Operating Frequency Range Research Articles

Design of a 39-GHz compact bi-directional variable gain amplifier in 65-nm CMOS

This paper presents a differential two-stage 39-GHz bi-directional variable gain amplifier (Bi-VGA) for 5G mm-Wave applications. Based on a phase compensated bi-directional structure with tail current tuning technique, a variable gain cell with small phase variation and compact area is realized. To boost the gain and ease the impedance matching, the cross-coupled transistor pairs are adopted. Analysis and simulations are undertaken to illustrate the working mechanism of accurate gain control and low phase variation. The measured Bi-VGA achieves peak gain of 15.6 dB with 3-dB bandwidth over 35–45 GHz, covering the 5G 39-GHz band (37–43.5 GHz), and a maximum OP1dB of 3.5 dBm. Fabricated in 65-nm CMOS process, the Bi-VGA consumes 67 mW from a 1.2 V power supply with a small core area of 0.46 × 0.14 mm2, and its minimum noise figure is about 6.4 dB at the maximum gain state. Across a gain tuning range of 12 dB, the phase variation is less than 6.1° over the operating frequency range.

An antenna array utilizing slotted conductive slab: inspired by metasurface and defected ground plane techniques for flexible electronics and sensors operating in the millimeter-wave and terahertz spectrum

This paper describes an innovative design of an antenna array that is metamaterial inspired using sub-wavelength slots and defected ground structure (DGS) for operation over millimeter-wave and terahertz (THz) spectrum. The proposed antenna array consists of a 2 × 4 array of conductive boxes on which are implemented rectangular slots. The presence of dielectric slots introduces resonant modes within the structure. These resonant modes result in enhancing the electromagnetic fields within the slots, which radiate energy into free space. The resonant frequencies and radiation patterns depend on the specific geometry of the slots and the dielectric properties. The antenna array is excited through a single microstrip line. The radiating elements in the array are interconnected to each other with a microstrip line. Unwanted mutual coupling between the radiating elements can degrade the performance of the antenna. This was mitigated by defecting the ground plane with rectangular slots. It is shown that this technique can enhance the array’s reflection coefficient over a wider bandwidth. The array was constructed on polyimide substrate having dielectric constant of 3.5 and thickness of 20 μm. The design was modelled, and its performance verified using an industry standard electromagnetic package by CST Studio Suite. The proposed array antenna has dimensions of 20 × 10 mm2 and operates between 80 and 200 GHz for radiation gain better than 4 dBi and efficiency above 55%. The peak radiation gain and efficiency are 7.5 dBi and 75% at 91 GHz, respectively. The operational frequency range of the array corresponds to a fractional bandwidth of 85.71%.

Performance analysis of all-optical 1-bit comparator using 2D-PhC nonlinear ring resonators based on threshold switching method

ABSTRACTIn this research, an all-optical 1-bit comparator (AOCMP) is designed using two-dimensional photonic crystals (2D-PhCs) nonlinear ring resonators (NRRs), and its performance is analyzed based on the threshold switching method. By optimizing the structural parameters of NRRs, such as the refractive index and radius of the rods, this resonator can operate with desired wavelength (1550 nm) within the operating frequency range determined by the transverse magnetic (TM) band diagram. The performance of the proposed AOCMP is analyzed in terms of various factors such as optical switching power, bit rate, time delay, and ON-OFF contrast ratio that are calculated using a finite difference time domain (FDTD) simulation. Also, the operating frequency range (the wavelength range of 1355–2178 (nm)) is investigated using the plane wave expansion (PWE) method. The optimized optical device has exhibited a high contrast ratio of 10.36 dB within a very small size of 325 μm2.

A New Technique for Broadband Matching of Open-Ended Rectangular Waveguide Radiator.

The maximum reflection at an open end of a standard rectangular waveguide is about -10 dB in its operating frequency range. It is often used without matching. For critical applications, it is desirable to further reduce the reflection coefficient. In this paper, a new technique is presented for the broadband impedance matching of an open-ended rectangular waveguide. The proposed technique employs three thin capacitive matching elements placed at proper intervals via a low-loss dielectric material. The capacitance of, and distance between, the matching elements are optimized for broadband impedance matching using a simulation tool. Based on the proposed technique, two design examples are presented for the matching of a WR75 waveguide radiator. A reflection coefficient of less than -16 dB and -20 dB has been achieved over a ratio bandwidth of 2.13:1 and 1.62:1, respectively.

