Low-loss Substrate Research Articles

Symmetric Engineered High Polarization-Insensitive Double Negative Metamaterial Reflector for Gain and Directivity Enhancement of Sub-6 GHz 5G Antenna.

A symmetric engineered high polarization-insensitive double negative (DNG) metamaterial (MM) reflector with frequency tunable features for fifth-generation (5G) antenna gain and directivity enhancement is proposed in this paper. Four identical unique quartiles connected by a metal strip are introduced in this symmetric resonator that substantially tunes the resonance frequency. The proposed design is distinguished by its unique symmetric architecture, high polarization insensitivity, DNG, and frequency tunable features while retaining a high effective medium ratio (EMR). Moreover, the suggested patch offers excellent reflectance in the antenna system for enhancing the antenna gain and directivity. The MM is designed on a Rogers RO3010 low loss substrate, covering the 5G sub-6GHz band with near-zero permeability and refractive index. The performance of the proposed MM is investigated using Computer Simulation Technology (CST), Advanced Design Software (ADS), and measurements. Furthermore, polarization insensitivity is investigated up to 180° angles of incidence, confirming the identical response. The 4 × 4 array of the MM has been utilized on the backside of the 5G antenna as a reflector, generating additional resonances that enhance the antenna gain and directivity by 1.5 and 1.84 dBi, respectively. Thus, the proposed prototype outperforms recent relevant studies, demonstrating its suitability for enhancing antenna gain and directivity in the 5G network.

Metamaterial-inspired quintuple band printed patch antenna for dense communication networks

A compact 15 mm × 15 mm multi-band metamaterial-inspiredprinted antenna, composed of a simple microstrip antenna and a metamaterial superstate, is developed to accommodate nowadays advanced wireless communication devices and networks, where multi-functional tasks are simultaneously performed in different frequency ranges efficiently. A quintuple homocentric circular split ring resonator is explicitly designed as a band enhancer metamaterial superstate. The metamaterial geometry and orientation associated with the antenna location and radiating are optimized for the greatest consequence, where the resonances electrically and magnetically couple with the antenna radiation, generating quintuple bands in the X band: 8–12 GHz. The main lobe directions indicate an excellent directional propagation. This metamaterial-inspired antenna was designed and fabricated using a low cost commercial FR4 substrate offering a good cost margin for potential mass production. Four of five bands have a gain greater than 6dBi, which can be improved by using low-loss substrate. The measured and simulated results are in good agreement.

Near-field probing of image phonon-polaritons in hexagonal boron nitride on gold crystals.

Near-field mapping has been widely used to study hyperbolic phonon-polaritons in van der Waals crystals. However, an accurate measurement of the polaritonic loss remains challenging because of the inherent complexity of the near-field signal and the substrate-mediated loss. Here we demonstrate that large-area monocrystalline gold flakes, an atomically flat low-loss substrate for image polaritons, provide a platform for precise near-field measurement of the complex propagation constant of polaritons in van der Waals crystals. As a topical example, we measure propagation loss of the image phonon-polaritons in hexagonal boron nitride, revealing that their normalized propagation length exhibits a parabolic spectral dependency. Furthermore, we show that image phonon-polaritons exhibit up to a twice longer normalized propagation length, while being 2.4 times more compressed compared to the case of the dielectric substrate. We conclude that the monocrystalline gold flakes provide a unique nanophotonic platform for probing and exploitation of the image modes in low-dimensional materials.

Design and Development of Substrate Integrated Waveguide Based Filtenna for X Band Application

In this paper, substrate integrated waveguide based filtenna operating at X band is proposed. The model is designed on a low-loss dielectric substrate having a thickness of 1.6 mm and comprises shorting vias along two edges of the substrate walls. To realize a bandpass filter, secondary shorting vias are placed close to primary shorting vias. The dimension and position of the vias are carefully analyzed for X band frequencies. The model is fabricated on Roger RT/duroid 5880 and the performance characteristics are measured. The proposed model achieves significant impedance characteristics with wider bandwidth in the X band. The model also achieves a maximum gain of 7.46 dBi in the operating band, thus making it suitable for X band applications.

