Frequency Selective Transmission Research Articles

1-Bit Reconfigurable Transmitarray Antenna with Out-of-Band RCS Reduction

Stealth reconfigurable transmitarray antennas (RTAs) are essential components in wireless communication and radar detection systems. Therefore, in this study, we propose a 1-bit RTA with out-of-band radar cross-section (RCS) reduction. The antenna consists of an absorptive frequency selective transmission (AFST) layer and RTA layer separated by air. Specifically, the AFST layer achieves out-of-band RCS reduction and in-band transmission utilizing the first three resonant modes of a bent metallic strip with a centrally loaded resistor. Meanwhile, the RTA layer adopts a receiver–transmitter structure with an active receiving dipole and a passive orthogonal transmitting dipole. 1-bit phase shift is achieved by alternating two pin diodes integrated on the active dipole to reverse its current direction. To evaluate the proposed design, a 16 × 16-element prototype was designed, fabricated, and measured. For scattering, the bandwidth of 10 dB RCS reduction was about 52.5% and 43.8%, respectively. For radiation, the measured gain was 20.1 dBi at 7.5 GHz, corresponding to an aperture efficiency of 12.7%. The gain loss of beam scans to ±60° was about 5 dB in both two principal planes.

Multifunctional and tunable bandpass filters with RF codesigned isolator and impedance matching capabilities

Abstract This paper presents the radio frequency (RF) design and experimental validation of a multifunctional bandpass filtering (BPF) concept with center frequency tunability and RF codesigned isolator and impedance matching functionality. The multifunctional bandpass filter/isolator (BPFI) concept combines frequency-tunable reciprocal resonators and nonreciprocal frequency-selective stages (NFSs) to realize center frequency tunability and fully directional transfer characteristics. The NFS, as the core component of the BPFI concept, exhibits frequency-selective transmission response in the forward direction and signal cancellation in the reverse direction. Its tunability is achieved by combining a transistor-based network with a tunable capacitively loaded coupled-line section. Furthermore, the NFS facilitates matching of different source loads allowing for the BPFIs to be used as reconfigurable matching networks. For experimental validation, an NFS and two BPFIs were designed, manufactured, and measured at L band. Their features include (i) NFS: center frequency tuning from 1.55 to 1.9 GHz with maximum directivity from 20 to 52 dB and gain from 0.3 to 1.3 dB. (ii) BPFI (topology A): center frequency tuning from 1.52 to 1.9 GHz with maximum directivity from 20 to 44 dB and gain from −1.5 to −0.5 dB. (iii) BPFI (topology C): ability to match complex loads with 26 + j18 Ω and 26 − j14 Ω.

Strain-Induced Electromagnetic Transmission Modulation via a Reconfigurable Kirigami Metasurface

Tunable three-dimensional (3D) electromagnetic (EM) metasurfaces are critical for dynamic modulation of EM responses but their construction and tuning mechanism are still complex. Here, we report a simple yet effective 3D reconfigurable EM metasurface, which was obtained from a planar kirigami polyimide substrate printed with periodically arranged copper split-ring resonator. Under mechanical stretch, the two-dimensional (2D) planar metasurface can be uniformly deformed into a 3D state, which is effective for tuning its EM transmission characteristic. By combining mechanics and EM simulations as well as experimental measurements, we revealed the deformation mode and active EM transmission modulation capability of the metasurface. It is shown that at the initial state, the planar kirigami metasurface exhibits ideal frequency selective transmission to transverse electric (TE) wave but allows for complete transmission for transverse magnetic (TM) wave. As the applied strain increases from 0% to 20%, the transmission was adjusted from −17.74[Formula: see text]dB to −9.74[Formula: see text]dB for TE wave but merely from 0[Formula: see text]dB to −3.25[Formula: see text]dB for TM wave. Meanwhile, the resonant frequency experienced a visible shift for both TE and TM waves. Finally, the equivalent circuit analysis and simulated surface current density were conducted to reveal the tuning mechanism of the proposed metasurface.

