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.     

A novel compact planar ultra‐wideband antenna with dual band‐notched characteristics

A novel planar ultrawideband monopole antenna with dual notched bands is presented. The antenna mainly consists of a radiation patch and a modified ground plane. To realize dual band‐notched characteristics, a U‐shaped stub embedded in the rectangular slot of the radiation patch and a novel coupled open‐/shorted‐circuit stub resonator are used on the backside of the substrate. The bandwidth of the dual notched bands can be controllable by adjusting some key parameters. The simulated and measured results indicate that the proposed antenna offers a very wide bandwidth from 2.6 to 18 GHz with Voltage Standing Wave Ratio (VSWR) < 2, except the dual notched bands of 3.3–3.7 GHz (World Interoperability for Microwave Access [WiMAX]) and 5.15–5.825 GHz (Wireless Local Area Network [WLAN]). Furthermore, good group delay and stable gains can be achieved over the operating frequencies. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:48–55, 2015.     

A printed dual‐band dipole filtenna with flexible frequency ratio and improved band‐notched performance

A printed dual‐band dipole filtenna with flexible frequency ratio and improved band‐notched performance is proposed. It consists of a driven dipole and three parasitic elements. For the driven dipole with short and long arms, a radiation null is found between two passbands, which achieves a band‐notched filtering characteristic. Two parasitic elements are introduced to enhance the passband bandwidth and an additional parasitic element is utilized to improve the band‐notched performance. In addition, the characteristics of the proposed design including flexible frequency ratio, independent controllable operating frequency, and controllable band‐notched bandwidth have also been demonstrated. A filtenna prototype is fabricated and tested. Measured results show that a fractional bandwidth of 21.1% and 18.1% is obtained in the lower and upper passbands, respectively. The measured efficiency is 84% in the lower band and 74% in the upper band but the efficiency sharply decreases to about 13% within the notched band.     

Fork‐shaped patch printed ultra‐wideband slot antenna with dual band‐notched characteristics using metamaterial unit cells

In this article, a miniaturized fork‐shaped patch ultra‐wideband (UWB) planar wide‐slot antenna with dual band‐notched characteristics is proposed. With fork‐shaped patch, ultra‐wideband impedance matching from 3.1 to 13.2 GHz is easily achieved. Then, two novel and simple methods are applied to solve the difficulty for UWB slot antennas with fork‐shaped patch to realize band‐notched characteristics. By etching one pair of I‐shaped resonators on both branches of the fork‐shaped structure and adding a rectangular single split‐ring resonator in the rectangular openings of fork‐shaped patch, the wireless local area network (WLAN) band from 5.5 to 6.1 GHz and the International Telecommunication Union (ITU) 8 GHz band from 7.9 to 8.7 GHz are rejected, respectively. The coplanar waveguide‐fed UWB antenna is successfully designed, fabricated, and measured. The measured and simulated results show a good agreement. The antenna provides nearly stable radiation patterns, high gains and high radiation efficiency.     

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.     

A vertex‐fed hexa‐band frequency reconfigurable antenna for wireless applications

Present article embodies the design and analysis of an octagonal shaped split ring resonator based multiband antenna fed at vertex for wireless applications with frequency‐band reconfigurable characteristics. The proposed antenna is printed on FR4 substrate with electrical dimension of 0.4884 λ × 0.4329 λ × 0.0178 λ (44 × 39 × 1.6 mm³), at lower frequency of 3.33 GHz. The antenna consists of SRR based vertex fed octagonal ring as the radiation element and switchable reclined L‐shaped slotted ground plane. Antenna achieves six bands for wireless standards viz: upper WLAN (5.0/5.8 GHz), lower WiMAX (3.3 GHz), super extended C‐band (6.6 GHz), middle X band (9.9 GHz—for space communication), and lower K_U band (15.9 GHz—for satellite communication systems operating band). Stable radiation patterns are observed for the operating bands with low cross polarization. The proposed design achieves hexa band characteristics during switching ON state of PIN diode located at reclined L‐shaped slot in the ground plane. Experimental characteristic of antenna shows close agreement with those obtained by simulation of the proposed antenna.     