Design of Miniaturized 5G SISL BPFs With Wide Stopband Using Differential Drive Inductor Resonators

In this article, the differential inductor, widely used as an inductive element, is modified as a resonator. This differential drive inductor resonator (DDIR) can achieve miniature size and extension of second-order mode based on the different electric field distributions on different modes. The second- and fourth-order bandpass filters (BPFs) are designed and fabricated with DDIRs at the promising 5G frequency band of 700-MHz spectrum. The low-loss platform substrate integrated suspended line (SISL) is adopted. The filters are centered at 0.76 GHz/ 0.77 GHz. The footprint areas are only 0.0023 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0052\lambda g^{2}$ </tex-math></inline-formula> without using any lumped elements or substrate with high permittivity. The second-order mode is 5.7/3.92 times the working band without introducing any extra method to broaden the stopband. To improve the rejection of stopband, a T-shaped coupling structure is first proposed on SISL to get the desired location of zeros by weakening the electric coupling and enhancing the magnetic coupling. The comparable version of second- and fourth-order BPFs with T-shaped coupling structure are designed and fabricated. The 20-dB roll-off rate has been decreased by 58.8% and 66.1%.

Impact of substrate resistivity on spiral inductors at mm-wave frequencies

The quality factor (Q) of two inductors for 5–60 GHz applications fabricated in an industrial back-end of line (22FDX® from GlobalFoundries) with thick Cu metal layers on top of several Si substrates of different bulk resistivities is analyzed in this paper. The low frequency RF inductor shows an improvement of up to 44% in Q with a high-resistivity substrate. However, no significant improvement is observed for the high-frequency MMW fabricated inductor. This is identified to be due to lower electric field concentration in the substrate due to the small geometry of this MMW inductor that is realized in the top metal Cu layer. Nevertheless, simulations show that a 30% improvement can be achieved with a low loss substrate when designing a MMW inductor as a stacked coil of all BEOL thick metal layers.

A Conformal Frequency Reconfigurable Antenna with Multiband and Wideband Characteristics.

A compact flexible multi-frequency antenna for smart portable and flexible devices is presented. The antenna consists of a coplanar waveguide-fed slotted circular patch connected to a rectangular secondary resonator (stub). A thin low-loss substrate is used for flexibility, and a rectangular stub in the feedline is deployed to attain wide operational bandwidth. A rectangular slot is etched in the middle of the circular patch, and a p-i-n diode is placed at its center. The frequency reconfigurability is achieved through switching the diode that distributes the current by changing the antenna’s electrical length. For the ON state, the antenna operates in the UWB region for −10 dB impedance bandwidth from 2.76 to 8.21 GHz. For the OFF state of the diode, the antenna operates at the ISM band (2.45/5.8 GHz), WLAN band (5.2 GHz), and lower X-band (8 GHz) with a minimum gain of 2.49 dBi and a maximum gain of 5.8 dBi at the 8 GHz band. Moreover, the antenna retains its performance in various bending conditions. The proposed antenna is suitable for modern miniaturized wireless electronic devices such as wearables, health monitoring sensors, mobile Internet devices, and laptops that operate at multiple frequency bands.

A 32-Bit Single Quadrant Angle-Controlled Chipless Tag for Radio Frequency Identification Applications.

A 32-bit chipless RFID tag operating in the 4.5–10.9 GHz band is presented in this paper. The tag has a unique multiple-arc-type shape consisting of closely packed 0.2 mm wide arcs of different radii and lengths. The specific tag geometry provides multiple resonances in frequency domain of an RCS plot. A frequency domain coding technique has also been proposed to encode the tag’s RCS signature into a 32-bit digital identification code. The tag has an overall dimension of 17.9 × 17.9 mm2, resulting in a high code density of 9.98 bits/cm2 and spectral efficiency of 5 bits/GHz. The proposed tag is built on a low loss substrate bearing a very small footprint, thereby making it extremely suitable for large-scale product identification purposes in future chipless RFID tag systems.

Research on the reflection-type ELC-based optomechanical metamaterial.

In this paper, we propose a new kind of optomechanical metamaterial based on a planar ELC-type absorbing structure fabricated on the low-loss flexible substrate. The nonlinear coupling mechanism and nonlinear response phenomenon of the proposed optomechanical metamaterial driven by electromagnetic induced force are analyzed theoretically. The mechanical deformation/displacement and the mechanical resonance frequency shift of the metamaterial unit deposed on the flexible substrate are also numerically and experimentally demonstrated to reveal the coupling phenomenon of electromagnetic field and mechanical field. These results will help researchers to further understand the multi-physics interactions of optomechanical metamaterials and will promote the developments of new type of metasurface for high-efficiency dynamic electromagnetic wave controlling and formatting.