Frequency selective low-loss transmission in negative curvature hollow-core fibers

A new low-loss negative curvature fiber design, named as the pole-anchored nested tubular negative curvature fiber, which exhibits frequency selective capabilities in the near-infrared region is proposed. This unique approach involves the addition of nested tubular elements anchored by vertical poles, which serve as an in-fiber resonator. The resulting frequency selective resonant loss dips exhibit high finesse and relative loss modulation depth. The concept of frequency selectivity in negative curvature fibers introduces unique possibilities for future applications of hollow-core structures.

Electrically Reconfigurable Metasurfaces for Frequency Selective Transmission via IPMC Kirigami

AbstractMetasurface with programmable configurations has attracted tremendous attention due to their exotic abilities to manipulate electromagnetic waves. Herein, an electrically reconfigurable metasurface for frequency selective transmission is developed based on ionic polymer–metal composite (IPMC) kirigami. First, low‐voltage driven IPMC actuators with stable actuation performance are realized, and then a thermomechanical equivalent model and a numerical electromagnetic analysis model are proposed for evaluating the deformation of the IPMC actuators and predicting the electromagnetic tunable properties of the IPMC kirigami metasurfaces, respectively. Subsequently, large‐area IPMC kirigami metasurfaces are proposed and produced by using programmable nanosecond laser micro‐processing technique that endows the uniformity of the kirigami units. Finally, the electromagnetic functionalities of these IPMC kirigami metasurfaces are researched and validated by experiments and numerical simulations. Both theoretical and experimental results demonstrate that the electromagnetic transmission frequency of the fabricated IPMC kirigami metasurface with 10 × 10 units can be tuned from 19.3 to 20.8 GHz by the application of a low voltage of 3 V. Compared with the existing reconfigurable metasurfaces, the proposed IPMC kirigami metasurface demonstrates clear advantages in its compact structure, lower driving‐voltage, low‐acoustic noise, and wide working frequency range.

Enhancing polarization maintenance and spectral filtering in negative curvature hollow-core fibers

A new design of polarization-maintaining and spectral filtering negative curvature hollow-core fiber tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates vertically nested tubes anchored radially by a pole structure. By contrast, standard nested tubes in the horizontal direction form the asymmetric fiber structure, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through fiber design optimization, a transmission loss below 0.1 dB/km for spectrally filtered wavelengths is achieved, with birefringence on the order of 10−5 within the wavelength range of 1.45 µm to 1.60 µm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmissions with specific polarization.

AlN high temperature co-fired ceramics with enhanced frequency selective transmission from X to Ku bands at elevated temperature

Syncretism of the functional structure and high temperature (HT) resistant ceramic are investigated to realize frequency selective transmission of device under HT environment. Focused on the electromagnetic (EM) properties of materials, metal tungsten with high-melting-point and ceramic AlN with stable permittivity under 1000 ℃ are selected as the functional structure and substrate of the proposed HT transmitter, respectively. To make the desired transmission, meta-structure is utilized into the design of W structure, which is designed inside AlN ceramic for metal’s conductivity protection. In terms of fabrication, the transmitter is manufactured by high temperature co-fired technique. Through stacking sheets, lamination, and co-fired, the metal structure is processed in the sealed interlayer to prevent oxidation. As demonstrations, single- and double- layer transmitters are designed to satisfy single and double passband from X to Ku bands, respectively. The success of proposed design manner profoundly increases the design freedom for HT EM manipulation, and we firmly believe that the proposed design-fabrication method has great application potential in future EM devices in extreme environments.

Performance analysis of pulse shaping rectangular pulse through frequency selective fading transmission channel in OFDM system

- Long Term Evolution or LTE is a fourth generation (4G) cellular network technology that uses OFDM as its multiplexing technique for fast and effective wireless communication services. OFDM uses the concept of orthogonality for bandwidth efficiency by multiplexing overlapping subcarriers. But in its implementation, this system will have problems in the transmission channel. In addition, OFDM has the major drawback of being susceptible to frequency offset between the transmitter and receiver. This offset frequency will cause the orthogonal character built in the OFDM system to experience a decrease in performance. This decrease in performance is due to the occurrence of ICI. To overcome this, a method is needed to improve system performance. The method used in this research is Rectangular Pulse. Therefore, this research is made to combine the advantages of OFDM and pulse shaping and is expected to produce a superior system and can contribute to the improvement of 4G-LTE implementation. The approach method in this research applies a quantitative descriptive approach to analyze system performance and in this research uses the simulation method as a reference to obtain research data using the Matlab application.

