Antonio Garcia-Pino

Analysis of slot antennas on a radial transmission line

Two methods for the analysis of slot-array radial-line antennas are presented. A moment method (MM) analysis is performed using a cosine basis function for each slot and the Galerkin method. The analysis can be extended to incorporate thickness of the metal plate supporting the slots. Closed form formulas are also derived to model the slot antenna as a multiport network. This model allows a faster antenna analysis when a large number of slots are present. The multiport model has been validated with the MM analysis in a two-slot case and through the measurements of a more complex antenna problem.

Scattering from conducting open cavities by generalized ray expansion (GRE)

The problem of electromagnetic scattering by metallic open cavities is addressed here using a generalized ray expansion (GRE) method. The wave coupled into the cavity is modeled as a combination of a number of spherical waves, the propagation of such waves being described in terms of geometrical optics. A brief description of the method including some details about aperture discretization as well as results for three-dimensional problems such as circular and rectangular cross-section cavities are presented. The GRE method gives results that agree well with those of modal analysis and allow, like ray methods, for greater flexibility in geometric modeling. Furthermore, the ray-tracing process must be done only once for different incident waves, so its computational cost is lower than that of the classic ray methods, where the incoming wave is described as a different bundle of parallel rays for each direction of incidence. >

Zooming and Scanning Gregorian Confocal Dual Reflector Antennas

The zooming and scanning capabilities of a Gregorian confocal dual reflector antenna are described. The basic antenna configuration consists of two oppositely facing paraboloidal reflectors sharing a common focal point. A planar feed array is used to illuminate the subreflector allowing the antenna to scan its beam. The resulting quadratic aberrations can be compensated by active mechanical deformation of the subreflector surface, which is based on translation, rotation and focal length adjustment. In order to reduce the complexity of the mechanical deformation, least squares fit paraboloids are defined to approximate the optimal correction surface. These best fit paraboloids considerably reduce scanning losses and pattern degradation. This work also introduces two different zooming techniques for the Gregorian confocal dual reflector antenna: the first consists of introducing a controlled quadratic path error to the main reflector aperture; and the second is based on reducing the size of the radiating aperture of the feeding array.

A Bifocal Ellipsoidal Gregorian Reflector System for THz Imaging Applications

Current terahertz imagers rely on reflector systems for the beam quality and imaging speed because the cross-range span that the system can cover is limited by the beam aberrations when the antenna scans. We present the design of a Bifocal reflector system that can rapidly scan a terahertz beam for standoff imaging applications while increasing the field of view of previous designs up to 50%. The design is based in a confocal Gregorian system where the nominal reflector surfaces are substituted by shaped surfaces to reduce the beam aberrations, while not increasing the manufacture cost of the reflector antenna. We also provide a set of useful design formulas for the design of this kind of reflector systems. The beam patterns obtained by the proposed designs are numerically calculated with the commercial software GRASP and compared with those obtained with previous approaches to the same problem, showing the better performance of the proposed solution.

3-D High-Resolution Imaging Radar at 300 GHz With Enhanced FoV

We have developed a 3-D high-resolution radar at 300 GHz with a cell resolution of 1×1.6×1.6 cm3 at a standoff distance of 8 m for security applications. The selection of an operating frequency of 300 GHz, a bandwidth of 27 GHz, and a field of view of 50×90 cm2 improves the through-clothes imaging of person-borne concealed objects. The radars antenna design allows single-pixel imaging at a frame rate of two frames per second. A reduction in cost and power consumption and improvements in image quality are additional requirements taken into account in the design of this radar system.

A shaped and reconfigurable reflector antenna with sectorial beams for LMDS base station

In this communication a reflector antenna is presented as a feasible solution for Local to Multipoint Distribution System base station with a reconfigurable number of sectorial beams. The antenna is an improved version of the hourglass reflector antenna with a shaped profile to obtain a cosecant-squared elevation pattern, and with a feed array which is designed to achieve adequate and reconfigurable beamwidth in the horizontal plane.

Bifocal Reflector Antenna for a Standoff Radar Imaging System With Enhanced Field of View

A unique multireflector bifocal antenna design for real-time standoff imaging applications is presented in this work. The antenna is used in combination with a 300 GHz radar sensor to acquire images at 8 m over a large (80 × 50 cm) field of view (FoV). The increased FoV is obtained by the use of an antenna system composed by a bifocal elliptical Gregorian with an extended subreflector to allow for fast scanning of a beam spot. The scanning is achieved by the combination of the rotation and vertical tilting of a flat small secondary mirror. The design, simulations, prototype description and experimental results of a manufactured working prototype are presented.

Millimeter Wave Imaging Architecture for On-The-Move Whole Body Imaging

This paper presents a novel interrogation system that combines multiple millimeter wave transmitters and receivers to create real-time high-resolution radar images for personnel security screening. The main novelty of the presented system is that the images can be created as the person being screened continuously moves across a corridor where the transmitters and receivers, working in a fully coherent architecture, are distributed. As the person moves, the transmitters and receivers are sequentially activated to collect data from different angles to inspect the whole body. Multiple images, similar to video frames, are created and examined to look for possible anomalies such as concealed threats. Two-dimensional (2-D) and three-dimensional (3-D) setups have been simulated to show the feasibility of the proposed system. The simulation results in 2-D have been validated using measurements.

Experimental radar imager with sub-cm range resolution at 300 GHz

This paper presents a high range resolution radar sensor working in the submillimeter-wave band for standoff detection and security applications. Low-cost technologies have been properly selected in order to implement a versatile and easily scalable radar system. A large operational bandwidth, required for high range resolution, is attained by means of a frequency multiplication-based architecture. This radar system sweeps a bandwidth of 27 GHz. The final application allows the generation of 3D images by means of the radar front-end integrated with a bifocal ellipsoidal Gregorian reflector system. The scene of interest is elliptically scanned at a standoff range of 8 m.

Shaped Solid Contour Beam Reflector Antennas That Adjust to Varying Operating Conditions With Just a Few Mechanical Actuators

The aim of this work is to design a shaped solid reflector mechanically reconfigurable and capable to comply changeable coverage requirements using few actuators. The method directly optimizes the actuators with a heuristic technique based in ant colony algorithm, where both mechanical and electromagnetic models are integrated in the same cost function in a simple and effective way using the mechanical concept of stiffness matrix. To illustrate this technique, we present an example of a reconfigurable reflector antenna that covers South America with a minimum directivity and, for some reduction of this minimum directivity, is able to increase the directivity in selected regions to respond to rain and other changing conditions in a few seconds.