위성 Synthetic-Aperture Radar (SAR) 시스템용 X-밴드 이중 편파 마이크로스트립 패치 부배열 안테나

In this study, a high-performance, dual linearly polarized patch array antenna is presented for satellite synthetic aperture radar (SAR) applications. The antenna features an aperture-fed stacked patch as the radiation element and a stripline feeding network. A high-performance and low-loss dielectric substrate RF-35 by Taconic, and a honeycomb substrate is used. The honeycomb substrate is used to maximize the impedance bandwidth and decrease the insertion loss of the antenna. The proposed antenna offers exceptional isolation between the antenna’s ports in excess of 55 dB owing to its stripline feeding network. The via stitching technique is utilized to suppress the parallel-plate mode excited by the discontinuities in the stripline. The antenna is designed to possess a wide impedance bandwidth. A prototype antenna of size 2×4 elements, which operates in the X-band, is fabricated. Its impedance and radiation performance are experimentally verified, and the results are presented. The antenna exhibits a 15.7 dB peak gain and more than 40 dB of cross-polarization discrimination. In addition, a wide bandwidth of 19.4 % at a −10 dB return loss (RL) level is obtained.

A 28 GHz 2 × 2 Antenna Array with 10 Beams Using Passive SPDT Switch Beamforming Network.

In this paper, a dual-polarized four-port 2 × 2 series fed antenna array operating at 28 GHz with beam-switching capability is proposed. The antenna array uses a simple passive beamforming network to switch the main beam. The presented antenna design is suitable for 5G user equipment and high data rates applications by which it has a compact size with low cost and complexity. The size of the antenna is 37.2 × 37.2 mm including the ground plane, and it produces 10 different switched beams by using only two simple 3 dB/90 couplers which create the required amplitudes and phase excitations for the antenna elements. A one-port simple feeding mechanism including Peregrine PE42525 SPDT switch modules and a power divider is used to generate and measure the 10 switched beams. The antenna design is implemented on a two-layer 0.203 mm thick low-loss ( = 0.0027) Rogers 4003C substrate, and it has a measured 10 dB impedance bandwidth of 4 GHz (14.3%, from 26 GHz to 30 GHz) for all ports. Measured peak isolation between any dual-polarized ports of the antenna is better than 30 dB. The antenna has an average measured realized gain of 8.9 dBi and around 10 dB side lobe level (SLL) for all beams. The antenna has 3-dB coverage of 80 to 90 in 2D space and it has a maximum of ±26 beam-steering angle. The antenna is designed and simulated using Ansys HFSS and fabricated using regular PCB processing.

Broadband complex permittivity and conductivity measurements in the millimeter-wave bands over variable temperatures using a balanced-type circular disk resonator

A broadband measurement system is developed to address the issue of temperature dependence of the complex permittivity and conductivity of low-loss substrates in the millimeter-wave bands for fifth/sixth generation wireless communication applications. The developed system can provide broadband material measurements from less than 20 GHz to over 100 GHz over variable temperatures by utilizing higher order mode resonances of a balanced-type circular disk resonator (BCDR). The broadband measurement capability of the developed system is attributed to the mode-selective behavior of the BCDR over a wideband. To demonstrate the developed system, we measure the complex permittivity of the following three substrate materials over variable temperatures from 25 °C to 100 °C: cyclo-olefin polymer (COP), ceramic-filled polytetrafluoroethylene composites, and fused silica. Furthermore, the temperature dependence of the conductivity of the surface-mounted metal is characterized for the COP substrate. The measurements indicate that the loss tangents and conductivities of the substrates increase and decrease, respectively, with the temperature and frequency in the millimeter-wave bands. The full-wave simulations using the measured complex permittivity and conductivity of the COP substrate reveal that the propagation loss of the microstrip line using the COP substrate increases with the temperature and frequency and that the increase in the loss is primarily attributed to the decrease in the conductivity.

Design and Construction of a Low Loss Substrate Integrated Waveguide (SIW) for S Band and C Band Applications

Design and Construction of a Low Loss Substrate Integrated Waveguide (SIW) for S Band and C Band Applications

Active Control of Nanodielectric-Induced THz Quasi-BIC in Flexible Metasurfaces: A Platform for Modulation and Sensing.

