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A planar reflectarray antenna based on liquid crystal materials is presented in this paper. First, a new type of loop dipole miniaturized liquid crystal antenna reflection unit is constructed. The reflector unit can achieve 400° phase shift at 35GHz, and the loss is less than 4.5dB. Then, an 11×11 liquid crystal reflectarray antenna is designed using this unit, and the main beam scanning angle range of the array antenna reached ±20°. When the deflection angle of the array antenna is 20°, the gain of the antenna is 14.9dBi, and the first sidelobe level is −9.1dB.

This paper designs a miniaturized reflective phase shifter based on liquid crystal. The phase shifter adjusts the dielectric constant of the liquid crystal to cause the load impedance to change, thereby realizing the phase change at the output of the coupler. Through the multilayer circuit structure, the miniaturization of the phase shifter is realized. In the operating bandwidth of 14GHz∼16GHz, the return loss is better than −10.89dB, the insertion loss is better than 5.7dB, and the maximum phase shift exceeds 320°.

In this paper, a terahertz phase shifter work in F-band (90–140 GHz) is designed based on the continuous tunability of liquid crystal and the excellent electrical properties of non radiative dielectric (NRD) waveguide. The simulation results show that the liquid crystal phase shifter is electrically controlled by the bias electrode network, and the maximum phase shift is 500 degrees. The phase shifter shows excellentl matching, and the return loss is almost less than −10 dB in the bandwidth up to 60 GHz.

Because the liquid crystal material has fluidity and electrical control characteristics, it is suitable for conformal phased array design, this paper designed a cylindrical conformal phased array antenna based on liquid crystal material. The designed conformal phased array antenna has a center frequency of 15GHz, a 5×5 uniform array, and a cylindrical radius of 80mm, which can achieve gradient gain scanning (14.17dBi-21.4dBi), and the scanning range is ±30°. The designed antenna array has certain practical prospects.

The NA is a basic parameter of a lens, which can determine its focusing spot size in the far field. High NA(close to 0.9 or above) metalens with a deep sub-wavelength focusing spot is an important metadevice in the modern optics and photonics. In this paper, a four-layer microwave metalens and its applications in the high-gain and low-profile antenna are studied and demonstrated. A high NA=0.88 (FWHM is 0.57λ) metalens based on high transmission phase gradient metasurface is firstly designed and is also verified by experimental result. Besides, a feeding source is placed at the focal spot of the proposed metalens, and a quasi-spherical wave is emitted and then transformed to a plane wave. Thus, a high gain antenna is obtained and the beam-width of the bare antenna is also significantly decreased. The simulated results show that the gain of the high NA metalens is largely enhanced by 10.47dB compared to bare antenna at the frequency of optimized 9GHz. More importantly, the relation between the focusing efficiency of high NA metalens and the enhanced gain of lens antenna is discussed and highlighted. The work opens new avenues to design high-gain lens antenna based on high NA plasmonic metalens in the microwave band.

A novel microwave absorber is presented in this paper. The absorber is a single layer structure based on the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by an active frequency selective surface (AFSS) controlled by PIN diodes. The reflectivity-amplitude of the tunable microwave absorber can be controlling by adjusting the current in PIN diodes. Experimental results are presented and prove the working mechanism of the new absorber, which show that the reflectivity amplitude can be modulated from -5dB to -42dB at 11.5GHz.

The numerical aperture (NA) of a lens determines its focusing resolution capability and the maximum light collection or emission angle. In this Letter, an ultrathin high NA metalens operating in the microwave band is designed and demonstrated both numerically and experimentally. The proposed element is constructed by a multi-layer complementary split ring resonator, which can cover full 2 π phase shift simultaneously with high transmission magnitude by varying its radius gradually. The numerical and experimental results reveal that the designed ultrathin (thickness is only ∼ 0.23 λ ) metalens can focus normal incident microwave efficiently to a spot of full width at half-maximum (FWHM) as small as ∼ 0.54 λ with a corresponding high NA exceeding 0.9. Besides, the high NA metalens also possesses a relatively large focusing efficiency with a peak 48% within considered broad frequency range from 7.5 to 10 GHz. The performances of the presented metalens can be comparable or even superior to nowadays high-quality optical metalenses and represent an important step to develop a high-performance metalens in low spectrum. Besides, it can greatly facilitate the development of some novel miniaturized devices like a high-gain low profile scanning antenna, an ultra-compact retroreflector, and cloaks.

