Multiform frequency selective surfaces optimal design based on topology optimization

This article proposes an optimization design method for various frequency selective surfaces (FSSs) based on topology optimization algorithm incorporated with the genetic algorithm. The present method takes the connectivity condition both in simulation and fabrication of the elements into consideration. For the filling elements structural design methodology, the novel hexagonal‐pixel filling element structural design is employed for improving the patch connection. As examples, various FSSs, such as a large‐angle‐stability band‐pass FSS, wideband band‐pass FSS, and multiple band‐pass FSS, are designed. Furthermore, the validity of the present method is proved by the agreement between the simulation and the measurement.     

Magnetic MEMS reconfigurable frequency-selective surfaces

A reconfigurable frequency-selective electromagnetic filter implemented by integrating hard magnetic materials with microelectromechanical systems (MEMS) provides a new variation of reconfigurable frequency-selective surfaces (FSS). By incorporating magnetically actuated dipole elements that are capable of being tilted away from the supporting surface, we can tune the FSSs operating frequency without having to physically alter the dimensions of the dipole elements. The 25/spl times/25 array of microactuators used in this work each consist of a 896/spl times/168/spl times/30 /spl mu/m/sup 3/ ferromagnetic plate made of 40Co-60Ni, layered with a 1-/spl mu/m-thick conductor (Au), attached to a pair of 400/spl times/10/spl times/1 /spl mu/m/sup 3/ polysilicon torsion beams, suspended just above the supporting substrate. The high remanent magnetization of the ferromagnetic material allows for relatively small magnetic fields (/spl sim/2.1 kA/m) to induce significant angular deflections (/spl sim/45/spl deg/). This innovative reconfigurable FSS design has successfully demonstrated electromagnetic-signal diplexing and tuning its resonant frequency over a bandwidth of 2.7 GHz at a frequency of 85 GHz.     

Analysis and design of band-pass frequency-selective surfaces using the FEM CAD tool

Three-dimensional (3D) full-wave analysis and design of bandpass frequency-selective surfaces (FSSs) is presented. By using the unique features of a unit cell and the periodic boundary conditions, infinite FSSs can be simulated. Wave propagation through FSSs, which is otherwise difficult to quantify, can be visualised by using a commercial CAD tool. The creation of the simulation model, interpretation and analysis of the outcome, and comparison with experimental results are presented for the square-slot and the square-loop-slot band-pass FSS. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 391–397, 2004.     

Ku波段宽带传输频率选择表面优化设计

通过调整频率选择表面(FSS)单元的结构参数来控制电磁波在某雷达波段内的传输是滤波器研究领域的重要内容。为实现圆环形FSS单元在Ku波段的宽带传输特性,并明确单元结构参数对其传输特性的影响规律,采用谱域分析法,从圆环形单元的大小、宽度、阵列周期等方面,对圆环形单元FSS进行了数值分析和优化设计。仿真结果表明,谐振频率点的主要影响因素为单元大小,而单元宽度主要控制传输带宽。经优化,当单元外半径为3.5mm,单元宽度为0.66mm,阵列周期为10.0mm时,谐振频率为14.8GHz,FSS传输带位于Ku波段内,传输带宽达5.7GHz。优化后的FSS结构适用于Ku波段宽带传输,为优化设计提供了依据。     

Generalized design approach to compact wideband multi‐resonant patch antennas

In this work, a generalized design approach to compact, wideband multi‐resonant microstrip patch antenna is proposed. Theoretical criterion of the length of the prototype dipole is laid down based on the simplest dipole model and the associated eigenmodes at first. Then, the criterion is employed to reveal the general relationship between the prototype dipole length, operational modes, sizes, and radiation behaviors of the resultant multi‐resonant circular sector patch antennas. Next, a compact wideband, dual‐resonant circular sector patch antenna is designed accordingly. It is operating at the TM_3/4,1 and TM_9/4,1 modes within a 240° circular sector patch radiator with its radii short circuited. The antenna fabricated on a single‐layered air substrate exhibits an available radiation bandwidth of 25.0%, with a profile as small as 0.043 guided wavelength at the center frequency. It is evidently verified that the approach can be employed to realize compact, dual‐resonant wideband microstrip patch antennas without increasing antenna profile, inquiring multiple radiators or employing reactance compensation techniques. In addition, it may lead to a series of novel wideband patch antenna designs with diverse performances.     

