Active Reflectarray Research Articles

Miniaturized Beam Reconfigurable Reflectarray Antenna With Wide 3-D Beam Coverage

A miniaturized electrical beam-scanning reflectarray antenna providing a directional beam and wide steering ranges with fixed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $ </tex-math></inline-formula> -polarization is proposed. To accomplish these properties, we devise a new active reflectarray cell that can control both the phase and polarization of incident waves. Accordingly, we can enforce all reflected waves to constructively interfere with each other in all target directions. To feed the proposed reflectarray cells, an omnidirectional monopole antenna is installed at the center of the reflectarray, which illuminates the reflectarray evenly. In addition, because the monopole feeder is directly connected to the reflectarray, we can significantly reduce the overall volume of the antenna down to about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5~\lambda ^{3}$ </tex-math></inline-formula> with a small F/D ratio of 0.147. Consequently, the proposed antenna attains a wide scan coverage and directional beam patterns. Moreover, the antenna can also maintain polarization direction stably, which is strongly required for dynamically moving platforms such as drones and unmanned aerial vehicles (UAVs). The experimental results agree well with the predictions, proving the validity of our approach.

Reconfigurable Reflectarray Antenna: A Comparison between Design Using PIN Diodes and Liquid Crystals

This work presents the design and analysis of active reflectarray antennas with slot embedded patch element configurations within an X‐band frequency range. Two active reflectarray design technologies have been proposed by digital frequency switching using PIN diodes and analogue frequency tuning using liquid crystal‐based substrates. A waveguide simulator has been used to perform scattering parameter measurements in order to practically compare the performance of reflectarray designed based on the two active design technologies. PIN diode‐based active reflectarray unit cell design is shown to offer a frequency tunability of 0.36 GHz with a dynamic phase range of 226°. On the other hand, liquid crystal‐based design provided slightly lower frequency tunability of 0.20 GHz with a dynamic phase range of 124°. Moreover, the higher reflection loss and slow frequency tuning are demonstrated to be the disadvantages of liquid crystal‐based designs as compared to PIN diode‐based active reflectarray designs.

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%.

A Low-Power 28-nm CMOS FD-SOI Reflection Amplifier for an Active F-Band Reflectarray

A new topology of a low-power F-band reflection amplifier for active reflectarrays is proposed and demonstrated using a CMOS fully depleted silicon-on-insulator 28-nm process. The design enables frequency response and center frequency tuning, as well as phase control of the reflected signal. The chip consumes a core area of only $90\times 80~\mu\text{m}^{2}$ and is incorporated into a $2\times 2$ printed reflectarray antenna, implementing the first co-polarized active reflectarray. Such implementation enables, for the first time, active reflectarrays with dual polarization ability, which can be used for full-duplex links, as well as polarization diversity applications. Design considerations for a stable reflection amplifier, as well as measurement results of the reflection amplifier and reflectarray, are presented in this paper. Variable stable gain of 5–25 dB at the frequency range of 106–127 GHz was achieved, with noise figure of 10.5–11.7 dB. The total power consumption was 6–20 mW, depending on the chosen frequency response. An active antenna gain of 28 dBi was measured for the $2\times 2$ reflectarray.

A Two-Bit Reflectarray Element Using Cut-Ring Patch Coupled to Delay Lines

In this paper, a two-bit element for reflectarray applications is presented. The proposed element is based on the cut-ring patch coupled to delay lines through an annular slot. The four states of the reflection phase with a step of 90◦ are achieved with two switches. This reported work is the first step towards the 2-bit active reflectarray element. Prototypes of the element have been fabricated and characterized in X-band using waveguide simulator. Measured results show good characteristics with low magnitude losses and the bandwidth of 1.7-bit resolution is over 5%.

