Distributed MEMS Transmission Line Research Articles

Ka‐band distributed microelectromechanical systems transmission line phase shifter using metal air metal switch

AbstractA new approach for designing a two‐state unit cell for a six‐bit distributed coplanar waveguide microelectromechanical systems (MEMS) phase shifter is proposed in this study. The proposed structure includes metal air metal (MAM) capacitors as switches and consists of a unit cell with one MEMS and two MAM switches to produce two phase shifts per unit cell. In the first state, the MAM switches are pulled down and a 5.625° phase shift is achieved, and in the second state, the MEMS switch is actuated to yield a phase shift of 11.25°. The designed structure is modeled using equivalent transmission line circuit model and simulated in the Ka‐band at 34 GHz, employing advanced design system (ADS), ANSOFT HFSS and COMSOL software. Based on the modeling and simulation results, the root‐mean‐square (RMS) phase error is 1.4°, and maximum return loss and minimum insertion loss for all 64 states are better than −10.1 and −1.45 dB, respectively. The main advantages of the designed structure are its small size, low loss, low phase error and a simple phase shift mechanism. A fabrication process is also proposed for the distributed MEMS transmission line (DMTL) phase shifter that shows the feasibility of the proposed design. The proposed structure can be easily scaled to other bands and used in applications with more bits as complex as phased array antennas.

Three-Bit DMTL Phase Shifter for Phased Array Antennas

RF MEMS phase shifter is a device that is used to modify the transmission phase of RF signal and provide signal control. Phase shifters are high-value components used in phased array antenna architectures. In phased array antenna the phase shifter is used to provide reliable electronic beam steering. The proposed 3-bit distributed MEMS transmission line (DMTL) phase shifter is designed using elevated coplanar waveguide (ECPW) transmission line for the first time, which results in better return loss of [Formula: see text]14.23[Formula: see text]dB and an average insertion loss of [Formula: see text]1.46[Formula: see text]dB. This paper discusses the development of ECPW-based 3-bit DMTL phase shifter designed to operate at 15[Formula: see text]GHz.

A New Structure for 6 Bit Distributed MEMS Transmission Line Phase Shifter in Ku Band

In this paper a new design for 6 bit DMTL phase shifter with only 32 MEMS switches is proposed. The reduction in number of switches in ordinary 6 bit phase shifter from 63 to 32 is due to combination of one 5.625 degree for least significant bit and 11.25 degree for the rest of the switches. Decreasing the number of the switches reduces the die-size as well as loss of the CPW line. Analytical study and simulation with HFSS and COMSOL software is carried out for the proposed structure. Maximum return loss of phase shifter is -10.5 dB and mean RMS phase error is 1.4o . Although two different structural switches are used but the pull in voltages are identical. The total structure size is 1.5*18.5 mm2 , and surface micromachining process is proposed for the phase shifter.

Ku to V-band 4-bit MEMS phase shifter bank using high isolation SP4T switches and DMTL structures

This work presents a micro-electro-mechanical system (MEMS) based on a wide-band 4-bit phase shifter using two back-to-back single-pole-four-throw (SP4T) switches and four different distributed MEMS transmission line (DMTL) structures that are implemented on 635 µm alumina substrate using surface micromachining process. An SP4T switch is designed with a series-shunt configuration and it demonstrates an average return loss of >17 dB, an insertion loss of <1.97 dB and maximum isolation of >28 dB up to 60 GHz. A maximum area of the SP4T switch is ~0.76 mm2. Single-pole-single-throw and SP4T switches are capable of handling 1 W of radio frequency (RF) power up to >100 million cycles at 25° C; they can even sustained up to >70 million cycles with 1 W at 85 °C. The proposed wide-band phase shifter works at 17 GHz (Ku-band), 25 GHz (K-band), 35 GHz (Ka-band) and 60 GHz (V-band) frequencies. Finally,a 4-bit phase shifter demonstrates an average insertion loss of <6 dB, return loss of >10 dB and maximum phase error of ~3.8° at 60 GHz frequency over 500 MHz bandwidth. Total area of the fabricated device is ~11 mm2. In addition, the proposed device works well up to >107 cycles with 1 W of RF power. To the best of the author’s knowledge, this is the best reported wide-band MEMS 4-bit phase shifter in the literature that works with a constant resolution.

