Circuit Analog Absorber Research Articles

A thin hybrid circuit-analog (CA) microwave absorbing double-slab composite structure

In this study, a thin hybrid circuit-analog (CA) microwave absorbing double slab composite structure is presented. Unlike conventional CA absorbers, the composite spacer in the proposed structure is made up of a glass/epoxy and high permittivity layer of glass/epoxy-MWCNT composite, which contributes to the stable absorption performance in the curved surface while maintaining the thin thickness of the composite spacer. To design the microwave absorber, the genetic algorithm which is the most used evolutionary algorithm technique in this field was used. The total thickness of the designed double slab CA absorber was very thin thickness of 2.37mm. Although the designed absorber has very thin thickness, it could satisfy the −10dB absorption in whole X-band (8.2–12.4GHz). The absorbing performance of the designed absorber was compared with other types of absorber. Also, to check the absorbing performance of the proposed structure in the curved surface, the echo radar cross section (RCS) was simulated in the X-band with other types of absorber. The simulated results proved an excellent performance of a proposed novel double slab CA absorber.

Frequency-Selective Rasorber Based on Square-Loop and Cross-Dipole Arrays

A novel design of a transmission window within the absorption band of a circuit analog absorber, named as frequency-selective rasorber (FSR), is presented. Based on an equivalent circuit model, the conditions are formulated to produce a passband with small insertion loss and to reduce the reflection at frequencies below and above the passband in the meanwhile. Simple design guidelines of our proposed FSR are then developed. With loaded lumped elements, the arrays of square-loop and cross-dipole are combined to realize its implementation. It is shown through measurements that an insertion loss of 0.68 dB can be obtained at 4.42 GHz and the fractional bandwidth for at least 10 dB reflection reduction within the lower and upper frequency bands is 92.3% under the normal incidence. A good agreement between simulated and measured results validates our design.

Circuit-analog (CA) type of radar absorbing composite leading-edge for wing-shaped structure in X-band: Practical approach from design to fabrication

In this paper, a circuit analog (CA) absorber consisting of a periodic, resistive-pattern sheet and glass-fiber/epoxy composite spacer; for integration into the leading edge of a wing-shaped structure, was introduced along with practical steps to take from design to fabrication. The CA absorber was designed in a flat-plate shape for the X-band (8.2–12.4 GHz). To fabricate a periodic-resistive-pattern surface compatible with a 180 °C autoclave process, a carbon-based conducting material was used. The reflection loss of this flat-plate CA absorber was measured with an X-band, free-space measurement system. A leading edge for a wing-shaped structure incorporating the new CA absorber was designed and fabricated based on data from a flat-plate-design CA absorber. The integrated leading edge was mounted on a wing-box, and its echo-RCS was measured in an anechoic chamber. When the CA absorber was applied to the leading edge of the wing-shaped structure, the echo-RCS level measured by compact range showed a reduction of about 10 dB in most of the X-band, in both polarizations. From a practical point of view, these results confirmed that CA absorbent materials have great potential in radar absorbing structures for stealth aircraft.

Design of Circuit-Analog (CA) Absorber and Application to the Leading Edge of a Wing-Shaped Structure

In this study, first, a circuit analog (CA) absorber consisting of a periodic pattern resistive sheet, glass-fiber/epoxy composite as a spacer, and carbon fabric composite was applied to the leading edge of a wing-shaped structure to reduce the echo radar cross section (RCS). This CA absorber was designed in a flat-plate shape through a parametric study that was performed to optimize the device in the X-band (8.2–12.4 GHz). The reflection loss of the fabricated flat-plate CA absorber was measured with an X-band free-space measurement system. The measured reflection loss was –49.5 dB at 10.15 GHz and the –10 dB bandwidth was about 4.2 GHz. When the CA absorber was applied to the leading edge, the measured echo RCS level showed a 15 dB reduction near 10 GHz and a 10 dB reduction in most of the X-band in both polarizations. Surface discontinuity due to gaps between the leading edge and the wing-box was discussed. From the analysis results, it can be seen that the permittivity of the glass-fiber/epoxy composite material used in the CA absorber was in the proper range for application to a wing-shaped structure.

On the Design of Single-Layer Circuit Analog Absorber Using Double-Square-Loop Array

A detailed study of a single-layer circuit analog absorber using double-square-loop array reveals that three resonances can be obtained within its operating frequency band. An equivalent circuit model is proposed to explain how these three resonances can be produced and its absorption bandwidth can be widened. Simple guidelines for the design of this double-square-loop absorber are then formulated. It is shown through measurements that the fractional bandwidth of 126.8% is realized for at least 10 dB reflectivity reduction under the normal incidence. Furthermore, the total thickness of the proposed design is only 0.088λL at the lowest operating frequency. A good agreement between simulated and measured results demonstrates the validity of our design.

