Zhi-Shuang Gong

Far-field subwavelength imaging with near-field resonant metalens scanning at microwave frequencies

A method for far-field subwavelength imaging at microwave frequencies using near-field resonant metalens scanning is proposed. The resonant metalens is composed of switchable split-ring resonators (SRRs). The on-SRR has a strong magnetic coupling ability and can convert evanescent waves into propagating waves using the localized resonant modes. In contrast, the off-SRR cannot achieve an effective conversion. By changing the switch status of each cell, we can obtain position information regarding the subwavelength source targets from the far field. Because the spatial response and Green’s function do not need to be measured and evaluated and only a narrow frequency band is required for the entire imaging process, this method is convenient and adaptable to various environment. This method can be used for many applications, such as subwavelength imaging, detection, and electromagnetic monitoring, in both free space and complex environments.

Compact Multiport Antenna With Radiator-Sharing Approach and Its Performance Evaluation of Time Reversal in an Intra-Car Environment

A compact multiport antenna with three ports sharing one radiator is presented. The radiator is composed of two Sierpinski fractal triangles. This antenna contains two main ports and one auxiliary port. The two main ports have the same operating frequency band of 1-4 GHz. The auxiliary port with a multiband at around 2.4, 3.4, and 5.2 GHz provides an additional WLAN/WiMAX port. Since all the three ports share one radiator, the dimension of this antenna is only about 0.21λ * 0.15λ * 0.01λ, where λ is the wavelength at the lowest operation frequency. Simulation results of time reversal (TR) propagation in an intra-car environment show that all the ports of the antenna have excellent TR focusing characteristic in each operation frequency band and the enhancement of the ratio of receiving signal amplitude to transmitting signal amplitude has been obtained. The radiator-sharing approach can be used to miniaturize the multiport antenna in TR time-domain communication systems.

Creation of an Arbitrary Electromagnetic Illusion Using a Planar Ultrathin Metasurface

An electromagnetic illusion method with planar metasurfaces is demonstrated numerically and experimentally. In the method, the scattering field of an arbitrary object can be built by using a planar ultrathin metasurface with dual-polarized subwavelength unit cells. The proposed planar illusion metasurface can disguise itself as an arbitrary object when the incident wave comes from a relative wide angle range, which means the proposed method is of great practical value.

Low profile circularly-polarized microstrip crossed antenna with wide beamwidth

A CP (Circularly-polarized) wide-beam microstrip antenna is proposed. A microstrip patch crossed dipole is inset in a slot with corresponding shape. Electric current is generated on the patch dipole, and electric field is generated in the slot. The radiation originated from the electric current is horizontal-polarization, and the radiation originated from the electric field is vertical-polarization. The synthetical radiation will obtain a CP radiation pattern. The result shows that the antenna can obtain its 3dB beamwidth wider than 134° at both x-z plane and y-z plane. Besides, the RHCP (Right-Hand Circularly-Polarized) beamwidth with AR<;3dB of the antenna is wider than 135° at both x-z plane and y-z plane. Meanwhile, the antenna is low profile. The thickness of the antenna is only 0.018λο. At last, the front-to-back ratio is high because there is an intact metal ground on the back of the antenna.

A wide-angle scanning array based on the image theory and time reversal synthesis method

A wide-angle scanning array based on the image theory and time reversal synthesis method (TRSM) is proposed. The main lobe of the array can scan from -75° to +75° with a gain fluctuation less than 4dB. It shows that the image theory can be used to design wide-beam antenna and the TRSM can be used to optimize the wide-angle scanning array efficiently.

Time reversal far-field super-resolution electromagnetic imaging aided by the near-field sub-wavelength structures

The resolution of traditional far-field imaging systems is restricted by the diffraction limit, because only the propagation waves, emitted by the source or scattered by the object, can be received by the devices of imaging systems. As we know, evanescent waves carry sub-wavelength information. But they cannot propagate to the far-field and exhibit exponential attenuation in the space. Therefore, how to receive the information of these waves in the far-field is a key to realize the super-resolution imaging.

Multi-frequency electrical resonant lens for far-field sub-wavelength imaging

Electrical resonant lens (ERL) consisting of periodically-distributed resonators with different working frequency is proposed for far-field sub-wavelength imaging. By the localized resonant modes, the evanescent waves can be converted into propagation waves. So the sub-wavelength image of the targets can be built from the spectral analysis in the far-field. The advantage is that Greens function is not needed to be measured or evaluated any more. Sub-wavelength images of point-like sources and scatterer are demonstrated at microwave range, with the resolution of λ/17.

A novel dual-band dual-polarized dielectric resonator antenna with high isolation

A novel dual-band dielectric resonator antenna(DRA) with dual-polarization is presented in this paper. It consists of a dielectric resonator, a square ground and a well designed feeding network. This antenna makes use of HEM111 mode and HEM113 mode to realize dual-band characteristics. Dual polarization is realized by exciting two orthogonal ports, and the port isolation is better than 65dB over the band of interest. For each port, the -10 dB impedance bandwidth of the lower and upper bands are given by 1.83-1.99GHz and 2.58-2.63GHz respectively. It can also achieve a peak gain of 6.5dB at the upper hemisphere for both modes.

Far-field frequency domain electromagnetic time reversal subwavelength imaging of scatterers assisted with grating plate

A far-field time reversal imaging system with the ability of distinguishing perfect electric conductor (PEC) targets separated with subwavelength distance is proposed. With the help of grating plate, evanescent waves are modulated and converted to propagative waves, thus recorded in the far-field region. Finally the subwavelength image of targets can be got by time reversal technology and demodulation operations in spatial spectrum domain. Example of two PEC spheres is presented, together with the image recovered by the proposed system.

Quasi-hemispherical-pattern antenna with complementary magnetic radiations

A compact microstrip antenna with a low profile of 0.03λ is proposed to obtain a hemispherical pattern, where λ is the free-space wavelength corresponding to the operation frequency 2.4 GHz. When the side length of the ground is infinite, the 3-dB beamwidths in the xz plane and yz plane are all 180° and the radiation pattern in the xy plane has a gain fluctuation less than 3 dB. When side length of the ground is 2λ, the simulated and measured 3-dB beamwidth in the xz plane are 156° and 157°, respectively; the simulated and measured 3-dB beamwidth in the yz plane are 160° and 155°, respectively. An excellent hemispherical pattern and a near-hemispherical pattern can be obtained when the ground is infinite and finite, respectively.