A simple planar monopole UWB slot antenna with dual independently and reconfigurable band‐notched characteristics

An extremely simple and compact planar monopole ultrawideband (UWB) slot antenna with dual band‐notched characteristics is proposed. The antenna is composed of a circular radiation patch, a microstrip‐fed line, and a partial ground. By etching an arc‐shaped slot on the radiation patch and a C‐like slot on the feed line, dual notched frequency bands at 3.3–3.7 GHz for WiMAX and 5.15–5.825 GHz for WLAN are achieved. And, the two notched bands can be adjusted independently by varying the length of the slots. Moreover, the band‐notched characteristics can be reconfigurable by shorting the corresponding slots. So, the antenna is capable of operating in one of multiple modes which makes it an excellent candidate for UWB applications. Meanwhile, experimental results indicate that the antenna has an available impendence bandwidth from 2.9 to 11 GHz which covers the UWB frequency band, and nearly omnidirectional patterns, stable gains, small group delay in operating band except rejected bands. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:706–712, 2014.     

Ultrawideband circularly polarized antenna with dual band‐notched characteristics

This article presents an ultrawideband (UWB) crossed dipole antenna with circularly polarized (CP) and dual band‐notched characteristics. The proposed design is based on two orthogonal tapered dipoles for UWB CP operation and a square‐shaped cavity for high broadside gain over the entire operating bandwidth (BW). To generate dual band‐notched characteristics, two separated slots are inserted into each dipole's arm. This antenna yields measured impedance BW of 100% (3.2‐9.6 GHz) with dual‐band rejection centered at 5.2 and 5.8 GHz. Correspondingly, dual rejected bands are also observed in the original UWB CP band, which ranges from 3.2 to 8.2 GHz. Additionally, the proposed antenna exhibits high broadside gains better than 6.2 dBic and radiation efficiency greater than 82%.     

Novel application of a new metamaterial complementary electric LC resonator for the design of miniaturized sharp band‐pass filters

In this article, we introduce a new metamaterial complementary electric LC resonator (CELC) and investigate its operational mechanism, characteristics, and potentialities for application in microwave components and devices, such as filters. We consider the excitation of CELC by the electric and magnetic fields of microstrip lines and its resonance characteristics by the diagrams of effective permittivity (ε_eff) and permeability (μ_eff). A circuit model is obtained by the consideration of its coupling with the loaded microstrip line. We then realize a novel left‐handed (LH) cell by the combination of the CELC resonator and a short circuited stub. It is designed by the least mean square method. We finally use the cascade connection of such LH cells for the design of a miniaturized narrow‐band band‐pass filter with high out of band rejection. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A compact band‐pass filter using multi‐element resonators

A compact, band‐pass filter utilizing multi‐element resonators, structured from sections of distributed transmission lines, is presented. A band‐pass filter design procedure is established that emphasizes CAD techniques to characterize the individual resonators and to determine the resonator coupling values required for a specified pass‐band response. Detailed band‐pass filter design examples are illustrated and simulation results are employed to validate the design procedure. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 447–458, 2003.     

Design and analysis of multiband notched pitcher‐shaped UWB antenna

To mitigate the interference with coexisting wireless systems operating over 3.3–3.6 GHz, 5.15–5.825 GHz, and 7.725–8.5 GHz bands, a novel triple band notched coplanar waveguide fed pitcher‐shaped planar monopole antenna is presented for ultrawideband applications. Bands notched characteristics are achieved using a novel mushroom type electromagnetic band gap structure like resonator and a split ring slot. A conceptual equivalent RLC (Resistor‐Inductor‐Capacitor)‐resonant circuit is presented for the band notched characteristics . Furthermore, the input impedance and VSWR (voltage standing wave ratio) obtained from the equivalent circuit are validated with simulated and measured results. Performances of the antennas in both, the frequency domain and the time domain are investigated. The simulated and measured results demonstrate that the proposed antennas have wide impedance bandwidth, nearly stable radiation patterns, and suppression of gain and total radiation efficiency at notched bands. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:795–806, 2015.     

Coupled‐line band‐pass filter with T‐shaped structure for high frequency selectivity and stopband rejection

A coupled‐line band‐pass filter (BPF) with T‐shaped stub structure is presented. Five transmission poles within the passband and eight deep transmission zeros (TZs) from 0 to 2f₀ (f₀ denotes filter's center frequency) are realized through input impedance calculations. With the simple T‐shaped structure, the positions of six TZs can be appropriately adjusted to achieve high frequency selectivity and stopband rejection. For demonstration, a BPF prototype centered at 2.05 GHz is designed and fabricated, whose measured rejection levels are of over 45.5 dB at lower stopband and better than 19.5 dB at upper stopband. The simulation and measurement results are in good agreement, which validates the design idea.     

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.     

