RF MEMS技术对小型化雷达的作用

该文采用至上而下的方式,介绍了应用RF MEMS技术的雷达系统,将雷达子系统与RF MEMS技术联系起来,具体分析了应用于雷达的RF MEMS开关、移相器、滤波器和谐振器。同时,文中以开关和移相器为例,讨论了如何提高RFMEMS雷达的性能:修改空气桥形状可以提高RF MEMS收发(T/R)组件的功率处理能力,从而减少雷达相控阵的T/R组件数量;缩短转换时间的RF MEMS移相器能够应用于高速电扫描阵列;蜿蜒型5位分布式MEMS传输线移相器面积仅为5.36mm×4.72mm,相比传统移相器长度降低70%,易于实现雷达阵列的小型化。     

微波MEMS移相器的特性分析与实现

从移相器的基本原理出发,分别介绍了开关线型、耦合器型和加载线型三种采用微机械加工技术制备而成的微波MEMS移相器的结构特点和工作原理。在此基础上,设计制备了CPW分布式加载线型MEMS移相器,并进行测试和分析,结果表明MEMS移相器较传统的移相器有微型化、低损耗、低成本、宽带等突出优点。     

Distributed MEMS analog phase shifter with enhanced tuning

The design, fabrication, and measurement of a tunable microwave phase shifter is described. The phase shifter combines two techniques: a distributed capacitance transmission line phase shifter, and a large tuning range radio frequency (RF) microelectromechanical system (MEMS) capacitor. The resulting device is a large bandwidth, continuously tunable, low-loss phase shifter, with state-of-the-art performance. Measurements indicate analog tuning of 170/spl deg/ phase shift per dB loss is possible at 40 GHz, with a 538/spl deg/ phase shift per centimeter. The structure is realized with high-Q MEMS varactors, capable of tuning C/sub max//C/sub min/= 3.4. To our knowledge, this presents the lowest loss analog millimeter wave phase shifter performance to date.     

MEMS移相器及其在微型通信系统中的应用

从传统移相器的构造和原理出发，进一步分析了MEMS移相器的结构、特性。结果表明，MEMS移相器具有传统移相器所无法比拟的体积小、损耗小、成本低、频带宽、易于集成等突出优点。随着高阻硅衬底在微波领域应用的扩展，MEMS移相器介质损耗大幅度降低，将能与信号处理电路一同集成于硅衬底上，便于相控阵雷达等通信系统实现微小型化。     

A 2-bit miniature X-band MEMS phase shifter

The design and performance of a compact low-loss X-band true-time-delay (TTD) MEMS phase shifter fabricated on 8-mil GaAs substrate is described. A semi-lumped approach using microstrip transmission lines and metal-insulator-metal (MIM) capacitors is employed for the delay lines in order to both reduce circuit size as well as avoid the high insertion loss found in typical miniaturized designs. The 2-bit phase shifter achieved an average insertion loss of -0.70 dB at 9.45 GHz, and an associated phase accuracy of /spl plusmn/1.3/spl deg/. It occupies an area of only 5 mm/sup 2/, which is 44% the area of the smallest known X-band MEMS phase shifter . The phase shifter operates over 6-14 GHz with a return loss of better than -14 dB.     

Electromechanical coupling modelling of distributed MEMS phase shifter for phased array antennas

MEMS phase shifter has many advantages as the ‘steering wheel’ of phased array antenna beam steering. The deformation of mechanical structures of MEMS phase shifter influenced by the complex environmental factors, which became the biggest obstacle to further enhance the performance of phased array antennas. The electromechanical coupling model between the bridge height and phase shift of the distributed MEMS phase shifter is developed. The coupling model could be used to predict the phase error and determine the bridge height tolerance for the deformed MEMS phase shifter. The simulation results of four-bit distributed MEMS phase shifter with 15 bridges illustrate the validity of coupling model and demonstrate the application potential for engineering design and test.     

A 2-bit RF MEMS phase shifter in a thick-film BGA ceramic package

The development of a thick-film hermetic BGA package for a radio-frequency (RF) microelectromechanical systems (MEMS) 2-bit phase shifter is presented. The measured packaged MEMS phase shifter average in-band insertion loss was 1.14 dB with an average return loss of 15.9 dB. The package transition insertion loss was less than 0.1 dB per transition with excellent agreement between simulated and measured results. It was also demonstrated that the RF MEMS phase shift performance could be improved to obtain a phase error of less than 3.3 degrees. The first reported measurements of the average rise and fall times associated with a MEMS circuit (in this case a 2-bit phase shifter) were 26 and 70 /spl mu/s, respectively. The advent of packaged RF MEMS phase shifters will reduce the cost (both design and building) of future phase arrays.     

