Yuping Shang

On the Design of Single-Layer Circuit Analog Absorber Using Double-Square-Loop Array

A detailed study of a single-layer circuit analog absorber using double-square-loop array reveals that three resonances can be obtained within its operating frequency band. An equivalent circuit model is proposed to explain how these three resonances can be produced and its absorption bandwidth can be widened. Simple guidelines for the design of this double-square-loop absorber are then formulated. It is shown through measurements that the fractional bandwidth of 126.8% is realized for at least 10 dB reflectivity reduction under the normal incidence. Furthermore, the total thickness of the proposed design is only 0.088λL at the lowest operating frequency. A good agreement between simulated and measured results demonstrates the validity of our design.

Frequency-Selective Rasorber Based on Square-Loop and Cross-Dipole Arrays

A novel design of a transmission window within the absorption band of a circuit analog absorber, named as frequency-selective rasorber (FSR), is presented. Based on an equivalent circuit model, the conditions are formulated to produce a passband with small insertion loss and to reduce the reflection at frequencies below and above the passband in the meanwhile. Simple design guidelines of our proposed FSR are then developed. With loaded lumped elements, the arrays of square-loop and cross-dipole are combined to realize its implementation. It is shown through measurements that an insertion loss of 0.68 dB can be obtained at 4.42 GHz and the fractional bandwidth for at least 10 dB reflection reduction within the lower and upper frequency bands is 92.3% under the normal incidence. A good agreement between simulated and measured results validates our design.

Design of Hybrid Patch/Slot Antenna Operating in Induced “TM120 Mode”

An ultralow-profile antenna based on a typical magnetic metamaterial unit cell, i.e., complementary electric resonator (CELC) structure, is introduced in this paper. The antenna behaves with an attractive performance of operating in induced “TM120 mode” as the fundamental resonance mode, which is much lower than TM100 mode. Compared to the reported miniature microstrip antennas based on slotting patch/ground technologies, the proposed antenna shows advantages in terms of low profile, high radiation efficiency, and low cross polarization. According to our investigation, even though the relatively strong backward radiation is accessorily caused due to the inherent complementary meander line (CML) slotting as a drawback for this type antenna, the peak gain in the broadside is much higher than a slot antenna with approximately the same dimensions.

Enhancement of backscattering by a conducting cylinder coated with gradient metasurface

This paper proposes a highly effective method for enhancing the backscattering by a conducting cylinder that is coated with a gradient metasurface. The employed metasurface exhibits a phase gradient continuously varying along the circumferential direction of the cylinder so that in-phase retroreflection can be produced to enhance the backscattering. It is demonstrated that the cylinder coated with the proposed gradient metasurface can generate backscattering very close to that from a conducting plate with the same dimensions as the cylinders cross-section perpendicular to the incident plane wave. Compared with a bare conducting cylinder, the backscattering is significantly enhanced by the gradient metasurface made of conducting strips printed on a grounded dielectric substrate. Effects of cell numbers along the cylinder axis, incident angle, and polarization of the incoming electromagnetic wave on the backscattering enhancement are examined and discussed. A good agreement between simulated and measured b...

An Electronically Controllable Method for Radar Cross Section Reduction for a Microstrip Antenna

PIN diodes are used to electronically switch a rectangular microstrip antenna between the optimal radiation state and the low radar cross section (RCS) state in this paper. A useful loading circuit is proposed. The circuit is connected between the patch and the ground plane of the antenna at each loading position. The loading positions of the circuit are determined by studying magnitude distributions of the induced electric fleld and analyzing statistically how many times that the maximum electric fleld occurs in each area for each discussed incident angle. PIN diodes are equivalent to capacitances and resistances when diodes are reverse-biased and forward-biased, respectively. When the antenna is not in service and excited by an incident plane wave, obvious RCS reduction is realized. In addition, the radiation performances are well maintained when the antenna is in service for transmitting or receiving signals.

Polarization-Independent Backscattering Enhancement of Cylinders Based on Conformal Gradient Metasurfaces

The electromagnetic backscattering enhancement of both elliptic and circular conducting cylinders is investigated in this paper through the design of conformal and polarization-independent gradient metasurfaces. The presented metasurface designs employ varying phase gradient along the circumferential direction of the involved cylinder so that effective retroreflection can be achieved through redirecting the scattering dispersed by the conducting cylinder back to the direction from which the plane electromagnetic wave is coming. Supported by a grounded thin substrate with a relatively high dielectric constant, a modified loop array with compact unit cell is used to implement the nonuniformly or uniformly sampled phase gradient of the metasurface. It is observed that the metasurface-coated elliptic and circular cylinders can generate backscattering very close to that by corresponding flat conducting plates with their main planes perpendicular to the incident wave vector, for both transverse magnetic (TM) and transverse electric (TE) polarizations. Compared with the conducting cylinders without coating, the backscattering is thus effectively enhanced by the conformal gradient metasurfaces. Good agreement between simulated and measured backscattering results validates the observations.

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 180 ° 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.

Out-of-service RCS reduction of a rectangular microstrip antenna

A microstrip antenna using PIN diodes to reduce the radar cross section (RCS) is investigated. The PIN diodes are equivalently simulated with resistances and capacitances when they are forward-biased and reverse-biased, respectively. When the antenna is in service, radiation performances are well maintained through the reverse bias operating characteristic of PIN diodes. When the antenna is out of service and excited by an incident plane wave, obvious RCS reduction is realized through the forward bias operating characteristic of PIN diodes.

Electromagnetic retroreflection augmented by spherical and conical metasurfaces

The focus of this paper is on phase gradient metasurfaces conformal to spherical and conical bodies of revolution, with an aim of engineering retroreflections and therefore augmenting backscattering cross-sections of those three-dimensional geometries under the illumination of a plane electromagnetic wave. Based on the conducting sphere and cone, the effect of the geometric revolution property on the selection of the unit inclusion of metasurfaces is considered. The procedure for using the selected unit inclusion to implement the proper reflection phase gradient onto the illuminated surfaces of those objects is formulated in detail. Retroreflections resembling conducting plates under normal incidence are observed for both the conducting sphere and cone coated with conformal metasurfaces. As a result, the redirection-induced retroreflection effectively contributes to the backscattering cross-section enhancement. A good agreement between full-wave simulations and measurements demonstrates the validity and e...

Backscattering from planar spiral antennas

Structural mode backscattering characteristics of planar spiral antennas with proper termination impedances are presented. The investigated spiral antennas contain a self-complementary two-arm Archimedean spiral, a self-complementary four-arm Archimedean spiral and our proposed four-arm bilayer spiral. Compared with the self-complementary two-arm spiral, it is observed that the self-complementary four-arm spiral has lower structural mode backscattering. Based on the observations of self-complementary two-arm and four-arm spiral antennas, a four-arm bilayer spiral is proposed and it is shown that this spiral can gain further reduction of co-polarized backscattering under the linear polarization incidence. Furthermore, the radiation characteristics of the spiral antennas are also presented. The good agreement between simulated and measured backscattering results of the fabricated spirals validates our design.