Absorptive Frequency-Selective Transmission Structures Based on Hybrid FSS and Absorber

The replacement of lumped resistors with absorbing materials for absorptive frequency-selective transmission (AFST) structures enables a wider range of applications in low radar cross section (RCS) radomes. However, the transmission band within the absorption band for most absorbers is naturally nonexistent. It is shown that such a limitation can be overcome with the engineered frequency-selective surfaces (FSSs) and microwave absorbers to obtain a frequency response of absorption–transmission–absorption. In particular, a transmission window of low insertion loss within the absorption band is introduced by the integration of bandpass FSS and wideband absorber, while a bandstop FSS in the front minimizes the insertion loss in the passband. This design methodology is successfully demonstrated by two examples of AFST structures with single and dual polarizations.

Analysis on Infrared Stealth Performance of Metal Nano-coating on Radome Surface

Infrared stealth technology used in aircraft is applied to reduce the infrared signal by controlling surface temperature and emissivity using internal heat sink, low emissivity material or metamaterial. However, there is one part of the aircraft where the use of this technology is limited, and that is the radome. Especially, radome should have transmittance for the specific radio frequency, therefore, common stealth technology such as emissivity control surfaces cannot be applied to radome surface. In this study, we developed metal nano-coating for infrared stealth which is applicable to radome surface. We designed slot-type pattern for frequency selective transmission in X-band, and also controlled thickness of metal nano-coating for long wavelength infrared emissivity control. As a result, our infrared stealth surface for radome has 93.2 % transmittance in X-band and various infrared emissivities from 0.17 to 0.57 according to nano-coatings thickness. Also, we analyzed infrared signature of radome through numerical simulation, and finally reduced contrast radiant intensity by 97.57 % compared to polyurethane surface.

Design and performance analysis of human body communication digital transceiver for wireless body area network applications

Wireless body area network (WBAN) is a prominent technology for resolving health-care concerns and providing high-speed continuous monitoring and real-time help. Human body communication (HBC) is an IEEE 802.15.6 physical layer standard for short-range communications that is not reliant on radio frequency (RF). Most WBAN applications can benefit from the HBC's low-latency and low-power architectural features. In this manuscript, an efficient digital HBC transceiver (TR) hardware architecture is designed as per IEEE 802.15.6 standard to overcome the drawbacks of the RF-wireless communication standards like signal leakage, on body antenna and power consumption. The design is created using a frequency selective digital transmission scheme for transmitter and receiver modules. The design resources are analyzed using different field programmable gate array (FPGA) families. The HBC TR utilizes <1% slices, consumes 101 mW power, and provides a throughput of 24.31 Mbps on Artix-7 FPGA with a latency of 10.5 clock cycles. In addition, the less than 10-4bit error rate of HBC is achieved with a 9.52 Mbps data rate. The proposed work is compared with existing architectures with significant improvement in performance parameters like chip area, power, and data rate.

입사각 안정성을 갖는 밀리미터파 대역 주파수 선택적 레이돔 설계

In this study, a frequency-selective radome in the millimeter-wave band with excellent incident-angle stability is designed. The hybrid structure comprising the designed radome combines a multilayered composite material, which has a rectangular loop-type FSS (frequency selective surface) structure with frequency-selective transmission characteristics in the millimeter-wave band. It has a low transmission loss of ≤1 dB in the pass band and a high blocking characteristic of ≥10 dB in the X-band for polarization TE (transverse electric). Additionally, the TM (transverse magnetic) modes and incidence angles ranged from 0° to 50°. To confirm the design performance, a hybrid composite structure is fabricated and the transmission characteristics in the millimeter-wave band and X-band are measured using free-space measurement. The results confirm that the normal incident wave has a passband center frequency and stopband center frequency of 0.62 and 13.45 dB, respectively.