A High Resolution Digital Phase Shifter using Distributed MEMS Transmission Lines-A New Approach

Distributed Micro Electromechanical systems Transmission Line (DMTL) is used for designing digital phase shifters, by using an array of shunt switches. In the present paper, a new approach for designing DMTL for small phase steps is proposed. In the present work, an additional single switch section is introduced, having half the phase shift as the other switch sections in the DMTL. The addition of the new switch section does not alter the characteristic impedance or total phase shift of the DMTL phase shifter. A high resolution phase shifter is designed using the proposed model and the simulation results are presented. The proposed method can be further extended for achieving smaller phase steps.

Low loss KU- to KA-band analog DMTL phase shifter with 360° phase shift

A 15 GHz distributed MEMS transmission line (DMTL) based analog phase shifter was designed and characterized. The designed and measured device was capable of full 360° degree phase shift with lower losses than reported for analog DMTL phase shifters. The full phase shift was achieved at 14.6 GHz with a 1.9 dB insertion loss. The achieved figure of merit (FOM) for the device was 188°/dB. Input matching was better than −12 dB across the full tuning range. The varactors loading the coplanar wave guide (CPW) were designed to have a large capacitance ratio by having the actuation electrodes on both sides of the CPW center conductor. The height of the varactor bridge was designed lower above the CPW center conductor to allow for larger capacitance ratio. Approximately a 50 V actuation voltage was required for the full phase shift. The size of the device is 19.4 mm long and 1.2 mm wide. The measured device operation shows the phase shifter can work and achieve the full phase shift of 360° in very wide bandwidth of 15–35 GHz with a FOM above 100°/dB. Even up to 50 GHz the device operates with full phase shift with low losses enabling a FOM above 50°/dB. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1401–1404, 2017

A tunable bandstop filter using T shaped DGS and MEMS switches on CPW

In the present work, a band stop filter with tunable resonant frequency and tunable bandwidth is proposed using micro electromechanical (MEMS) switches. The band stop filter is based on defected ground structures (DGS). Tunability of resonant frequency is achieved through two methods for fine and coarse tuning. The various switching states of the filter are represented by equivalent circuit models. Four MEMS series switches are loaded over each of the four branches of a T-shaped DGS structure. The switches are successively actuated to increase the resonant frequency of the filter in narrow steps. A coarser method of tuning the resonant frequency makes use of two switches connected across the gaps of the DGS. In this method, the resonant frequency varies nonlinearly with the height of the switch beam. The bandwidth of the filter is tuned by actuation of MEMS shunt switches, forming a distributed MEMS transmission line (DMTL) in the spacing between the DGS structures. The actuation of the MEMS shunt switches in the DMTL results in a slow wave effect. This increases the effective electrical length between the DGS structures leading to increase in bandwidth.

Design of Reliable Analog DMTL Phase Shifter with Improved Performance for Ku Band Applications

&lt;p&gt;An analog phase shifter based on distributed MEMS transmission line (DMTL) is designed for Ku band applications. Traditional RF MEMS phase shifter comprising 6 switches has limited phase shift of 37.75° due to instability region. A new concept of stopper is incorporated to achieve high phase shift. In the present paper, optimisation of the analog phase shifter is done to increase its phase shift upto 88.63°. Phase shift is a strong function of capacitance ratio which is increased from 1.75 to 2.95. The maximum operating voltage and mechanical resonant frequency for the phase shifter are 16 V and 8.3 KHz, respectively. The switching time is calculated to 56 μs. The simulated insertion loss of the phase shifter is -1.75 dB with return loss of -20.49 dB at 17 GHz. The simulated results are verified with analytical modelling which are in close match.&lt;/p&gt;

10–25 GHz frequency reconfigurable MEMS 5-bit phase shifter using push–pull actuator based toggle mechanism

