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 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).

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 novel four-port multiple-input multiple-output (MIMO) antenna system is designed using concentric square-ring patch antennas. All four ports are made to resonate at 2.4 GHz ISM band with an overall system dimension of 60 x 60 x 1.6 mm(3). This design uses complementary split-ring resonator (CSRR) loaded on its ground plane for enhanced isolation of 22 dB between patch antenna elements. CSRR reduces mutual coupling by about 6.5 dB. The antenna operates with a 2:1 VSWR bandwidth of 75 MHz centered at 2.45 GHz. This collocated antenna system satisfies MIMO diversity performance with low envelope correlation between its waveforms. The effectiveness of concentric rings in MIMO design along with proposed isolation enhancement technique is validated using measurements from a prototype.

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.