Design of a low-frequency broadband circuit analog absorbers based on wire media

A circuit analog absorber (CA) with wire medium is presented. Both the original CA and the structure presented are analyzed. It is shown that original CA cannot have more than one resonant frequency in low frequency band, owing to the limitation by the effective resistance. The presented structure breaks the limitation using artificial plasma resonance, with the wave dispersion in the structure analyzed using the quasi-static model. The experimental results, consistent with simulation results based on the finite-difference time-domain (FDTD) method, show that the structure obtains dual-band absorption, thus broadening the absorption band in low frequency band.

A Circuit Analog Absorber With Optimum Thickness and Response in X-Band

A wideband circuit analog absorber in X-band is proposed. The design is discussed by the unit cell and equivalent circuit model. A unit cell of the periodic structure for the absorber is designed and simulated. The absorber consists of two RO 4003 layers separated by air distance. With the thickness of 3 mm, the absorber offers a -20-dB bandwidth of 40%. A novel method for estimating the optimality ratio of planar absorbers is also proposed. The optimality ratio of the designed X-band absorber is calculated with the proposed method, and the result is about 80% optimality in frequency response and total thickness.

Design of thin circuit‐analogue multilayer absorber and application to leading edge of wing structure

A new thin multilayer circuit-analogue (CA) absorber design consisting of a patterned resistive sheet, glass/epoxy, and glass/MWCNT-epoxy for X-band radar is presented. The proposed thin multilayer CA-absorber (a total thickness of 2.23 mm) has smaller thickness by 0.71 mm than a single-layer CA-absorber (a total thickness of 2.93 mm). Although the absorption bandwidth of the multilayer CA-absorber in the X-band was slightly narrower than the single-layer CA-absorber, the absorption performance of the multilayer CA-absorber was comparable to that of the single layer. Also, when the CA-absorber was applied to the leading edge of a wing-shaped structure, the radar cross-section level was comparable with the single-layer CA-absorber even though the thickness of the multilayer CA-absorber was less than that of the single-layer CA-absorber.

Design of a Switchable Microwave Absorber

A novel circuit analog absorber is presented in this letter, which consists of three layers: a complex impedance surface, a dielectric layer containing p-i-n diodes, and a conducting ground plane. The complex impedance surface is a periodic array of unit cells with lumped elements. p-i-n diodes are employed to control the RF signal path to realize different effective thicknesses, which results in different absorbing frequencies. An example is fabricated and tested to demonstrate that the proposed absorber can achieve two switchable operations, one of which covers from 0.85 to 1.88 GHz with a -10-dB reflection coefficient, and the other from 2.66 to 5.23 GHz.

Semi-cylindrical Radar Absorbing Structures using Fiber-reinforced Composites and Conducting Polymers in the X-band

This paper presents a low observable structure with curved surfaces made by fiber-reinforced composites, conducting polymers and shows the possibility of developing stealth platforms for military applications. We propose radar absorbing structures (RAS) based on a circuit analog absorber in order to reduce the radar cross-section (RCS) of an object with curved surfaces. First, semi-cylindrical RAS with a periodic square patterned layer using a conducting polymer was designed and simulated by a commercial 3-D electromagnetic field analysis program. The designed semi-cylindrical structure with low RCS was then fabricated using fiber-reinforced composites and conducting polymer materials. Finally, the radar cross-section was measured in order to evaluate the radar absorbing performance of the fabricated RAS at a compact range facility. The measured radar absorption of the fabricated RAS showed that the target's RCS declined in a range of 65% to 94% within the X-band relative to a non-radar absorbing specimen.

Wideband Microwave Absorber Based on a Two-Dimensional Periodic Array of Microstrip Lines

The modeling and design is presented of a new kind of circuit analogue absorber, which intercepts the electromagnetic waves through a two-dimensional periodic array of microstrip lines loaded with lumped circuit elements. For a plane wave incidence of polarization perpendicular to the strips, virtual magnetic walls are formed between the strips, and the geometry can be divided into many identical unit-cells. We first study the propagation characteristics of the unit-cell using the singular integral equation method. An RC network is then proposed to match this array with the free space and to dissipate the intercepted energy over a wide frequency range. The complete design procedure is explained through a design example that exhibits a bandwidth of 113% while the absorber thickness is less than 10% of the free space wavelength at the lowest operating frequency.

Multilayered Wideband Absorbers for Oblique Angle of Incidence

Design procedures of Jaumann and circuit analog absorbers are mostly formulated for normal angle of incidence. Only a few design methods considering oblique angle of incidence are published. The published methods are restricted to single resistive layer circuit analog absorbers or multilayered Jaumann absorbers with low permittivity spacers. General design procedures are developed in this paper for multilayered Jaumann and capacitive circuit absorbers. By expanding the scan and frequency compensation techniques to multilayered structures, Jaumann absorbers with outstanding performances are designed. A capacitive circuit absorber is presented with a stable frequency response up to 45 for both polarizations, having an ultrawide bandwidth of 26 GHz.