Finite-dimensional control of a flexible space structure: A new view based on input-output space

How to design a simple, finite-dimensional controller for complex, infinite-dimensional Flexible Space Structures (FSSs) with uncertain physical parameters is the main topic of this paper. The research shows that a simple controller that makes the controlled FSS system of high stable degree can be obtained by using only the input-output property instead of the poles-zeros property of the FSS system, which is a new result in the control of uncertain FSS systems. The main idea can be summarized as: (1) it is difficult, even impossible, to obtain convergent poles and zeros estimation for an uncertain FSS system, which is different from that in a finite-dimensional system; (2) there is an inherent relation between the input-output property and the poles-zeros property for the FSS system, which means that modelling and controlling, based on the input-output property, may guarantee the high authority control of the FSS system; (3) in the H sense and based on input-output space to make the model error as small as possible and the controller tolerate a model error as large as possible, will result in a very low dimensional controller.     

Polarization independent quad‐bandpass frequency selective surfaces with wide‐band ratio

A single layer polarization independent quad‐bandpass frequency selective surface (FSS) with wide‐band ratio is demonstrated theoretically as well as experimentally. The proposed structure passes four frequency bands with wide band ratio. The proposed FSS design is implemented by incorporating alternate arrangement of four units which are rotated 90° clockwise to form a unit cell of metal over a FR4 substrate. The geometrical dimensions of proposed unit cell are optimized and arranged in such a way that the structure possesses the quad bandpass characteristic and aspect dimensions of one unit is 0.11λ × 0.11λ with respect to first resonant frequency. This FSS provides stable response for different angle of incidence in transverse electric (TE) mode and transverse magnetic (TM) mode. To validate the results proposed FSS array has been fabricated and measured in free space environment. The measured results are in good agreement with the simulated results. Excellent stability is also observed for different incident angle.     

Gain enhanced multipattern reconfigurable antenna for vehicular communications

This article presents the design and implementation of a high‐gain tunable dual‐band pattern reconfigurable antenna for vehicular communications. The proposed antenna consists of a slotted patch loaded with a double‐side FSS acting as superstrate. The proposed slotted antenna operates at 2.45 and 3.5 GHz and the frequency tuning over the dual‐band is accomplished by employing a varactor diode for tuning the center frequency from 2.41 to 2.62 GHz and from 3.38 to 3.65 GHz at lower and upper frequency bands, respectively. To obtain pattern reconfiguration, the slotted patch is divided into four regions by using two diagonal lines of vias. By properly choosing the excitation port combinations, 14 different radiation patterns are realized with a maximum realized gain of 8.4 and 7.9 dB. Further enhancement of gain is achieved using frequency‐selective surface (FSS) screens which act as a partially reflecting surface. The unique feature of this design is to provide reflection coefficient with high reflectivity in two predetermined frequency ranges. The prototype antenna is fabricated and the measurement results are reported. The experimental results show that the prototype antenna with FSS offers tunable dual‐band with beam reconfigurable properties.     

A compact angularly‐stable frequency selective surface for GSM 900/1800‐MHz shielding using cascaded 2.5‐dimension structure

In this article, a novel compact dual‐band frequency selective surface (FSS) with stable response is proposed for GSM shielding. This FSS is designed using 2‐layer cascaded 2.5‐dimension structure of which element is composed of two via‐based modified swastika unit cells. The proposed structure has created two stop bands around frequency 900 and 1800 MHz, respectively, with maximum attenuation value close to 70 dB. Besides, this FSS performs an excellent miniaturization characteristic with overall size of 0.048λ₀ × 0.048λ₀, where the λ₀ represents the free space wavelength of the lower resonance frequency. More important, this FSS exhibits a very stable frequency response up to 80° for TE and TM polarization. To understand the structure better, the design procedure of this FSS is introduced in detail. Since the proposed FSS has an excellent comprehensive performance, this FSS has great potential in shielding GSM signal for small electronic devices. Finally, a prototype of proposed FSS is fabricated and measured. The measurement results prove the validity of simulation results.     

