M. Akbari

Gain Enhancement of Circularly Polarized Dielectric Resonator Antenna Based on FSS Superstrate for MMW Applications

In this communication, a high gain circularly polarized (CP) dielectric resonator antenna (DRA) is proposed. The radiating DR is coupled to a 50 Ω microstrip line through an X-shaped slot etched off the common ground plane. Using a frequency selective surface superstrate layer, a gain enhancement of 8.5 dB is achieved. A detailed theoretical analysis is given and used to optimize the superstrate size and the air gap height between the antenna and superstrate layer. The proposed DRA is designed, simulated, implemented, and tested. The high gain CP DRA has the potential to be used for millimeter wave wireless communication and imaging systems.

High gain circularly-polarized Fabry-Perot dielectric resonator antenna for MMW applications

This paper presents a Fabry-Perot dielectric resonator antenna with capability of high gain and circular polarization for millimeter-wave (MMW) applications. The optimized design can cover impedance bandwidth from 29.1 GHz to 31.6 GHz with an axial-ratio bandwidth from 29.7 to 30.5 GHz, and realized gain of 15.2 dB at 30 GHz simultaneously.

Spatially Decoupling of CP Antennas Based on FSS for 30-GHz MIMO Systems

In this paper, an effective approach for mitigating the near-field coupling between four-port circularly polarized (CP) antennas in a 30-GHz multiple-input, multiple-output (MIMO) system is suggested and investigated. This is obtained by incorporating a two-layer transmission-type frequency selective surface (FSS) superstrate based on planar crossed-dipole metal strips. This paper presents a comparison between the mutual coupling when the patches are radiating in free space and in the presence of the FSS layers. The simulated results, when the FSS layers are applied, show an average of 6–12-dB improvement in the isolation between four adjacent CP-MIMO antennas. In addition, an accurate study is carried out on the insignificant reflections produced by the FSS layers to redirect those and also prevent any interference. The proposed

Ka-Band Linear to Circular Polarization Converter Based on Multilayer Slab With Broadband Performance

2\times 2

SIW beamforming of 2 × 2 and 4 × 4 AFLTSA arrays for MMW applications

CP-MIMO antenna along with the superstrate is implemented and tested to validate the simulation results. Experimental results of the coupling and reflection coefficients and axial ratio show an acceptable agreement with the corresponding simulated ones.

A linear to circular polarizer based on frequency selective surface operating 30GHz applications

In this paper, a Ka-band polarization converter is presented, which is based on multilayer slab. In order to improve impedance matching, metallic circular traces are printed periodically on each dielectric multilayer slab. Simulated results of the polarizer show that it can transform linearly polarized (LP) to circularly polarized (CP) fields over a frequency band from 23 to 35GHz (42%) with an insertion loss less than 0.5 dB. The transmitted CP wave by the polarizer is approximately robust under oblique illuminations. The polarizer is fabricated and measured by a wideband horn antenna satisfying the simulated results. Next, in order to design a high-gain CP structure around 30 GHz, an 8-element LP array antenna with Chebyshev tapered distribution is designed and integrated with the polarizer. Obviously, the antenna limits the overall bandwidth (nearly 28 to 31.5 GHz) due to the narrowband nature of the LP antenna array. When the polarizer is illuminated by an incident LP wave, the two linear components of the transmitted wave with approximately equal amplitudes and 90° phase difference on the frequency band of interest are produced. Experimental results of the proposed structure show a pure CP with a gain of 13 dBi at 30 GHz, which can be suitable for millimeter wave communication.

Broadband RCS reduction based on AMC technology for MMW applications

In this paper, a beamforming technique using multimode section based on s-parameters has been analyzed for antipodal fermi-linear tapered slot antenna (AFLTSA). The analysis is proposed for 2 × 2 and 4 × 4 sub arrays on Rogers 5880 substrate with a relative dielectric permittivity εr=2.2 in order to achieve an objective of high gain and narrow beamwidth, which can be used for target tracking and precise detection applications. The solution frequency is chosen as 32.5 GHz which yields 3 dB beamwidth of ~ 20° and ~13° for 2 × 2 and 4 × 4 AFLTSA structures respectively. The realized gain achieved for these two structures is 12.39 dB and 14.19 dB respectively. The simulation results for multimode section and sub array antenna structures are presented using Ansoft HFSS simulation tool.

UWB Antenna with 3.5-/5.5-GHz Dual Band-Notched Characteristics Using Two Radiating Stubs

The Paper presents a FSS which theoretically converts linear polarization to pure circular polarization at the center frequency 30GHz. The polarizer consists of new structure printed on a RT-5880 substrate. In order to decrease size of traditional design of Jerusalem-cross, a ring is used in the center of FSS. The polarizer provides the required 90° phase difference between the TE and TM polarizations, which are equal in magnitude.

Scattering behavior of AMC chessboard for RCS reduction application

The following contribution focuses on analysis of RCS reduction provided by combination of two kinds of AMC structures in a chessboard. The former is ring-shaped AMC, the latter circle one. The aim of the following paper is to change the direction of the fields scattered by features of reflection coefficient phase. By combination of both AMC slabs in a new chessboard structure, a 180+37° phase difference is obtained resulting the RCS along the boresight is reduced over a wide frequency range from 27GHz to 34GHz.

Wideband RCS suppression based on FSS structures for millimeter applications

In this letter, a new microstrip antenna for UWB applications is suggested. The antenna is able to filter both of the interference frequency bands of WiMAX and WLAN. The antenna consists of two radiating stubs, a partial ground, and a feed-line. In the configuration, by etching an inverted T- shaped slot on the ground plane, extra resonance is excited, thus broad impedance bandwidth can be obtained. The measured results exhibits that the antenna can cover the bandwidth from 2.7 to 13.0 GHz for VSWR≤ 2 excluding the rejected bands from 3.0 to 3.7 GHz and from 4.9 to 6.0 GHz.