Miniaturized dual‐band metamaterial inspired antenna with modified SRR loading

A miniaturized dual‐band CPW‐fed Metamaterial antenna with modified split ring resonator (SRR) loading has been presented in this paper. Proposed antenna comprises a tapered rectangular patch with a slot in which an elliptically SRR has been loaded to achieve miniaturization. Proposed antenna shows dual band operations in the operating band 3.25‐3.42 and 3.83‐6.63 GHz, respectively. It has been observed that lower mode (at 3.36 GHz) is originated by means of modified SRR. SRR is being modified by small meandered line inductor which is placed instead of strip. This provides an extra inductance to SRR resulting miniaturization. Overall electrical size of the proposed antenna is 0.222 × 0.277 × 0.017 λ₀ at 3.36 GHz. Second band is due to coupling between feed and ground planes. The antenna offers an average peak gain of 1.72 and 3.41 dB throughout the first and second band respectively. In addition to that this antenna exhibits perfect omnidirectional and dipolar radiation patterns at xz‐ and yz‐ plane respectively. Due to consistent radiation pattern, ease of fabrication, and compact nature this antenna can be used for wireless applications such as worldwide interoperability for microwave access (WiMAX), industrial, scientific and medical (ISM) band, WLAN/Wi‐Fi bands.     

Gain enhancement of the ultra‐wideband tapered slot antenna using broadband gradient refractive index metamaterial

In this article, a broadband gradient refractive index (GRIN) metamaterial is designed and used to enhance the gain of the tapered slot antenna (TSA). The proposed GRIN is implemented using nonresonant parallel‐line unit cell with different refractive index values. GRIN lens are placed in front of the tapered slot direction in the direction of x‐axis. The designed GRIN metamaterials have broad bandwidth (2‐12 GHz) characteristics due to the nonresonant parallel‐line elements which is suitable for the ultra‐wideband frequency band. The measurement results indicates that the radiated beam becomes more directive with narrow beam width. The measured reflection coefficient is below ?10 dB over the frequency bandwidth of 3‐11 GHz. The peak gain of TSA is obtained up to 14 dB at 10 GHz using GRIN lens.     

Dual segment rectangular dielectric resonator antenna with metamaterial for improvement of bandwidth and gain

The simulation and experimental studies of an aperture‐coupled wideband dual segment rectangular dielectric resonator antenna with metamaterial for C‐band applications are presented in this paper. The antenna consists of Alumina (Al₂O₃) ceramic as upper segment and Teflon as lower segment. The combination of circular‐shaped coplanar split‐ring resonator and conducting strip has been used as metamaterial superstrate. With the use of metamaterial superstrate, the bandwidth of the antenna is increased by 48% through simulation and 22% experimentally. The broadside radiation pattern of the antenna is converted into directive radiation pattern with reduced beamwidth when metamaterial superstrate is used. The peak gain of the antenna is also enhanced by 33% through simulation and 31% experimentally with the use of metamaterial superstrate. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:646–655, 2014.     

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.     

Gain enhancement of slot antenna using zero‐index metamaterial superstrate

This article presents a technique to enhance the broadside gain of a CPW fed slot antenna using a single layer metamaterial (MTM) superstrate. A finite array of 3 3 ring unit cell has been designed on both sides of a dielectric substrate to form the MTM superstrate. The gain enhancement is obtained using the zero‐index property of the metamaterial. The broadside gain enhancement for the proposed antenna is 7.4 dB more in comparison to that of the reference slot antenna. The proposed MTM superstrate loaded antenna provides a minimum overall thickness in the context of using ZIM superstrate for gain enhancement of antennas reported in earlier literatures. The overall thickness of the MTM loaded antenna is 0.13λ₀, where λ₀ is the free‐space wavelength at the resonance frequency of the antenna. Also, a high efficiency of about 93.2% is obtained in this case. The loading of the MTM superstrate produces a minimal effect on the cross polarization performance of the proposed slot antenna.     

High‐gain magnetic‐dipole quasi‐Yagi antenna using higher‐order‐mode dielectric resonator with near‐zero‐index metamaterial

For the first time, the rectangular dielectric resonator (DR) operating in higher‐order TE_3δ1 mode is investigated and used as a magnetic‐dipole driver to design quasi‐Yagi antenna with high gain. For further enhancing the antenna gain, a near‐zero‐index (NZI) metamaterial (NZIM) is proposed instead of the traditional directors and put in the front of DR driver. It is a simple structure and composed of a set of the parallel metallic lines printed on a substrate along the end‐fire direction. Benefiting from the higher‐order mode operation of the DR and NZIM, the realized gain of the proposed antenna can reach 10.3 dBi, including the gain improvement of 2 dBi resulting from the employed NZIM. To verify the design concept, the prototype of quasi‐Yagi DR antenna with NZIM is fabricated and characterized. The measured results agree very well with the simulated results.     

Planar antenna beam deflection using low‐loss metamaterial for future 5G applications

A method to tilt the beam of a planar antenna in the E‐plane is demonstrated by implementing a metamaterial (MM) structure onto the antenna substrate at the fifth‐generation (5G) band of 3.5 GHz. The beam tilting is achieved due to the phase change that occurs when the electromagnetic (EM) wave traverses through two media with different refractive indices. A new adjacent square‐shaped resonator (ASSR) structure is proposed to achieve the beam tilting in a dipole antenna. This structure provides a very low loss of ?0.2 dB at 3.17 GHz. The simulation and measurement results illustrate that the radiation beam of the dipole antenna is tilted by +25° and ?24° depending on the position of the ASSR array onto the dipole antenna substrate. In addition, no degradation in the gain is observed as in the conventional beam‐tilting methods; in fact, gain enhancement values of 3 dB (positive deflection) and 2.7 dB (negative deflection) are obtained compared with that of a dipole antenna with no ASSR array. The reflection coefficient of the dipole antenna with ASSR array has a good agreement with that of the dipole antenna with no ASSR array. The measured results agree well with the simulated ones.     

