新型坡度同轴布喇格反射器数值模拟比较研究

将一种新型加坡度方式同轴布喇格反射器的多模耦合理论与电磁仿真软件(CST)进行了数值模拟比较研究.结果表明:两者吻合较好,但多模耦合理论方法计算编程容易,运算速度快,参数调整非常方便;具有正圆锥形坡度的同轴布喇格反射器的带宽随着所加坡度角的增大而变窄,具有倒圆锥形坡度的同轴布喇格反射器的带宽随着所加坡度角的增大而变宽;...     

TM模式同轴布喇格结构频率响应研究

基于多波耦合理论,利用Fortran编程软件,以TM模式为工作模式,对工作在太赫兹频段的开正弦槽同轴布喇格反射器的频率响应进行了仿真研究.研究结果表明,在高频高阶TM模式下,竞争模式和所需工作模式带隙之间的带隙重叠可以通过初始相位差的逐渐增大得到明显改善;频响特性曲线的残存旁瓣可通过加窗技术得到有效抑制;加正圆锥或者倒圆锥渐变波纹时,工作模式影响较小,竞争模式会相应地偏离中心频带,对带隙重叠的分离也有一定的影响.研究为同轴布喇格反射器在太赫兹领域以TM模式工作提供了可能性.     

高阶耦合模倒圆锥双重正弦同轴结构频率响应

为了形成带宽窄、品质因数Q高、选择性好的同轴布喇格反射器,提出一种倒圆锥型双重正弦同轴结构设计。基于耦合模式理论,在普通正弦槽结构的基础上,叠加刻蚀周期较小的辅助正弦分布,在导体内外壁上增加倒锥度,形成倒圆锥型双重正弦同轴布喇格结构。通过FORTRAN软件仿真得出,与普通正弦槽相比,倒圆锥型双重正弦同轴布喇格结构的工作模式和竞争模式的带宽更窄,品质因数Q得到提高,残余旁瓣现象得到抑制。同时,竞争模式的中心谐振频率点远离工作模式,带隙重叠进一步分离,频率选择性得到提高。该结构设计简单,方法合理,可以更好地分离工作模式和竞争模式,构建高品质因数Q、高功率的单一高次模谐振腔。     

混合型开槽同轴布喇格结构的比较研究

基于电磁仿真软件(Computer Simulation Technology,CST)平台,对几种不同开槽形状同轴布喇格结构的频率响应特性分别进行了数值模拟比较研究.结果表明:三角形开槽带宽最窄而矩形开槽带宽最宽;交替混合型开槽时耦合模式的反射率明显提高,而分半混合型开槽时不仅耦合模式的反射率提高,且其带宽也明显变宽,但两种开槽方式时工作模式的反射率和带宽都位于单一开矩形槽和三角形槽之间;叠加混合型开槽克服了单一矩形槽和三角形槽存在奇点和边界突变的缺点,对模式的选择性能优于矩形开槽,反射率和带宽又大于正弦开槽和三角形开槽,仅其谐振频率点有偏移.这些特点有利于同轴布喇格结构的模式选择、散热和工业生产.     

毫米波多内导体布喇格结构电磁特性研究

基于多模耦合理论,利用三维电磁仿真软件CST对毫米波双内导体和三内导体布喇格结构电磁特性分别进行了比较研究。结果表明：双内导体布喇格结构相比同轴布喇格结构可以抑制竞争模式,反射率稳定并接近1,对称性结构电磁特性优于非对称性结构;随着内导体距离同轴轴心距离的增大,双内导体布喇格结构频率响应带宽变宽,且当内导体距离同轴轴心距离较远时,带宽变宽趋势明显,而反射率值趋于稳定;对于三内导体布喇格结构,随着内导体距离同轴轴心距离的增大,频率响应带宽变窄,且当内导体距离同轴轴心距离较近时,带宽变宽趋势明显。因此,可根据实际需要恰当选择毫米波多内导体布喇格结构参数,拓宽其作为反射器或者滤波器的性能,提高模式的选择性及模式的纯度,改善布喇格结构的性能。     

