Directional Couplers.doc

Size: px

Start display at page:

Download "Directional Couplers.doc"

增磋艾
6 years ago
Views:

Directional ouplers [] THE QUADRATURE (90 ) HYBRID The Hybrid coupler is often made of microstrip or stripline as shown in Figure. The microstrip form is also pictured in Figure 2.

1 Directional ouplers [] THE QUADRATURE (90 ) HYBRID The Hybrid coupler is often made of microstrip or stripline as shown in Figure. The microstrip form is also pictured in Figure 2. These couplers are 3 db directional couplers with a 90 phase difference between the outputs of the through and coupled lines. It is also known as a branch-line hybrid. Figure. Geometry of a Quadrature Hybrid coupler. [] Figure 2. Photograph of a microstrip Quadrature Hybrid coupler. [] Referring to the geometry of Figure, the ideal branch-line coupler, with all ports matched and power entering port, has evenly divided outputs at ports 2 and 3 with a 90 phase difference between them. The isolated port (port 4) has no power exiting it. The resulting [S] matrix is then given by () 0 j [ S] 2 0 j j 0 j 0 Because of this symmetry, we can use any port at the input port. The output ports will be on the opposite side of the junction from the input port and the remaining port will be the isolated port. This symmetry is reflected in the scattering matrix, as each row can be obtained as a transposition of the first row.

2 The even and odd mode analysis of Figure is carried out in detail in []. Because of the length requirements on the lines, the [S] matrix is not frequency independent. This easily illustrated by doing Example 7.5. EXAMPLE 7.5 Design and performance of a Quadrature Hybrid [] Design a 50 Ω branch-line quadrature hybrid junction, and plot the S parameter magnitudes from 0.5 f 0 to.5 f 0 where f 0 is the design frequency. Solution The design is trivial. The lengths of the lines are λ/4 at the design frequency and the impedances are 50 Ω and Ω. We now use Serenade Design Suite to simulate the coupler over the frequency range of interest. A quadrature hybrid is one of the microstrip circuit elements available. We choose that geometry with a substrate that is 3 mils thick and a dielectric constant of 2.2. The transmission line tool is used to get the physical lengths and widths of the transmission lines. The circuit diagram and analysis results follow in Figures 3 and 4. Notice that in the microstrip form, the center frequency is at.99 f 0 where with ideal lines the response is as shown in Figure 7.25 of []. an you explain this? Figure 3. Serenade Design Suite schematic of a branch-line coupler using microstrip. 2

oupled Line ouplers Figure 4. Simulation results for the microstrip branch-line coupler. We begin this section with a review of coupled line theory.

3 oupled Line ouplers Figure 4. Simulation results for the microstrip branch-line coupler. We begin this section with a review of coupled line theory. Figure 5 shows some coupled transmission line geometries that can be represented by the equivalent circuit shown in figure 6. There are two modes that can be excited for this geomentry - even and odd. They are depicted in Figure 7. Figure 5. Figure 6. A three-conductor coupled transmission line and its equivalent circuit. [] 3

4 Figure 7. Even- and od-mode excitations for a coupled line, and the resulting equivalent capacitance networks. (a) Even-mode excitation. (b) Odd-mode excitation. Analysis of the equivalent circuits of Figure 7 result in the following equations for the even- ( e ) and oddmode ( o ) capacitances: (2) (3) e o These in turn give the following values for the even- and odd-mode impedances (4) (5) Z Z 0e 0o L e L o L e L o e o v v e o where v is the phase velocity of the wave. The even- and odd-mode capacitances can be determined analytically for coaxial, parallel plate, or stripline. Quasi-TEM lines, such as microstrip require approximate analysis or numerical techniques. Imperical equations for design of coupled lines can be found in [2]. These equations are used in a Mathcad document to do Example 7.7 in []. We can also use the Transmission Line Tool in Serenade Design Suite to get the dimensions of the coupled stripline. The screenshot for Example 7.7 is shown in Figure 9. Notice that the dimensions are slighly different for the two methods. an you explain this? We can now simulate this design over the bandwidth of interest using Serenade Design Suite. We take the design from the Mathcad document. Figures 0 and show the schematic and results for coupling and isolation respectively. 4

5 Figure 8. Mathcad document used to design a 20 db stripline coupled line coupler. 5

6 Figure 9. Transmission Line Tool for design of the 20 db stripline coupled line coupler. Figure 0. Serenade Design Suite Schematic for the 20dB stripline coupled line coupler. 6

