CPW Transmission Line Research Articles

Ku-band RF MEMS tunable comb line band reject filter on coplanar transmission line

A band reject filter with tuning capability is presented on a CPW transmission line on silicon substrate using comb line and RF MEMS variable capacitor, enabling compatibility with planar IC technology. A conventional CPW on a substrate consists of a central strip conductor with semi-infinite ground planes on either side. A comb line is etched on the signal line of the CPW and the MEMS bridge capacitor is put on the same line in shunt. Tunability of the filter is achieved by putting the MEMS bridge in either up or down state. The rejection at the centre frequency of stop bands are around −40.24dB for down state and −38.21dB for up state of the bridge. A low insertion loss, as low as −0.68dB, is obtained in the pass band. The proposed device structure is simulated using ANSOFT HFSS v13® for RF analysis and COVENTORWARE (2008)® for mechanical and electromechanical characterization, both static and transient analysis.

Fabrication of void-free copper filled through-glass-via for wafer-level RF MEMS packaging

A novel fabrication method of copper filled through-glass-via is presented for wafer-level RF MEMS packaging. By using glass reflow and seedless electroplating process, a void-free copper via with a smooth side wall can be obtained. This enables a vertical interconnection between the electrical pads through the glass substrate. Furthermore, the proposed through-glass-via was applied to the packaging of a CPW transmission line to investigate its effects on the RF performances. For the encapsulation of the packaged device, which is the CPW line in this case, the glass cap with the cavity is anodically bonded to the substrate. The measured insertion loss of the whole packaging including the copper vias and the CPW line covered with the glass cap was 0.197 dB and the return loss was 20.032 dB at 20 GHz.

Passive Circuit Technologies for mm-Wave Wireless Systems on Silicon

The performance characteristics of transmission lines, silicon integrated waveguides, tunable LC resonators and passive combiners/splitters and baluns are described in this paper. It is shown that Q-factor for an on-chip LC tank peaks between 20 and 40 GHz in a 65 nm RF-CMOS technology; well below the bands proposed for many mm-wave applications. Simulations also predict that the Q-factor of differential CPW transmission lines on-chip can exceed 20 at 60 GHz in RF-CMOS when a floating shield is applied, outperforming unshielded variants employing more advanced metal stacks. A PA circuit demonstrator for advanced on-chip passive power combiners, splitters and baluns realizes peak-PAE of 18% and Psat better than 20 dBm into a 50 Ω load at 62 GHz. An outlook to the enablement of digitally intensive mm-wave ICs and low-loss passive interconnections (0.15 dB/mm measured loss at 100 GHz) concludes the paper.

High-Performance Shielded Coplanar Waveguides for the Design of CMOS 60-GHz Bandpass Filters

This paper presents optimized very high performance CMOS slow-wave shielded CPW transmission lines (S-CPW TLines). They are used to realize a 60-GHz bandpass filter, with T-junctions and open stubs. Owing to a strong slow-wave effect, the longitudinal length of the S-CPW is reduced by a factor up to 2.6 compared to a classical microstrip topology in the same technology. Moreover, the quality factor of the realized S-CPWs reaches 43 at 60 GHz, which is about two times higher than the microstrip one and corresponds to the state of the art concerning S-CPW TLines with moderate width. For a proof of concept of complex passive device realization, two millimeter-wave filters working at 60 GHz based on dual-behavior-resonator filters have been designed with these S-CPWs and measured up to 110 GHz. The measured insertion loss for the first-order (respectively, second-order) filter is -2.6 dB (respectively, -4.1 dB). The comparison with a classical microstrip topology and the state-of-the-art CMOS filter results highlights the very good performance of the realized filters in terms of unloaded quality factor. It also shows the potential of S-CPW TLines for the design of high-performance complex CMOS passive devices.

Novel Compact CPW-Fed Antennas with Harmonic Suppression and Bandwidth Enhancement

Novel compact CPW-fed antennas with harmonic suppression are presented and investigated in detail. By inserting symmetrical slots connected to the end of CPW transmission line in the ground plane, and exploiting parasitic technique, harmonic suppression, compact size, as well as wide bandwidth are obtained. General performances of the proposed antennas are studied by equivalent transmission line circuits. Moreover, the steps of constructing such harmonic suppression antennas are derived. Eventually, the experiment results verified the validation of the proposed harmonic suppression antennas.