This paper presents a frequency tunable 5-bit true-time-delay digital phase shifter using radio frequency microelectromechanical system (RF MEMS) technology. The phase shifter is based on the distributed MEMS transmission line (DMTL) concept utilizing a MEMS varactor. The main source of frequency tuning in this work is a bridge actuation mechanism followed by capacitance variation. Two stages of actuation mechanisms (push and pull) are used to achieve a 2:1 tuning ratio. Accurate control of the actuation voltage between the pull to push stages contributes differential phase shift over the band of interest. The functional behavior of the push–pull actuation over the phase shifter application is theoretically established, experimentally investigated and validated with simulation. The phase shifter is fabricated monolithically using a gold based surface micromachining process on an alumina substrate. The individual primary phase-bits (11.25°/22.5°/45°/90°/180°) that are the fundamental building blocks of the complete 5-bit phase shifter are designed, fabricated and experimentally characterized from 10–25 GHz for specific applications. Finally, the complete 5-bit phase shifter demonstrates an average phase error of 4.32°, 2.8°, 1° and 1.58°, an average insertion loss of 3.76, 4.1, 4.2 and 4.84 dB and an average return loss of 11.7, 12, 14 and 11.8 dB at 10, 12, 17.2 and 25 GHz, respectively. To the best of the authors’ knowledge, this is the first reported band tunable stand alone 5-bit phase shifter in the literature which can work over the large spectrum for different applications. The total area of the 5-bit phase shifter is 15.6 mm2. Furthermore, the cold-switched reliability of the unit cell and the complete 5-bit MEMS phase shifter are extensively investigated and presented.

Low Loss 2-Bit Distributed MEMS Phase Shifter using Chamfered Transmission Line

Objectives: The objective of this paper is to design a 2-bit DMTL phase shifter with low insertion loss, improved phase shift per dB loss with minimum number of switches. Methods/Analysis: In order to reduce the insertion loss tapered impedance section proposed previous researchers introduces impedance discontinuity at the end of the taper that introduces a fringing capacitance at the transition region which cannot be neglected while calculating the loaded line capacitance. The proposed chamfered transmission line design for phase shifter overcomes this shortcoming with a uniform high impedance line that does not have any discontinuities and causes variations of propagation constant along the length of the transmission line. The proposed design also reduces the discontinuity effects associated with step width junction and reflection is much reduced. Findings: Chamfering the corners at the contact area of switch with the transmission line reduces the discontinuity effects associated with step width junction. The achieved phase shift is 178.87o at 17GHz with an insertion loss of -0.87dB and return loss in both up, down states less than -15dB. Design and simulation results of the phase shifter with respect to pull-in voltage of the switch, RF characterization is done using Coventorware and HFSS. Keywords: Chamfered, Co-Planar Waveguide (CPW), Distributed MEMS Transmission Line (DMTL), Pull-In, Lift-Off, Radio Frequency Micro Electro Mechanical Systems (RF MEMS)

Microfabricated Thick-Cu PZT-MEMS Millimeter-Wave Topologies and Devices

This letter reports the design, fabrication, and performance of millimeter-wave transmission lines and devices in a tri-layer thick-copper (Cu) process. Beneath the Cu layers is a low-voltage lead zirconium titanate (PZT) MEMS stackup atop a nitride membrane, on high-resistivity silicon. The 10 μm thick Cu layers enable several transmission-line topologies, and the PZT-MEMS functionality enables tunability. We designed transmission lines and un-optimized noncontact distributed MEMS transmission line (DMTL) phase shifters for 75-110 GHz, and present static measurements here. Simulation and measurements are in close agreement, with measured CPW line loss 0.15 dB greater than simulated (0.27 dB/mm at 95 GHz). Excess loss is attributed to Cu roughness, conductivity, and membrane/strap supports. Measured noncontact DMTL phase shifters exhibit a mean of 40 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /dB when intrinsic line loss is subtracted.

Design, development and characterization of an x-band 5 bit DMTL phase shifter using an inline MEMS bridge and MAM capacitors

