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A simple and low-cost single substrate layer Luneburg lens-based beamforming network (BFN) operating in $W$ -band is proposed. A multibeam antenna is then realized using the novel BFN and fabricated using a low-cost printed circuit board process. The Luneburg lens is realized by drilling holes in a substrate, and to extend the refractive index variation, a high dielectric constant substrate is embedded at the lens center. The lens is excited by radially placed open-ended substrate integrated waveguides (SIWs) at the lens circumference, feeding a subset of antenna ports placed on the opposite side of the lens. The proposed BFN thus provides half-power beamwidth (HPBW) and beam steering angle flexibility for multibeam antennas. An antenna generating seven beams was prototyped at 79.5 GHz to validate this BFN, providing measured beam steering of approximately ±41° with a broadside HPBW of 10°. The bandwidth of the proposed BFN is determined by the single-mode operation of the SIW. The fabricated multibeam antenna impedance bandwidth is, however, about 2% at 79.5 GHz because of the radiating elements. The radiating elements are series fed slot arrays placed on SIWs. [ABSTRACT FROM AUTHOR]

In this paper, several conformal leaky-wave antennas (CLWAs) are designed, which utilize backward radiating waves to focus the beam. They employ a metal strip grating (MSG) in order to introduce the required phase constant ($\beta$) on a curved aperture to compensate for the defocusing due to the curvature. The required $\beta$ is obtained by modulating the distance between adjacent strips/slots to scan the beam toward broadside. Using backward waves with a modulated MSG on a smoothly curved CLWA is a novel design. Using a backward wave allows for a doubling of the aperture size as compared to the forward-wave case. This, in turn, leads to a doubling of the directivity. A simple two-dimensional (2-D) Fourier-series model is used to explain the radiation physics. Full-wave analyses using the FEKO and HFSS software packages are carried out to design and analyze these CLWAs in 2-D and three-dimensional (3-D), and to verify the concept. A CLWA with a focused backward wave, supported by a modulated MSG, is fabricated and tested. The calculations and experimental results confirm that directive beaming is possible with a backward wave on a curved, modulated MSG. [ABSTRACT FROM PUBLISHER]

A generalized methodology to design low-profile transmitarray (TA) antennas made of several stacked layers with nonresonant printed phasing elements is presented. A study of the unit cell bandwidth, phase-shift range and tolerances has been conducted considering different numbers of layers. A structure with three metalized layers with capacitive and inductive elements enabling a phase range of nearly 360° and low insertion loss is introduced. A study of the four-layer structure shows improvement in the performance of the unit cells in terms of bandwidth from 2% to more than 20% and a complete phase coverage. Implementations on a flexible substrate of TAs with progressive phase shift operating at 19 GHz are used for validation. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a dual-surface reflector (DSR) antenna working in dual circular polarization (CP). This DSR consists in a linearly polarized dual-gridded reflector (DGR) that is made of a solid parabolic reflector on which a reflectarray that reflects horizontal polarization (HP) and is transparent to the vertical polarization (VP) is affixed. The conversion from linear polarization (LP) to CP of this antenna is realized by introducing a three-layer meander-line circular polarizer optimized for oblique incidence. The antenna system was designed to generate two main beams in different directions and orthogonal CPs. This antenna has been fabricated and characterized. For the two polarizations, the realized gain is higher than 30 dB with a cross-polarization discrimination (XPD) higher than 27 dB in the 18–20 GHz frequency band. [ABSTRACT FROM PUBLISHER]

In this communication, a new broadband antenna with a very low profile is proposed. The antenna inherits the wide bandwidth of the blade antenna, while its height is considerably reduced to 0.03\lambda0, where \lambda0 is the wavelength of the lowest operating frequency. This new design consists of a top loaded monopole with several shorting pins and an inductive loading. The antenna resonates at two distinctive frequencies determined by the shorting pins and inductive loading and the wideband characteristic is achieved by the control of the resonance separations. The inductive loading is created by a shorted metallic disk embedded into the antenna structure. This new method of inductive loading facilitates the antenna fabrication while the physical size of the antenna is kept compact. A prototype was fabricated and its VSWR and far field radiation pattern were measured. The antenna provides a bandwidth of 17% for VSWR smaller than 3. Also, a minimum realized gain of 1 dBi was achieved over the frequency bandwidth in which the antenna is well matched. [ABSTRACT FROM PUBLISHER]