Cooperative Active Power Management in Multifrequency Microgrid With an Energy Storage System Based on Distance of Source to Load

A multifrequency microgrid (MFMG), which has different frequency voltages and currents on the multifrequency (MF) bus can be constructed based on superposition theorem, orthogonal power flow theory, and frequency selective power transmission criteria. It is a unique system where different frequency powers are present on the bus and all active powers maintain orthogonality by flowing simultaneously through a conductor without mixing. Due to the uncertainty and intermittency of renewable sources, an energy storage system (ESS) needs to be installed with MFMG to maintain stability and reliability. The ESS will be charged/discharged based on different frequency active power imbalances in the MF bus. Due to the presence of different frequency voltages and currents on the MF bus, the integration of ESS with MFMG is challenging but not yet discussed in any literature. In this paper, an architecture of MFMG is proposed with ESS. It is found that different new power imbalance cases arise in MFMG due to different frequency sources and loads, which are not present in traditional microgrids. Here, active power balancing conditions for all power imbalance cases are defined for grid connected and islanded mode. An algorithm is proposed to coordinate the ESS and different renewable sources to balance different frequency active power demands in MFMG for optimum power generation through communication under a cooperative framework. The framework is created based on the assumption that any load prefers to take power from the nearest source to minimize the power loss and cost. Different source load pairs are categorized based on the physical distance by different frequencies and accordingly the algorithm is structured. Finally, Matlab simulation of a sample 9 bus MFMG is performed to validate the algorithm and all results are presented.

Dual‐polarized frequency selective rasorber with dual absorption bands

AbstractA dual‐polarized three‐dimensional absorptive frequency selective transmission (AFST) structure consisting of bent metallic strips embedded with chip‐resistors, and a parallel plate waveguide has been introduced. The structure exhibits two wide absorption bands which flank both sides of the passband, and each absorption band contains two reflection zeros contributing to the wideband performance. An equivalent circuit model is derived to investigate the design concept. A prototype is fabricated and measured, and good agreement between the simulated and experimental results is obtained. In addition, the AFST shows a stable response even for oblique angles and for both TE‐ and TM‐polarizations.

Numerical study of an acoustic leaky wave antenna

Acoustic leaky wave antennas (LWAs), introduced as frequency scanning devices, have been studied in recent years for Direction of Arrival (DOA) and highly directional frequency-selective transmission due to their advantages over multi element arrays such as compactness and low-power requirements. This work presents a numerical study through Finite Element Method (FEM) that solves the Helmholtz Equation using code based on the open-source FEniCS Project. The model under study is a one-dimensional acoustic LWA with axysimetric open channels that performs as a transmitter from broadside to endfire directions. We describe the numerical method applied and validate the code with a lumped-element analysis approximation over the frequency range of interest, showing good agreement in the results. Visualization of different aspects of the LWA like the dispersion relation and scattering parameters, among others are presented. Discussion also focus on the scripting possibilities for automation and inspection of large parameter spaces. This approach proves useful when considering termination effects like end-correction or when exploring new designs with irregular geometries that could provide better performing, but where theoretical modeling turns complicated. [Work supported by UNAM-PAPIIT TA100620.]

Subjective quantification of music instrument practice disturbances: A machine audition based approach

Music instrument practice usually causes disturbance to neighbors, especially at tight living spaces with common walls or building structural transmissions. However, the severity of disturbance is difficult to quantify because of the varieties of musical sound, music content, and many subjective factors. We present three studies on the quantification of such disturbances using machine audition tools. In the first study, musical sound at a music practice room and an adjacent room is recorded and analyzed for quantifying the disturbance caused to adjacent rooms. This study builds a quantification framework for disturbance by applying musical pattern recognition tools such as pitch tracking and onset detection to imitate humans' musical perceptions. The machine audition results are correlated with subjective rating results for calibrating the disturbance scales. The second study explores the frequency-selective transmission profiles and ambient noise patterns and their correlations to machine-rated disturbance levels and subjectively rated disturbance levels. The third study explores the effect of acoustical environment on musicians. A professional musician can adapt to the acoustical environment by making adjustments to the performance he has prepared for and these adjustments form a feedback loop that affects both the practice experience and the perceived disturbance level.

