Coplanar Waveguide Research Articles

A Transparent Antenna Using Metal Mesh for UWB MIMO Applications

This paper presents a transparent ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna based on a wired metal mesh (MM) structure. Transparent antennas (TAs) can be integrated on various building materials with little visual impact to facilitate flexible massive indoor wireless device deployment. The proposed antenna achieves 77% transparency by hollowing out both metal and substrate into a mesh shape, while maintaining more than 83% radiation efficiency. The MIMO antenna consists of 4 elements, each being a co-planar waveguide (CPW) fed UWB monopole and adjacent elements being placed orthogonally to produce dual polarisation. The operating band of the MIMO antenna spans over 3.2-11.2 GHz. A parasitic decoupling structure aligned with the mesh grid is designed to enhance the isolation between MIMO elements without degrading the transparency. Within the entire operating band, the isolation between any two elements is more than 20 dB. The peak gain varies from 3.3 dBi to 7.2 dBi within the bandwidth. The envelop correlation coefficient (ECC) is less than 0.004. The channel capacity and time domain response are analysed. The antenna can be easily fabricated by conventional PCB and laser cutting techniques with a low cost.

Ultrawideband De-Embedding Calibration for Magnetic Field Probes by Using Symmetric GCPW Calibrators

Microstrip line is commonly used as a calibrator for probe calibration. However, some issues need to be addressed for high frequency application, such as ripple and attenuation caused by the embedded part of the calibrator. In this paper, an ultra-wideband de-embedding calibration method (DCM) for magnetic field probe is proposed. Two symmetric non-soldering grounded coplanar waveguide (GCPW) calibrators, including Through and Line standards, are used to solve the de-embedded <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameter matrix of a 3-port calibration system. Compared with the traditional calibration method (TCM), the proposed method can reduce the influence of the reflection and attenuation caused by the embedded part and preserve the intrinsic properties of the probe itself. By using the DCM with a symmetric and good matched GCPW calibrator, the ripples of the DCM decreases by 6.57 dB, which is 82 % of the TCM with a microstrip line, and the attenuation has been compensated by about 0.7 dB at 10 GHz. In addition, a new characterization method of common mode suppression ratio for H-field probe is also presented, and it is applicable to conducted emissions measurement in which a probe can detect signals without 90° rotation.

Fully Aerosol Jet-Printed Passive Components for 140–220-GHz Operation

This letter focuses on the unique capabilities that aerosol jet printing (AJP) provides for manufacturing electronics at near-THz frequencies. For the first time, we demonstrate fully aerosol jet-printed passive components above the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$</tex-math> </inline-formula> -band. Dielectric substrates and conductors are printed on metal carriers via AJP. These components include microstrip (MS) transmission lines (TLs) and radial stubs, and utilize vialess grounded coplanar waveguide (GCPW)-to-MS TL launches. Two separate sets of components and calibration structures are realized, for two different dielectric thicknesses. For the TLs, measured from 140 to 220 GHz, the average loss varies from 0.86 to 2.6 dB/mm. The radial stub return loss, measured from 200 to 220 GHz, is closely aligned with simulations.

Wideband SIW based slot antenna for RADAR applications

In this case, a substrate integrated waveguide technology is used in conjunction with a cavity-backed slot antenna. The modified slot antenna, in comparison to the dumbbell-shaped slot, not only adds numerous additional resonance spots, but it also enables the antenna to attain a better gain. In addition to this, the high-order resonant modes that are contained inside the sub cavity may be stimulated by the ground coplanar waveguide feeding structure if the high-order modes are brought into close proximity with one another. Based on the results of the test, it has been determined that the suggested antenna achieves an impedance bandwidth of 26.7% between 18.2 and 23.8 GHz and a peak gain of 9.5 dBi at 20.4 GHz. At each of the three frequencies that were tested, the cross-polarization levels of the antenna are around 40 dB. Antennas are recognised as being among the most important parts of any communication system. Because of this, antenna design is now one of the most active areas of study within the field of communication studies. In contrast, applications like as air traffic radar, satellite communications, and point-to-point terrestrial connection demand highly concentrated radiation patterns that also have a wideband and high gain. Because of this more focused radiation pattern, there will also be an increase in the communication range.

