无线通信系统中的MEMS天线

本文分析了常见的MEMS天线及其应用,包括多对称锥形弯曲缝隙微带天线、用于WLAN中的微尺度宽频天线、开关式微机械毫米波天线、微机械自适应贴片天线等,对这些天线的结构原理、制造方法及其性能做了分析。这些天线设计简单、可用CMOS工艺制造、利于集成,兼有宽频、高辐射效率、小尺度等优点。但相对普通天线而言,这些制造工艺明显复杂、尺度更微小,增加了实现难度,要实现MEMS天线批量应用,还需要在基础理论及其微细工艺进行研究。最后,对MEMS天线在无线通信系统中的应用作出展望。     

Reconfigurable antennas for wireless devices

New technologies in communications electronics, such as software-defined radio (SDR) and RF switches implemented using micro-electromechanical systems (MEMS), present new challenges and opportunities for antenna design. In sharp contrast to digital technology where Moore's law reigns, a fundamental law of physics constrains the ability to realize electrically small antennas that are both efficient and broadband. As a result, covering several frequency bands concurrently with a single antenna having enough efficiency and bandwidth is a major challenge. One possible solution to this problem is to use reconfigurable antennas that tune to different frequency bands. Such an antenna would not cover all bands simultaneously, but provides narrower instantaneous bandwidths that are dynamically selectable at higher efficiency than conventional antennas. Such tunable-antenna technology is an enabler for software-definable radios, the RF front ends of which must be reprogrammable on the fly. This paper discusses the practical implementation issues, limitations, and measured results of small, narrowband, tunable antennas within portable handsets. Many of the concepts discussed in this paper will likely become practical and cost effective in the near future because of recent advances in RF MEMS switches.     

RF MEMS switches fabricated on microwave-laminate printed circuit boards

A novel fabrication process has been developed for directly constructing radio frequency microelectrical mechanical systems (RF MEMS) capacitive switches on microwave-laminate printed circuit boards (PCBs). The integrated process uses metal wet etching to form the metal lines for coplanar waveguides, compressive molding planarization (COMP) to planarize uneven surface heights for switch membrane formation, and high-density, inductively coupled plasma chemical vapor deposition (HDICP-CVD) for low-temperature silicon nitride deposition. This technology promises the potential of further monolithic integration with antennas on the same PCBs to form reconfigurable antennas without the concerns of mismatching among components.     

MEMS开关可重构矩形缝隙环天线的设计

提出一种基于MEMS开关的可重构矩形缝隙环天线设计.其关键部件之一是射频微波MEMS开关,选取了接触式MEMS开关.该天线为用共面波导馈电的多频率可重构天线,通过多个MEMS开关来改变矩形缝隙环天线的拓扑结构,按照一定的规则控制开关可实现多频率可重构.其结构简单,剖面低,易于与电路集成.     

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.     

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.     

Reconfigurable RF MEMS Phased Array Antenna Integrated Within a Liquid Crystal Polymer (LCP) System-on-Package

For the first time, a fully integrated phased array antenna with radio frequency microelectromechanical systems (RF MEMS) switches on a flexible, organic substrate is demonstrated above 10 GHz. A low noise amplifier (LNA), MEMS phase shifter, and 2 times 2 patch antenna array are integrated into a system-on-package (SOP) on a liquid crystal polymer substrate. Two antenna arrays are compared; one implemented using a single-layer SOP and the second with a multilayer SOP. Both implementations are low-loss and capable of 12deg of beam steering. The design frequency is 14 GHz and the measured return loss is greater than 12 dB for both implementations. The use of an LNA allows for a much higher radiated power level. These antennas can be customized to meet almost any size, frequency, and performance needed. This research furthers the state-of-the-art for organic SOP devices.     

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.     

Large jobs for little devices [microelectromechanical systems]

Microelectromechanical systems (MEMS) may become key components of radio frequency devices, particularly in the mobile marketplace. In filters, they may lower radio size and power consumption while increasing sensitivity. In switches, they could herald the construction of cheaper, electronically steerable antennas for radar and communications applications. MEMS are electromechanical devices with tiny moving parts. They can be built using IC-compatible materials, such as polysilicon, allowing their integration on a silicon chip, side-by-side with semiconductor circuits. Experimental filters are now reaching hundreds of megahertz, and operation up in the gigahertz ranges needed for most wireless and some satellite communications should be feasible. Their ability to kill several birds with one stone is making them very attractive to researchers and developers     