用于X波段移相器的RF MEMS开关设计

针对某片上集成开关线式MEMS移相器设计了一款串联接触式悬臂梁开关。该移相器要求结构紧凑,工作频段为X波段,工作电压低于27V。利用Ansoft HFSS软件仿真分析了开关关键结构参数对电磁性能的影响,包括传输线断开间距d,接触金属与传输线之间的垂直间距h,接触金属的宽度B,总结了各参数对开关电磁性能的影响趋势,确定了本设计中各结构参数的最优取值;利用MEMS CAD软件CoventorWare对初始设计的开关进行机电耦合仿真,确定了开关的详细结构参数。仿真结果表明,设计的串联接触式悬臂梁开关驱动电压约为18V;中心频率为10GHz时,开关闭合态回波损耗为0.02dB,隔离度为36dB,导通态下,插入损耗为0.028dB。     

交直流隔离的分布式MEMS移相器设计

设计了一种五位分布式微电子机械系统（MEMS）移相器,通过分析对比传统分布式MEMS移相器加载直流偏置的两种方式,提出了一种新的直流偏置的加载方式,能解决传统方式带来的交直流干扰和引线繁杂问题,同时工艺容易实现。采用ADS软件对移相器进行级联仿真,优化了微波性能参数,仿真得出移相器在35 GHz时移相精确度小于3°,移相器的插入损耗小于0.5 dB,回波损耗大于23 dB。给出了五位分布式MEMS移相器的工艺流程,同时验证了所设计加载直流偏置方式工艺简单的优势。     

A Monolithic Phased Array Using 3-bit Distributed RF MEMS Phase Shifters

This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high-Q metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters.     

分布式MEMS移相器桥高度与相移量的机电集成模型及应用

移相器是控制相控阵天线空间波束捷变的方向盘,其性能的优良决定着相控阵天线性能的高低。微机电系统(MEMS)移相器优势明显,但由于相控阵天线工作环境复杂,环境载荷会导致MEMS移相器结构变形,进而直接降低整个相控阵天线的性能。为此,该文研究MEMS移相器关键结构参数和电性能之间的耦合关系,将复杂环境要素对物理结构的影响传递到结构参数和电参数上,推导出分布式MEMS移相器的机电集成模型,并利用集成模型对变形MEMS移相器进行电性能快速评估和结构公差计算。仿真结果说明了集成模型的有效性和工程应用价值。     

一个DC-32GHz两位微机械移相器

采用分布式微机械传输线结构实现了两位移相器,并且为了减小传输线负载电容和驱动电压首次提出了用共面波导传输线来驱动微机械桥的结构(共面波导驱动结构).结果显示驱动电压小于20V,20GHz时两位移相器的相移为0°/20.1°/41.9°/68.2°,插入损耗为-1.2dB.在DC到32GHz的范围内相移具有良好的线性,插入损耗小于-1.8dB,反射损耗好于-11dB.实验结果表明了该结构在高介电常数衬底上制造低插损、宽带数字微机械射频移相器的潜力.     

基于SP4T开关的4位MEMS开关线式移相器设计

设计了一款4位MEMS开关线式移相器,由SP4TMEMS开关和微带传输线构成,工作于X波段。单刀四掷(single pole 4throw,SP4T)开关用于切换两条不同电长度的信号通道,即参考相位通道和延迟相位通道。每个SP4T开关包含4个悬臂梁接触式RF MEMS串联开关。介绍了4位MEMS开关线式移相器的总体设计,并给出了其关键部件SP4T开关和相位延迟线的设计细节。采用ADS软件仿真分析了器件的电气性能。仿真分析得到:SP4T开关在中心频率10GHz处的回波损耗为-36dB,插入损耗约为0.18dB;移相器各相位的回波损耗均低于-15dB,插入损耗为-0.8～-0.4dB。这种射频MEMS移相器具有小型化、低功耗和高隔离度的优点。     

Frequency Scalable Model for MEMS Capacitive Shunt Switches at Millimeter-Wave Frequencies

This paper presents an approach to RF microelectromechanical systems (MEMS) capacitive shunt switch design from $K$-band up to $W$-band based on the scalability of the RF MEMS switch with frequency. The parameters of the switch's equivalent-circuit model also follow scaling rules. The measurement results of the fabricated switches show an excellent agreement with simulations that allow to validate the MEMS model in the entire band from 20 up to 94 GHz. This model is going to be used in the phase shifter circuit design for antenna array applications. The first 60-GHz phase shifter results are also reported here.      

A compact V-band 2-bit reflection-type MEMS phase shifter

Air-gap overlay CPW couplers and low-loss series metal-to-metal contact microelectromechanical system (MEMS) switches have been employed to reduce the loss of reflection-type MEMS phase shifters at V-band. Phase shift is obtained by changing the lengths of the open-ended stubs using series MEMS switches. A 2-bit [135] reflection-type MEMS phase shifter showed an average insertion loss of 4 dB with return loss better than 11.7 dB from 50 to 70 GHz. The chip is very compact with a chip size as small as 1.5 mm /spl times/ 2.1 mm.     