A 124-to-152-GHz Power Amplifier Exploiting Chebyshev-Type Two-Section Wideband and Low-Loss Power-Combining Technique in 28-nm CMOS

This article presents a high-power wideband power amplifier (PA) with a four-way power-combining technique for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$</tex-math> </inline-formula> -band high-resolution radar. The power combiner is based on a two-section Chebyshev impedance converter to achieve a large bandwidth (BW) and is realized with slow wave coplanar waveguides (S-CPWs) to reduce the insertion loss and chip area. Therefore, our developed technique can provide broadband and low-loss power-combining scheme in a very compact size. A high-power PA with four-way combining has been fabricated in a 28-nm CMOS bulk technology. The unit PA uses low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$</tex-math> </inline-formula> transformer-based coupled-resonator networks to realize wideband matching. The measured results of the PA prototype demonstrate the peak gain of 22.6 dB, the saturated output power of 16.2 dBm, and the peak power added efficiency of 8.6% at 135 GHz with a 3-dB BW of 28 GHz from 124 to 152 GHz. Meanwhile, the total area of this PA die is merely 0.66 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 0.73 mm.

Development of a Photopolymer-Based Dielectric Nanocomposite for High Resolution Direct-Write Processes

A UV curable dielectric ink composition, which enables adaptable and high-resolution direct ink writing, is presented. The UV curable dielectric ink composition is designed using non-hazardous, low cost, commercially available ingredients. The ink manufacturing procedure was devised to require only fundamental lab equipment, without the need for complex reaction conditions or harmful processes. The UV dielectric ink composition was engineered to meet a range of direct ink writing application specific needs. These needs include a tailored rheology, cured film rigidity, dielectric performance, and adhesive ability. The versatility of this ink composition is demonstrated through the fabrication of dielectric bridges for printed coplanar waveguides, bare die chip integration, and interconnects between printed circuit board regions.

A compact and economical AMC backed antenna solution for wearable biomedical applications

AbstractA rectangular monopole antenna with an extended ground, excited by Coplanar Waveguide (CPW) and backed by a 6 × 6 array of fractal artificial magnetic conductor (AMC) unit cells, resonating at 5.8 GHz in Industrial, Scientific, and Medical (ISM) band, is presented in this manuscript. To attain the objective of proposing a compact and economical antenna solution for employment in wearable biomedical domain, a novel approach of utilizing both surfaces of the same dielectric for engraving antenna element as well as AMC array is adopted. It results in the elimination of layers of expensive substrate (RO3003) and of thick separator (foam) between antenna and AMC array. During measurement in open space, the proposed antenna system exhibited an impedance bandwidth of 570 MHz with a gain of 7.9 dBi. While a total realized gain of 7.5 dBi, amounting to a gain enhancement of about 3 dB as compared to that of monopole alone, is observed when the integrated antenna system is placed just over a three-layer rectangular human body equivalent model. Specific absorption rate values, as calculated at 5.8 GHz and averaged over 1 and 10 g of human tissue, are 0.0117 and 0.00244 W/kg, respectively. Obtained results strongly advocate the use of the proposed antenna system in smart wearable healthcare devices.

Modeling and Analytical Description of Parasitic Probe Effects in Measurements of Conductor-Backed Coplanar Waveguides

Abstract. On-wafer measurements are of fundamental importance to the characterization of active and passive devices at millimetre-wave frequencies. They have been commonly known to be ambitious and challenging due to the occurrence of parasitic effects originating from probes, multimode propagation, crosstalk between adjacent structures and radiation. While a lot of investigations have been performed for conventional coplanar waveguides (CPW) measured on ceramic chucks, the parasitic effects occuring in conductor-backed CPWs (CB-CPWs) have not been fully understood yet. Therefore, this paper presents a thorough study for CB-CPWs based on electromagnetic simulations. Additionally, this paper proposes an analytical description accounting for the probe geometries to predict the occurrence of resonance effects due to the propagation of the parallel-plate-line (PPL) mode. For the first time, a new analytical description including the effects of the probe geometries is presented and validated by both measurements and simulations.

Method to Change the Through-Hole Structure to Broaden Grounded Coplanar Waveguide Bandwidth.

A grounded coplanar waveguide (GCPW), as a millimeter wave special transmission line, can be used to calibrate broadband oscilloscope probes. A method to change the through-hole structure to widen the GCPW is investigated in this paper. The effect of the through-hole array on the band-width of the GCPW is investigated and verified using COMSOL Multiphysics simulation software. Finally, the S-parameters of the fabricated GCPWs are measured by a vector network analyzer, and the results show that they have an insertion loss > -3 dB and return loss < -10 dB in the frequency range of DC to 60 GHz, which satisfies the design requirements.

