Anisotropic impedance surfaces are employed as low-profile and broadband reflectors that convert orthogonal linear to right- and left-handed circular polarization respectively. By virtue of ...anisotropy, it is possible to independently control the reflection characteristics of two orthogonal linearly polarized incident plane waves and therefore achieve linear to circular polarization conversion. Equivalent circuits for anisotropic impedance surfaces with arbitrarily shaped elements are employed to demonstrate the operating principle and a design procedure is proposed. The proposed design procedure is demonstrated by means of an example involving a dipole array. A prototype is designed and its performance characteristics are evaluated. The 3-dB relative axial ratio bandwidth exceeds 60%, while low loss and angular stability are also reported. Numerical and experimental results on a fabricated prototype are presented to validate the synthesis and the performance.
This communication demonstrates for the first time the capability to independently control the real and imaginary parts of the complex propagation constant in planar, printed circuit board compatible ...leaky-wave antennas. The structure is based on a half-mode microstrip line which is loaded with an additional row of periodic metallic posts, resulting in a substrate integrated waveguide SIW with one of its lateral electric walls replaced by a partially reflective wall. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty that the leaky-mode leakage rate can be controlled by virtue of a sparse row of metallic vias. For this topology it is demonstrated that it is possible to independently control the antenna pointing angle and main lobe beamwidth while achieving high radiation efficiencies, thus providing low-cost, low-profile, simply fed, and easily integrable leaky-wave solutions for high-gain frequency beam-scanning applications. Several prototypes operating at 15 GHz have been designed, simulated, manufactured and tested, to show the operation principle and design flexibility of this one dimensional leaky-wave antenna.
The concept of frequency steerable two-dimensional electromagnetic focusing by using a tapered leaky-wave line source embedded in a parallel-plate medium is presented. Accurate expressions for ...analyzing the focusing pattern of a rectilinear leaky-wave lens (LWL) from its constituent leaky-mode tapered propagation constant are described. The influence of the main LWL structural parameters on the synthesis of the focusing pattern is discussed. The ability to generate frequency steerable focusing patterns has been demonstrated by means of an example involving a LWL in hybrid waveguide printed-circuit technology and the results are validated by a commercial full-wave solver.
A complete contextual marketing platform including an indoor positioning system (IPS) for smartphones is proposed and evaluated to later be deployed in large infrastructures, such as malls. To this ...end, we design and implement a novel methodology based on location-as-a-service (LAAS), comprising all the required phases of IPS generation: mall digital map creation, the tools/procedures for offline calibration fingerprint acquisition, the location algorithm, the smartphone app acquiring the fingerprint data, and a validation procedure. To select an appropriate fingerprint location algorithm, a comparison among K-nearest neighbors (KNN), support vector machine (SVM), and Freeloc is accomplished by employing a set of different smartphones in two malls and assessing different occupancy levels. We demonstrate that our solution can be quickly deployed at shop level accuracy in any new location, resulting in a robust and scalable proposal.
A theoretical study on the design of broadbeam leaky-wave antennas (LWAs) of uniform type and rectilinear geometry is presented. A new broadbeam LWA structure based on the hybrid printed-circuit ...waveguide is proposed, which allows for the necessary flexible and independent control of the leaky-wave phase and leakage constants. The study shows that both the real and virtual focus LWAs can be synthesized in a simple manner by tapering the printed-slot along the LWA properly, but the real focus LWA is preferred in practice. Practical issues concerning the tapering of these LWA are investigated, including the tuning of the radiation pattern asymmetry level and beamwidth, the control of the ripple level inside the broad radiated main beam, and the frequency response of the broadbeam LWA. The paper provides new insight and guidance for the design of this type of LWAs.