基于ADIS16209MEMS的基站天线倾斜度测试系统设计

文章介绍了基于MEMS技术的用于基站天线维护的天线倾斜度测试系统．首先介绍MEMS技术及其发展前景,然后重点介绍天线倾斜度测试系统的构成,以ADIS16209MEMS倾斜计、ARM控制器和SN65HVD1781为主体,通过Modbus远程配置以及通信,上位机实时显示监测数据,本系统精确度高,满足实际使用的需要。     

Low-voltage small-size double-arm MEMS actuator

The fabrication and characterisation of a double-arm cantilever-type metallic DC-contact MEMS actuator with low pull-down voltage are reported. Bi-layer TiW cantilevers with an internal stress gradient were fabricated using a microwave-compatible fabrication process. Owing to its small size, cantilever length (L = 5-50 mum) and width (W = 2-40 mum), i.e. ~10-100 times smaller in lateral dimensions than a standard MEMS actuator, this actuator showed actuation voltages lower than 10 V. RP measurements of the 10 mum-wide actuators yielded an average insertion loss less than 1 dB and isolation higher than 40 dB up to 25 GHz. The developed actuator is well suited for integration in reconfigurable microwave circuits and systems such as reconfigurable antennas and arrays.     

Reconfigurable leaky-mode/multifunction patch antenna structure

A reconfigurable aperture where different types of antennas and arrays with multiband coverage and multiple functions share a common planar physical aperture is proposed. Using either conventional or MEMS switches, a microstrip-based leaky-mode antenna array can easily be reconfigured to patch antennas operating at multiple frequency bands as well as monopulse radars for both azimuth and elevation tracking. The feasibility of the concept has been demonstrated by prototype design and measurement of a single-channel X-band leaky-wave/S- and C-band patch antenna structure     

基于MEMS技术的射频移相器

微波与毫米波移相器是通讯和雷达应用上相控阵天线的基本单元，MEMS技术的引入提供了一个在移相器设计中用最小损耗的开关来大量减少移相器插入损耗的方法，该方法可以降低器件的功耗，改善插入损耗、隔离度、频带宽度等性能。相比于GaAs移相器，基于MEMS开关的射频移相器，无论是开关线型、分布式或是反射型，都有很好的RF性能。     

An Analog RF MEMS Slotline True-Time-Delay Phase Shifter

An analog RF microelectromechanical systems (MEMS) slotline true-time-delay (TTD) phase shifter is presented for use in conjunction with tapered slot antennas, such as the Vivaldi aerial and the double exponentially tapered slot antenna. The design is a scalable distributed loaded-line cascade of 62 novel differential slow-wave unit cells. Each differential slow-wave unit cell comprises an electrically short slotline section, which is loaded with a shunt impedance consisting of two center-pulled contactless fixedfixed beam RF MEMS varactors in series, sharing a common electrode. The analog RF MEMS slotline TTD phase shifter is demonstrated on a borosilicate glass wafer using a microfabrication process requiring six masks. It is designed for transistortransistor logic bias voltage levels and exhibits a measured phase shift of 28.2$^{circ}/{hbox{dB}}$ (7.8 ps/dB) and 59.2$^{circ}/{hbox{cm}}$ at 10 GHz, maintaining a 75-$Omega$ differential impedance match $(S_{11_{dd}}<-15.8 {hbox{dB}})$ . The input third-order intercept point is 5 dBm at 10 GHz for a $Delta{ f}$ of 50 kHz, measured in a 100-$Omega$ differential transmission line system. Design and fabrication opportunities, concerning distortion and loss reduction, as well as packaging, are highlighted.      

Compact 3D-MEMS-meander monopole antenna

A MEMS meander monopole antenna is fabricated in the form of a folded microstrip on the upper and bottom surfaces of the substrate. This design is based on the meander line principle with a three-dimensional structure to achieve reduced size compared to many other small size printed antennas. The MEMS technologies, such as excimer laser drilling and copper electroplating were used in the fabrication of this antenna. This antenna can be mounted on the silicon wafer by anodic bonding technology. The design features 2.45 GHz operating frequency with 190 MHz bandwidth for WLAN applications. The geometric length of the antenna is 21 mm, and the width is 4 mm. Measured results have good agreement with simulation data.     