A bound state in the continuum (BIC) is a nonradiating state of light embedded in the continuum of propagating modes providing drastic enhancement of the electromagnetic field and its localization at micro-nanoscale. However, access to such modes in the far-field requires symmetry breaking. Here, it is demonstrated that a nanometric dielectric or semiconductor layer, 1000times thinner than the resonant wavelength (λ/1000), induces a dynamically controllable quasi-bound state in the continuum (QBIC) with ultrahigh quality factor in a symmetric metallic metasurface at terahertz frequencies. Photoexcitation of nanostrips of germanium activates ultrafast switching of a QBIC resonance with 200% transmission intensity modulation and complete recovery within 7 ps on a low-loss flexible substrate. The nanostrips also form microchannels that provide an opportunity for BIC-based refractive index sensing. An optimization model is presented for (switchable) QBIC resonances of metamaterial arrays of planar symmetric resonators modified with any (active) dielectric for inverse metamaterial design that can serve as an enabling platform for active micro-nanophotonic devices.

Wearable Dual-Band High-Gain Low-SAR Antenna for Off-Body Communication

A wearable dual-band folded-ring antenna, that has directional radiation pattern and offers high-gain, high-efficiency, and low-specific absorption rate (SAR) performance, is presented for 2.45/3.45 GHz off-body communication. The proposed antenna is comprised of two substrates; a folded-ring antenna as a main radiator is printed on a low-loss rigid substrate and a conductive textile is attached to a felt substrate. The conductive textile is used as the ground plane and as a protective shield to prevent incidental electromagnetic waves from propagating toward the human body. The felt substrate provides a comfortable surface for wearers. The antenna performance is verified and shows very good agreement both in free space and on phantom body environment. The measured bandwidths of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> on human body are 5.76% and 4.7% at each frequency band. The maximum broadside gains within the operating bandwidth are 5.1 and 8.6 dB, respectively. The measured radiation efficiencies on human phantom are 91% and 94%, respectively. The SAR values at lower mode based on US and EUR standards under 1 g average and 10 g average are 0.2 and 0.1 W/kg, respectively. At higher mode, the SAR values are 0.1 and 0.04 W/kg, respectively.

Flexible millimeter‐wave Butler matrix based on the low‐loss substrate integrated suspended line patch hybrid coupler with arbitrary phase difference and coupling coefficient

In this paper, a millimeter-wave Butler matrix with flexible phase differences is proposed using the substrate integrated suspended line technology. To begin with, a low-loss substrate integrated suspended line (SISL) circular patch coupler consisting of four circular sectors is presented, achieving arbitrary phase difference and coupling coefficient by adjusting the angle and radii of the sectors. Based on the proposed coupler, two prototypes of the SISL Butler matrix are designed, fabricated and measured for the demonstration. In prototype I, the crossovers are removed and a flexible phase difference is obtained with an area size of 2.5 λg × 2.8 λg. In prototype II, both the crossovers and 45° phase shifters are removed and the phase differences of ±45° and ±135° are obtained with an area size of 1.86 λg × 2.24 λg. Low crosstalk between components and minimal radiation loss can be achieved by the SISL self-packaged characteristic and electromagnetic shielding. For both prototypes, the measured insertion losses are less than 2 dB at 26 GHz, including the loss of transitions and connectors, and the measured phase errors are less than ±10° within a bandwidth of more than 10%. The proposed Butler matrix shows the advantages of compact size, low loss and high integration.

Broadband and wide angle microwave absorption with optically transparent metamaterial

Abstract An optically transparent metamaterial for microwave absorber with wide operation angle, polarization insensitivity, broadband and high absorptivity was demonstrated. The metamaterial is composed of planar indium tin oxide (ITO) structures and low-loss glass substrates. By tailoring the reflection response of ITO patterns and the position of arrayed ITO resonators between quartz glass dielectric substrates, more than 90% absorption in the frequency ranges of 8–20 GHz and within a wide angular range from 0° to 60° is achieved. Meanwhile, by employing transparent substrates, including soda-lime glass and quartz glass, good optical transmittance (80%) is obtained. The dielectric loss of quartz glass is lower than other dielectric substrates, which implies that the high absorptivity was achieved mainly due to the contribution of planar ITO metamaterial structure. The reflectivity of proposed MMAs is simulated and measured experimentally. Both of which demonstrate excellent absorption performance of the metamaterial. The optically transparent broadband metamaterials absorber with high absorptivity and polarization insensitivity opens a horizon of potential applications in many fields.

