Design and simulation of self-biased circulators in the ultra high frequency band

Theoretical models were developed to design self-biased Y-junction circulators operating at ultra high frequency (UHF). The proposed circulator designs consist of insulating nanowires of yttrium iron garnet (YIG) embedded in high permittivity barium-strontium titanate (BSTO) substrates. A design with as many as 10⁵ or greater wires may be considered in its entirety to determine the electromagnetic scattering S-parameters of a circulator design, thus helping to mitigate the computational limitations of the available finite element method (FEM) tools. The approach seeks to represent the nanowires and the BSTO substrate by an equivalent medium with effective properties inclusive of the average saturation magnetization, dynamic demagnetizing fields, and permittivity. The effective medium approach was validated in comparison with the FEM models. Using the proposed approach, a self-biased junction circulator consisting of YIG nanowires embedded in a BSTO substrate was designed and simulated in which the center frequency insertion loss was calculated to be as low as 0.16 dB with isolation of −42.3 dB at 1 GHz. The 20 dB bandwidth was calculated to be 50 MHz. These results suggest that practical self-biased circulators at the UHF band are feasible.     

A mm-wave four-port quasi-optical circulator

A four-port quasi-optical circulator has been designed, built and tested for operation in the millimetre wave band. The specific circulator reported here was investigated over a 20 GHz bandwidth, centred on 94 GHz. Good performance characteristics were obtained over this bandwidth. Isolations of better than 30 dB and insertion losses of around 0.5 dB were achieved. The input vswr was found to be less than 1.35 over the whole bandwidth investigated and vswr's of less than 1.1 were achieved for narrower bandwidths. It is possible of course to configure the 4-port circulator as a 3-port circulator or indeed as 2-port isolator. Further optimization and consequent improvements in performance are almost certainly obtainable.     

A broadband Ka-band microstrip circulator for integrated millimeter wave systems

A Ka-band microstrip circulator, using ferrite with 4 M=5000 G, have been developed. By optimizing the circulator configuration, broadband n=2 Chebyshev response performance are obtained over 7 GHz bandwidth. The circulator have isolation of greater than 15 dB, and insertion loss of less than 1.0 dB.     

94 GHz phase-shift-keying modulator

This paper describes a kind of low insertion loss phase-shift-keying modulators used in 94GHz digital communications systems. A BPSK modulator with a insertion loss lower than 3.8dB has been achieved by connecting a circulator and a fin-line PIN diode phase shifter in series. The bandwidth is 2.5GHz given a phase error of ±5⁰. The circuits and experimental results are also given out.     

A novel polarization converter based on the band-stop frequency selective surface

A dual-passband single-polarized converter based on the band-stop frequency selective surface(FSS)with a low radar cross-section(RCS)is designed in this article.The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface.The simulation results reveal that the co-polarization reflection coefficients below-10 d B are achieved in 3.82–13.64 GHz with a 112.4%fractional bandwidth(the ratio of the signal bandwidth to the central frequency).Meanwhile,a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%.Moreover,the 1 d B transmission window is obtained in two nonadjacent bands of 3.42–7.02 GHz and 10.04–13.91 GHz corresponding to the relative bandwidths of 68.9%and 32.3%,respectively.Furthermore,the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz,and the 10 d B RCS reduction in the range of 4.10–13.35 GHz is achieved.In addition,the equivalent circuit model of this converter is established,and the simulation results of the Advanced Design System(ADS)match well with those of CST Microwave Studio(CST).The archetype of the designed converter is manufactured and measured.The experiment results match the simulation results well,which proves the reliability of the simulation results.     

A 300 GHz quasioptical faraday rotation isolator

A quasioptical isolator has been developed at 285 GHz with insertion loss2 dB and isolation 18 dB over a 1% bandwidth. By improving matching techniques, the device should perform as well over bandwidths up to 5%. This design can be easily modified to make a circulator.     

Investigation of Waveguide Y-Junction Circulator with a Triangular Ferrite Post

An H-plane waveguide Y-junction circulator with a triangular ferrite post is investigated by a modified analysis of jointly resonance theory and simple field theory. Good agreement between the theoretical obtained performances and experimental results is observed. The circulator exhibits a very low insertion loss and a wide bandwidth.     

基于极化旋转超表面的圆极化天线设计

本文通过设计出一种反射型极化旋转超表面,在8—12 GHz频域内实现高效的极化旋转,并将其加载于微带缝隙天线下方构成新型的极化旋转超表面天线,利用超表面的90°极化旋转效应,成功实现了天线的圆极化辐射调制.仿真与实验结果表明:圆极化天线的中心工作频率为GHz,阻抗带宽为8.3—10 GHz.当微带缝隙天线与极化旋转超表面的间距H=4.5mm时,天线在8.3—8.8 GHz频带内实现了圆极化辐射;当mm时,天线在8.8—9.3 GHz频带内实现了圆极化辐射;当=8mm时,天线在9.3—10 GHz频带内实现了圆极化辐射.实验结果与仿真结果相符,证明了此种设计方法的有效性,也为微带缝隙天线的圆极化设计提供了一种新的途径.     