Multifunctional reconfigurable MEMS integrated antennas for adaptive MIMO systems

Multi-input multi-output systems with associated technologies such as smart antennas and adaptive coding and modulation techniques enhance channel capacity, diversity, and robustness of wireless communications as has been proven by many recent research results both in theory and experiments. This article focuses on the antenna aspect of MIMO systems. In particular, we emphasize the important role of the reconfigurable antenna and its links with space-time coding techniques that can be employed for further exploitation of the theoretical performance of MIMO wireless systems. The advantages of the reconfigurable antenna compared to the traditional smart antenna are discussed. Establishment of reconfigurable antennas requires novel radio frequency microelectromechanical systems technology, which has recently been developed in the authors' group. We briefly introduce this technology with emphasis on its distinct advantages over existing silicon-based MEMS technologies for reconfigurable antennas. A reconfigurable antenna design that can change its operating frequency and radiation/polarization characteristics is described. Finally, we present the experimental and theoretical results from impedance and radiation performance characterization for different antenna configurations.     

Optical True Time-Delay for Two-Dimensional X -Band Phased Array Antennas

An optical true time-delay (TTD) scheme for two-dimensional (2-D) X-band phased array antennas (PAAs) has been proposed. It is composed of a multiwavelength optical source and a delay line matrix consisting of 2times2 optical microelectromechanical system (MEMS) switches with fiber-optic delay lines connected between cross ports. A 2-bit times 4-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength-dependent TTD (WD-TTD) with a unit time delay of 12 ps in the x-direction and a wavelength-independent TTD (WI-TTD) with that of 6 ps in the y-direction. The time delay error for WD-TTD was measured to be less than 2.8 ps, mainly due to jitter incurred from gain-switching. On the other hand, the error for WI-TTD was less than 0.8 ps, which is within the equipment resolution. Insertion loss of both delay line matrices was less than 1 dB due to the column-wise control of the MEMS switches. This prevents the feed current applied to each antenna element from fluctuating at any radiation angles so that antenna gain and sidelobe level do not deteriorate in this scheme     

A Programmable Lens-Array Antenna With Monolithically Integrated MEMS Switches

This paper describes a reconfigurable millimeter-wave lens-array antenna based on monolithically integrated microelectromechanical systems (MEMS) switches. This device is constructed as a planar array of 2-bit programmable MEMS antenna–filter–antenna (AFA) unit cells that are used to provide a 1-D programmable “aperture transfer function” between the input and output wavefronts. The fully integrated device consists of 484 (22 $times$ 22) AFA elements and 2420 switches. Switches, bias lines, antennas, and the rest of the RF structure are fabricated on two quartz wafers ($varepsilon_{ r}=3.8$, $tandelta=0.002$) that are subsequently stacked using adhesive bonding to form the tri-layer metal structure of the AFA array. The bonded structure also forms a package for the MEMS switches. This paper investigates the design and fabrication issues and presents the measured data related to yield and frequency response of this lens-array. It also characterizes the performance of this device as a steerable antenna. Measured results show that this lens-array can be used to steer the beam of a low gain horn antenna to $pm {hbox{40}}^{circ}$ in either the $E$- or the $H$-plane. For the fabricated prototype, the yield is estimated to be 50% for the best region of the array, resulting in a relatively high insertion loss and sidelobe level.      

Design of MEMS C-Band Microstrip Antenna Array Based on High-Resistance Silicon for Intelligent Ammunition

In recent years, microstrip antennas have been more widely applied in satellite communications, mobile phones, unmanned aerial vehicle (UAV), and weapons. A micro-electro-mechanical systems-based (MEMSbased) high-resistance silicon C-band microstrip antenna array has been designed for the intelligent ammunition. The center frequency is 4.5 GHz. A cavity has been designed in substrate to reduce the dielectric constant of silicon and high-resistance silicon has been used as the material of substrate to improve the gain of antenna. It is very easy to be manufactured by using MEMS technology because of the improved structure of the antenna. The results show that the gain of the antenna is 8 dB and voltage standing wave ratio (VSWR) is less than 2 by the analysis and simulation in high frequency structure simulator (HFSS).     

Fabrication, assembly, and testing of RF MEMS capacitive switches using flexible printed circuit technology

A novel approach for cost effective fabrication, assembly, and packaging of radio-frequency microelectromechanical systems (RF MEMS) capacitive switches using flexible circuit processing techniques is reported. The key feature of this approach is the use of most commonly used flexible circuit film, Kapton-E polyimide film, as the movable switch membrane. The physical dimensions of these switches are in the mesoscale range. For example, electrode area and gap height of a capacitive shunt switch on coplanar waveguide are 2 /spl times/ 1 mm/sup 2/ and 43 /spl mu/m, respectively. Pull-down voltage is in the range of 90-100 V. In the ON state (up-position), the insertion loss is less than 0.3-0.4 dB up to 30 GHz. In OFF state (down-position), the isolation value is about 15 dB at 12 GHz and increases to 36 dB at 30 GHz. These switches are uniquely suitable for batch integration with printed circuits and antennas on laminate substrates.