A Highly Transparent Flexible Antenna Based on Liquid Metal Mesh Film

In this paper, a convenient process for the fabrication of flexible liquid metal mesh films (LMMF) is proposed first. Then, the light transmittance and square resistance characteristics of LMMF are studied theoretically and experimentally. The light transmittance of the LMMF can reach 85% when the line width and spacing are 50 μm and 1000 μm, respectively. Furthermore, as an example of LMMF, a coplanar waveguide loop antenna is designed and fabricated that contains an LMMF with a line width of 50 μm and a line spacing of 500 μm. The measured square resistance and transmittance for the LMMF are 0.0456 Ω/sq and 72%, respectively. The measured peak gain of the antenna is 3.38 dBi while the average efficiency is 61%. The antenna’s working frequency covers most of the S-band, C-band, and X-band, as well as multiple channels of fifth generation (5G) communication. Therefore, the antenna can be used in fields such as radar and mobile communication. Uniquely, the fabricated antenna performs well in terms of light transmission, conductivity, and flexibility. In particular, it remains stable in stretching and bending deformation. As a highly light-transmissive stretchable flexible antenna, the antenna is equipped with various functions such as concealability, conformability, and reconfigurability. This LMMF-based antenna has good prospects for applications in the fields of flexible electronics and transparent electronics.

Proposal for quantum memory miniaturization in superconducting circuit QED

Superconducting circuit quantum electrodynamics is the main architecture for implementation of quantum processors. This work presents a proposal to miniaturize quantum memory devices by combining the quantum memory qubits encoded directly in the first two Fock states ${|0\ensuremath{\rangle},|1\ensuremath{\rangle}}$ and the bus channel in the same specially designed multimode cavity. One key feature of the resonant modes used for quantum memory is that the microwave current is localized, which facilitates the storage and retrieval of information in superconducting qubits while preventing crosstalk from other resonant modes. Frequency design and distinct coupling strengths in this kind of device are analyzed with electromagnetic simulations and numerical calculations. The quantum memory properties, e.g., storage speed, fidelity, and stability, are examined in four cases: (1) memory operation of single-qubit state, (2) disturbing effects, (3) coupling operation, and (4) entangled states storage. Decoherence time of the quantum processor can be extended to more than one order of magnitude longer than that without the memory. By integrating transmons with optimally designed coplanar waveguide multimode quantum memories, the present study could provide an optimistic perspective for the development of large-scale superconducting quantum processors.

Characterising nematic liquid crystals using a circular patch resonator

ABSTRACT Reconfigurable microwave material is a promising candidate for designing and manufacturing tunable microwave components. Nematic liquid crystals (NLC) are such materials since their permittivity can be tuned by an external electric field. However, many NLC mixtures were not properly characterised at higher frequency bands due to requiring a complex measurement setup. In this work, a novel method using circular patch resonator (CPR) is developed to measure the dielectric constant and loss tangent of NLCs at microwave frequencies. In addition to using the cavity model for the preliminary design and analysing the fringing effect for a better accuracy, full-wave simulations are employed to confirm the final design and aid the characteristic analysis. Three prototypes were fabricated and measured to reduce uncertainty from manufacturing defects. To avoid the possible damage when higher voltage is required for a large range tuning, a coupling mechanism is proposed between the microstrip line and coplanar waveguides (CPWs) to replace connection through vias. A high accuracy with an uncertainty of 0.02 for relative permittivity estimate has been demonstrated with experiment verification, approximate 80% improvement than other typical methods. The simple design and PCB-based manufacturing techniques can be widely employed to characterise the properties of newly-developed LC mixtures.

High-resistivity with PN interface passivation in 22 nm FD-SOI technology for low-loss passives at RF and millimeter-wave frequencies

In this paper, GlobalFoundries’ 22 nm fully depleted (FD) silicon-on-insulator (SOI) process is run on standard and high-resistivity wafers with a specially designed PN junctions interface passivation solution to counteract parasitic surface conduction (PSC) effects. Substrate quality is evaluated at RF and mm-wave frequencies through the on-wafer measurements of a set of passives: coplanar waveguides (CPW) lines, two inductors and a crosstalk structure. The effective resistivity (ρeff), losses and harmonics generated by the substrate are monitored based on CPW lines measurements, fabricated in either bottom or top metal layers. Several PN patterns are examined and they demonstrate effective passivation of the PSC, enabling ρeff values in the kΩ.cm range (up to ∼6 GHz) and > 100 Ω.cm up to ∼60 GHz. Patterns with intrinsic region separating the P- and N- doping regions show better performance, which can further be improved applying a reverse PN bias to widen the depletion regions. 50 Ω CPW line designed with PN interface passivation achieves 0.22 dB/mm lower propagation losses at 50 GHz than 50 Ω thin-film microstrip line in this technology. Impact of substrate quality on two spiral inductors is analyzed by comparing substrates with standard resistivity, high-resistivity with PSC and high-resistivity with PN junction solution. The high-resistivity substrate with PN junction solution shows an up to 62% and 15% increase in quality factor with respect to the standard substrates for the 5–20 GHz and 30–60 GHz inductors, respectively. Finally, measurements of a crosstalk structure show a strong isolation improvement in crosstalk through the substrate with the PN interface passivation solution.