Analysis of Ferrite Coplanar Waveguide Transmission Line

In this paper, we introduce detailed analysis of electromagnetic wave propagation along a planar ferrite coplanar waveguide transmission line. The analysis was done using the electromagnetic full wave of CPW transmission lines implemented on ferrite substrate. All the possible excitation directions of the applied DC magnetic bias were studied. The analytical study was verified using full wave simulations of electromagnetic waves propagation along different types of ferrite coplanar waveguide. The simulation results confirmed the propagation characteristics derived in the analytical study.

A Ka-band low-noise amplifier using semicircle stacked-GCPW transmission line

A high-gain Ka-band 0.18-μm CMOS low-noise amplifier with semicircle stacked grounded coplanar waveguide (SCS-GCPW) structure transmission line is proposed. SCS-GCPW transmission line is adopted to reduce the signal loss by shaping the electric fields under the signal line especially at microwave and millimeter wave applications. The SCS-GCPW demonstrated a similar electric field distribution of coaxial cable and achieved a substrate dielectric attenuation constant of 0.075 Np/m. It is superior to 0.081 Np/m and 0.144 Np/m of traditional microstrip transmission line and CPW transmission line, respectively. By adopting the low loss SCS-GCPW transmission line, the Ka-band LNA demonstrated a 24.5 dB gain together with a noise figure (NF) of 7.5 dB at 33 GHz operation. The measured output power 1 dB compression point (P1 dB) was −2 dBm. The dc power consumption was 40 mW and chip size was 0.6 × 1 mm2 for this Ka-band LNA. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1131–1134, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25910

Impact of technology dispersion on slow-wave high performance shielded CPW transmission lines characteristics

Shielded coplanar waveguides are promising candidates for the development of high quality factor transmission lines in millimeter-wave frequency bands. In this article, state-of-the-art experimental results carried out on a CMOS 0.35 μm low-cost technology are presented. This letter especially deals with the benchmark of slow-wave transmission lines in focusing on the impact of technology dispersion on the measurement results. Eight dies have been measured, each from a different wafer, showing a robust design versus the technology. These results open new possibilities for the development of miniaturized low-loss compact passive devices. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2786–2789, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25598

A novel folded slot antenna for UWB applications

AbstractThis letter presents a compact and novel folded antenna with curved slots for ultra‐wideband (UWB) applications.The proposed antenna originates from an antenna, which consists of a pair of symmetrically curved radiating slots fed by a CPW transmission line. This pair of planar curved slots is symmetrically folded in relation to the central feeding lines so that the size is shrunk to one half of the original geometric size. Using the HFSS software, the simulated results shows that the folded type antenna still preserves the UWB transmission characteristics. The impedance bandwidth, radiation pattern, and radiation gains of this shrunken UWB antenna are investigated and further measurement are performed to verify its UWB characteristics. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1872–1877, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25299

CPW-fed Antenna Covering Wimax 2.5/3.5/5.7 GHz Bands

In this paper, a CPW-fed slot antenna covering three WiMAX bands (2.5/3.5/5.7 GHz) is presented. The design is by widening and extending center conductor of a CPW transmission line to form a rectangular patch within an aperture. For a fixed width of the patch, triple bands can easily be tuned and matched by tuning the length of the patch. While triple bands are matched, an outside parasitic ring can further be added to boost gain at 5–6 GHz band.

CRLH CPW Antenna on Magnetically Biased Ferrite Substrate

The aim of this paper is to describe the results obtained by experimenting with a Composite Right/Left Handed Co Planar Waveguide (CRLH CPW) zeroth-order resonating antenna on a ferrite substrate magnetically biased with a DC magnetic field. The CRLH structure consists of a series of connected CPW interdigital capacitors and parallel ground connected CPW transmission lines as inductors to form an antenna structure working at the frequency of 13,350 GHz. The ferrite substrate for this antenna has the saturation magnetization of 550 G, the dielectric constant of 13.5 and the resonance linewidth of 16.8 kA/m. If this device is subjected to a magnetic biasing field ranging between 0 T and 0.26 T, modeling demonstrates an antenna frequency tuning of about 450 MHz (meaning ∼ 3.4%) as a result of this magnetic field variation. Also, a scanning of the antenna radiation pattern occurs when the ferrite substrate is magnetically polarized. Data obtained by measurements indicate a deviation of the radiation pattern between +12° and −10° for a variable magnetic biasing field between 0 T and 0.16 T respectively. The originality of this approach consists in highlighting the possibility of changing the working parameters of a ferrite supported antenna by using an external biasing magnetic field. The experiment validates the data obtained by modeling.