Designing Advanced Multistatic Imaging Systems with Optimal 2D Sparse Arrays

This study introduces an innovative optimization method to identify the optimal configuration of a sparse symmetric 2D array for applications in security, particularly multistatic imaging. Utilizing genetic algorithms (GAs) in a sophisticated optimization process, the research focuses on achieving the most favorable antenna distribution while mitigating the common issue of secondary lobes in sparse arrays. The main objective is to determine the ideal configuration from specific design parameters, including hardware specifications such as number of radiating elements, minimum spacing, operating frequency range, and image separation distance. The study employed a cost function based on the the point spread function (PSF), the system response to a point source, with the goal of minimizing the secondary lobe levels and maximizing their separation from the main lobe. Advanced simulation algorithms based on physical optics (PO) were used to validate the presented methodology and results.

Broadband metasurface based on metallic stereo split-ring structure for full-space terahertz beam deflection and focusing effect

In this paper, we proposed an all-metal metasurface that enables circular polarization (CP) conversion and wavefront manipulation of the both transmitted and reflected terahertz (THz) waves over a wide frequency range. The proposed metasurface consists of a periodic array of the metallic stereo split-ring (MSSR) structure adhered on an ultrathin dielectric substrate made of benzocyclobutene (BCB). Numerical simulations show that the incident CP waves through the proposed MSSR can be converted into their orthogonal components in the full-space in a broadband range, with transmission conversion coefficients exceeding 40 % and reflection conversion coefficients exceeding 50 % between 0.8 and 1.1 THz (relative bandwidth of 31.6 %). Based on the geometric phase principle, 2π-phase full coverage can be realized by changing the rotation angle of the MSSR structure in the operating frequency range. Specifically, to demonstrate the multifunctional wavefront manipulation, we numerically simulated the anomalous deflection of THz beams and the full-space planar focusing functionality, respectively. Our research provides a valuable reference for the study of multifunctional components that possess full-space amplitude and phase modulation capabilities. This work holds particular significance in the field of device research in the THz region.

Negative capacitors and inductors enabling wideband waveguide metatronics

Waveguide metatronics, known as an advanced platform of metamaterial-inspired circuits, provides a promising paradigm for millimeter-wave and terahertz integrated circuits in future fifth/sixth generation (5/6G) communication systems. By exploiting the structural dispersion properties of waveguides, a lumped type of waveguide integrated elements and circuits could be developed in deep subwavelength scales with intrinsic low loss and low crosstalk. In this study, we focus on constructing negative capacitors and inductors for waveguide metatronics, effectively expanding the operating frequency range of waveguide integrated circuits. The incorporation of negative elements enables wideband impedance matching in waveguide, which have been both theoretically explored and experimentally validated within the waveguide metatronics paradigm. Furthermore, we have demonstrated that the negative elements can also be realized in the optical domain through the utilization of a silicon waveguide with photonic crystal cladding, indicating the feasibility and universality of wideband waveguide metatronics. The negative lumped elements could boost the progress of the waveguide metatronic technique, achieving superior performance on the conventional lumped circuits within waveguides that solely rely on positive elements.

A novel slotted dumbbell-shaped dielectric resonator antenna with enhanced bandwidth for C-band and 5G sub-6 GHz applications

Abstract This manuscript presents a novel aperture-coupled fed slotted dumbbell-shaped (SDS) dielectric resonator antenna (DRA) with enhanced bandwidth for 5G sub-6 GHz, short-range wireless communications, and C-band applications. The DRA is excited by HEM11δ mode. The proposed SDS-DRA is designed by assembling the four frustums of conical DRAs with the base and apex of one on top of another. The measured operating frequency of SDS-DRA is from 3.5 GHz to 9.6 GHz (impedance bandwidth of 93.1 %). The SDS-DRA shows a peak gain of 9.7 dBi in the operational frequency range, with an average peak gain of 6.02 dBi. The antenna’s average radiation efficiency is found to be 84.6 %. The proposed SDS-DRA produces omnidirectional-like radiation patterns with significantly low cross-polarization in the broadside direction. The size (l × w × h) of the proposed SDS-DRA is 1.55λ g × 1.55λ g × 0.67λ g where, λ g is the guided wavelength in mm at 3.5 GHz for effective permittivity (ϵ eff ), 7.1. To validate the simulation results, the proposed antenna structure is built, and its performance is measured. The findings of simulation and measurement results are found to be quite congruent.

