Broadband Antennas and Antenna Arrays

Abstract is not available in fulltext.Published versio

Wide-angle, Ultra-wideband, and Polarization-insensitive Circuit Analog Absorbers

Most previous circuit analog absorbers only considered absorption performance under normal incidences, leading to bad absorption for large incident angles, particularly those > 30°. With the advancement in modern bistatic radar detection technology, radar electromagnetic waves may come from different spatial directions, thereby necessitating radar absorbers with high absorption performance under normal and oblique incidences. Thus, in this paper, we present a novel wideband absorber comprising a conductive square-loop array embedded with lumped resistors and a well-designed Wide-Angle Impedance Matching (WAIM) layer. Results show that the WAIM layer can significantly improve absorption under oblique incidences. To make the absorber design clear and simple, an Equivalent Circuit (EC) and strict calculating formulas are proposed under normal and oblique incidences. Fractional bandwidth is increased into 137.1% through measurement under normal incidence, and the structure has a common fractional bandwidth of at least 110.5% for at least 10 dB reflection reduction when the incidence angle < 45°. The similarity among EC calculated, simulated, and measured results proves the validity of the designed absorber

Edge-on backscattering enhancement based on quasi-superdirective reradiation

A concept based on superdirective reradiation is presented for the sake of backscattering enhancement of a thin conducting plate at edge-on incidence. A passive structure consisting of a thin plate loaded with two conducting posts is proposed to demonstrate the concept. Through properly choosing the heights of two posts and the spacing between them, it is observed that the induced surface currents on the two loaded posts are almost 180º out of phase. An obvious enhancement of backscattering can then be obtained as a result of the quasi-superdirective reradiation produced by induced currents on the two loaded posts with each post height shorter than a quarter-wavelength. The induced current distribution is explained by virtue of the image method. Relatively small dimensions of the loaded posts make the design concept appropriate to the backscattering enhancement for airborne applications. The agreement between simulated and measured results validates our design.Accepted versio

Design and Analysis of Thinned Array Pattern Reconfigurable Antenna to Enlarge the Scanning Range

A novel thinned array with symmetric distribution along the array center is proposed in this paper. The proposed symmetric thinned array is based on the theory of unequally spaced array and the amplitude of each element in the array can be changed by introducing the weighted function. The pattern of the proposed array can be properly adjusted by changing the weighted function and the amplitude of the weighted factor, which obviously releases new degrees of freedom in array design. It has advantages such as low side lobe level (SLL) in the visible region, no grating lobes, and low nearby side lobe level (NSL), which has good potential for wide-angle scanning. Both simulation and experiment have been done; the experiment results show that, by applying this novel symmetric thinned array with pattern reconfigurable quasi-Yagi antenna, the scanning range of the array is −70°~70° in H-plane with SLL almost −10 dB below the maximum of the main beam. The 3 dB beam-width coverage is −86°~86°, which means that the proposed array can realize the entire upper-space beam coverage and restrain the SLL at the same time

Super-resolution characteristics based on time-reversed single-frequency electromagnetic wave

International audienceA sub-wavelength three-antenna array that is able to perform super-resolution focusing with single-frequency signal excitations is investigated using time-reversal. The antenna array is loaded with a set of uniformly distributed thin metal wires, which when combined with single-frequency electromagnetic waves from a time-reversal mirror yields a 1=35 wavelength super-resolution focusing at the targeted antenna. The length of the metal wires in particular determines the frequency band enabling super-resolution performance. The results have signicance for the super-resolution investigation of multi-band compact antenna ar- rays involving micro-structures, with potential linkage with recent studies on super-resolution mechanisms in deterministic complex media