Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

Tunable Reflectarray Cell for Wide Angle Beam-Steering Radar Applications

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46 -reflectarray cell is designed at the frequency of 11.5 GHz, obtaining a phase agility of about 330 ∘ . The cell is successfully adopted for the design of a 21 × 21 reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated within a wide angular range

ELECTRONICAL LY RECONFIGURABLE FS S - INSPIRED TRANSMITARRAY FOR TWO DIMENS IONAL BEAMSTEERING FOR 5G ANDRADAR APPL ICATIONS AT 2 8 GHZ

In this dissertation, the author’s work on a 28 GHz transmitarray capable of antenna beamsteering for various wireless applications, is presented. Such device allows for the adjustment of the radiation pattern of an antenna by changing its main lobe direction, without the need of any mechanical means. A unit-cell based on a square-slot Frequency Selective Surface (FSS) is designed, simulated and optimised through several full-wave simulations, using an electromagnetic solver (CST MWS). Subsequently, the unit-cell was extended to a 10x10 array configuration in order to enable Two-dimensional (2D) beamsteering. This work yielded the fabrication of a prototype composed of four passive transmitarray lens, which were experimentally tested and characterised. Finally, a novel unit-cell based on a double square-slot intended aiming at active beamsteering was also studied and optimised in simulation environment. From this work, it was demonstrated that transmitarray can be seen as feasible alternative to many traditional beamsteering techniques, such as phased antenna arrays, while reducing the RF burden of the overall system using only a single radiation source. This fact, allied with it’s ease of integration, reduced cost and low-profile characteristics make transmitarrays a desirable solution for 5G and RADAR applications, among others

A Transportable Reflectarray Antenna for Satellite Ku-band Emergency Communications

The design of a Ku-band reconfigurable reflectarray antenna for emergency satellite communications is presented. Bidirectional high data rate satellite links are needed in emergency conditions where other telecommunication infrastructures are not available. In order to operate in this type of scenario, an antenna should be deployable, transportable, and easily repointable. The need of an automatic and fast satellite location and pointing system leads to a completely electronic reconfigurable antenna. The operative bandwidth is from 10.7 to 12.5 GHz for reception and from 14 up to 14.5 GHz for transmission (30% of relative bandwidth). The selected antenna architecture is based on a dual reflectarray system comprising a passive subreflectarray and an active main reflectarray made of reconfigurable 1-bit elementary cells based on PIN diodes

Dual-Layer Single-Varactor Driven Reflectarray Cell for Broad-Band Beam-Steering and Frequency Tunable Applications

A dual-layer active reflectarray configuration is proposed for broad-band beam-steering and/or frequency-tunable applications. A unit cell composed by two stacked fixed-size rectangular patches, properly loaded with a single varactor diode, is designed to realize the dynamic phase tuning mechanism. The proposed approach offers wider bandwidths, with respect to the existing varactor-based reflectarray cells, and quite good frequency reconfigurability features, as demanded by several radar or satellite communication applications. An X-band reflectarray cell is fabricated and tested, to prove the effectiveness of the proposed approach, achieving a 318° phase agility within a measured frequency range of about 14.6% with respect to the central design frequency (i.e., 11 GHz). Wideband beam-steering reflectarray designs are demonstrated, showing 1-dB gain bandwidths equal to 9-10%

Additively Manufactured Shape-changing RF Devices Enabled by Origami-inspired Structures

The work to be presented in this dissertation explores the possibility of implementing origami-inspired shape-changing structures into RF designs to enable continuous performance tunability as well as deployability. The research not only experimented novel structures that have unique mechanical behaviour, but also developed automated additive manufacturing (AM) fabrication process that pushes the boundary of realizable frequency from Sub-6 GHz to mm-wave. High-performance origami-inspired reconfigurable frequency selective surfaces (FSSs) and reflectarray antennas are realized for the first time at mm-wave frequencies via AM techniques. The research also investigated the idea of combining mechanical tuning and active tuning methods in a hybrid manner to realize the first truly conformal beam-forming phased array antenna that can be applied onto any arbitrary surface and can be re-calibrated with a 3D depth camera.Ph.D

Development of Characterization Methods for Antennas and Quasi-Optics

This dissertation focuses on the development of characterization methods for antennas and quasi-optical components. The dissertation presents three new methods to deal with certain limitations occurred during the antenna measurement processes. First, a new technique using the Chebyshev polynomials has been proposed to process the antenna measurements obtained in non-anechoic sites to obtain equivalent free space radiation patterns. This new technique combines the principle of a FFT-based method with the special relationship between coefficients of the Bessel-Chebyshev polynomials. Experimental results are presented to demonstrate the potential of this approach over conventional time gating techniques for a certain class of problems. Second, a new antenna pattern retrieval method is proposed. In this method, the antenna reflection coefficient is measured many times when a unique reflective load with known spatial reflection properties is placed near the antenna in each measurement. The antenna pattern is obtained from the measurements with an inversion algorithm. Simulations have been used to verify the theoretical basis and the method has been experimentally demonstrated at 30 GHz. The results show that the method could enable sufficient accuracy with low gain antennas or in the vicinity of main lobe with directive antennas. Third, a new technique is presented to realize a wideband hologram compact antenna test range (CATR) by linearly adjusting the feed location. The wideband formulas for linearly adjusting the feed have been discussed and verified. The performance of the wideband operation has been demonstrated by the measured results at W (95 GHz) and D (170 GHz) bands for the hologram aperture diameter of 350 mm. The dissertation also discusses characterization of quasi-optics, namely, MEMS-based high-impedance surface (HIS) and reflectarray elements. First, the reflection properties of the single unit cell structure of MEMS-based HIS is studied, tunability of the MEMS varactors and beam steering of a large structure at 80 GHz has been demonstrated with a simplified model. The structure allows steering of the beam within the range from -45º to +45°. A quasi-optical measurement setup has been built for the experimental characterization. Second, the design and optimization process of reconfigurable reflectarray element integrated with MEMS-based phase shifter at 120 GHz is studied. Also, the dielectric properties of SU-8 substrate have been characterized with on-wafer measurements. Several design parameters which could affect the modulation efficiency have been studied

Potential of utilizing solar chimney as an energy efficiency measure in Malaysian hospitals

Many energy efficiency measures were proposed to reduce the high energy demand in hospitals. Solar chimney is a form of passive solar heating and cooling system that can be used for temperature regulation and ventilation of a building This paper explores the solar chimney’s performance in terms of air changes per hour (ACH) in Malaysian tropical climate were thus, investigated for its feasibility in Malaysian hospitals. A 2D CFX model is simulated at four different times (8 am, 10 am, 2pm and 4 pm). Openings provided at the bottom and top of the chimney and at the right of the cabin with dimension of 1 m located 1 m from the floor level to allow air with room temperature to enter the cabin and towards the solar chimney. Simulations were validated form previous study and the study use solar irradiance from previous study to simulate Malaysia’s solar irradiance and outside temperature. Steady state and laminar flow were used in this study to model air turbulence in the cabin to the solar chimney. The results show that the simulations have been validated and all 4 of different time have been simulated. 2 pm with the highest solar irradiance have the most air changes per hour (ACH), while 8 am with the lowest solar irradiance have the least ACH. Further experimental study is currently ongoing