A tightly coupled dipole array used for radiation power improvement on finite radiation aperture

Radiation power of an electromagnetic wave plays a decisive role in its transmission distance. Traditionally, the radiation power can be improved by expanding the radiation aperture size of the antenna array or increasing input power of the unit cell. However, the radiation aperture size is always restricted by assembly space. The input power improvement of the unit cell is always limited by the signal source. It is difficult to improve radiation power on a finite radiation aperture. However, the radiation power on a finite radiation aperture is related closely to the number of antenna elements and the radiation efficiency of the antenna array. It is useful to arrange more elements and improve radiation efficiency of the antenna array to improve the radiation power on a finite radiation aperture. Wideband wide-angle scanning phased array is able to make full use of a finite radiation aperture. The wide-angle scanning properties make it possible for the radiated power to cover a wide area. In this paper, a compact wideband wide-angle scanning tightly coupled dipole array (TCDA) is proposed. A high permittivity substrate and compact wideband balun are used for miniaturizing the antenna array. The period of the unit cell is only 0.144&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; × 0.144&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; (&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; is the wavelength at the highest operation frequency in free space). Parameters of the balun are optimized to improve impedance matching between the balun and the antenna array. Two bilateral frequency selective surfaces (FSSs) are used to replace traditional dielectric superstrate to improve the impedance matching between the antenna array and free space. A low-loss dielectric substrate is used to reduce dielectric loss of the antenna array. In these ways, the radiation efficiency is greatly improved. The simulation results show that the proposed antenna array operates at 1.7–5.4 GHz (3.2:1) while scanning up to 65° in the E plane, 45° in the H plane and 60° in the D plane with following a rigorous impedance matching criterion (active VSWR &lt; 2). A 16 × 16 prototype array is fabricated and measured. Good agreement is achieved between the simulation results and the measurement results. Compared with the designs in the literature, the proposed antenna array has an excellent performance in radiation power on a finite radiation aperture.

A Triple-Band Dual-Open-Ring High-Gain High-Efficiency Antenna for Wearable Applications

This paper presents a triple-band open-ring high-gain high-efficiency antenna for 2.45/3.0/3.45 GHz wearable applications. The proposed antenna operates at 2.45 GHz for Industrial, Specific, and Medical (ISM) applications, 3.0 GHz for military applications, and 3.45 GHz for Worldwide Interoperability for Microwave Access (WiMAX) applications. The proposed triple-band antenna has excellent features for off-body communication, which has directional radiation pattern, high gain, high efficiency, low-specific absorption rate (SAR), and comfortability for wearers. In order to attain these features, the antenna structure consists of two substrates, a rigid substrate and a textile substrate. Two open-ring radiators and a 1 by 2 power divider feeding network are printed on a low-loss rigid substrate. In addition, a square conductive textile is adhered on the backside of the textile substrate. The open-ring radiator generates triple-band at 2.45, 3.0, and 3.45 GHz, in which the inner open-ring excites two resonant modes at high frequencies of 3.0 and 3.45 GHz. The outer open-ring excites a single resonant mode at a low frequency of 2.45 GHz. The outer annular ring is shorted to the ground plane by a shorting pin to miniaturize the antenna size and additionally maintain antenna stability. The conductive textile works as a full-ground plane or protective shield to reduce the electromagnetic waves toward the human body. Therefore, the SARs are significantly minimized. The compatibility of the proposed antenna for off-body communication is verified by measuring the antenna performance in free-space and on phantom/human bodies. The simulated and measured results show very good agreement.

UV Flash Sintering of Aerosol Jet Printed Silver Conductors for Microwave Circuit Applications

Recently, there has been significant research focus on the design of high functional density electronic systems, especially for 5G applications. In parallel, to address accurate, high-quality, fine-resolution circuit geometry requirements, increased research into additive manufacturing (AM) printing techniques, such as aerosol jet printing (AJP), has emerged. The issues are complicated by low-loss flexible substrates, such as liquid crystal polymers (LCPs), which are commonly used in the design of high-frequency circuits and systems. These substrates cannot be taken through high sintering temperature processes that are commonly required for silver inks. To avoid permanent damage, it is essential that the sintering temperature remains below the glass transition temperature ( ${\text{T}}_{g}$ ) of the substrates. Recent work on LCP substrates has demonstrated 10%–20% bulk silver (Ag) conductivity by using low-temperature thermal sintering techniques. This article investigates the use of a rapid ultraviolet (UV) flash annealing technique to achieve high conductivity of Ag on LCP for use in high-frequency circuits while maintaining the integrity of the substrate. Results are compared against thermally sintered films. The resulting conductivity was studied as a function of UV exposure time and energy, printed film thickness, surface roughness of the substrate, and multilayer deposition.