Single-fed broadband CPW-fed circularly polarized implantable antenna for sensing medical applications.

Biomedical telemetry relies heavily on implantable antennas. Due to this, we have designed and tested a compact, a circularly polarized, a low-profile biomedical implantable antenna that operate in the 2.45 GHz ISM band. In order to keep the antenna compact, modified co-planar waveguide (CPW) technology is used. Slotted rectangular patch with one 45-degree angle slot and truncated little patch on the left end of the ground plane generate a frequency-range antenna with circular polarization. Using a 0.25-millimeter-thick Roger Duroid-RT5880 substrate with a thickness of εr = 2.2, tanδ = 0.0009 provides flexibility. The volume of the antenna is 21 mm x 13.5 mm x 0.254 mm (0.25λg × 0.16λg × 0.003λg). The antenna covers 2.35-2.55 GHz (200 MHz) in free space and 1.63-1.17 GHz (1.17 GHz) in epidermal tissue. With skin tissue that has more bandwidth, the (x and y)-axis bends of the antenna are also simulated via the simulation. Bended antenna simulations and measurements show excellent agreement. At 2.45 GHz, the skin-like gel had -10dB impedance and 3dB axial ratio (AR) bandwidths of 47.7 and 53.8%, respectively. The ultimate result is that the SAR values are 0.78 W/kg in skin over 1 g of bulk tissue, as determined by simulations. The suggested SAR values are lower than the FCC's maximum allowable limit (FCC). This antenna is small enough to be implanted in the body, making it perfect for biomedical applications.

Realization of superconducting transmon qubits based on topological insulator nanowires

Topological-material-based Josephson junctions have the potential to be used to host Majorana zero modes and to construct topological qubits. For operating the topological qubits at an appropriate timescale to avoid decoherence and quasiparticle poisoning, one would eventually go to the time domain and embed the topological qubits into quantum electrodynamic circuits. Here, we constructed a topological-insulator-nanowire-based transmon qubit and demonstrated its strong coupling to a coplanar waveguide resonator. The flux-tunable spectrum and Rabi oscillations with a qubit lifetime T 1 of ∼ 0.5 μ s were observed. Such a hybrid platform, containing topological materials and quantum electrodynamic circuits, can further be used to study the physical properties such as Majorana zero modes in topological quantum circuits.

Chemical mechanical planarization for Ta-based superconducting quantum devices

We report on the development of a chemical mechanical planarization (CMP) process for thick damascene Ta structures with pattern feature sizes down to 100 nm. This CMP process is the core of the fabrication sequence for scalable superconducting integrated circuits at a 300 mm wafer scale. This work has established the elements of various CMP-related design rules that can be followed by a designer for the layout of circuits that include Ta-based coplanar waveguide resonators, capacitors, and interconnects for tantalum-based qubits and single flux quantum circuits. The fabrication of these structures utilizes a 193 nm optical lithography along with 300 mm process tools for dielectric deposition, reactive ion etch, wet-clean, CMP, and in-line metrology—all tools typical for a 300 mm wafer CMOS foundry. Theprocess development was guided by measurements of the physical and electrical characteristics of the planarized structures. Physical characterization such as atomic force microscopy across the 300 mm wafer surface showed that local topography was less than 5 nm. Electrical characterization confirmed low leakage at room temperature, and less than 12% within wafer sheet resistance variation for damascene Ta line widths ranging from 100 nm to 3 μm. Run-to-run reproducibility was also evaluated. Effects of process integration choices including the deposited thickness of Ta are discussed.