A triple‐layer dual‐bandpass frequency selective surface of third order response with equivalent circuit analysis

A multilayered cascaded and polarization‐dependent frequency selective surface (FSS) exhibiting dual bandpass frequency response is proposed in this article. The FSS is composed of two metal‐based square patch layers in the two ends and one aperture type layer in the middle, separated by two dielectric substrates. The FSS exhibits bandpass response of third order with two transmission poles in the 5‐6 GHz band and one pole at 2.5 GHz. The passbands are separated well enough with a transmission zero at 3.5 GHz leading to significant out‐of‐band rejection. The structure is ultrathin with the thickness on the order of 0.01λ₀ with respect to the lowest resonating frequency. It is shown with parametric studies how the poles can be tuned individually. Principle of operation of the FSS is explained with its equivalent circuit model. Transmission phase of the FSS varies linearly with frequency in the upper band. Simulation result is verified experimentally for the fabricated prototype.     

Design and FEM simulation study of the electro-thermal excitation resonant beam with slit-structure

This paper proposes a slit-resonant beam based on the double clamped resonant beam theory of silicon micro-machined resonant pressure sensors. The slit structure can enhance surface alternating stress in the root area of beam while vibrating. Finite element method (FEM) is applied to calculate the stress concentration magnification, and we carry out a computational study of the effects of size and location of slit structure in terms of mechanical properties of resonant beam, such as stress concentration on resonant beam and natural frequency of resonant beam, as well as sensing performance, such as resonant beam amplitude sensitivity. Our simulations show that the slit structure could strengthen the stress concentration and increase the amplitude detection sensitivity, and the variations of these parameters can substantially influence the performance of slit structure. The research of stress concentration, caused by silt structure, could provide reference for further optimization and design for the resonant beam.     

Resonant frequency of a microstrip patch in the vicinity of an identical radiator

The resonant frequency of a microstrip patch (rectangular, square, and circular) changes as soon as an identical patch is brought closer than 0.2λ to it. Closed-form expressions are presented for the H-plane-coupled configuration (the two adjacent patches are excited by same phase excitation) from which this altered resonant frequency may be easily computed. From the same expression the resonant frequency of an isolated patch antenna may also be calculated. A procedure utilizing these closed-form expressions for the design of microstrip patch antennas which will resonate at the desired frequency is also outlined. These expressions may be readily used in the computer-aided design of microstrip antenna arrays. © 1996 John Wiley & Sons, Inc.     

Polarization independent dual‐bandpass frequency selective surface for Wi‐Max applications

In this article, the performance of polarization independent dual‐bandpass frequency selective surface (FSS) is investigated. The proposed design of FSS unit cell comprises of metallic structure is based on customized plus shape within plus ring inside a square ring and etched on one side of FR4 substrate. The geometrical dimensions of unit cell are optimized in such a way that the structure possesses the dual‐bandpass characteristic for Wi‐Max applications. The aspect dimensions of unit cell are 0.16 λ × 0.16 λ × 0.013 λ with respect to first resonant frequency. The FSS provide stable response for different angle of incidence in transverse electric and transverse magnetic polarization. An equivalent circuit model of FSS is established and its results are verified by Advanced Design System tool. A prototype of FSS is designed, fabricated and measured. Good agreement between simulated and measured results verifies the dual‐bandpass FSS.     

Theory and FEM simulation study of the double-clamped resonant beam with slit-structure

In this paper, we established the vibration model of double-clamped resonant beam with slit structure, and we theoretically analyzed the effect of rectangular slits with round corners on vibration amplitude and natural frequency of the resonant beam. The effect of rectangular slits on detection sensitivity of resonant beam is also analyzed. According to the theoretical analysis, computational studies of slit size and location influence on vibration amplitude, natural frequency and detection sensitivity of the resonant beam were carried out. Meanwhile, stress concentration of proposed slit structure with rounded corners was calculated by finite element method (FEM) and was compared with the stress concentration of slit with right corners. Finally, for resonant beams with slits of different size and location, theoretical calculation results and the FEM simulation results of natural frequency were compared. Theoretical analysis and FEM simulation are in good agreement.     