基于十字变形结构的高效超宽带线性极化转换超表面

提出了一种基于十字变形结构超表面的极化转换器,在反射模式下获得了高效超宽带的交叉极化反射.在8.4到20.7GHz频段内交叉极化反射率大于-0.2dB,而共极化反射率小于-12dB,在谐振频率点处交叉极化反射率大于-0.03dB,而共极化反射率达到-60dB,即在谐振点处几乎可实现完全的交叉极化转换;相对带宽达84.5%,交叉极化的平均转换效率为96.7%;此外,利用电路板刻蚀制备了此极化转换器样品,实验测试其交叉极化反射率在工作频段内大于-1dB,而共极化反射率小于-10dB,实验结果与模拟结果吻合,验证了此超表面可以在超宽的频带内实现线极化电磁波的交叉极化转换.本文设计的超宽带极化转换超表面具有转换效率高和几何结构简单的优点,可被扩展到太赫兹甚至是可见光频段.     

一款基于多物理场调控的超宽带线-圆极化转换器

为了在微波波段实现可调谐的线-圆极化转换器的设计,结合固态等离子体与二氧化钒设计了一种基于多物理场调控的超宽带线-圆极化转换器,通过改变固态等离子体谐振单元激励状态和人为改变外部温度(T)来实现对该线-圆极化转换器工作频段的调控.采用了全波仿真的方法对该极化转换器的极化转换率曲线、反射相位曲线、轴比曲线、表面电流图进行了计算,并讨论了参数r_1与r_3对轴比的影响.仿真结果表明,当固态等离子体区域均未激励且T68℃时,3 dB轴比频带为14.3—29.7 GHz,相对带宽为70%;当固态等离子体区域均被激励且T68℃时,3 dB轴比频带为14.4—23.4 GHz与28.6—35.9 GHz,相对带宽分别为47.61%和22.64%;当固态等离子体区域未激励且T≥68℃时,3 dB轴比频带为8.4—11.2 GHz与18.7—29.5 GHz,相对带宽分别为28.57%与44.81%.通过改变固态等离子体的激励状态和外部温度,实现了该超宽带线-圆极化转换器工作带宽向高频和低频区域的移动.     

A linear-to-circular polarization converter based on I-shaped circular frequency selective surfaces

In this paper, a linear-to-circular polarization converter using a three-layer frequency selective surface based on Ishaped circular structure resonant is presented and investigated. Numerical simulations exhibit that when the normal ypolarized waves impinge on this device propagating towards +z direction, the two orthogonal components of the transmitted waves have a 90° phase difference as well as the nearly equal amplitudes at the resonant frequency of 7.04 GHz, which means that the left-hand circular polarization is realized in transmission. For validating the proposed design, a prototype which consists of 25 × 25 elements has been designed, manufactured and measured. The measured results are in good agreement with the simulated ones, showing that the polarization conversion transmission is over-3 dB in the frequency range of 5.22–8.08 GHz and the axial ratio is below 3 dB from 5.86 GHz to 7.34 GHz.     

Axial ratio improvement of an Archimedean spiral antenna over a radial AMC reflector

This paper presents a method to improve the circular polarization of an Archimedean spiral antenna placed over a radial Artificial Magnetic Conductor (AMC). Results have been compared with the same radiating element over a more classical AMC reflector. A prototype of an Archimedean two-wire spiral antenna has been built to operate from 0.5?GHz to 6?GHz. Measurement results with this radial AMC give a relative bandwidth of 79?%, in which the broadside RHCP gain is improved. In this bandwidth the axial ratio of Archimedean spiral antenna placed over a radial AMC is less than 2?dB whereas it is higher than 3?dB with a classical cartesian shape of AMC reflector.     

W Band Circular Waveguide Y-Junction Circulator

In this paper, a new type of W band circular waveguide Y-junction circulator is presented. The structure of this type of Y-junction is a cylindrical cavity connecting with three circular waveguides. The performances of the type of circulator are analyzed by the edge-based vector finite element method hybridized with the modal expansion. The numerical results show that this type of waveguide Y junction circulator has good circulation performance.     

