Realization of reconfigurable filtering horn antennas using active frequency selective surfaces for GSM and LTE signal filtering

Herein, it is aimed to design an Active Frequency Selective Surface (AFSS) based high performance reconfigurable filtering antenna (Filtenna). The proposed AFSS unit element is consist of a single PIN diode with a simple microstrip patch design which performance characteristics are varies with the state of the diodes. The proposed unit elements have been used to form an array that is placed at the aperture of a double ridge horn antenna. With the variation in state of diodes, the antenna acts as a Filtenna module to filtering the incoming electromagnetic waves in frequency band of 1.8 to 2.8 GHz. From the experimental results, it is shown that the proposed Filtenna achieves a signal attenuation of 7.3 dBi at 2.1 GHz.     

A compact uniplanar ultra‐wideband frequency selective surface for antenna gain improvement and ground penetrating radar application

A simple structured single layered frequency selective surface (FSS) that has unit cell size of 11 × 11 mm², substrate thickness of 0.8 mm only and capable to work in a very widespread band from 0.001 to more than 17 GHz is proposed in this article. The FSS is competent to augment the gain of a UWB monopole antenna by 2 to 3.5 dBi when integrated at the back of antenna. The performances of “antenna‐FSS” structure is evaluated by simulation and experimental measurement where good correlations are obtained. The integrated structure provides wide impedance band (S₁₁ < ?10 dB) from 2.82 to 19.94 GHz (more than 150%) with improved broadside radiation and high radiation efficiency profile. The transient and frequency domain characteristics of “antenna‐FSS” composite structure are also evaluated in close proximity of diverse sub‐surfaces such as dry sand, wet sand, wood and concrete where an almost unaltered impedance band profile, linear transfer function response and non‐varying group delay responses are achieved which establishes the applicability of the composite structure in ground penetrating radar for low depth sub‐surface scanning applications.     

A spatial power limiter using a nonlinear frequency selective surface

A novel spatial power limiter based on nonlinear frequency selective surface (FSS) is presented for high power electromagnetic (HPEM) wave protection. Embedded with Schottky diodes, the nonlinear FSS not only reflects out‐of‐band electromagnetic incidence like a filter, but also exhibits a power‐limiting characteristic, allowing low‐loss transmission for an in‐band low‐power incidence while rejecting a high‐power one. Such a FSS with 4 × 4 unit cells is designed, fabricated and measured. Results demonstrate its pass‐band centering at 2.5 GHz, power density threshold of about 0.27 W/m² and shielding effectiveness (SE) up to 20 dB at 2.5 GHz.     

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 novel miniaturized frequency selective surface

A novel single layer miniaturized frequency selective surface made of circular unit cell elements is presented in this article. The frequency selective surface (FSS) unit cell measures 0.055λ₀ × 0.055λ₀, where λ₀ corresponds to its free space wavelength. The proposed FSS offers band stop characteristics with bandwidth of 137.5 MHz centered at 1.39 GHz. The symmetrical structure of the unit cell elements provides polarization independency. The miniaturized unit cell elements help achieving angular independency for both TE and TM mode of polarization. The miniaturized design provides excellent angular independency with negligible frequency shift for varying incident angles. A prototype of the FSS is fabricated and its simulation results are validated using measurements.     

A wideband switchable absorber/reflector based on active frequency selective surface

A wide‐band absorber and reflector using PIN diodes based on active frequency selective surface (AFSS) is presented, which the AFSS is performed as a wide‐band absorber and reflector with OFF and ON state diodes. By changing the states of the PIN diodes, the measured reflectivity of the structure can dynamically switch from reflection to less than ?10 dB absorptivity ranging from 7.5 to 18 GHz under normal incidence. The unique characteristic of the proposed structure lies in its capability to switch between two working states. In addition, the bandwidth of the designed structure covers a wider band compared with earlier switchable absorber/reflector structures. The fabricated structure shows good agreement with the simulated results.     

Design of compact patch type curved frequency selective surface

Miniaturized FSS is very useful in communication system. It is obtained by lowering the resonant frequency. Many good research works are reported on compact planar FSS, but it is challenging to decrease the resonant frequency in case of curved FSS. This article deals with the design and fabrication of compact patch type curved FSSs. Here maximum 50.31% compactness is achieved in semicylindrical curved FSS with square slit. Also the parametric studies have been analyzed by introducing same slit in circular and hexagonal patch elements of the curved FSSs. The proposed design has been fabricated. Simulated result has been ratified with experiment result.     

Reconfigurable active frequency selective surface for ultra‐wideband applications

A reconfigurable active frequency selective surface (AFSS) with ultra‐wideband (UWB) characteristics is presented in this article. The proposed AFSS consists of a periodic array of three metal layers and two dielectric layers. PIN diodes are arranged on the top and bottom metal layers which can rebuild the function of AFSS. The transmission bandwidth of the AFSS with OFF‐state diodes is 8 to 12.5 GHz with a fractional bandwidth of 44%, and the transmission coefficient of the FSS with ON‐state diodes is lower than ?10 dB from 2 to 18 GHz. Additionally, the AFSS is angular stable and polarization‐insensitive for both transverse electric and transverse magnetic polarizations. The simulation results show that the proposed AFSS is an effective candidate for radome applications.     