A radio frequency micro-electro-mechanical system (RF-MEMS) 5 bit phase shifter based on a distributed MEMS transmission line concept with excellent phase accuracy and good repeatability is presented in this paper. The phase shifter is built with three fixed–fixed beams; one is switchable with electrostatic actuation and the other two are fixed for a metal–air–metal (MAM) capacitor. The design is based on a coplanar waveguide (CPW) configuration using alumina substrate. Gold-based surface micromachining is used to develop the individual primary phase bits (11.25°/22.5°/45°/90°/180°), which are fundamental building blocks of the complete 5 bit phase shifter. All of the primary phase bits are cascaded together to build the complete phase shifter. Detailed design methodology and performance analysis of the unit cell phase shifter has been carried out with structural and parametric optimization using an in-line bridge and MAM capacitors. The mechanical, electrical, transient, intermodulation distortion (IMD), temperature distribution, power handling and loss performances of the MEMS bridge have been experimentally obtained and validated using simulations up to reasonable extent. A single unit cell is able to provide 31 dB return loss, maximum insertion loss of 0.085 dB and a differential phase shift of 5.95° (at 10 GHz) over the band of interest. Furthermore, all primary phase bits are individually tested to ensure overall optimum phase shifter performance. The complete 5 bit phase shifter demonstrates an average insertion loss of 4.72 dB with return loss of better than 12 dB within 8–12 GHz using periodic placement of 62 unit cells and a maximum phase error of ±3.2° has been obtained at 10 GHz. Finally, the x-band 5 bit phase shifter is compared with the present state-of-the-art. The performance of the 5 bit phase shifter when mounted inside a test jig has been experimentally investigated and the results are presented. The total area of the phase shifter is 19.4 mm2. To the best of our knowledge, this is the first reported digital distributed MEMS transmission line type RF-MEMS phase shifter that has undergone different reliability stages.

Design, fabrication and characterization of miniature RF MEMS switched capacitor based phase shifter

This paper aims to present in detail the design, fabrication and the various characterization techniques adopted in realizing a novel miniature-size switched capacitor based phase shifter. The work strives to provide an all-round development of a DMTL (Distributed MEMS Transmission Line) based phase shifting unit yielding an overall phase shift of 15° at a frequency of 15GHz. The RF MEMS (Radio Frequency Micro Electro Mechanical Systems) Switched Capacitor based phase shifter has highly miniaturized dimensions, and is capable of solving many limitations to which the conventional Switched Capacitors are mostly susceptible. This miniature RF MEMS switched capacitor actuates at a low actuation voltage of 12V, exhibits a fundamental frequency of vibration as high as 1.468MHz and a switching time of 1.4µs which is an improvement over the other reported designs. Various characterization results seem to validate the simulations.

A novel design of RF MEMS dual band phase shifter

In this paper a novel design of RF MEMS dual band phase shifter is presented. The new design is switched-line type phase shifter which has been constructed by distributed MEMS transmission line (DMTL). Since the constant phase of DMTL can be changed, the proposed design has capability for working at two or more frequencies. The performances of the new design are compared with conventional switched-line design that has been constructed by transmission line of coplanar waveguide. The results show the feasibility of the new design and also show the new design reduces the size and loss of the structure compared with conventional switched-line design. The proposed design is unique approach to achieve a dual band phase shifter using MEMS technology which has low loss and weight with high linearity respect to the other technologies. This dual band phase shifter has very small size than the other passive dual band phase shifters.

RF MEMS-Based Biosensor for Pathogenic Bacteria Detection

A biosensor which is used for determining the concentration of substances and other parameters of biological interest is an integral part of the public health systems. Micromachined sensors based on radio frequency–microelectromechanical systems are an emerging field of study for biosensing applications. In this work, we propose a novel detection method for pathogenic bacteria using a coplanar waveguide (CPW) as well as distributed microelectromechanical systems transmission line (DMTL). Escherichia coli has been chosen for the study due to the widespread food poisoning outbreaks caused by its infective strains. But, the model can be easily extended to other pathogenic bacteria as well. The E. coli bacterium was modeled as a three-shell structure based on the electrical properties of the E. coli cell. An initial study was done using a CPW. The scattering parameters and voltage standing wave ratio were analyzed and found to vary as the number of bacteria positioned on the CPW increased. Reflection parameters were found to have more deviation than the transmission parameters. DMTL was designed by introducing periodic structures in CPW, to allow increased interaction between the electromagnetic waves and the measurand. This improved the quality factor of the resonant peaks in reflection coefficient, thereby allowing us to correlate the number of bacteria to the shift in resonant frequency. Selectivity towards E. coli bacteria can be achieved by immobilizing a functionalization layer of anti E. coli antibody on the central conductor of CPW/DMTL. With sufficient calibration, this method can be used to detect and measure the concentration of other pathogenic bacteria as well.

