开槽深度和坡度对高频高阶模带宽和中心频移的影响

为对构建太赫兹频率下高阶单模工作的同轴布喇格谐振腔提供理论依据,基于模式耦合理论,比较研究了不同开槽深度和不同开槽坡度形状及坡度角对工作在太赫兹频率高频高阶耦合模式下工作模式和竞争模式带宽、中心频率偏移特性的影响. 结果表明:工作模式和竞争模式的带宽随着开槽深度的加深都变宽,但中心谐振频率点几乎没有偏移,槽深加深,带隙重叠现象会恶化,不利于模式选择;正圆锥形坡度方式时随着坡度角的增加,工作模式的中心频率点没有发生偏移,竞争模式中心频率点靠近工作模式中心频率点,不利于带隙重叠现象的抑制;倒圆锥形坡度方式时,随着坡度角的增大,竞争模式的中心频率点远离工作模式中心频率点,很好地抑制了带隙重叠;正圆锥形坡度和倒圆锥形坡度对带宽的影响都不大. 这些特性有利于拓展同轴布喇格结构作为反射器和滤波器的性能.     

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。     

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。     

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.     

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.     

FBG的衍射光学特性和耦合模理论分析

从衍射光学的角度出发研究了光纤布喇格光栅（ Ｆ Ｂ Ｇ） 的光学特性,进而采用理想模展开的耦合模理论对光纤布喇格光栅的模场分布进行了详细分析,推导出反射率、布喇格反射波长及反射主峰带宽等特性参数的表达式。计算结果表明,理论与实验结果吻合较好,从而验证了理论结果的正确性     

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。     

纵向应力法制作双波长布喇格光栅

介绍了一种用一个均匀相位模板制作双波长布喇格光栅的方法;对这种方法制作的双波长布喇格光栅进行了理论分析,用矩阵分析法,对其进行了数值模拟.采用了移动曝光技术,通过调节所加应力的大小、光栅长度及曝光次数可以控制两个布喇格波长的间隔和反射率;写制了一个双波长光栅,两个透射峰均为19.5 dB,两个布喇格波长的间隔为0.78 nm.     

布喇格反射型宽带单晶薄膜体声波滤波器

该文研究了一种新型布喇格反射型薄膜体声波（BAW）滤波器的设计方法与制备技术。BAW器件选择机电耦合系数较大的Y43° 铌酸锂（Y43° LN)单晶薄膜作为压电层材料,并以苯并环丁烯（BCB）作为晶圆键合层,采用离子注入剥离法将亚微米厚度的Y43° LN单晶薄膜转移至具有布喇格反射层的衬底。BCB既作为键合层,也作为布喇格反射层的第一低声阻抗层,实现了单晶BAW滤波器的制备。设计并制备了三阶BAW滤波器,中心频率为2.93 GHz,绝对带宽和分数带宽分别为247 MHz和8.4%。结果表明,采用薄膜转移技术制备的高机电耦合系数LN单晶薄膜能够实现大带宽BAW滤波器的制备。     

基于双光纤布喇格光栅的液位传感器

设计了一种基于双光纤布喇格光栅的新型液位传感器,导出了双光纤布喇格光栅的波长漂移差与液位的关系.圆盘上受到的液体压力导致等腰三角形悬臂梁变形,从而导致安装在悬臂梁两边的光纤布喇格光栅的布喇格波长漂移.通过检测两个布喇格光栅的波长漂移差,得到被测液位.双光纤布喇格光栅通过补偿温度效应,解决了光纤布喇格光栅传感器的交叉敏感问题.该液位传感器的动态测量范围为2～3 000 mm.实验表明,双光纤布喇格光栅的中心波长随液位的增加分别向长波和短波方向漂移,而带宽几乎不变,实验和理论符合较好,该设计方案是切实可行的.     

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.     

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     

Comparitive Study of Coaxial Bragg Resonators

A coaxial Bragg resonator can be performed in four kinds of structures: it is constructed by inserting a regular waveguide between two selective Bragg reflectors (being called the upstream reflector and downstream reflector, respectively), or it consists of only two Bragg reflectors without regular waveguide section between them, where connection of these two reflectors is smooth with phase difference Δ??=?0 or is step-changed with corrugation phase difference Δ? = +π or ?π, respectively. The present paper is devoted to a comparative study for the response of reflectivity and quality factor on frequency in these four kinds of coaxial Bragg resonators, including the influences of the location and corrugation-phase difference of the step-changed connection of the two reflectors. Results show that a coaxial Bragg resonator possesses most attractive properties when the corrugation-phase difference is Δ? = +π at the point of connection and the upstream reflector is longer than the downstream reflector.     

多模反射面天线理论与技术研究

在卫星星座跟踪、远距离微波能传输等需要构建大功率均匀场的领域,都需要具有平顶波束的高增益反射面天线.受多模和混合模喇叭天线的启发,文中创新性地在反射面天线设计中引入了多模的理念.首先提出了双模反射面的思路,即在标准抛物面天线的最大辐射方向上引入相位差为180°的反相模式场,由两种模式合成平顶波束.然后,将双模的理念推广...     

Analysis of nonplanar wave propagation through multilayered Braggreflectors for folded cavity and vertical cavity surface emitting laserstructures

A theoretical approach to nonplanar wave propagation through Bragg reflector multilayer structures is presented. The theory is applied to the optical coupling and feedback in a folded cavity surface emitting laser using a 45° deflection mirror-epitaxial Bragg reflector arrangement. The effects of the nonplanar wave propagation on the Bragg mirror reflectivity in vertical cavity surface emitting lasers is also examined. Experimental verification of the theory is presented in a novel folded cavity surface emitting laser structure integrating a horizontal cavity InGaAs-GaAs laser grown on a structured substrate with a high reflectivity Bragg reflector     

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.     

Suppression of Residual Side-lobes in a Coaxial Bragg Reflector

This note demonstrates the existence and possible suppression of the residual side-lobes in a coaxial Bragg reflector by employing Blackman window distribution, no matter if the phase difference between the outer and inner corrugations is 0, or π/2, or π. Physical explanation is qualitatively given to the effect of the window distribution.