Broadband metalenses consisting of sub-wavelength phase gradient elements are indispensable in modern science and technology. So far, several broadband optical metalenses are demonstrated but mostly with either small NA or relatively low focusing efficiency. Herein, an ultra-thin broadband microwave metalens (frequency range from 8.0 to 10.5 GHz) with a relatively high-efficiency above 40% and a large NA of more than 0.6 is presented. The metalens is also fabricated and the measurement results agree with the simulations very well. The performances of the presented broadband metalens can surpass nowadays microwave metalenses largely and open up new vistas for low-profile, low-cost and light-weight microwave components.

A novel broadband metamaterial absorber (MMA) is presented in this paper. The absorber is a single layer structure based on the topology of a high impedance surface (HIS), but in which the conventional top layer is replaced by an active frequency selective surface (AFSS) loading with resistors and varactor diodes. The absorbing resonant frequency of the MMA changes by adjusting the capacitance of varactor. Simulated results show that the absorption of the absorber covers a broadband of 2.35 GHz-11.45 GHz above 98% when the capacitance increases from 0.1 pF to 5 pF. At the same time, the total thickness of this absorber, 2 mm, is only λ/64 of the lower limit frequency.

High numerical aperture (NA) metalenses with large focusing efficiency are crucial for various applications in modern optics and photonics, particularly in high resolution imaging, high directivity lasing process and so on. Recent progresses have been achieved in designing high NA metalenses which can surpass conventional ones but mainly in the visible and infrared regimes by using all-dielectric metasurfaces. Here, multilayer phase gradient metallic metasurfaces sandwiched by filling dielectrics are employed to design high NA and large efficiency metalenses in the low spectrums. Benefiting from its high transmission amplitude and the full phase control to the incident waves of the proposed gradient meta-atoms with a double split ring resonator, the designed ultra-thin and small footprint four-layer metalens (5λ × 5λ × 0.23λ, λ is wavelength) demonstrates a high NA in the order of 0.8 and the large focusing efficiency around 40% according to the full-wave simulations and experimental measurements. Furthermore, the influences of the dielectric thickness and the layer number of stacked meta-atoms on the presented high NA metalens are investigated. The results reveal that the NA of proposed metalens can be surprisingly further improved from 0.8 to 0.9 by increasing dielectric thickness and/or the focusing efficiency can be enhanced to above 50% by adding the layer number of the stacked meta-atoms. These findings also imply that our high NA metalens in low spectrum can be compatible to the standard printed circuit board fabrication and also posses of good robustness to the metasurface layer number. The presented work provides new vistas to develop high NA and large efficiency metalens in low microwave or Terahertz (THz) spectrum, where the metallic metasurfaces are commonly used. Besides, it can benefit to the development of various novel metadevices such as miniaturized high-gain lens antenna, compact cloaks and many others in modern microwave engineering and/or THz optics.

In this paper, a gradient index metasurface lens (metalens) for planar wide-angle and high-efficient focusing is designed, fabricated and tested. By properly designing the ultra-thin double-layer metasurfaces with gradient meta-atoms, the proposed metalens can focus wide-angle incident wave efficiently working at transmission regime. The numerical and experimental results demonstrate that the metalens can focus oblique incident wave continuously up to 40°within half maximum focused field intensity of normal one on one side. Besides, the accurate focused spot mapping dependent on both the normal and oblique incident angle is established and analyzed quantitatively. The designed metalens demonstrate good achromatic capability with large spatial incident angle view. This work of wide-angle and high-efficient metalens enhances the performance of conventional ones which operate within narrow incident angle range and can opens up new ways to develop some novel ultra-thin devices like wide-angle scanning antenna and planar retro-reflector in microwave band.

An ultrathin tunable absorber for the ultrahigh frequency (UHF) band is presented in this paper. The absorber is a single-layer structure based on the topology of a Salisbury screen, in which the conventional resistive layer is replaced by an active frequency-selective surface (AFSS) loaded with resistors and varactors. The reflectivity response of the absorber can be controlled by adjusting the reverse bias voltage for the varactors, which is verified by both simulated and measured results. The experimental results show that the reflectivity response of the absorber can be modulated below &minus, 10 dB over a frequency band ranging from 415 to 822 MHz. The total thickness of the absorber, 10 mm, is equivalent to only &lambda, /72 of the lower limit frequency. The absorbing mechanism for the designed absorber is illustrated by simulating the volume loss density distributions. A detailed analysis is also carried out on the basis of these parameters, such as the AFSS shape, resistor, thickness of the foam, thickness and permittivity of the dielectric substrate, and incident angles, which contribute to the reflectivity of the AFSS absorber.

A novel radar absorber for use in ultrahigh frequency (UHF) band is presented in this paper. The absorber is a single layer structure based on the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by a high impedance surface (HIS). This absorber is loaded with resistors to match with the free space. Experimental results show that the reflectivity of the absorber cover a broadband of 0.56-l.85GHz below −6dB. The total thickness of this absorber, 30mm, is only λ/18 of the lower limit frequency.