Design of wideband bandpass filter using short‐circuited circular patch resonator loaded with slots

This paper presents a wideband bandpass filter design based on a short‐circuited circular patch resonator with inductively loaded slots. The cavity model method is used to analyze the excited resonances of the resonator. According to the illustration of the cavity model, the TM₀₁₀ mode is excited as the fundamental mode, the resonant frequency of which is much lower than that of the TM₁₁₀ mode and can be further lowered by the loaded arc‐oriented slots. Therefore, the proposed resonator can be used to design a filter with compact size. In addition, one of the two orthogonal degenerate TM₁₁₀ modes can be independently tuned by the slot along the symmetric plane without affecting the TM₀₁₀ mode. Since the resonant frequency of each mode can be tuned independently by the parameters of the slots, and the coupling between resonant modes of the resonator and source/load can be adjusted by the feeding angle and the capacitive loaded stubs on the feeding lines, the center frequencies and bandwidths of the designed bandpass filters can be tuned easily. The analysis is theoretically and experimentally verified by two examples with good agreement between the simulated and measured results.     

A frequency reconfigurable MIMO antenna with agile feedline for cognitive radio applications

A novel frequency agile multiple‐input‐multiple‐output (MIMO) patch antenna based on a reconfigurable feedline is proposed. The proposed antenna structure has two hexagonal‐shaped patch antenna elements. A defected ground structure having hexagonal shape is included in the ground plane to make the design compact and improve isolation among antenna elements. Further compactness is achieved using reactive loading. Frequency reconfigurability is realized by employing varactor diodes in the microstrip feedline. The proposed antenna achieves a frequency reconfigurable band with wide tuning range from 1.42 to 2.27 GHz with good gain and efficiency. Furthermore, an envelope correlation coefficient value of less than 0.2 and minimum isolation of 12 dB was achieved, displaying good MIMO performance. The presented antenna has a planar, low profile design with compact size of 100 × 50 mm². Thus, frequency agility, wide range tuning, compactness, and planar structure of the proposed antenna design make it suitable for modern wireless handheld devices particularly in cognitive radio applications.     

Radio frequency response of flexible microstrip patch antennas under compressive and bending loads using multiphysics modeling approach

This research article studies the effect of compression and bending loads on resonant frequency of microstrip patch antennas using COMSOL Multiphysics software (will be called COMSOL hereafter). In this study, copper microstrip patch antenna of dimension 30 mm × 25 mm on polydimethylsiloxane (PDMS) substrate of dimension 50 mm × 50 mm is considered. The interface bonding is assumed to be ideal between the patch and substrate. Both Ansoft HFSS and COMSOL are used to model and analyze the original geometry of the microstrip patch antenna without applying physical load to make sure that the design and the impedance match is satisfactory. Then, COMSOL is used to find deformed shape of the microstrip patch antenna under different values of compression and bending loads. The deformed geometries are reanalyzed using COMSOL radio frequency (RF) simulation. The resonant frequencies at different load levels are obtained and the effect of loading and boundary conditions on the resonant frequency shift is discussed.     

Modeling and design of printed antennas using neural networks

A single neural network is developed to model the resonant frequency of rectangular patch printed on uniaxially anisotropic substrate with air gap using effective parameters in conjunction with spectral dyadic Green's function. Also, the strength of ANN models in antenna design is demonstrated by considering two case studies: the design of circular patch antenna and planar inverted‐F antenna. Results show good agreement with literature. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

High gain CPW‐fed UWB planar monopole antenna‐based compact uniplanar frequency selective surface for microwave imaging

In this article, a novel uniplanar ultra‐wideband (UWB) stop frequency selective surface (FSS) was miniaturized to maximize the gain of a compact UWB monopole antenna for microwave imaging applications. The single‐plane FSS unit cell size was only 0.095λ × 0.095λ for a lower‐operating frequency had been introduced, which was miniaturized by combining a square‐loop with a cross‐dipole on FR4 substrate. The proposed hexagonal antenna was printed on FR4 substrate with coplanar waveguide feed, which was further backed at 21.6 mm by 3 × 3 FSS array. The unit cell was modeled with an equivalent circuit, while the measured characteristics of fabricated FSS array and the antenna prototypes were validated with the simulation outcomes. The FSS displayed transmission magnitude below ?10 dB and linear reflection phase over the bandwidth of 2.6 to 11.1 GHz. The proposed antenna prototype achieved excellent gain improvement about 3.5 dBi, unidirectional radiation, and bandwidth of 3.8 to 10.6 GHz. Exceptional agreements were observed between the simulation and the measured outcomes. Hence, a new UWB baggage scanner system was developed to assess the short distance imaging of simulated small metallic objects in handbag model. The system based on the proposed antenna displayed a higher resolution image than the antenna without FSS.