High-Q Slow-Wave Coplanar Transmission Lines on 0.35 $\mu$m CMOS Process

In this letter, experimental results and trends for shielded coplanar waveguide transmission lines (S-CPW) implemented in a 0.35 μm CMOS technology are provided. Because of the introduction of floating strips below the CPW transmission line, high effective dielectric permittivity and quality factor are obtained. Three different geometries of S-CPW transmission lines are characterized. For the best geometry, the measured effective dielectric permittivity reaches 48, leading to a very high slow-wave factor and high miniaturization. In addition, measurements demonstrate a quality factor ranging from 20 to 40 between 10 and 40 GHz, demonstrating state-of-the-art results for transmission lines realized in a low-cost CMOS standard technology.

Microwave frequency detector at X-band using GaAs MMIC technology

The design, fabrication, and experimental results of an MEMS microwave frequency detector are presented for the first time. The structure consists of a microwave power divider, two CPW transmission lines, a microwave power combiner, an MEMS capacitive power sensor and a thermopile. The detector has been designed and fabricated on GaAs substrate using the MMIC process at the X-band successfully. The MEMS capacitive power sensor is used for detecting the high power signal, while the thermopile is used for detecting the low power signal. Signals of 17 and 10 dBm are measured over the X-band. The sensitivity is 0.56 MHz/fF under 17 dBm by the capacitive power sensor, and 6.67 MHz/μV under 10 dBm by the thermopile, respectively. The validity of the presented design has been confirmed by the experiment.

Design guidelines for low‐loss slow‐wave coplanar transmission lines in RF‐CMOS technology

AbstractSlow wave coplanar transmission lines (S‐CPW) based on conventional coplanar CPW transmission lines with a floating patterned ground plane are good candidates for the integration of distributed RF circuits for front‐end modules. They offer high quality factors when compared to conventional coplanar transmission lines. In this article, guidelines are carried out for the design of such transmission lines. Simulations are first compared to already published measurements thus validating the simulation method used throughout the article. Next, considering a standard 0.35 μm CMOS process, design guidelines are presented in order to determine the characteristic impedance, the phase velocity, and the dielectric effective constant of the S‐CPW transmission lines, along with the attenuation loss and the quality factor. The effects of CPW dimensions, the floating strips duty cycle, the floating strip width, and the ground plane width are studied, and an optimized 50‐Ω transmission line is designed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3029–3036, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23865

Behaviour Study of Low-Loss Slow-Wave Coplanar Transmission Lines for RFIC Applications

Slow wave coplanar transmission lines (S-CPW), based on conventional coplanar CPW transmission lines with a floating patterned ground plane, consisting in floatting strips below the line, are good candidates for the integration of distributed RF circuits for front-end modules. They offer high quality factors when compared to conventional coplanar transmission lines. In this paper, guidelines are carried out for the design of such transmission lines. Simulations are first compared to already published measurements thus validating the simulation method used throughout the paper. Next, considering a standard 0.35 µm CMOS process, a design guideline is drawn in order to determine the characteristic impedance, the phase velocity and the dielectric effective constant of the S-CPW transmission lines, along with the attenuation loss and the quality factor. The effects of the floating strips duty cycle, the floating strip width and the ground plane width are studied.

Coplanar waveguide basics for MMIC and PCB design

In this article, basic CPW design information geared towards a practicing microwave circuit designer, including the applicability and benefits of CPW transmission line configuration, design and modeling tips, and two microphotographs of implemented CPW MMIC amplifiers are provided. Supported by the CPW geometry (coupled slotline) and modes that can occur for practical implementation of CPW (parallel-plate waveguide mode). CPW has a significant number of applications in microwave design, and we hope this brief tutorial will provide enough of an introduction to aid designers in beginning CPW design.