A novel fixed-frequency electronically-steerable one-dimensional (1-D) leaky-wave antenna is presented. The antenna is based on a parallel-plate waveguide loaded with a planar partially reflective ...surface and a tunable high impedance surface (HIS), which creates a 1-D Fabry-Perot leaky-waveguide. The tunable HIS consists of printed patches loaded with varactor diodes that allow the electronic tuning of the cavity resonance condition. Using a simple Transverse Equivalent Network, it is theoretically shown how the variation of the varactors' junction capacitance allows the scanning of the antenna pointing angle from broadside towards the endfire direction at a fixed frequency. Experimental results of an antenna prototype operating at 5.6 GHz are reported, demonstrating that the new reconfigurable leaky-wave antenna can provide electronic beam scanning in an angular range from 9 ^{\circ} to 30 ^{\circ}
A new type of one-dimensional leaky-wave antenna (LWA) with independent control of the beam-pointing angle and beamwidth is presented. The antenna is based on a simple structure composed of a bulk ...parallel-plate waveguide (PPW) loaded with two printed circuit boards (PCBs), each one consisting of an array of printed dipoles. One PCB acts as a partially reflective surface (PRS), and the other grounded PCB behaves as a high impedance surface (HIS). It is shown that an independent control of the leaky-mode phase and leakage rate can be achieved by changing the lengths of the PRS and HIS dipoles, thus resulting in a flexible adjustment of the LWA pointing direction and directivity. The leaky-mode dispersion curves are obtained with a simple Transverse Equivalent Network (TEN), and they are validated with three-dimensional full-wave simulations. Experimental results on fabricated prototypes operating at 15 GHz are reported, demonstrating the versatile and independent control of the LWA performance by changing the PRS and HIS parameters.
The possibility of microwave near-field focusing using a simple width-tapered microstrip leaky-wave antenna is theoretically and experimentally proven in this paper. The design procedure to obtain ...the modulation of the microstrip width along the antenna length is described, illustrating the conditions and limitations for optimum focusing at a certain focal point and using a given substrate. A 7.5 λ 0 -long microstrip lens is designed to operate at 15 GHz, and its focusing properties are studied. An array of two in-phase microstrip lenses located front-to-front is proposed to obtain a symmetric focusing pattern with higher spatial resolution. Theoretical and experimental results demonstrate the optimum synthesis of a focusing region with focal length of 3 λ 0 , presenting focal width of only 0.33 λ 0 , and focal depth of 1.25 λ 0 . Finally, it is reported the frequency focus-scanning performance in the range 14-17 GHz. All these features make the proposed microstrip lens a simpler alternative solution to focused planar phased-arrays.
A central feeding array radiating at broadside and manufactured in substrate-integrated waveguide (SIW) technology is shown in this work. The single-layer array consists of N = 8 line-source ...leaky-wave antennas (LWAs), which are designed to satisfy the splitting condition (α = β) of the leaky mode. The LWAs are arranged in a radial configuration, in this manner, by properly designing the SIW width W and the spacing between SIW vias P for each SIW LWA, the leaky mode can be independently controlled to fulfil the splitting condition, and all the individual beams from each SIW LWA can merge into one at broadside direction (θ = 0°) for a given design frequency. The two-dimensional radiating surface allows obtaining a pencil beam radiation pattern, which is linearly polarised because of the radial arrangement. A prototype with a radiating length of LA = 60 mm for each SIW LWA, and a total radius of R = 73 mm has been manufactured for a design frequency of 15 GHz. Input matching, gain and radiation patterns at several planes have been measured and compared with full-wave simulations, obtaining good agreement between them.
An extension of the pole-zero matching method proposed by Stefano Maci for the analysis of electromagnetic bandgap (EBG) structures composed by lossless dipole-based frequency selective surfaces ...(FSS) printed on stratified dielectric media, is presented in this paper. With this novel expansion, the dipoles length appears as a variable in the analytical dispersion equation. Thus, modal dispersion curves as a function of the dipoles length can be easily obtained with the only restriction of single Floquet mode propagation. These geometry-dispersion curves are essential for the efficient analysis and design of practical EBG structures, such as waveguides loaded with artificial magnetic conductors (AMC) for miniaturization, or leaky-wave antennas (LWA) using partially reflective surfaces (PRS). These two practical examples are examined in this paper. Results are compared with full-wave 2D and 3D simulations showing excellent agreement, thus validating the proposed technique and illustrating its utility for practical designs.
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