Pattern squint elimination for quad‐ridged conical and pyramidal horn antennas using bended probes

This article describes a new technique for pattern squint elimination of quad‐ridged conical and pyramidal horn antennas by introducing bended coaxial probes. Because of the phase difference and mutual coupling between vertical and horizontal polarizations, the radiation patterns of the conventional quad‐ridged conical and pyramidal horn antennas squint over a wide bandwidth. The proposed technique substantially reduces the phase difference and coupling between the two probes, so a significant improvement in the radiation patterns over the frequency band of 8–18 GHz can be achieved. The designed modified horn antennas are most suitable as a feed element in reflectors of radar systems and EMC applications. The proposed modified antennas have a voltage standing wave ratio (VSWR) less than 2.2 for the frequency range of 8–18 GHz. Moreover, the proposed antennas exhibit high gain, dual‐polarization performance, good isolation, low SLL, low back lobe, low cross polarization, and satisfactory far‐field radiation characteristics for the entire frequency band. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

Design of optimum gain pyramidal horn with improved formulas using particle swarm optimization

In this article, a new method to design an optimum gain horn antenna is presented. This method is based on improving existing design equations along with the use of particle swarm optimization technique. The obtained results are more accurate than those available in the literature since no path length error approximation is involved. Improved horn dimensions, for different 15 designs, are obtained which give the desired gain almost exactly. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Investigations on fractal frequency selective diaphragms in rectangular waveguide

In this article, self‐similarity and space‐filling properties of fractal structures are explored as frequency selective diaphragms in rectangular waveguide, which can find applications in the design of compact, lightweight, and multiband waveguide filters with better out‐of‐band rejection ratio. Some self‐affine fractal structures, based on Sierpinski gasket and plus shape fractals, are proposed, and the effect of scaling factor on the location of transmission bands is investigated. Self‐similar structures like Hilbert curve, Koch curve, and Minkowski fractals are shown to be efficient in reducing resonant frequency of the diaphragm. Numerical results are presented along with the results obtained from HFSS, which show a good agreement. A typical application of the fractal diaphragm in the design of waveguide bandstop filter has also been demonstrated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

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.     

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.     

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.     

Application of metamaterials for performance enhancement of planar antennas: A review

Metamaterials are assemblies of metallic and/or dielectric materials with properties that are not readily found in naturally existing materials. Hence, metamaterial structures are commonly loaded on/near the patch, embedded in the substrate, loaded/etched from the ground plane or placed as a superstrate layer for enhancing bandwidth and gain, and size miniaturization of conventional patch antennas. The demand for wide bandwidth, high gain, and compact antennas is highly contemplated in recent wireless communication research studies. Despite their lightweight, ease of fabrication, low profile, and simplicity for integration, patch antennas have performance limitations as result of their narrow bandwidth, lower gain, larger size, and lower power handling capacity. To address these problems, metamaterial‐based antennas have gained massive interest. There exist inadequate literatures about review of current state of extensive study reports on metamaterial application for patch antenna performance enhancement. Thus, this paper has reviewed and discussed latest research works on metamaterial applications for performance enhancement of planar patch antennas.     

An angular‐stable multi‐layer reconfigurable frequency selective surface based on varactor with wide tuning range

An angular‐stable multi‐layer reconfigurable frequency selective surface (FSS) based on varactor with wide tuning range is proposed in this article. The working principle of the FSS is analyzed by the equivalent circuit model (ECM). By tuning the DC bias voltage applied to the varactors loaded on the top and bottom layers, the pass band of the FSS can be located in the C, X, and Ku band respectively with a wide reconfigurable range. In addition, due to the introduction of the miniaturized structure and the four metal vias in Z‐direction, the FSS provides good angular stability under TE and TM polarization. Finally, the fabrication and experiment are provided to verify the validity of the reconfigurable FSS.     

Design of optimum gain pyramidal horn using self‐adaptive differential evolution algorithms

In this work, we apply classical and new self‐adaptive differential evolution (DE) algorithms to the design of optimum gain pyramidal horns. The application of DE algorithms to pyramidal horn design allows the accurate calculation of their physical dimensions in a short amount of time. Moreover, self‐adaptive DE does not require the prespecified choice of control parameters reducing significantly the users' effort. Representative examples demonstrate the applicability of our proposal. Our study shows that self‐adaptive DE algorithms outperform or produce similar results with other methods in the literature in terms of solution accuracy and convergence speed. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Design of conical DRH antennas for K and Ka frequency bands

Two conical double‐ridged horn (DRH) antennas for K and Ka frequency bands are presented. Detailed simulation and experimental investigations are conducted to understand their behaviors and optimize for broadband operation. The designed antennas were fabricated with 0.01 mm accuracy and satisfactory agreement of computer simulations and experimental results was obtained. The designed conical DRH antennas have voltage standing wave ratio (VSWR) less than 2.1 and 2.2 for the frequency ranges of 18–26.5 GHz (K band) and 26.5–40 GHz (Ka band), respectively. Meanwhile, the proposed antennas exhibit low cross‐polarization, low sidelobe level, and simultaneously achieve slant polarization as well as symmetrical radiation patterns in the entire operating bandwidth. An exponential impedance tapering is used at the flare section of the horns. Moreover, a new cavity back with a conical structure is used to improve the VSWR. Numerous simulations via Ansoft HFSS and CST Microwave Studio CAD tools have been made to optimize the VSWR performance of the designed antennas. Simulation results show that the VSWR of the proposed antennas is sensitive to the probe spacing from the ridge edge and the cavity back structure. The designed conical DRH antennas are most suitable as a feed for the reflectors of radar systems and satellite applications. Results for VSWR, far‐field E‐plane and H‐plane radiation patterns, and gain of the designed antennas are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Rapid design optimization of antennas using space mapping and response surface approximation models

A computationally efficient method for design optimization of antennas is discussed. It combines space mapping, used as the optimization engine, and response surface approximation, used to create the fast surrogate model of the optimized antenna. The surrogate is configured from the response of the coarse‐mesh electromagnetic model of the antenna, and implemented through kriging interpolation. We provide a comprehensive numerical verification of this technique as well as demonstrate its capability to yield a satisfactory design after a few full‐wave simulations of the original structure. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.