RF MEMS Extended Tuning Range Varactor and Varactor Based True Time Delay Line Design

MEMS varactors are one of the important passive MEMS devices. Their applica- tions include use in VCOs, tunable impedance matching networks, tunable fllters, phase shifters, and true time delay lines. The shunt capacitive structure has been employed in most of the conventional MEMS varactor designs because of its simplicity. However, the capacitance ratio of this conventional shunt capacitive MEMS varactor is limited to 1.5 because of the MEMS Pull- In efiect, which happens when the de∞ection between the MEMS top and bottom metal plates increase beyond 1/3 of the airgap between the two metal plates. At that time, the top metal plate will quickly snap down. This efiect is the major limitation in MEMS varactor designs and can cause nonlinearity and mechanically instability. In order to eliminate this Pull-In efiect, the author employed the so-called MEMS extended tuning range structure. This structure utilizes a variable height top metal beam with separate actuation parts. The airgap between the center part of the top beam and the bottom plate has been designed to be less than 1/3 of the airgap between the top beam and the bottom actuation pads. When DC bias is applied to the actuation parts, the entire top beam will move down together. Consequently, before the Pull-In efiect happens at the actuation parts, the center part has already traveled through its entire tuning range, which means that the capacitive ratio of this kind of MEMS varactor can go to inflnity. A fabrication process employing a GaAs substrate has been designed based on surface micro- machining technology. The maximum capacitance ratio of the designed MEMS extended tuning range varactor is 5.39 with a Cmax value of 167fF. Based on this MEMS varactor design, a Ka-band MEMS varactor based distributed true time delay line has been designed. This dis- tributed true time delay line includes a high impedance CPW transmission line with 70› un- loaded impedance at 28GHz and eight MEMS extended tuning range varactors based on the varactor design periodically loaded on the CPW line. The testing results show that a 56 - phase delay variation has been achieved at 28GHz. The measured insertion loss at 28GHz is i1:07dB at the up-state and i2:36dB at the down-state. The measured return losses, S11 and S22, are both below i15dB at 28GHz and below i10dB over the entire tested frequency range of 5GHz to 40GHz.

A fully wafer-level packaged RF MEMS switch with low actuation voltage using a piezoelectric actuator

In this paper, a fully wafer-level packaged RF MEMS switch has been demonstrated, which has low operation voltage, using a piezoelectric actuator. The piezoelectric actuator was designed to operate at low actuation voltage for application to advanced mobile handsets. The dc contact type RF switch was packaged using the wafer-level bonding process. The CPW transmission lines and piezoelectric actuators have been fabricated on separate wafers and assembled together by the wafer-level eutectic bonding process. A gold and tin composite was used for eutectic bonding at a low temperature of 300 °C. Via holes interconnecting the electrical contact pads through the wafer were filled completely with electroplated copper. The fully wafer-level packaged RF MEMS switch showed an insertion loss of 0.63 dB and an isolation of 26.4 dB at 5 GHz. The actuation voltage of the switch was 5 V. The resonant frequency of the piezoelectric actuator was 38.4 kHz and the spring constant of the actuator was calculated to be 9.6 N m−1. The size of the packaged SPST (single-pole single-through) switch was 1.2 mm × 1.2 mm including the packaging sealing rim. The effect of the proposed package structure on the RF performance was characterized with a device having CPW through lines and vertical feed lines excluding the RF switches. The measured packaging loss was 0.2 dB and the return loss was 33.6 dB at 5 GHz.

RF MEMS--Enabling Technology for Millimeter-Waves

This paper presents high-performance millimeter-wave passive devices using MEMS technology. The purpose of this paper is to show the possibility of MEMS technology as an enabling technology for millimeter-waves. The loss and cost issues, which have been the inherent barrier for commercialization of mm-waves, can be solved by RF MEMS technology. Successful demonstrations of MEMS technology for mm-waves include novel CPW transmission lines, digital impedance tuners, analog tunable band-pass filters, reconfigurable low-pass filters, V-band digital distributed phase shifters and 2-D mechanical beam-steering antennas. All these circuits were implemented for 30-65 GHz frequency range, and show the state-of-the-art performance, which is beyond the limit set by the conventional technology.

A wideband balun and vertical transition between conductor-backed CPW and parallel-strip transmission line

A wideband vertical transition between conductor-backed coplanar waveguide (CBCPW) and parallel-strip (PS) transmission line is presented. By choosing the same widths for the two conductor strips comprising the PS transmission line, the transition performs unbalanced-to-balanced transformation as well. Back-to-back configurations of the transition have been realized and their transmission, reflection, and direct-coupling characteristics have been measured. It is shown that the placement of vias connecting the top and the bottom grounds of the CBCPW along the entire gap between the truncated center conductor and the ground is crucial in preventing spurious resonances of the CBCPW structure. The fabricated back-to-back transition features low insertion loss over the 28:1 frequency range that has been tested.