Modeling and controlling a rotary piezo actuator

In this study, a novel piezo rotary stick–slip actuator was designed and investigated. This approach employs two piezo actuators to deform a flexible mechanism in order to generate a variable stick-and-slip force that drives the rotor. The compliant mechanism is composed of the bridge amplifiers and lever mechanism. They are arranged in sequence to amplify the piezo actuator's displacement. Hence, the operating range of the actuator, which includes rotation speed and resolution, can be increased. To optimize the fundamental dimensions of the actuator, the method of finite elements was investigated. The mechanical structure is detailed, the operating principle is elucidated, and a dynamic model is developed. From experimental data, the dynamic model of the structure is identified. The actuator achieves an angular displacement resolution of 0.028 degree at an applied voltage of 45 V and an operating frequency range up to 140 Hz, allowing it to be employed in applications requiring high precision positioning. Besides, the closed-loop control scheme is proposed to control the actuator in both directions. The simulation and experimental results have demonstrated that the position of the stick–slip actuator can be effectively controlled through this proposed controller. This is expected to increase the potential application of the stick–slip actuator in industrial practice.

The Reference Wideband Inductive Current Transformer

The aim of this paper is to show that the developed inductive current transformer may ensure the required wideband transformation accuracy and it may be applied, as the reference source, in the measuring system for the evaluation of the transformation accuracy of inductive current transformers for harmonics of distorted current. This device ensures 5 A and 1 A RMS secondary currents to provide the opportunity to use the differential measuring setup. Such solutions are characterized by the significantly reduced measurement uncertainty in relation to the comparative measurements made between two current/voltage channels. The problems required to ensure the high wideband transformation accuracy, including the self-generation phenomenon of the low order higher harmonics to the secondary current and a too-low frequency range of operation, were overcome in the design process. The values of its ratio error and the phase displacement of the developed reference wideband inductive current transformer did not exceed ±0.2%/° up to 1 kHz, ±0.4%/° from 1 kHz up to 1.5 kHz and ±0.5%/° from 1.5 kHz up to 3 kHz, as is required to perform the test procedure in accordance with the optional requirements for the inductive current transformers defined in the new edition of the standard IEC 61869-1.

A Novel Low-frequency Radio Astronomical Observation Array (1 ∼ 90 MHz) and its First Light

The extremely low frequency (f < 40 MHz) is a very important frequency band for modern radio astronomy observations. It is also a key frequency band for solar radio bursts, planetary radio bursts, fast radio bursts detected in the lunar space electromagnetic environment, and the Earth’s middle and upper atmosphere with low dispersion values. In this frequency band, the solar stellar activity, the early state of the universe, and the radiation characteristics of the planetary magnetosphere and plasma layer can be explored. Since there are few observations with effective spatial resolution in the extremely low frequency, it is highly possible to discover unknown astronomical phenomena on such a band in the future. In conjunction with low frequency radio observation on the far side of the Moon, we initially set up a novel low-frequency radio array in the Qitai station of Xinjiang Astronomical Observatory deep in Tianshan Mountains, Xinjiang, China on 2021 August 23. The array covers an operating frequency range of 1 ∼ 90 MHz with a sensitivity of −78 dBm/125kHz, a dynamic range of 72 dB, and a typical gain value of 6 dBi, which can realize unattended all-weather observations. The two antennas due south of the Qitai Low-Frequency Radio Array were put into trial observations on 2021 May 28, and the very quiet electromagnetic environment of the station has been confirmed. So far, many solar radio bursts and other foreign signals have been detected. The results show that this novel low frequency radio array has the advantages of good performance, strong direction, and high antenna efficiency. It can play a unique role in Solar Cycle 25, and has a potential value in prospective collaborative observation between the Earth and space for extremely low frequency radio astronomy.

A Fibonacci Series Motivated Circularly Polarized L-Band Slotted Antenna for GNSS Application

This paper proposes a co-planar waveguide-fed circularly polarized L-band antenna for GNSS Applications. The Fibonacci series inspired us to decide the physical dimensions of the radiating structure. The proposed antenna with the dimensions of 60 × 40 × 0.8 mm3 is fabricated by etching out several slots from the patch and ground plane as well. The circular polarization (CP) behavior is observed from different shaped slots in the ground plane as well as in radiating patches. The experimental and simulation results revealed good agreement over the entire operating frequency range.