H-plane cross-shaped waveguide circulator in magneto-photonic crystals with five ferrite posts

A novel H-plane cross-shaped circulator based on magneto-photonic crystals is experimentally investigated.The band gap of the TE mode for the photonic crystals is calculated by the plane wave expansion method.The transmission characteristics of the circulator are simulated by the finite element method.We perform the experiments in the microwave regime to validate the numerical results.At the central frequency of 10.15 GHz,the measured isolation and insertion loss of the circulator reaches-30.2 and-3.93 d B,respectively.The bandwidth of the circulator is about 550 MHz.The optimal experimental value of isolation is higher than the numerical value.     

1.3μm光学环行器正向损耗及反向隔离比的理论及实验研究

在理论及实验上分析了影响光环行器插入损耗及反向隔离比的因素,讨论了环行器中起、检偏镜参数对其性能的影响.结果表明,起、检偏镜的各组参数存在最佳选择,以保证环行器具有低插损、高隔离比及与偏振无关的特性.作者研制的环行器正向损耗小于1dB,反向隔离比在25.5dB与28dB之间.     

基于宽带吸波体的微带天线雷达散射截面缩减设计

利用加载集总电阻的方式设计出一种极化稳定且宽入射角的宽带超材料吸波体(wide-band metamaterial absorber, WBMA), 在平面波垂直入射时, 其吸波半波功率带宽达12.7 GHz, 吸波率大于90%的带宽达10.42 GHz, 峰值吸波率达99.9%. 将其与微带天线共基板共接地板的方式加载, 制备出WBMA微带天线, 实现了天线宽频域内雷达散射截面(radar cross section, RCS)大幅缩减. 仿真与实测结果表明: 将WBMA加载于微带天线后, 天线的前向增益提高了0.53 dB, 整体辐射特性基本保持不变; 在不同极化波下, 天线的工作频带带内和带外等宽频域(6.95-17.91 GHz)内的单站RCS缩减大于3 dB以上, 最大缩减值达21.2 dB; 在天线的中心频点8 GHz处± 48°的宽角域内, 双站RCS缩减效果明显, 很好地实现了天线的宽频域大角度的隐身设计.     

行波电极偏振无关干涉型光开关

提出并实现了一种Ｘ切ＬｉＮｂＯ３上的行波电极偏振无关干涉型光开关。达到的指标为：串间地－１４ｄＢ，偏振无关的开关电压为１９Ｖ，带宽达到６ＧＨｚ以上。进一步减小定向耦合器部分中光波导间距的分级步距，串音可达到－２０ｄＢ以下 。     

基于磁/电介质混合型基体的宽带超材料吸波体的设计与制备

本文设计了一种基于磁/电介质混合型基体的宽带超材料吸波体, 吸波体基本单元由电阻膜、磁/电介质混合型基体以及金属背板组成. 采用时域有限差分法对超材料吸波体吸波性能进行了仿真, 使用遗传算法优化了反射率小于-10 dB的带宽. 仿真结果表明, 当超材料吸波体厚度为2.5 mm时, 在7.8–18 GHz频率范围内的反射率小于-10 dB, 具有厚度薄、宽带、极化不敏感等优点. 通过等效电路模型对其工作机理进行了分析与讨论. 最后制备样品进行测试, 测试结果与仿真结果一致.     

24 GHz宽波束阵列天线的设计

利用Rogers 5880为介质材料设计了一款应用于车载防撞雷达前端的圆极化微带阵列天线,该阵列天线采用直线阵结构,运用了多个四分之一波长阻抗变换器实现了阻抗匹配。仿真和测试结果表明: 该阵列天线的阻抗带宽(S₁₁ < -10 dB)为23.45~25.65 GHz,最大增益为15.54 dB;轴比带宽24.56~25 GHz,轴比最小为1.25 dB;第一副瓣电平小于-20 dB,E面半功率波瓣宽度为10°,H面波瓣宽度为75°,其尺寸为70.94 mm×14.72 mm×0.508 mm。该天线具有高增益、低副瓣、体积小、性能稳定等优点,在汽车防撞雷达系统中有广阔的应用前景。     

Bandwidth scaling and spectral flatness enhancement of optical frequency combs from phase-modulated continuous-wave lasers using cascaded four-wave mixing

We introduce a new cascaded four-wave mixing technique that scales up the bandwidth of frequency combs generated by phase modulation of a continuous-wave (CW) laser while simultaneously enhancing the spectral flatness. As a result, we demonstrate a 10?GHz frequency comb with over 100?lines in a 10?dB bandwidth in which a record 75?lines are within a flatness of 1?dB. The cascaded four-wave mixing process increases the bandwidth of the initial comb generated by the modulation of a CW laser by a factor of five. The broadband comb has approximately quadratic spectral phase, which is compensated upon propagation in single-mode fiber, resulting in a 10?GHz train of 940?fs pulses.