A method to extract complex permittivity of liquids using a coplanar waveguide fed open stub resonator is proposed in this paper. A quarter-wave long open stub printed on a substrate is used as the sensor for the computation of complex permittivity. The free-standing unloaded sensor is designed to operate at 1.8 GHz and resonates at a lower frequency when immersed in a test liquid. The resonant frequency and the reflection phase from the sensor are recorded for the computation of real and imaginary parts of the permittivity of the test sample. The simulated response of the sensor, when immersed in liquid samples of different permittivities, is validated by measurements. Equations for the extraction of real and imaginary values of permittivity are also presented in this paper. The experiments demonstrate that the sensor is capable of characterizing complex permittivity of liquids with minimal error.

A novel idea for generating directional electromagnetic beam using a metamaterial absorber for enhancing radiation from a microwave antenna in the S-band is presented herewith. The metamaterial structure constitutes the well-known stacked dogbone doublet working in the absorption mode. The reflection property of the dogbone metamaterial absorber, for the non-propagating reactive near-field, is utilized for achieving highly enhanced and directional radiation characteristics. The metamaterial absorber converts the high-spatial reactive spectrum in the near-field into propagating low-spatial spectrum resulting in enhanced radiation efficiency and gain. The gain of a printed standard half-wave dipole is enhanced to 10 dBi from 2.3 dBi with highly directional radiation characteristics at resonance.

The detailed experimental and simulation studies of the stacked dogbone metamaterial particles are presented in this article. Besides the conventional left handed propagation mode, it is observed that the structure supports Fabry-Perot resonant modes and the excitation of this mode can be identified from the right handed resonant tunnel band in the dispersion diagrams. It is shown that the coupling between the Fabry-Perot and left handed resonant modes gives flat tunnel band characteristics in the dispersion diagram and is associated with huge electromagnetic absorption. The spectral response can be tailored by varying the stacking thickness of the sample making it suitable for microwave absorption and left handed transmission applications. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1347-1353, 2016

A stepped impedance (SI) based frequency tunable dipole antenna for WLAN (2.4-2.48 GHz)/Bluetooth (2.4-2.48 GHz)/LTE (2.5-2.7 GHz)/wireless power transfer/UMTS (2.1 GHz)/WiMAX (2.5-2.7 GHz) applications has been investigated in this paper. The proposed antenna has an overall dimension of 0.408 lambda(0) x 0.245 lambda(0) x 0.013 lambda(0), where k o represents the free-space wavelength at the frequency 2.45 GHz. By embedding varactor diodes on the SI dipole antenna arms and varying the bias voltage, the effective electrical length of the antenna can be changed, leading to an electrically tunable antenna without changing the length of the antenna. The simulation and experiments are well matched and offer a 2:1 VSWR (S11 <-10 dB) bandwidth of 780 MHz. Experimental results show that by trimming the varactor diode, the operating frequency of the antenna can be electrically tuned from 1.98 to 2.76 GHz. (C) 2019 Elsevier GmbH. All rights reserved.

A compact multiband four port diversity-based antenna with high isolation between elements is proposed for multiple-input-multiple-output applications. The antenna resonates at following three bands: 1.95-2.5 GHz (covering UMTS, LTE 2300, and 2.4-GHz ISM bands), 3.15-3.85 GHz (covering WiMAX band), and 4.95-6.6 GHz (covering 5.2/5.8-GHz ISM bands). The stub-loaded meander-line antenna is loaded with split-ring resonators arranged in the form of a ring to enhance isolation by 17 dB at 2.4 GHz. All four elements radiate with equal efficiency with measured peak gains of 2.5, 3.7, and 4.4 dBi, respectively, in three bands and have a very low envelope correlation coefficient between elements. The overall size of the compact multiport antenna system is 0.26 lambda x 0.26 lambda x 0.01 lambda with a minimum isolation of 22 dB between its elements. The antenna elements and the isolation enhancement structure are fully planar for an easier integration.

The theory of diffraction limit proposed by H.A Bethe limits the total power transfer through a subwavelength hole. Researchers all over the world have gone through different techniques for boosting the transmission through subwavelength holes resulting in the Extraordinary Transmission (EOT) behavior. We examine computationally and experimentally the concept of EOT nature in the microwave range for enhancing radiation performance of a stacked dipole antenna working in the S band. It is shown that the front to back ratio of the antenna is considerably enhanced without affecting the impedance matching performance of the design. The computational analysis based on Finite Difference Time Domain (FDTD) method reveals that the excitation of Fabry-Perot resonant modes on the slots is responsible for performance enhancement. (C) 2015 Author(s).

An experimental realization of resonant toroidal dipole excitation in the microwave regime is presented in this paper. The metasurface proposed herewith is an asymmetric double split-ring resonator exhibiting Fano-like resonance profile. One could observe that cascading the metasurface results in near-field transverse and longitudinal coupling creating dual-band toroidal moments on the structure. This planar scheme will simulate the development of enhanced light-matter interaction, electromagnetic wave slowdown and sensor design. Here we report the experimental realization of the phenomenon in the S-band frequencies, and the results are verified using multipole scattering analysis.

This article reports the radiation performance enhancement of an electrically small antenna using sub-wavelength metal strip grating, in the microwave frequency regime. The sub-wavelength grating converts the high spatial-frequency components of radiation emitted from an inductor loaded truncated-ground open coplanar antenna into a low spatial far-field spectrum. The spectral conversion results in enhanced efficiency and radiated power gain in the S-band corresponding to TE polarization. The gain of the antenna is enhanced from -9.74 dBi to 1.6 dBi for TE polarization. The prototypes are fabricated in-house and the design is validated experimentally.

A four-port planar multiple input multiple output antenna system employing polarisation and pattern diversity technique is proposed. The antenna system, resonating at 2.4 GHz ISM band, includes a dual polarised two-port cross-patch antenna and an orthogonally polarised two-port square ring patch antenna. Undesired high coupling between elements is reduced by incorporating an interdigital structure on the ground. This reduces coupling between elements by 12.5 dB, ensuring a high isolation of about 28 dB between any set of elements in the antenna system. The overall size of the quad element antenna is about 0.5 x 0.5, which makes it fairly compact. The cross-patch antenna has low cross-polarisation levels, which reduces the coupling between its orthogonal elements. The narrow bandwidth of the higher order modes of the square ring antenna is doubled by adding half wavelength slits along its arms. All four elements have a 2:1 voltage standing wave ratio (VSWR) bandwidth of 85 MHz and have low envelope correlation in the operating band. The antenna is printed on a low cost FR4 substrate and does not require any intricate fabrication.

Achieving super-resolution beyond the diffraction limit is an intriguing research topic over the last century. In this paper, the split-ring resonator array-based evanescent amplification in the microwave regime is implemented for strongly enhancing radiation from an electrically small radiator. The electrically small radiator considered here is a chip inductor loaded open coplanar waveguide antenna. This weakly radiating source when placed in the vicinity of split-ring resonator array, it is seen that the radiated power could be greatly enhanced. The split-ring resonator array working under the magnetic resonant excitation could amplify evanescent fields emitted by the source. Field probing reveals that the split-ring resonator array could convert the amplified evanescent waves into propagating ones resulting in significantly enhanced radiation from the source.