60GHz缺陷态同轴布喇格波导窄带带通滤波器设计及性能分析

基于缺陷态同轴布喇格波导的通带特性,该文采用多波耦合理论及Ansoft HFSS对一种工作频率为60 GHz的新型波导滤波器原型进行了概念性设计,并进行性能分析。结果表明:大尺寸的缺陷态布喇格滤波器在高频工作时,主模与竞争模式之间的寄生耦合会破坏通带结构;当波纹幅度引入汉明窗分布,可以有效地消除这一负面影响。该滤波器具有通带窄(相对带宽小于0.1%)、中心插入损耗小(低于1.5 dB)、结构横向大尺寸大(半径7~10 mm)的优点,能够适用于毫米波段高功率应用场合中对窄频带信号选择。     

基于北斗卫星导航系统的一种圆极化微带天线

介绍一种用于北斗卫星导航系统的圆极化微带天线。该天线的主辐射器由开槽的圆形贴片构成,采用单点的同轴馈电,设计的中心工作频率为2．492GHz。仿真结果显示,调节圆形贴片中开槽的长度,可以分离出简并模,激励两个正交的模式,当两个分量相位为90deg,可以实现圆极化。实际测试中,｜S11｜于-10dB的阻抗带宽为0．09GHz,3dB轴比带宽为0．033GHz,与仿真结果基本吻合。     

一种2.4GHz小型化微带天线

设计了一种新型小型宽频带微带天线。通过在贴片和地板上”开槽”形成特殊形状的方法,达到小型化和宽频带的目的。仿真结果表明,在中心频率2．4GHz时,相对带宽为15％,与原始的理论值相比较,小型化后的天线尺寸缩小了33％。     

含负折射率材料的1维光子晶体掺杂缺陷模研究

为了研究含有负折射率材料的光子晶体掺杂缺陷模的光学传输特性,利用传输矩阵理论进行数值分析.采用插入和替代两种方式对排列整齐的光子晶体进行掺杂,产生了缺陷模式.结果表明,引入正折射率缺陷只能在布喇格带隙中产生缺陷模,引入负折射缺陷能够同时在全方位光子带隙和布喇格带隙中产生缺陷模.同时研究了掺杂方式、入射方向、缺陷厚度、缺陷位置、缺陷类型对缺陷模式的影响,并对含有两层缺陷的光子晶体进行研究,得到两缺陷层的距离与带隙产生的关系,即距离越近越容易产生缺陷模式,且缺陷模的深度越深.这对于制造新型的全方位滤波器是有指导作用的.     

含负折射率材料的1维光子晶体掺杂缺陷模研究

为了研究含有负折射率材料的光子晶体掺杂缺陷模的光学传输特性,利用传输矩阵理论进行数值分析。采用插入和替代两种方式对排列整齐的光子晶体进行掺杂,产生了缺陷模式。结果表明,引入正折射率缺陷只能在布喇格带隙中产生缺陷模,引入负折射缺陷能够同时在全方位光子带隙和布喇格带隙中产生缺陷模。同时研究了掺杂方式、入射方向、缺陷厚度、缺陷位置、缺陷类型对缺陷模式的影响,并对含有两层缺陷的光子晶体进行研究,得到两缺陷层的距离与带隙产生的关系,即距离越近越容易产生缺陷模式,且缺陷模的深度越深。这对于制造新型的全方位滤波器是有指导作用的。     

Effect of Ripple Taper on Coupling Modes in a Coaxial Bragg Structure

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on coupling modes on the frequency response in a coaxial Bragg structure. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of a positive taper, but is expanded if a negative taper is employed, and the influence of the negative taper is more obviously advantage than the positive taper. The residual side-lobes of the frequency response on coupling modes can be effectively suppressed by employing the windowing-function technique. These characteristics of a tapered coaxial Bragg structure are favorable to improvement of the performance as a reflector or a filter in its application, also favorable to the mode selectivity and further weaken the excitation of unwanted spurious modes.     