Design and development of a surface micro-machined push–pull-type true-time-delay phase shifter on an alumina substrate for Ka-band T/R module application

A radio frequency micro-electro-mechanical system (RF-MEMS) phase shifter based on the distributed MEMS transmission line (DMTL) concept towards maximum achievable phase shift with low actuation voltage with good figure of merit (FOM) is presented in this paper. This surface micro-machined analog DMTL phase shifter demonstrates low power consumption for implementation in a Ka-band transmit/receive (T/R) module. The push–pull-type switch has been designed and optimized with an analytical method and validated with simulation, which is the fundamental building block of the design of a true-time-delay phase shifter. Change in phase has been designed and optimized in push and pull states with reference to the up-state performance of the phase shifter. The working principle of this push–pull-type DMTL phase shifter has been comprehensively worked out. A thorough detail of the design and performance analysis of the phase shifter has been carried out with various structural parameters using commercially available simulation tools with reference to a change in phase shift and has been verified using a system level simulation. The phase shifter is fabricated on the alumina substrate, using a suspended gold bridge membrane with a surface micromachining process. Asymmetric behaviour of push–pull bridge configuration has been noted and a corresponding effect on mechanical, electrical and RF performances has been extensively investigated. It is demonstrated 114° dB−1 FOM over 0–40 GHz band, which is the highest achievable FOM from a unit cell on an alumina substrate reported so far. A complete phase shifter contributes to a continuous differential phase shift of 0°–360° over 0–40 GHz band with a minimum actuation voltage of 8.1 V which is the highest achievable phase shift with the lowest actuation voltage as per till date on the alumina substrate with good repeatability and return loss better than 11.5 dB over 0–40 GHz band.

RF-MEMS switches with AlN dielectric and their applications

This paper reports on the potential of RF-MEMS technology based on aluminum nitride capacitive dielectric and nickel-suspended membranes to provide RF circuit functions in reconfigurable front-end radios. The RF performance of capacitive switches, distributed MEMS transmission lines (DMTLs) phase shifters for beam steering and tunable filters, including center frequency and bandwidth tuning of bandpass and band-stop filters are presented. Detailed characterization based on S-parameter data demonstrates very promising figures of merit of all fabricated demonstrators from 5 to 40 GHz.

A LOW-COST PHASED ARRAY ANTENNA INTEGRATED WITH PHASE SHIFTERS COFABRICATED ON THE LAMINATE

This paper presents the design, development and experimental characterization of a monolithic phased array antenna integrated on a microwave laminate. A four-element linear antenna array is realized by cofabricating the corporate feed network, microstrip-CPW transitions, DC blocks, and mesoscale phase shifters on the same substrate. The phase shifters used here are electrostatically actuated and their operation is similar to that of the distributed MEMS transmission line phase shifters. Various components of the array are designed and are individually evaluated before fabricating together. The measured radiation pattern characteristics for this array shows a scan angle of 10 - in the X- band. All fabrication processes employed here can be performed at a good printed circuit manufacturing facility. This simple approach of cofabricating various components can be readily extended for large phased arrays required in radar and space communication applications.

SIMULTANEOUS DETECTION OF ORGANIC AND INORGANIC SUBSTANCES IN A MIXED AQUEOUS SOLUTION USING A MICROWAVE DIELECTRIC SENSOR

This letter reports a new technique that enables simultaneous detection of concentrations of the organic and inorganic substances in a hybrid ∞uidic solution. The technique is based on a coplanar microwave distributed MEMS transmission line. Measurement results show that a hybrid aqueous solution with a mixture of 0M{0.2M NaCl and 0mg/ml{350mg/ml glucose can be easily detected simultaneously from measured one-port scattering parameter (S11).

Design Methodology and Optimization of Distributed MEMS Matching Networks for Low-Microwave-Frequency Applications

A design methodology for the distributed microelectromechanical system (MEMS) impedance matching networks based on the optimization of the uniformity of the Smith chart coverage has been developed. The proposed approach was validated through a comparison between a traditional coplanar waveguide (CPW) design and an improved design based on a slow-wave (SW) structure. The enhanced reconfigurable impedance matching network has been developed for low-frequency applications. The network is based on a distributed MEMS transmission line (DMTL) coupled with the SW structure to reduce the total physical length of the network by 25% in comparison with a traditional DMTL. An extensive analysis was performed to identify the impact of each design parameter in order to optimize the structure and reduce the required size for relatively low-frequency applications. Several parameters are extracted from the electromagnetic simulation results and are used to design the proposed impedance matching network. Measurement results confirm the efficiency of the proposed design methodology in improving the impedance coverage and also miniaturization of the DMTL impedance matching networks.