Low RCS Transmitarray Employing Phase Controllable Absorptive Frequency-Selective Transmission Elements

A low radar cross section (RCS) transmitarray is presented in this communication using phase controllable absorptive frequency-selective transmission (AFST) elements. The element consists of asymmetrical resonators with resistors to obtain an absorption-transmission-absorption response. The transmission phase within the transmission band can be controlled by rotating the AFST elements, achieving a 1 bit phase change. A low-RCS transmitarray using the developed elements is designed, fabricated, and measured. Compared with a reference transmitarray, the radiation performance of the low-RCS one is almost unchanged with a realized gain of 24.4 dBi. Significant RCS reductions have been realized for dual polarizations of the impinging electromagnetic (EM) waves. The 10 dB RCS reduction bandwidths are 18% and 14% for the lower and upper absorption bands, respectively.

A 3-D Lumped-Components-Free Absorptive Frequency-Selective Transmission Structure Featuring Very Wide Two-Sided Absorption Bandwidths

A 3-D absorptive frequency-selective transmission (AFST) structure that does not require any lumped components and featuring very wide two-sided absorption bandwidths is proposed in this letter. The fundamental design concept is illustrated and the possibility to design AFST structure without lumped components is discussed. The proposed AFST structure exhibits a passband at 6.3 GHz with two-sided absorption bands from 1.15 to 5.45 GHz (130.3% bandwidth) for the lower absorption band and from 7.1 to 12.9 GHz (58% bandwidth) for the upper absorption band. The proposed structure is modeled and simulated using two different full-wave simulation tools. An equivalent circuit model is constructed based on an approximated unit cell. To verify the simulated results, a prototype is fabricated and measured with the free-space method. A comparison with related designs presented in recent literature is also performed to ascertain the implications of the proposed design regarding the lumped component-free feature and wide absorption bandwidth.

Reconfigurable Frequency Selective Rasorber Covering Extremely Wide Transmission Frequency Range

Rasorbers with reconfigurable transmission frequency are of great interest over the past few years. However, existing devices exhibit a limited number of operation modes and cover a narrow transmission frequency range, making them unacceptable for wideband applications. In this work, a high-performance reconfigurable rasorber with mechanically-controlled frequency selective surface (FSS) and an electronically-tuned resistive layer is proposed. Theoretical analysis based on transmission line theory and numerical simulations is performed to investigate the performance of the proposed device. The rasorber were fabricated and free-space measurements were also carried out to validate the simulation results. The device can operate between single-, dual- and triple-passband modes by mechanically tuning the FSS under a fixed external bias voltage. Under single-passband mode, the transmission frequency can also be tuned continuously through simultaneously controlling the mechanically-tunable FSS and electronically-tunable resistive layer. A minimum insertion loss as low as 0.16 dB at 4.03 GHz is achieved from the measurement results. The maximum measured fractional absorption bandwidth is 87.9%, comparable to the state-of-art maximum absorption bandwidth of existing reconfigurable rasorber. The measured overall fractional transmission frequency range under normal incidence wave is 63.9%, far beyond that of any other existing reconfigurable counterparts.

Aperture Antenna Embedded Notched Parallel Plate Waveguide and Its Application to Dual-Polarized 3-D Absorptive Frequency-Selective Transmission Structure

This paper introduces an angular-insensitive dual-polarized 3-D absorptive frequency-selective transmission structure (AFST), which has a transmission window and an upper absorption band. The transmission band is produced by lossless resonators implemented using an aperture antenna embedded notched parallel plate waveguide with a metalized via hole in the center. The absorption band is obtained by lossy resonators constructed by the single resistor embedded bent metallic strips. In addition, the whole structure is constructed without backing discontinuous metallic ground plane, which overcomes the fabrication difficulty of conventional 3-D structures. Physical mechanism of the proposed AFST is explained with the aid of an equivalent circuit model, as well as current and electric field distributions. A prototype of the designed AFST is fabricated and measured, and experimental results show that a fractional transmission bandwidth of 20.5% and an upper absorption bandwidth of 28.8% with absorptivity around 90% for both TE- and TM-polarizations are achieved under oblique incident wave up to 50°.