Design and fabrication of a new high gain multilayer negative refractive index metamaterial antenna for X‐band applications

This article presents the design of a planar high gain and wideband antenna using a negative refractive index multilayer superstrate in the X‐band. This meta‐antenna is composed of a four‐layer superstrate placed on a conventional patch antenna. The structure resonates at a frequency of 9.4 GHz. Each layer of the metamaterial superstrate consists of a 7 × 7 array of electric‐field‐coupled resonators, with a negative refractive index of 8.66 to 11.83 GHz. The number of layers and the separation of superstrate layers are simulated and optimized. This metamaterial lens has significantly increased the gain of the patch antenna to 17.1 dBi. Measurements and simulation results proved about 10 dB improvement of the gain.     

Miniaturized substrate integrated waveguide filter using fractal open complementary split‐ring resonators

A miniaturized substrate integrated waveguide (SIW) bandpass filter using fractal open complementary split‐ring resonators (FOCSRRs) unit‐cell is proposed. The proposed structure is realized by etching the proposed FOCSRR unit‐cells on the top metal surface of the SIW structure. The working principle of the proposed filter is based on the evanescent‐mode propagation. The proposed FOCSRRs behave as an electric dipoles in condition of the appropriate stimulation, which are able to generate a forward‐wave passband region below the cutoff frequency of the waveguide structure. Since, the electrical size of the proposed FOCSRRs unit‐cell is larger than the conventional OCSRRs unit‐cell; therefore, the FOCSRR unit‐cell is a good candidate to miniaturize the SIW structure. The proposed filter represents high selectivity and compact size because of the utilization of the sub‐wavelength resonators. The introduced filter is simulated by a 3D electromagnetic simulator. In order to validate the ability of the proposed topology in size reduction, 1‐ and 2‐stage of the proposed filters have been fabricated based on the standard printed circuit board process. The measured S‐parameters of the fabricated filters are in a good agreement with the simulated ones. The proposed SIW filters have many advantages in term of compact size, low insertion loss, high return loss, easy fabrication and integration with other circuits. It is the first time that the FOCSRR unit‐cells were combined with the SIW structure for miniaturization of this structure. Furthermore, a wide upper‐stopband with the attenuation >20 dB in the range of 3–8 GHz is achieved. The results show that, a miniaturization factor about 75.5% has been obtained.     

Microwave subsurface imaging of dielectric structures using fractal geometries of complementary split ring resonators

In this paper, newly proposed complementary split ring resonator (CSRR) structures of fractal geometries are used for microwave imaging of coated dielectric structures in order to detect concealed voids or similar inclusions. The proposed fractal‐based CSRR structures are found to display improved sensitivity as compared to the conventional square CSRR sensors of same cross‐sectional dimensions, and thus appear to be more appropriate for imaging applications. Detailed analyses of different orders of square Sierpinski fractals have been carried out. Raster scanning of the test region is performed and various parameters such as the magnitude and phase at unloaded resonant frequency, along with the shift in resonant frequency when loaded with the test structure are measured. Furthermore, both qualitative and quantitative images of the test structure are retrieved in terms of all the three measured parameters. Simulation and experimental results demonstrate the applicability of the proposed sensor for microwave imaging.     

Isolation enhancement of rectangular dielectric resonator antennas using wideband double slit complementary split ring resonators

A wideband epsilon‐negative structure is employed as one‐layer and two‐layer isolators to reduce mutual coupling in multiple‐input multiple‐output systems composed of two E‐coupled rectangular dielectric resonator antennas. The proposed unit cell with ?15 dB bandwidth for S₂₁ extending from 1970 to 3317 MHz, is a double slit complementary split ring resonator etched on the ground plane of a stripline. Each layer is composed of a 2 × 3 array of the suggested unit cell. Reduction in isolation of more than 11 dB for the one‐layer case and higher than 20 dB for the two‐layer case are measured within the frequency range of 2.604 to 2.64 GHz which includes WiMAX. The highest isolation level of 36 dB is realized at 2.868 GHz. The impedance matching, gain, radiation efficiency, and envelope correlation are improved compared to the original case. A prototype is designed, fabricated, and tested. Simulation data and measurement results are in good agreement.     

Design of an efficiency‐enhanced Greinacher rectifier operating in the GSM 1800 band by using rat‐race coupler for RF energy harvesting applications

Radio frequency energy harvesting (RFEH) circuits can convert the power of communication signals from radio frequencies (RF) in the environment into direct current and voltage (DC power). In this study, the Greinacher full‐wave rectifier circuit topology was combined with a 180° hybrid ring (rat‐race) coupler which was a passive RF/microwave circuit. Thus, higher RF‐DC conversion efficiency was obtained. First, using the Greinacher rectifier topology, RFEH circuit operating at the center frequency of 1850 MHz was designed. Then, at this frequency, designing of the rat‐race coupler having 1000 MHz bandwidth was made. The S‐parameter measurements and simulation data of the designed coupler circuit were compared. Finally, the high efficiency rectifier circuit where these two circuits were used together was designed. The proposed rectifier circuit was constructed on 70 × 70 × 1.6 mm³ FR4 substrate material with a permittivity of 4.3 (ε_r = 4.3). The power conversion efficiency (PCE) of the rectifier circuit, which had 125 MHz bandwidth at the center frequency of 1850 MHz and was developed with rat‐race coupler, was calculated as 71% at 4.7 dBm input power. In addition, with this study, at ?15 dBm input power, which was a relatively low power level, 40% PCE value was obtained.