Comparison between Single-mode Treatment and Multi-mode Treatment of a Coaxial Bragg Resonator for a Terahertz Cyclotron Autoresonance Maser Oscillator

As a coaxial Bragg structure has more complex geometry configuration than a cylindrical or a planar Bragg structure, for simplicity of calculation a single-mode treatment is often adopted. However, heterogeneity of a coaxial Bragg structure always gives rise to the multi-mode conversion, which can change the performance of the resonator. Based on the scattering matrix method, detailed comparison between the single-mode treatment and the multi-mode treatment is presented to a coaxial Bragg resonator for a cyclotron autoresonance maser (CARM) oscillator operating in the higher-order mode TE₆₁ at frequency of 0.35 THz. Results indicate that there is a little difference between the results obtained by these two treatments to the upstream reflector due to its shallow ripple amplitude, whereas to the downstream reflector, due to its relatively deep ripple amplitude, an apparent difference occurs at the operating frequency and consequently it gives notable difference to the frequency response and Q-factor of the whole resonator. Optimization shows possible application of a coaxial Bragg resonator with a single higher-order mode operation in constructing a terahertz CARM oscillator.     

三次泛音单片式、高频及高阻带晶体滤波器

研究了三次泛音模式下单片式晶体滤波器的设计方法、制作工艺。通过优化滤波器结构、合理控制晶片镀回频率等方法,实现了晶体滤波器的高阻带和高杂波抑制。制作出一种工作频率为41.4 MHz,响应模式为三次泛音的单片式晶体滤波器。结果表明,该晶体滤波器的-1 dB带宽为2.9 kHz,带内波动为0.3 dB,阻带抑制为82 dB。     

Power penalty due to the amplitude and phase response ripple of a dispersion compensating fiber Bragg grating for chirped optical signals

A concise method is presented for rigorously calculating the power penalty due to the combined implications of the amplitude and phase response ripples of a dispersion compensating fiber Bragg grating and the chirp of the transmitted optical signal. By using trigonometric series to represent the ripples, the calculated penalty can be positive or negative, as obtained in numerical simulations and measurements, depending on the signal chirp and ripple within the modulated signal bandwidth. An approximate upper bound on the power penalty is also presented as an extension of earlier results that always yield positive penalties. Calculated and measured results are compared for two 10-Gb/s return-to-zero (RZ) signals with distinct chirp properties.     

A novel direct torque controlled interior permanent magnet synchronous machine drive with low ripple in flux and torque and fixed switching frequency

A modified direct torque control (DTC) scheme for interior permanent magnet synchronous machine (IPMSM) is investigated in this paper, which features in very low flux and torque ripple and almost fixed switching frequency. It is based on the compensation of the error flux linkage vector by means of space vector modulation. Modeling and experimental results show that the flux and torque ripples are greatly reduced when compared with those of the basic DTC. With the new scheme, very short sampling time is not essential. All the advantages of the basic DTC are still retained. In addition, fixed switching frequency at different operating conditions becomes possible. The field-weakening control of this drive is also studied; an IPM DTC drive with a wider operation range and lower flux and torque ripple has been achieved experimentally.     

A 360/spl deg/ Reflection-Type Diode Phase Modulator (Correspondence)

A 360/spl deg/ phase modulator using two series-tuned varactors in a parallel connection is described. The design minimizes the change in total phase shfit with frequency and gives a small attenuation ripple. The modulator is centered at 2 GHz and gives a total phase shift at 360/spl deg/ at the center frequency, an attenuation ripple of 1.3 dB over a 10-percent bandwidth and a 7/spl deg/ decrease of phase shift at the band edges.     

A Coaxial Bragg Reflector for Cyclotron Autoresonance Maser Oscillators

A coaxial Bragg reflector is suggested for the application in the cyclotron autoresonance masers (CARMs), where both the outer wall and inner rod are corrugated with weak axisymmetric-sinusoidal-ripple, and a concept design is presented. It is found that, compared to the cylindrical Bragg reflector, the coaxial Bragg reflector has larger dimensional size, narrower bandwidth, and larger eigenvalue intervals. These peculiarities are favorable to the mode selectivity, the ability of dissipating the ohmic heat on the wall, the oscillating startup of the operating mode, and machining manufacture, and therefore, this new kind of Bragg reflector can be developed into a coaxial resonator for the high-power CARMs