Arezou Edalati

High-Gain Reconfigurable Sectoral Antenna Using an Active Cylindrical FSS Structure

A novel design of a high-gain reconfigurable sectoral antenna using an active cylindrical frequency selective surface (FSS) structure is presented. The FSS structure consists of metallic discontinuous strips with PIN diodes in their discontinuities, and it is placed cylindrically around an omnidirectional electromagnetically coupled coaxial dipole (ECCD) array. The cylindrical FSS structure is divided into two semi-cylinders. By controlling the state of diodes in each semi-cylinder, a directive radiation pattern is obtained that can be swept in the entire azimuth plane. The effect of the diode-state configuration and the radius of the cylindrical structure are carefully studied to obtain an optimum sectoral radiation pattern. In addition, a solution for increasing the matching bandwidth of the antenna is also proposed. An experimental prototype was fabricated, and the measured results show a beamwidth of 20° in elevation and 70° in the azimuth plane at 2.1 GHz with a gain of 13 dBi. With these features, the proposed antenna is suitable for base-station applications in wireless communication systems.

Frequency Selective Surfaces for Beam-Switching Applications

A novel design of a beam-switching antenna based on reconfigurable frequency selective surfaces (FSSs) is presented. The antenna is composed of a cylindrical FSS with PIN diodes and divided into six equal sectors by metallic sheets. Metallic cones at the top and bottom of the structure are used to create a directive beam. The antenna is fed by a simple dipole at its center. To switch the radiation pattern of the antenna, the diodes in one FSS-sector are set off to be transparent to the incident EM waves, whereas the diodes in other sectors are on to reflect the incident wave. The direction of the radiation pattern is defined by the off-state sector. In this design, the beam-switching is achieved with only one layer and minimum size of the cylindrical active FSS in order to decrease the number of active elements, and the amount of the power supply. The antenna can sweep the entire azimuth plane with 60° radiation beamwidth in six steps. The fabricated antenna prototype operates from 2.3 GHz to 3 GHz with maximum measured gain of 10 dBi and 3-dB beamwidth of 60°. This antenna can be used in the base station of the wireless communication systems.

BAND STRUCTURE ANALYSIS OF RECONFIGURABLE METALLIC CRYSTALS: EFFECT OF ACTIVE ELEMENTS

The band structure for the normal propagation of crystals formed by periodically loaded metallic wires is analyzed for different wire diameters and for various loads, which are assimilated as diodes. The diodes are simulated by using an equivalent R-C circuit. The influences of the values of the R-C elements in On-state and Off-state are studied, and the results are compared with the band structures obtained for continuous and discontinuous-wire materials. To validate the proposed analysis, experimental results for a reconfigurable crystal are presented.

Reconfigurable Beamwidth Antenna Based on Active Partially Reflective Surfaces

This letter presents a new method to design a new reconfigurable antenna by using an active cylindrical electromagnetic band-gap (EBG) structure for wireless communication systems. The antenna provides a reconfigurable elevation beamwidth while the azimuth radiation pattern maintained omnidirectional. The EBG structure that is composed of periodic discontinuous metallic strips and PIN diodes behaves as an active partially reflecting surface (PRS). By changing the diode states, the reflection coefficient of the structure is controlled so that the radiation beamwidth and directivity of the antenna can be reconfigured. To validate the proposed concept, the final prototype is fabricated, and measurement results are also presented and discussed.

Beam-switching antenna based on active Frequency Selective Surfaces

A novel method for designing a beam-switching antenna using active Frequency Selective Surfaces (FSSs) is presented. The antenna is composing of a single dipole placed at the center of an active cylindrical FSS that is divided in six equal sectors by metallic sheets. Metallic cones at the top and bottom of the structure are used to enhance the radiation performance of the antenna. In each step, the diodes in one FSS-sector are off, whereas other diodes are on. The FSS-sector with off-state diodes defines the direction of the radiation pattern. The proposed antenna operates from 2.4 GHz to 2.8 GHz with gain of 11 dBi. The antenna radiation pattern can be swept in the entire azimuth plane in six steps with a 3-dB beamwidth of 60°. This antenna could be used in the base station of the wireless communication systems.

Active control on EBG structures for multiband antenna applications

In this work, a parametric analysis of an EBG layer behaviour based on continuous and discontinuous strips has been presented. The obtained results show that continuous and discontinuous strips present dual behaviour when considered as basic elements in the EBG structure. In addition, it has been observed that the discontinuity periodicity act on duality bandwidth. Thus, this duality can be electronically controlled by using diodes to switch between dual cases. Diode capacitor feature may introduce a shift on the duality bandwidth; this shift can be either compensated by the structure dimension or exploited to achieve bandwidth tuning. Experimental results have been presented and validate the simulated ones.

A Phase Confocal Method for Near-Field Microwave Imaging

A new fast imaging algorithm only using the phase information of electromagnetic fields for near-field microwave imaging is presented. This algorithm first compensates the phase shift as the wave back-propagates to the source, and then calculates the variance of phase of the shifted signals in terms of unit vector. This process is repeated at all focal points in the interested domain to form an image. The algorithm was validated by simulation and experiments; acceptable results were seen in both methods. To carry out the experimental test, we developed a fully automated microwave detection system containing a twin-antenna system whose movement can be controlled to form a synthetic aperture. Experiments were fully controlled by our self-developed software supporting remote operations. Although only 2-D imaging tests are discussed in this paper, the algorithm and the measurement system are able to fulfill 3-D rapid microwave scans.

Reduction of active elements in agile EBG antennas using their second band-gap

In this paper, a new design method of CEBG antennas has been proposed for reducing the required number of active elements and power supply in agile CEBG antennas. The proposed technique consists of using a continuous-metallic-rod structure in its second bandgap and in passband of discontinuous rods. Numerical simulations have been presented to validate the proposed concept. An antenna operating from 5.4 to 5.95 GHz has been designed. Good impedance matching and directivity have been achieved. It has been shown that the proposed technique allows reducing the number of active elements and power supply by more than 50%.

Reconfigurable antenna with high-directive beam using active cylindrical PRS

In this paper, the design method for an antenna with the high level of the directivity in the E-plane and the capability of turning radiation pattern has been proposed. The array of dipoles is used as radiating source. The antenna has advantage of using active PRS for controlling the direction of radiation pattern instead of using phase shifters. The active PRS also increase the directivity of antenna about 7 dB. With these features, the proposed antenna is suitable for applications in the base station of wireless communication systems.

Analysis of different defect configurations in CEBG structures for directive patterns

Electromagnetic bang gap (EBG) materials are periodic structures characterized by forbidden propagation of electromagnetic waves in their band-gap and by the ability to open localized modes inside the band-gap by introducing defects. Cylindrical electromagnetic band gap (CEBG) structures are radially and circularly periodic, and they present pass-band and stop-band to cylindrical electromagnetic waves. By applying a horn-shaped defect in these structures, it has been shown that a re-configurable directive pattern can be obtained. In (P. Ratasjack et al., 2004), experimental results for a reconfigurable CEBG-based antenna have been presented, whereas in (H. Boutayeb et al., 2006), an analysis of the transmission coefficient of CEBG structures and experimental results for a CEBG directive antenna have been proposed. In (H. Boutayeb et al., 2006), a new defect configuration has been proposed for reducing the power supply, but this solution leads to a narrower band. In this paper, new defect configurations are analyzed in order to reduce the number of active elements and the required power supply in CEBG-based agile antennas. The solution with the widest bandwidth is indicated.