radiation for 5G Handset Applications(2020-04); ; ; ; This communication proposes a dual-polarized end-fire phased array for 5G handset devices at 28 GHz. The proposed four-element array has low profile of 1.1 mm, small clearance of 2.7 mm, and symmetric patterns in the vertical plane. The array element is fed by substrate-integrated waveguide (SIW), which works as a waveguide (WG) antenna with vertically polarized radiation pattern. Two transition plates are introduced to improve the impedance matching of the WG antenna. The horizontal polarization is generated by exciting one of the transition plates as an antenna. The other transition plate is modified as a group of triangle strips to minimize its reflection to the horizontal radiation patterns. A -10 dB frequency bandwidth of 5.3% and a -6 dB bandwidth of 25% are achieved, overlapping between the vertical and horizontal polarization. The array scanning angle is from -54° to 44° at 29 GHz for both polarization. Within the scanning range, the end-fire gain varies from 7.48 to 8.14 dBi for the horizontal polarization, whereas from 4.49 to 8.05 dBi for the vertical polarization. Good agreements between simulations and measurements are well achieved and shown in this communication.Publicationtype: Journal Article51 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Low-Dispersive Leaky-Wave Antennas for mmWave Point-to-Point High-Throughput CommunicationsIn this article, we present two efficient leaky-wave antennas (LWAs) with stable radiation pattern, operating at 60 GHz. Both antennas exhibit attractive properties such as significantly reduced beam-squint, low loss, low sidelobes, high directivity, and simple manufacturing. The beam-squint of conventional LWAs is reduced by refracting the leaked waves in a dispersive lens and the low sidelobe levels are achieved by tapering the leakage rate along the aperture. Since the antennas are implemented in groove gap waveguide technology, the losses are low. The two antennas are different in terms of their asymmetric/symmetric leakage tapering with respect to the broadside direction. Both designs are optimized for low sidelobes, but since symmetry is enforced in one, the resulting performance in terms of sidelobes is suboptimal. However, in the symmetric design, multiple stable beams can be obtained, simultaneously or independently. Twenty percent bandwidth is obtained with less than ±0.5° beam-squint. In this frequency range, the gain is stable at 17 and 15 dBi for the asymmetric and symmetric designs, respectively. The designs are intended for point-to-point links in mmWave communication networks where low losses, directive beams, and low sidelobes are expected to be key features.Publicationtype: Journal Article85 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Wideband Leaky-Wave Antennas Loaded with Gradient Metasurface for Fixed-Beam Radiations with Customized Tilting Angles(2020-01); ; ; ; We propose a hybrid dispersion compensation method to design wideband fixed-beam leaky-wave antennas (LWAs), with the tilting angle customizable in both forward and backward quadrants. In a previous work, a triangular dispersive prism constituted by metallic pins was presented to compensate for the dispersion of traditional LWAs and achieve a squint-free radiation in a relative bandwidth of 20%. However, that design suffered from the drawbacks of large geometry and limited angular range. To overcome these limitations, here a broadband gradient metasurface based on geometric phase theory is loaded in front of the prism to customize the radiation angle and reduce the total prism size. In addition, a novel ridged gap waveguide is employed to improve the linearity of LWA dispersion, which is beneficial to maintain the bandwidth of LWA with reduced size. Two examples are presented to demonstrate the excellent performance of the designed antennas. One antenna radiates at an angle of 39.5° in a squint-free bandwidth of 20%, but the prism size is decreased to a quarter of the original one, while the other realizes a broadside radiation with a squint-free bandwidth of 18%. Good agreement is exhibited between simulated and experimental results. The proposed method can be further extended to compensate for the dispersion of antenna arrays and improve the angular stability of the radiation beams in a large frequency band.Publicationtype: Journal Article99 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Introducing a mixed-mode matrix for investigation of wireless communication related to orbital angular momentumThis paper introduces a mixed-mode matrix representation of scattering parameters that is suitable for the investigation of wireless communication based on orbital angular momentum (OAM). For this purpose, a unitary transformation matrix is defined, which contains the transmitted and received amplitudes as basis vectors corresponding to OAM-based communication between two antenna arrays. The mixed-mode matrix is then obtained from the corresponding similarity transformation of the standard scattering matrix available, e.g., from numerical simulations or measurements. The mixed-mode matrix allows better physical insight into OAM-based communication by clearly separating all modes and is more efficient than postprocessing of single-antenna results in a system simulator. Mode conversion/isolation and proper mode termination can be easily quantified. Also, it allows generalizing the interpretation of OAM-based communication by focusing on the property of a constant phase difference within each antenna array. The usefulness of this approach is demonstrated using method of moments (MoM) simulations of dipole radiators in various arrangements of a transmitting and a receiving array. Systematic parameter studies that reveal dependencies of OAM-based communication are possible by using the mixed-mode matrix. As an application, communication patterns are studied, in order to obtain the suitable position and relative orientation in space for good mode isolation or communication.Publicationtype: Journal Article130