Tunable broadband terahertz beam splitting using gated graphene metasurfaces [Invited

Active control of split ratios in terahertz (THz) beam splitters holds substantial potential for applications in imaging and spectroscopy. In this study, we introduce an approach for electrically controlling THz beam splitting with near non-dispersive characteristics, using the metasurface hybridized with single-layer graphene. Specifically, the resonant frequency of the metasurface is meticulously chosen to provide an enhanced effective conductivity that is almost frequency-independent. Furthermore, the split ratio can be manipulated by adjusting the gate voltage applied to graphene, thereby altering the effective conductivity of the hybrid metasurface without affecting its non-dispersive transmission and reflection characteristics. The feasibility of our approach is confirmed by the near non-dispersive split ratio across a wide operating frequency range, from 0.5 to 1.5 THz. The demonstration of this efficient, broadband, and tunable beam splitting ability validates the potential of gated graphene metasurfaces for advanced THz applications.

Design of a Broadband Transition from a Coaxial Cable to a Reduced-Height Rectangular Waveguide

For miniaturization, rectangular waveguides with a reduced height are often required, along with a coaxial transition for signal launching. We present a simulation-based design of a broadband transition from a coaxial cable to a rectangular waveguide with the height(b)-to-width(a) ratio b/a ranging from 0.125 to 0.375. The proposed transition consists of a coaxial probe with a cylindrical head or a disk and two symmetrically placed tuning posts. To extend the operating frequency range, three sections of the rectangular waveguide are employed with properly chosen dimensions. Design examples are presented for the WR75 waveguide transition with a b/a of 0.125, 0.25, and 0.375, having a bandwidth of 83.4%, 92.7%, and 84.4%, respectively. Compared with previous works, our design offers the largest bandwidth in a right-angle coaxial-to-rectangular waveguide transition employing the aforementioned structure.

Some Practical Applications of Discretely Tunable Couplers’ Matrix Model

The findings of a research of the practical application of a previously developed model of a decametric waves discrete coupler are presented. Due to the high accuracy achieved in describing the transforming properties of Coupler in the operating frequency range, together with the apparatus of the theory of complex variables, in particular with the method of conformal maps of fractional linear functions, it was possible to solve a number of applied problems. A method for calculating the area of consistent loads of discretely tunable power circuits of arbitrary structure has been developed. For completeness of the result, the case of matching a generator with a complex value of internal resistance with a given quality (with an acceptable value of the traveling wave coefficient) has been considered. The proposed approach to matching assumes that for any possible antenna load there must be appropriate combinations of discretely tunable elements of the Coupler power circuit that ensure matching with a given quality. The design ratio for images of arbitrary circles and straight lines conformally mapped by a matching quadrilateral to a given complex domain (i.e., expressions for calculating the coordinates of the circle center and its radius, as well as coefficients of the equation of straight lines) has been obtained. Studies of the matching properties of various circuits implemented on discrete elements have been carried out. The results of this study are important when choosing the structural design of the Coupler power circuit. Calculation formulas are obtained that allow us to estimate the relative losses of active power in the Coupler power circuit. This contributes to the reasonable choice of the best configuration option from several, similar in quality matching, thereby avoiding complicated temperature settings of the circuit elements. An exhaustive search method of tuning the discrete contour of the Coupler has been proposed, which is extremely simple and does not require heavy calculations with matrices and complex numbers.

Broadband dual-polarized antenna array with enhanced radiation pattern stability

ABSTRACTIn this paper, a broadband dual-polarized antenna array with stable radiation pattern is proposed for 5 G base station applications. The proposed antenna array consists of a 2 × 2planarantennaarray, four 2 × 2 circle patch parasitic structures and a metal reflector. Based on the principal of the FP (Fabry-Perot) antenna to achieve the stable radiation pattern, when the parasitic loading height meets the resonant height of the FP antenna, serious radiation pattern distortion in large reflector environment could be improved effectively. A prototype of the 2 × 2 broadband dual-polarized antenna array is designed and fabricated. The measured results show that the −10 dB bandwidth of the proposed broadband dual-polarized array is able to cover 3.23–5.06 GHz with high isolation which is greater than 25 dB over the entire operating band. The antenna elementsofthearrayarecapableofmaintainingstable radiation pattern throughout the operating frequency range. The HPBW (half-power beam-width) in the horizontal plane is effectively controlled at 67°±5°with a gain of 8.8 ± 0.5 dBi. Due to the stable radiation performance mentioned above, the proposed dual-polarized array can be applied to future 5 G and sub-6 G base station applications.