With the development and update of science, the structure of targets such like aircraft become much more complex, the surface of target is always not slippery in the research of electromagnetic scattering characteristics emulation and testing, the interceptive structures such like the slot and the cavity exist with the technic requirements, these can bring several affections to the RCS of the target, this paper mainly discusses about the affections to electromagnetic scattering characteristics of targets with the emulation result of Method of Moments.

In this paper, an ultra-wideband, wide angle and polarization-insensitive metasurface is designed, fabricated, and characterized for suppressing the specular electromagnetic wave reflection or backward radar cross section (RCS). Square ring structure is chosen as the basic meta-atoms. A new physical mechanism based on size adjustment of the basic meta-atoms is proposed for ultra-wideband manipulation of electromagnetic (EM) waves. Based on hybrid array pattern synthesis (APS) and particle swarm optimization (PSO) algorithm, the selection and distribution of the basic meta-atoms are optimized simultaneously to obtain the ultra-wideband diffusion scattering patterns. The metasurface can achieve an excellent RCS reduction in an ultra-wide frequency range under x- and y-polarized normal incidences. The new proposed mechanism greatly extends the bandwidth of RCS reduction. The simulation and experiment results show the metasurface can achieve ultra-wideband and polarization-insensitive specular reflection reduction for both normal and wide-angle incidences. The proposed methodology opens up a new route for realizing ultra-wideband diffusion scattering of EM wave, which is important for stealth and other microwave applications in the future.

There are two stealth mechanisms of conventional radar absorbing materials, which operate either by phase cancellation or by absorbing incident electromagnetic energy and converting it to heat. A novel microwave absorber is presented in this paper, called Phase-Modulated Surface (PMS). The PMS differs from passive radar absorbing materials, which does not absorb any electromagnetic energy, but makes a frequency spectrum excursion of reflected wave, so that most electromagnetic energy falls out of pass-band of the receiver. The PMS is a single layer structure based on the topology of a Salisbury screen, while in which the conventional resistive layer is replaced by a switchable impedance sheet. In this paper, the PMS will be analyzed by frequency spectrum and reflectivity.

There are many factors of influencing precision of test in the RCS (Radar Cross Section) measurements. Usually applying the method of background subtraction eliminates the influence that interference signal brings. In the paper, four parts that froth support structure, the timeliness of calibrated data, the temperature of the apparatus room influencing the signal of PNA and the precision of target rotary table are studied.

Plane reflector is a two dimensional array which consists of apertures or patchesthis kind of reflectarray is always illuminated by a primary feed hornand then compensate the spatial phase delay by the elements printed on the surface. The main advantage of this structure is the main beam can be designed to tilt or scan a number of beamwidths away from its broadside direction. But the most significant defect is it's narrow bandwidth, which is caused by the elements and reflector's operating principle. In this paper, we introduced a new kind of broadband element consist of hexagon loops and patch, which has more than 500 degree linear phase. And we give an offset-fed reflectarray antenna comprised of this elements which acquire 23.6% 1 dB bandwidth, this has a significant improvement for traditional structures.

Developing high-performance radar absorption material (RAM) is always important in the stealth projects. Circuit analog (CA) absorber studied in this thesis is better than traditional Jaumann absorber in many aspects, such as thickness and absorption band. The principle and design method of CA absorber is explored in this thesis. One sample of single-layer CA absorber is designed, and the simulation results agree well with the measurement results, so the validity of this design method is verified sufficiently. The contributions of this thesis provide the foundation for further designing CA absorber.

In this paper, a metasurface (MS) is designed based on the hybrid array pattern synthesis and particle swarm optimization method for wideband monostatic and multistatic radar stealth. The non-absorptive MS is composed of two kinds of electronic band gap structures with the reflection phase difference of 180° (±37°) over a wide frequency range. Far field scattering pattern of the MS can be quickly and accurately synthetized by the method of moments and array pattern synthesis. A new strategy is proposed for realizing the diffusion reflection of electromagnetic waves by redirecting electromagnetic energies to more directions through optimizing the reflected phase arrangement for the MS by hybrid array pattern synthesis and particle swarm optimization algorithm. Due to the non-uniform distributions of phase gradient between neighboring lattices, numerous scattering lobes are produced in the upper half-space, leading to a great reduction of bistatic radar cross section (RCS). The −10 dB RCS reduction bandwidth of 80.2% is achieved for both monostatic and bistatic at normal incidence. The specular reflection and bistatic scattering for oblique incidence with TE and TM polarizations are also considered in detail. The measured results are in good agreement with the corresponding simulations.