A WLAN band‐notched compact four element UWB MIMO antenna

A compact four‐element multiple‐input‐multiple‐output (MIMO) antenna for ultra‐wideband (UWB) applications with WLAN band‐notched characteristics is proposed here. The proposed antenna has been designed to operate from 2 to 12 GHz while reject the frequencies between 4.9 to 6.4 GHz. The four antenna elements are placed orthogonal to attain the polarization diversity and high isolation. A thin stub connected to the ground plane is deployed as a LC notch filter to accomplish the rejected WLAN band in each antenna element. The mutual coupling between the adjacent elements is at least 17 dB while it has low indoor and outdoor envelop correlation (<0.45) and high gain with compact size of two boards, each measuring 50 × 25 mm². To validate the concept, the prototype antenna is manufactured and measured. The comparison of the simulation results showed good agreement with the measured results. The low‐profile design and compact size of the proposed MIMO antenna make it a good candidate for diversity applications desired in portable devices operating in the UWB region.     

Reconfigurable ultra‐wideband monopole antenna with single‐, dual‐, and triple‐band notched functions

A miniaturized ultra‐wideband (UWB) monopole antenna with reconfigurable multiple‐band notched performance is demonstrated. By modifying the shape of the patch and the ground plane, the UWB operation is achieved. The first and second band‐notches are respectively generated by etching a rectangular slot with open ends and a U‐shaped slot in the patch, and the third band‐notch is produced by loading a C‐shaped parasitic element beneath the patch. To realize the reconfigurable band‐notched functions, four PIN diodes are inserted in three band‐rejected structures. The antenna has a compact dimension of 30 mm × 26 mm. It can switch between a UWB state and several band‐notch states by alternating the states of the diodes. Also, good radiation patterns are obtained.     

A state‐of‐art review on band‐notch characteristics in UWB antennas

Ultra‐wideband technology has experienced a rapid growth over the last decade for its contribution in different sectors of human society. Printed antennas are considered as preferred platform for implementing this technology because of its alluring characteristics like light weight, low cost, ease of fabrication, integration capability with other systems, etc. Antennas developed for ultra‐wideband applications are desired to have notch characteristics for avoiding interference with other existing radio communication systems. The techniques related to design and developments of printed band‐notched antennas are continuously upgraded for improving the antenna performance. In this article, a comprehensive review has been carried out on ultra‐wideband antennas with band notch characteristics proposed in around last decade. The band notched UWB antennas available in the literature have broadly been classified into five different categories based on their notch characteristics like single band‐notch, dual band‐notch, triple band‐notch, quad/multiple band‐notch, and reconfigurable/tunable band‐notch, respectively. This review exercise may be helpful for beginners working on ultra‐wideband band‐notched antennas and also such a review process is not available in the open literature to the best of author's knowledge.     

Triple‐band polarization‐insensitive metamaterial absorber with low profile

In this article, a triple‐band metamaterial low‐profile absorber with polarization independence is proposed. The proposed metamaterial unit cell is composed of two modified rings with square patch at corners. In addition, the proposed absorber is consists of 10 × 10 periodic unit cells with size of 100 mm × 100 mm. To explain the mechanism, the electric field, the surface current distribution, and equivalent circuit model are present. The structure exhibiting three absorption peaks of 99.01%, 97.18%, and 99.53% under normal incidence at 8.92‐9.11 GHz, 13.78‐14.05 GHz and 14.92‐15.21 GHz which cover X and Ku‐band, respectively. In addition, the proposed structure is insensitive for the transverse magnetic/transverse electric field polarization of incident waves and also the angle of incidence. Furthermore, the three operating bands of the absorber can be adjusted independently and offers low profile which makes the design suitable for different curved surface applications. The proposed structure is fabricated and experiments are carried out to validate the design principle. Good agreements are observed between the measured and the corresponding simulated results.     

Spoof surface plasmon polariton band‐stop filter with single‐loop split ring resonators

A novel band‐stop filter with single‐loop split ring resonators (SRRs) is proposed for spoof surface plasmon polaritons (SPPs) at millimeter wave frequencies, achieving a miniaturized size of 0.052λ₀ × 0.278λ₀ at its resonant frequency. The SRRs provide both a low‐pass response as the rectangular corrugations used in the conventional SPPs and an additional band‐stop response induced by the resonance of SRRs. To verify this design, a back‐to‐back device with two coplanar waveguides as the input and output feeding was fabricated and characterized, the measured S‐parameters of which agree well with the simulation. The measured stop band is centered at 49 GHz with a ?10‐dB bandwidth of 4.1 GHz and a high Q‐factor of 93, in which the maximum attenuation is 31 dB. The filter has a low insertion loss of less than 2.8 dB in the pass band. Such approaches may find many applications to achieve compact millimeter wave circuits.