低电压驱动的硅基Ka波段级联式MEMS移相器

通过在共平面波导上周期性地分布微机械电容,外加电压驱动改变电容值,可实现级联式MEMS移相器.本文讨论了优化相移特性对共平面波导特性阻抗及下拉电压的要求,通过工艺参数优化制备了高阻硅基上的Ka波段级联式MEMS移相器,测试结果表明制备器件具有较低的驱动电压,8V时即产生明显的相移量,在36GHz处15V驱动电压时相移量为118°,25V时为286°.对微结构弹性膜的机械振动寿命测试表明,13级级联的MEMS移相器所有弹性膜同步振动的寿命为3×10⁶次.为器件的实用化提供了重要保障.     

基于微机电系统开关的四位移相器设计

为了解决相控阵雷达小型化和低损耗的问题,设计了一个工作频率为2.2 GHz的射频微机电系统(MEMS)四位开关线型移相器。首先分析了直接接触式MEMS串联开关的插入损耗和隔离度,并得到仿真结果。在此基础上设计了基于该开关的移相范围为0~180o的四位移相器电路,相移量为12o每步。采用HFSS软件对其进行仿真,得到移相精确度、插入损耗和隔离度等关键结果,移相器工作在2.2 GHz时,隔离度大于20 dB,插入损耗小于1 dB。该设计与传统移相器相比体积更小,且具有更小的插入损耗和更大的隔离度。     

Distributed 2- and 3-bit W-band MEMS phase shifters on glass substrates

This paper presents state-of-the-art RF microelectromechanical (MEMS) phase shifters at 75-110 GHz based on the distributed microelectromechanical transmission-line (DMTL) concept. A 3-bit DMTL phase shifter, fabricated on a glass substrate using MEMS switches and coplanar-waveguide lines, results in an average loss of 2.7 dB at 78 GHz (0.9 dB/bit). The measured figure-of-merit performance is 93/spl deg//dB-100/spl deg//dB (equivalent to 0.9 dB/bit) of loss at 75-110 GHz. The associated phase error is /spl plusmn/3/spl deg/ (rms phase error is 1.56/spl deg/) and the reflection loss is below -10 dB over all eight states. A 2-bit phase shifter is also demonstrated with comparable performance to the 3-bit design. It is seen that the phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis, thereby making the design quite easy up to 110 GHz. These results represent the best phase-shifter performance to date using any technology at W-band frequencies. Careful analysis indicates that the 75-110-GHz figure-of-merit performance becomes 150/spl deg//dB-200/spl deg//dB, and the 3-bit average insertion loss improves to 1.8-2.1 dB if the phase shifter is fabricated on quartz substrates.     

Low power digital TTL command for 1 bit 60 GHz RF MEMS phase shifter

This paper presents a circuit used to actuate Radio Frequency MicroElectroMechanical Systems (RF MEMS) based phase shifters for 60 GHz beam forming. Wireless transmission in the 60 GHz band show a dramatic free space loss, thus making it mandatory to use antennas with high gain in a desired direction. Beam forming is then necessary to optimize the link budget between communicating nodes. Antenna arrays can be used for beam forming. The work done at LAAS was aiming to provide RF MEMS based phase shifters working with a standard digital command. RF MEMS commonly have high actuation voltages usually obtained with charge pumps. This paper presents a full 1 bit phase shifter with a digital translation part, an analog DC–DC converter, and an RF MEMS based loaded line phase shifter for 60 GHz signals. This converter is built using boost converters as an alternative to the use of charge pumps for driving RF MEMS in the field of wireless communications. Boost converters, despite relatively high current peaks, allow shorter settling times compared to charge pumps.     

五位分布式MEMS传输线移相器的优化设计

通过在共面波导传输线上周期性地加载分布电容,外加驱动电压改变电容值,实现分布式MEMS传输线移相器。从三个方面优化了五位分布式MEMS传输线移相器的设计:一是分别设计了11.25°和22.5°两种微桥,单元在Ka波段的插入损耗均大于-0.8 dB,回波损耗均小于-15 dB,相移精度小于0.4°,新的五位移相器以2种单元、19个微桥的结构替代了传统单一单元、31个微桥的结构,可减少微桥的总数;二是CPW传输线采用折叠布局,通过共用部分地线,移相器平面尺寸减小至1.81 mm×3.84 mm,相比传统五位分布式移相器,面积减小了56%,实现了器件的小型化;三是设计了一种新型的直流偏置结构,结构简单、工艺容易实现。