A Conformal Mapping-Based Broadband Method to Extract Propagation Properties of Dielectrics Using Coplanar Waveguides With Air Pockets

In recent years, advances in material science for high-frequency electronics have generated novel materials that offer superior performance. Additive manufacturing (AM) has expanded the frontiers of microwave material manufacturing going beyond flat geometries and unique properties such as graded permittivity materials. Accurate electromagnetic (EM) material characterization for AM materials remains challenging given the printing volume constraints for manufacturing processes, as traditional EM property extraction techniques often require electrically large samples. Furthermore, loss extraction techniques typically cannot differentiate dielectric and conductor losses in waveguides. This paper presents a novel conformal mapping-based characterization technique using coplanar waveguides (CPW) with air pockets that allows for dielectric permittivity and dielectric loss extraction. The underlying principle of the techniques is to use a set of CPWs with different air slot depths to extract the loss behavior as a function of the slot depth. A new loss-slot rate metric is introduced to decouple the dielectric and conductor losses in the structure. The theoretical foundation of the technique is used to develop a physical-mathematical model for dielectric property extraction that is verified with simulations and experiments for materials with permittivity in the range 2.33–29, and loss tangents of 0.02–0.055. The average error for the equivalent capacitance of the CPW with air pockets (CPW-AP) between the presented model and simulated or measured data is 2.4% for all the studied cases. The experimental confirmation is performed with traditionally manufactured FR-4 and additively manufactured yttria-stabilized zirconia (YSZ) dielectrics up to 10 GHz.

Microwave Rotation Sensor Based on Reflection Phase in Transmission Lines Terminated With Lumped Resonators

A phase variation-based rotation sensor is presented in this article. The sensor is realized using a coplanar waveguide (CPW) terminated with a stepped impedance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit {LC}$ </tex-math></inline-formula> resonator. A circular dielectric slab is rotating above the resonator. Rotation of the slab modifies the overall capacitance and, thus, the input impedance of the resonator. This, in turn, modifies the phase of the reflection coefficient, which is translated to the rotation angle. The sensor’s linearity is eventually enhanced by tapering the width of the capacitive metallic patch along the rotation direction. The operation and sensing performance are studied in detail, using a circuit-based analysis and electromagnetic (EM) simulations. The designed sensor is capable of detecting the direction of rotation. A sensor prototype is fabricated and experimentally measured to prove the developed design and analysis procedure.

Realization of a novel dual-band bandpass filter with coupled series gaps and stepped impedance complementary split ring resonators

In this article, a bandpass filter (BPF) is proposed by etching stepped impedance complementary split ring resonators (SICSRRs) pairs in parallel with series gaps on the top side of a coplanar waveguide (CPW). The Nicolson-Ross-Weir (NRW) method is used to analyze the left-handed (LH) behavior of the filter. The effects of the resonators parameters on the left-handed BPF are studied. The parameters and number of the resonators are adjusted properly to obtain the desired filter characteristics. Split ring resonators (SRRs) are magnetically coupled to the BPF to realize a novel left-handed dual-band bandpass filter. Besides, The dual-band filter is described by means of the lumped-element equivalent circuit model. Also, the quasi-static analysis is used to obtain the equations for the resonant frequencies of the resonators. The efficient electrical size of the dual-band filter is 0.51λg × 0.42λg where λg represents the guided wavelength at the first passband center frequency. The prototype of the compact dual-band BPF is fabricated and measured. The measured results reveal low insertion loss and high return loss at the passbands along with wide upper stopband attenuation. The measured result is in a good agreement with the corresponding simulation result.

A Broadband Circularly Polarized Single-Layer Metasurface Antenna Using Characteristic-Mode Analysis

In this work, we propose a low-profile single-layer coplanar waveguide (CPW)-fed metasurface (MTS) antenna with broadband circular polarization (CP) radiation. With the help of characteristic-mode analysis (CMA), a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {3}\times \textbf {4}$ </tex-math></inline-formula> MTS is analyzed to reveal the useful modes supported by the structure. Consequently, two modes with orthogonal current distribution, broadside radiation, and nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{90}^{\circ} $ </tex-math></inline-formula> phase difference over a wide frequency band are chosen as operation modes. Moreover, the modal near field of the aforementioned modes shows that, unlike conventional microstrip patches, the entire proposed MTS supports two kinds of extraordinary TM modes, namely, e-TM30 and e-TM04. Accordingly, a rotated CPW feeding line is used to excite the two modes without adding an extra layer as reported in the literature, making the design simpler and easier to manufacture. Based on that, a low profile antenna of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {0.058}\lambda _{0}$ </tex-math></inline-formula> has been designed and fabricated. The measured results show an impedance bandwidth (IBW) of 25% (4.870–6.26 GHz), 3 dB axial ratio (AR) band of 19.42% (5.30–6.44 GHz), and a maximum gain of 8 dBi.