Ventilated silencer based on layered Helmholtz resonators

This study investigates the performance of a multilayer sound-attenuating metamaterial with ventilation capabilities. The design incorporates arrays of Helmholtz resonators embedded within the wall structure. Each cell of the barrier's front wall is a Euclidean polygon, triangular, square, or hexagonal, housing a parallel array of resonators interconnected via an axial ventilation duct. The sound attenuation performance of these barriers is meticulously examined using the lumped parameter theory and the transfer matrix method (TMM), complemented by finite element (FE) simulations. The results indicate that sound attenuation in the audible frequency range (300–2000 Hz) can be significantly enhanced by employing multiple layers of resonators, each layer assigned a unique peak resonance frequency. Despite the design's inherent trade-offs between barrier thickness, ventilation capacity, operational frequency range, and overall sound attenuation, its structural simplicity and straightforward theoretical performance estimation methods make it a promising candidate for applications requiring a specific attenuation spectrum. The sound-blocking performance of the design is further validated through impedance tube experiments, which show a reasonable agreement with the numerical predictions, thereby affirming the efficacy of the proposed design. The performance of multilayer design is also compared with the similar ventilated barriers proposed in the recent studies.

Metamaterial Adaptive Frequency Switch Rectifier Circuit for Wireless Power Transfer System

In this paper, a novel metamaterial adaptive frequency switch (MAFS) rectifier circuit is proposed to expand the operating frequency range of the rectifier circuits for wireless power transfer (WPT) systems. Due to the nonlinearity and complex input impedance of the rectifying circuit, the MAFS technology is introduced to improve the matching performance of the rectifier circuit working in different bands. We can use MAFS technology to achieve independent regulation of a single rectifier circuit at different bands, simplifying the rectifier's topology and complexity. A dual-band rectifier circuit and a broadband rectifier circuit are designed to verify the feasibility of the structure. The experimental results show that the designed dual-band rectifier circuit has high conversion efficiency (more than 50%) in two broad bands, 3.2-3.6 and 5.2-6.2 GHz, for 5G and Wi-Fi bands. In addition, the conversion efficiency of the designed broadband rectifier circuit from 4.7 to 6.2 GHz is higher than 50% at 13 dBm. The fractional bandwidth is expanded by 10% compared to the multiplexed rectifier circuit structure. Therefore, the proposed rectifier circuit structure can significantly broaden the operating frequency range and has a simple design, which can be widely used in a wireless power transfer system.

Realization of a memcapacitance emulator utilizing a singular current-mode active block

Abstract This paper introduces a novel circuit design for a memcapacitance emulator, employing a single Voltage Differencing Current Conveyor (VDCC) as its core element. The emulator circuit has been intricately designed, employing only capacitors as grounded passive components. One remarkable aspect of these circuits is their inherent electronic tunability, allowing for precise control of the achieved inverse memcapacitance. The theoretical analysis of the emulator includes a comprehensive examination of potential non-idealities and parasitic influences. Careful selection of passive circuit elements has been made to minimize the impact of these undesirable effects. In contrast to extant designs cataloged in the existing literature, the presented circuitry manifests remarkable simplicity in its configuration. Furthermore, it exhibits a wide operational frequency range, extending up to 50MHz, and effectively clears the non-volatility criterion. To substantiate the efficacy of the devised circuits, comprehensive LTSpice simulations have been conducted, employing a 0.18 μm TSMC process parameter and a power supply of ±0.9 V. These simulations provide robust evidence of the emulator’s performance, reaffirming the feasibility and practicality of the proposed approach in the domain of memcapacitance emulation.

A High-Frequency Planar-Configured Millimeter-Wave MIMO Antenna for Fifth-Generation NR Operations

This article presents a simple planar millimeter-wave (mm-wave) multiple input multiple output (MIMO) antenna with four closely spaced radiating elements. The antenna is intended to enhance the bandwidth for 5G new radio (NR) applications and also cover the industrial Ka-band (26.5-40 GHz), Q-band (30-50 GHz), and U-band (40-60 GHz) frequency ranges. The antenna is designed using Rogers RT/duroid 5880 substrate with a size of 25 × 26 × 1.6 mm3. The proposed antenna consists of four identical radiating elements with two of them positioned in a linear configuration facing each other, while the other two elements are placed opposite to the first two, which improves isolation between the elements. Across the entire operating frequency range (26-60 GHz), the antenna demonstrated excellent performance, including 34 GHz wide bandwidth, high isolation of &gt;25 dB, nearly omnidirectional radiation patterns, high gain of 11.1 dB with a high radiation efficiency of 94%, low envelope correlation coefficient (ECC) of 0.0068, and high diversity gain (DG) of 9.967 dB. The simulated findings exhibit a strong positive correlation with the experimental results. The proposed MIMO antenna design is a promising solution for 5G NR applications.