7 Figure. Serenade Design Suite simulation results for the 20dB stripline coupled line coupler. As Figure shows, the coupling and isolation for the coupled line coupler are frequency dependent because of the λ/4 length requirement. As with matching sections, the bandwidth can be increased by using multiple sections of coupled lines. The details of the design are shown in Section 7.6 of []. A Mathcad document was created for the solution of Example 7.7 in []. The design procedure yields even- and od-mode impedances for the three coupled line sections. They are: Z 0e Z 0o ohm Z 0e ohm Z 0e3 : Z 0e ohm Z 0o ohm Z 0o3 : Z 0o From this information, we can design the coupler using equations from [2] or by using the Transmission Line Tool in Serenade Design Suite. Simulation of this three section coupler yields the results shown in Figure 2. 7

8 Figure 2. Simulation results for the 3-section 20dB stripline coupled line coupler. [] David M. Pozar, Microwave Engineering, John Wiley & Sons, Inc., New York, 998. [2] Inder Bahl and Prakash Bhartia, Microwave Solid State ircuit Design, John WIley & Sons, New York,

易迪拓培训专注于微波射频天线设计人才的培养网址 :http://www.edatop.

9 易迪拓培训专注于微波射频天线设计人才的培养网址 : H F S S 视频培训课程推荐 HFSS 软件是当前最流行的微波无源器件和天线设计软件, 易迪拓培训 ( 是国内最专业的微波射频和天线设计培训机构为帮助工程师能够更好更快地学习掌握 HFSS 的设计应用, 易迪拓培训特邀李明洋老师主讲了多套 HFSS 视频培训课程李明洋老师具有丰富的工程设计经验, 曾编著出版了 HFSS 电磁仿真设计应用详解 HFSS 天线设计等多本 HFSS 专业图书视频课程, 专家讲解, 直观易学, 是您学习 HFSS 的最佳选择 HFSS 学习培训课程套装该套课程套装包含了本站全部 HFSS 培训课程, 是迄今国内最全面最专业的 HFSS 培训教程套装, 可以帮助您从零开始, 全面深入学习 HFSS 的各项功能和在多个方面的工程应用购买套装, 更可超值赠送 3 个月免费学习答疑, 随时解答您学习过程中遇到的棘手问题, 让您的 HFSS 学习更加轻松顺畅课程网址 : HFSS 天线设计培训课程套装套装包含 6 门视频课程和本图书, 课程从基础讲起, 内容由浅入深, 理论介绍和实际操作讲解相结合, 全面系统的讲解了 HFSS 天线设计的全过程是国内最全面最专业的 HFSS 天线设计课程, 可以帮助您快速学习掌握如何使用 HFSS 设计天线, 让天线设计不再难课程网址 : 更多 HFSS 视频培训课程 : 两周学会 HFSS 中文视频培训课程课程从零讲起, 通过两周的课程学习, 可以帮助您快速入门自学掌握 HFSS, 是 HFSS 初学者的最好课程, 网址 : HFSS 微波器件仿真设计实例中文视频教程 HFSS 进阶培训课程, 通过十个 HFSS 仿真设计实例, 带您更深入学习 HFSS 的实际应用, 掌握 HFSS 高级设置和应用技巧, 网址 : HFSS 天线设计入门中文视频教程 HFSS 是天线设计的王者, 该教程全面解析了天线的基础知识 HFSS 天线设计流程和详细操作设置, 让 HFSS 天线设计不再难, 网址 : 更多 HFSS 培训课程, 敬请浏览 :

10 ` 专注于微波射频天线设计人才的培养易迪拓培训网址 : 关于易迪拓培训 : 易迪拓培训 ( 由数名来自于研发第一线的资深工程师发起成立, 一直致力和专注于微波射频天线设计研发人才的培养 ; 后于 2006 年整合合并微波 EDA 网 ( 现已发展成为国内最大的微波射频和天线设计人才培养基地, 成功推出多套微波射频以及天线设计相关培训课程和 ADS HFSS 等专业软件使用培训课程, 广受客户好评 ; 并先后与人民邮电出版社电子工业出版社合作出版了多本专业图书, 帮助数万名工程师提升了专业技术能力客户遍布中兴通讯研通高频埃威航电国人通信等多家国内知名公司, 以及台湾工业技术研究院永业科技全一电子等多家台湾地区企业我们的课程优势 : 成立于 2004 年,0 多年丰富的行业经验一直专注于微波射频和天线设计工程师的培养, 更了解该行业对人才的要求视频课程既能达到现场培训的效果, 又能免除您舟车劳顿的辛苦, 学习工作两不误经验丰富的一线资深工程师讲授, 结合实际工程案例, 直观实用易学联系我们 : 易迪拓培训官网 : 微波 EDA 网 : 官方淘宝店 : 专注于微波射频天线设计人才的培养易迪拓培训官方网址 : 淘宝网店 :

PowerPoint Presentation

PowerPoint Presentation Sizing Handbook I 6 to 10 10w, w or 5w (3 to 4), w < Note: Port sizing guidelines are not inviolable rules true in all cases. For example, if meeting te eigt and widt requirements outlined result in a