It is known that for reflectarrays designed to radiate in an off-specular direction, part of the scattered field may still be directed in the specular direction. In this paper, a reflectarray made of single-layer patch elements is considered. The dependence of the unwanted specular reflection on the size of the patches is examined. Moreover, in a global analysis of the reflectarray, we show that this specular reflection can be due to a periodic error occurring in the applied phase shift. It is found that this periodic error is also responsible for the occurrence of a parasitic lobe in backward directions. [ABSTRACT FROM PUBLISHER]

A novel type of short monopole antenna is proposed. Its structure consists of a periodically slotted coaxial line radiating in linear polarization (LP). The structure can be easily modified by the addition of a thin layer of dipoles in order to generate circular polarization (CP). The number of slots along the structure, their periodicity and the tuning of the terminating load allow control of the antenna main beam' angle and width. One advantage of the proposed design over conventional monopoles is that the antenna does not require a ground plane. Both left-hand and right-hand CP are possible with the same design, simply by inverting the symmetry of the printed dipoles. Design details for the annular slotted coaxial line and for the LP and CP mast antennas are given. Prototypes in both LP and CP were fabricated and their characteristics were measured. Simulations and measurement are in good agreement. The proposed CP mast antenna is compliant with the requirements of the XM digital satellite radio system, with a frequency bandwidth of more than 1.7% in which VSWR < 2, and an AR < 4 dB in the elevation range of ±30° < θ < ± ± 70°. [ABSTRACT FROM AUTHOR]

A new design of two-dimensional cylindrical Luneberg lens is introduced based on TE10 mode propagation between parallel plates, with special focus on ease of manufacturing. The parallel plates ace partially filled with low cost polymer material (Rexolite ϵr =2.54) to match Luneberg's law. A planar linear tapered slot antenna (LTSA) is inserted into the air region between the parallel plates at the edge of the Luneberg lens as a feed antenna, with fine positioning to the focal point of the Luneberg lens to optimize the antenna system performance. A combined ray-optics/diffraction method is used to obtain the radiation pattern of the system and results are compared with predictions of a time domain numerical solver. Measurements done on a 10-cm Luneberg lens designed for operation at 30 GHz agree very well with predictions. For this prototype, 3-dB E- and H-plane beamwidths of 6.6° and 54° respectively were obtained, and the sidelobe level in the E-plane was -17.7-dB. Although the parallel plate configuration should lead to a narrow band design due to the dispersion characteristics of the TE10 mode, the measurement results demonstrate broadband characteristics with radiation efficiencies varying between 43% and 72% over the tested frequency hand of 26.5-37 GHz. The designed cylindrical Luneberg lens can be used to launch multiple beams by implementing an arc array of planar LTSA elements at the periphery of the lens, and can be easily extended to higher mm-wave frequencies. [ABSTRACT FROM AUTHOR]

A set of tools to accomplish beam synthesis for synthetic-aperture radar antennas is presented. The synthesis process optimizing the beam properties is guided by criteria of the radar performance in terms of range ambiguities and noise-equivalent backscattering coefficient. The tools implemented with MATLAB® are validated with examples of beams generated by RADARSAT. [ABSTRACT FROM AUTHOR]

The equivalent magnetic currents method can be used to characterize radiating structures and to obtain information about the current distribution on the radiating device under test (DUT). In order to do so, the system is assumed to be linear and inversion from near-field measurements can be carried out using numerical techniques such as the singular value decomposition. However this approach is very sensitive to modeling and measurement errors, which is a consequence of the ill-conditioned nature of the inversion process. Here, we propose to account for the ill-conditioning by using a Tikhonov regularization technique to perform the inversion. This technique requires a regularization parameter to be set to an appropriate value, and we show that a generalized cross-validation approach yields adequate determination of the regularization parameter directly from the measured data. The proposed method can be tailored to account for specific characteristics of the DUT. This point is illustrated by the estimation of the current distribution of a bidimensional radiating structure for which prior information about the orientation of radiating edges is incorporated into the inversion method. [ABSTRACT FROM AUTHOR]

Demonstrates the potential of equivalent magnetic current (EMC) in the prediction of low-directivity printed antenna radiation patterns based on the measurements in the reactive near-field. Near-field measurement system; EMC modeling of printed radiators; Accuracy of the far-field patterns obtained after processing the near-field measurements.