섬유강화 복합재료를 이용한 반원통형 전자파 흡수구조의 설계 및 제작

스텔스 기술은 적진에서 항공기나 함정의 생존 가능성을 향상시키고 임무 수행 능력을 향상 시킬 수 있다. 본 논문의 목적은 섬유강화 복합재료를 이용하여 하중지지가 가능한 곡면부 형상을 갖는 저피탐지 구조를 제안하고 군사적 활용을 위한 전방위 스텔스 플랫폼의 개발 가능성을 보여주는 것이다. 본 연구에서는 곡면을 갖는 물체의 레이더 반사면적을 줄이기 위해서 기존의 circuit analog 흡수체에 기반을 둔 전자파 흡수구조를 개발하였다. 먼저 상용 3차원 전자기장 해석 프로그램을 이용하여 사각 주기격자 패턴의 전도성 고분자 층을 갖는 전자파 흡수구조를 설계하고 성능을 해석하였다. 다음으로 섬유강화 복합재료와 전도성 고분자 재료를 이용하여 설계된 반원통형 전자파 흡수구조를 제작하였다. 저항성 시트로 작용하는 주기격자 패턴층을 제작하기 위해서 PEDOT를 기반으로 하여 폴리우레탄을 바인더로 갖는 전도성 고분자 페이스트를 사용하였다. 마지막으로 제작된 RAS의 전자파 흡수 성능을 평가하기 위해 POSTECH의 compact range 장비를 이용하여 레이더 반사면적을 측정하였다. The stealth technology can increase the survivability of aircrafts or warships and enhance the capability of mission completion in hostile territory. The purpose of this paper is to present the low observable structure with curved surfaces made by fiber-reinforced composites and to show the possibility of developing omnidirectional stealth platforms for military applications. In this study, we developed a radar absorbing structures(RAS) based on a circuit analog absorber to reduce the radar cross section(RCS) of an object with curved surfaces. Firstly, the RAS with a periodic square patterned conducting polymer layer was designed and simulated using a commercial 3-D electromagnetic field analysis program. Secondly, the designed semi-cylindrical structure with low RCS was fabricated using fiber-reinforced composites and conducting polymer. To make the periodic pattern layer, acts as resistive sheet, the intrinsic conducting polymer paste containing PEDOT with a polyurethane binder was used. Finally, the radar cross section was measured to evaluate the radar absorbing performances of the fabricated RAS by the compact range facility in POSTECH.

Capacitive Circuit Method for Fast and Efficient Design of Wideband Radar Absorbers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A simple, fast and efficient method for designing wideband radar absorbers is proposed. The idea is to modify the circuit analog absorber method without perturbing the bandwidth. This is done by utilizing the asymptotic behavior of such an absorber at low frequency and replacing the band-stop resonating frequency selective surfaces with low-pass capacitive ones, which can be synthesized by square patches. It is shown that higher frequencies are not influenced by these modifications. A thin wideband capacitive circuit absorber (CCA) is presented with 28% reduction of thickness and 57% increase of bandwidth in comparison to the Salisbury screen. It is also explained why some optimized metamaterial designs fail to compete with the CCA method. For high permittivity layers, it is shown that the CCA is a better solution than the Jaumann absorber and improvements both in thickness and bandwidth are possible. A three layered ultrawideband CCA is presented with total thickness of 15.1 mm. </para>

Simple design of thin and wideband circuit analogue absorber

A new and simple design for thin and broadband circuit analogue absorbers is presented. The proposed absorber is composed of a two-dimensional periodic array of multiple patches printed on a conductor-backed substrate, which exhibits the property of multiple resonances and provides a wide absorbing bandwidth. Measured results show that this simple absorber has a bandwidth of 76% for 10 dB RCS reduction and its thickness is only one-eighth free-space wavelength at the centre frequency

On Designing Jaumann and Circuit Analog Absorbers (CA Absorbers) for Oblique Angle of Incidence

Most investigations of Jaumann and circuit analog absorbers (CA absorbers) consider normal angle of incidence only. This paper expands our investigation to also include oblique angle of incidence as well as arbitrary polarization. Essentially two problems are encountered for oblique angle of incidence: An upward shift of the center frequency; and a mismatch that, in general, will vary with angle of incidence of the incident field. The new contribution given in this paper is that it considers ways to combat both of these dilemmas. Finally, comparison will be made with similar designs obtained by the genetic algorithm (GA) approach. It will be observed that the analytic approach, as used in this paper, in general leads to designs that are not only superior to the GA designs but also simpler, at least in the present case

A spectral iteration technique for analyzing scattering from circuit analog absorbers

An iterative technique is described for solving for the current and field distributions in a structure composed of a periodic array of sheet conductors, deposited on a dielectric layered substrate, whether or not backed by a conductor. The incident field must be a plane wave but can be oblique. The periods array is taken into account by use of a Floquet mode field formalism, and an iterative method has been chosen that permits a numerical solution on personal computers by avoiding matrix inversions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>