Yannan Jiang

Bandwidth broadening of a graphene-based circular polarization converter by phase compensation

We present a broadband tunable circular polarization converter composed of a single graphene sheet patterned with butterfly-shaped holes, a dielectric spacer, and a 7-layer graphene ground plane. It can convert a linearly polarized wave into a circularly polarized wave in reflection mode. The polarization converter can be dynamically tuned by varying the Fermi energy of the single graphene sheet. Furthermore, the 7-layer graphene acting as a ground plane can modulate the phase of its reflected wave by controlling the Femi energy, which provides constructive interference condition at the surface of the single graphene sheet in a broad bandwidth and therefore significantly broadens the tunable bandwidth of the proposed polarization converter.

Ultra-wideband high-efficiency reflective linear-to-circular polarization converter based on metasurface at terahertz frequencies

The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 - 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0.7, and the phase difference between the two orthogonal electric field components of the reflected wave is close to 90° or -270°. The results indicate that the relative bandwidth reaches 80% and the efficiency is greater than 88%, thus, ultra-wideband high-efficiency LTC polarization conversion has been realized. Finally, the physical mechanism of the polarization conversion is revealed. This converter has potential applications in antenna design, EM measurement, and stealth technology.

Method for Synthesis of

A method for synthesis of TE01- TE11 waveguide mode converters is proposed based on the non-uniform rational B-spline technique. An application of the method to a 30.5-GHz serpentine circular waveguide converter of TE01- TE11 mode is given. The serpentine circular waveguide synthesized by the method has coaxial-parallel input and output ports and smooth axial curvature distribution, as well as short length and high conversion. The method offers good solutions to the problems of the mode converter design in the situation where two successive waveguides are asked to fit together strictly.

{\rm TE}_{01}\!\!-\!\!{\rm TE}_{11}

Terahertz wave has been widely used in communication fields due to its unique penetrability, high image analyticity and non-ionizing property, in which antenna is highly necessary. However, traditional terahertz antenna based on noble metal has several problems such as severe loss, low bandwidth and bad radiation performance. In this study, an antenna with graphene radiation and feeding structure was designed based on the impedance characteristic of graphene in terahertz frequency, which has efficiently increased the bandwidth and improved the radiation performance of the antenna. Experimental results indicate that the relative bandwidth reaches to 73.2% and the radiation efficiency retains above 95% when radiation structure is made of graphene; and that the relative bandwidth is almost the same with PEC feeding structure (73.2%) and the antenna has omnidirectional radiation, high gain and radiation efficiency in its impedance bandwidth.

Mode Converter for Gyrotron by the NURBS Technique

A miniaturized power divider based on composite right/left-handed transmission line (CRLH-TL) is proposed in this paper. The simulated results show that the each output port of the power divider is able to achieve equal-amplitude and in-phase electromagnetic (EM) signal in the frequency range from 2.35GHz to 2.42GHz. The measured results is good agreement with the simulated one. The proposed power divider is very compact which can be acted as feeding network of miniaturized microstrip antenna array.

A broadband terahertz antenna using graphene

An ultra-wideband pattern reconfigurable antenna is proposed. The antenna is a dielectric coaxial hollow monopole with a cylindrical graphene-based impedance surface coating. It consists of a graphene sheet coated onto the inner surface of a cylindrical substrate and a set of independent polysilicon DC gating pads mounted on the outside of the cylindrical substrate. By changing the DC bias voltages to the different gating pads, the surface impedance of the graphene coating can be freely controlled. Due to the tunability of graphenes surface impedance, the radiation pattern of the proposed antenna can be reconfigured. A transmission line method is used to illustrate the physical mechanism of the proposed antenna. The results show that the proposed antenna can reconfigure its radiation pattern in the omnidirectional mode with the relative bandwidth of 58.5% and the directional mode over the entire azimuth plane with the relative bandwidth of 67%.

Compact power divider based on composite right/left-handed transmission line

The dispersion curve of a ka-band slow wave structure consisting of modified photonic band gap is tested by resonant method. A mode launcher combined with a wheel radiator and coupling probe has successfully excited all the resonant modes of TM01-like mode in cold test.

An ultra-wideband pattern reconfigurable antenna based on graphene coating*

In this paper, an interdigital resonator that can greatly decrease mutual coupling between adjacent patches is proposed to realize an ultra-compact microstrip antenna array operating in 2.4 GHz wireless communication system. Due to its remarkable performance of decoupling, the edge to edge distance between adjacent patches can be reduced to 0.08λ0 and even less. Meanwhile, a miniaturized feeding network, which is composed of a CRLH-TL-based phase shifter and T-junction-based power divider, is used to feed the compact antenna array. The simulation results show that the proposed antenna array has an impedance bandwidth of 8.34%. We fabricate the antenna array to verify its performance. The experimental results are in good agreements with the simulations. Compared to the published designs, the proposed antenna array has an ultra-compact structure and hence can be used in space limited communication systems.

Cold test of slow wave structure with modified photonic band gap

The development of modern radar technology has a great threat to the stealth of military targets such as aircrafts. Absorber can be used to enhance the stealth of military targets. In this paper, an ultra-broadband THz absorber based on graphene is proposed. The absorption rate over 90% is from 0.48THz to 1.82THz and the relative absorption bandwidth is 117%. Then the absorbing mechanism of the absorber is analyzed by the method of impedance matching. The results show the validity of the simulation. Moreover, the absorber has excellent properties of insensitive polarization and wide incident angle range.

Ultra-Compact Microstrip Antenna Array and Miniaturized Feeding Network

Detection radar is a great threat and challenge for military target like aircraft in modern war. In order to effectively reduce the radar cross section (RCS) from the objects surface to achieve the stealth performance, a novel graphene absorber based on partial non-periodic plane is presented in this paper. The absorption rate of the proposed graphene absorbing screen is more than 90% in the range of 45GHz-160.5GHz with the relative bandwidth of 112.4%. Furthermore, the properties of polarization insensitive and the reduction of RCS are validated and confirmed by the full-wave simulation.