Characteristics of digitised millimetre‐wave metal reflectarray antennas

Reflectarray antennas composed of rectangular grooves with a digitised phase-shift element are designed for the millimetre-wave region. The digitised metal antennas have been realised by quantising the phase shift of each rectangular groove. For 4 bit quantised antennas, the far-field patterns are very similar to those of the non-digitised case and especially show that the measured gain of the 2 bit reflectarray is only 1 dB lower than that of a non-digitised reflectarray antenna. These results will contribute to saving manufacturing cost and time and the guidance of the phase shifter for an active metal reflectarray antenna for millimetre-wave wireless networking or imaging systems.

Passive and Active Reconfigurable Scan-Beam Hollow Patch Reflectarray Antennas

The design concept of passive and active reconfigurable reflectarray antennas has been proposed and tested. The antenna elements in the array are identical hollowed patches. In the first phase of study the slots are loaded with a SMD capacitor to set the required phase shift needed for array implementation. Simulations show promising results. Mounting a SMD capacitor in such a configuration can be considered as the first step in using capacitive loading on a slotted patch for active microstrip reflectarrays. It is shown that by adjusting the capacitance values it is possible to scan the beam. In the second phase, the patch elements are loaded with active varactor-diode device which its reflected phase can be varied. This phase alteration is based on the variation of the diode capacitance which can be achieved by varying the biasing voltage of the active varactor device. In latter approach by activating these varactor devices, the phase of each antenna element in the array configuration can be adopted dynamically and consequently, its beam direction can be reconfigured. The reflectarrays incorporating passive and active elements have been built and tested at 7.0 GHz and 6.0 GHz, respectively. The performance of the proposed reconfigurable antennas is excellent, and there is good agreement between the theoretical and measurement results which pioneers design of arbitrarily reconfigurable antennas.

Active Reflectors: Possible Solutions Based on Reflectarrays and Fresnel Reflectors

An overview about some of the recent Spanish developments on active reflectors is presented. In the first part, a novel beamsteering active reflectarray is deeply studied. It is based on implementing in each elementary radiator an IQ modulator structure, in which amplitude and phase control of the scattered field is achieved. Finally, a special effort is made in offering solutions to overcome the active antenna integration problems. In the second part, the active concept is firstly extended to Fresnel reflectors. Thanks to the development of a proper simulator, this special structure can be easily analysed. This simulator allows the study of performance of this kind of reflectors and, applying evolutionary algorithms, to find optimal configurations of reflector in accordance with the given specifications for the conformal radiation pattern.

Controlling the scattered field in a reflectarray element using a novel technique

AbstractIn this paper, a novel gain/phase adjustment unit to be employed as the cell of an active reflectarray is proposed. Based on accurate control of PHEMT behaviour in normal and inverse operation, a dual‐device variable‐gain biphase amplifier (VGBPA) has been designed for each branch of such an IQ modulator. Its proper integration in a dual‐feed aperture‐coupled square patch allows the use of orthogonal polarizations for retransmitting the received signal after selecting the desired amplitude and phase for the scattered field. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 808–810, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21481

Active reflectarray with beamsteering capabilities

This paper presents an active reflectarray topology with the capability of steering the main beam and achieving different amplitude distributions. An aperture-coupled patch with perpendicular feeds was selected as the radiating element. One of its ports is employed to receive the signal and the other to retransmit it with the phase and gain selected in an IQ modulator. A 4 × 2 lab model is implemented and the measurement results of the radiation pattern control are shown. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 101–105, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21275

An integrated active microstrip reflectarray element with an internal amplifier

A new active microstrip reflectarray element (unit cell) with an internal microwave integrated circuit amplifier is introduced. The amplifier resides in a small slot within the footprint of the square patch antenna and is connected between the feed points for the patch's orthogonal polarizations. This element results in reduced array element spacing, reduced transmission line losses through elimination of long feed lines, and a simplified fabrication process compared to other active reflectarray unit cells. Patch geometries with several slot shapes are studied with simulations to arrive at an antenna configuration with good return loss and isolation characteristics. The stability and gain of the system are analyzed over frequency. Measured radiation pattern and gain data for a single element and a small array agree well with predictions and demonstrate the element's capabilities. Limitations of the active element, approaches to mitigate these limitations, and directions for future work are discussed.