Reconfigurable Apertures Research Articles

Silicon-based optical phased array with a reconfigurable aperture for “gaze” scanning of LiDAR

Light detection and ranging (LiDAR) serves as one of the key components in the fields of autonomous driving, surveying mapping, and environment detection. Conventionally, dense points clouds are pursued by LiDAR systems to provide high-definition 3D images. However, the LiDAR is typically used to produce abundant yet redundant data for scanning the homogeneous background of scenes, resulting in power waste and excessive processing time. Hence, it is highly desirable for a LiDAR system to “gaze” at the target of interest by dense scanning and rough sparse scans on the uninteresting areas. Here, we propose a LiDAR structure based on an optical phased array (OPA) with reconfigurable apertures to achieve such a gaze scanning function. By virtue of the cascaded optical switch integrated on the OPA chip, a 64-, 128-, 192-, or 256-channel antenna can be selected discretionarily to construct an aperture with variable size. The corresponding divergence angles for the far-field beam are 0.32°, 0.15°, 0.10°, and 0.08°, respectively. The reconfigurable-aperture OPA enables the LiDAR system to perform rough scans via the large beam spots prior to fine scans of the target by using the tiny beam spots. In this way, the OPA-based LiDAR can perform the “gaze” function and achieve full-range scanning efficiently. The scanning time and power consumption can be reduced by 1/4 while precise details of the target are maintained. Finally, we embed the OPA into a frequency-modulated continuous-wave (FMCW) system to demonstrate the “gaze” function in beam scanning. Experiment results show that the number of precise scanning points can be reduced by 2/3 yet can obtain the reasonable outline of the target. The reconfigurable-aperture OPA (RA-OPA) can be a promising candidate for the applications of rapid recognition, like car navigation and robot vision.

Theoretical Study and Systematic Design of Multiport Wire Antenna

This work presents a systematic study of multi-port wire antennas (MPWA) as a step toward reconfigurable radiation apertures, an essential component in modern wireless systems. We predict the surface current distribution (SCD) of the multi-port structure and derive a closed-form relation for the radiation pattern of the aperture as a function of its input port excitations. Based on this, we present a design procedure for optimal selection of port locations and their respective input excitations with a desired radiation pattern in mind. Finally, we develop a computationally efficient method to derive the impedance matrix of the multi-port aperture all without the need for full-wave simulation. As an example, we use this method to design a 15-port mm-wave antenna. We demonstrate that for a selected aperture size and port locations and only by adjusting the phases and amplitudes of excitation, we can reconfigure the MPWA to synthesize a desired beam at any frequency within the 20-40GHz range. There is good agreement between results predicted by this method compared to those from EM-based simulations, enabling an efficient and scalable approach for designing multi-port radiators.

Micro-fabrication considerations for MEMS-based reconfigurable antenna apertures: with emphasis on DC bias network

This note addresses the main challenges involved in monolithic micro-fabrication of large capacitive-MEMS-based reconfigurable electromagnetic apertures in antenna applications. The fabrication of a large DC bias line network, and also the metallic features in such apertures, requires special attention and optimization. It is shown that the choice of DC bias network material can impact DC and RF performance of the structure, and a trade-off between switching time and radiation pattern integrity should be considered.

Electronically reconfigurable metal-on-silicon metamaterial

Reconfigurable metamaterial-based apertures can play a unique role in both imaging and in beam-forming applications, where current technology relies mostly on the fabrication and integration of large detector or antenna arrays. Here, we report the experimental demonstration of a voltage-controlled, silicon-based electromagnetic metamaterial operating in the W-band (75-110 GHz). In this composite semiconductor metamaterial, patterned gold metamaterial elements serve both to manage electromagnetic wave propagation while simultaneously acting as electrical Schottky contacts that control the local conductivity of the semiconductor substrate. The active device layers consist of a patterned metal on a 2-{\mu}m-thick n-doped silicon layer, adhesively bonded to a transparent Pyrex wafer. The transmittance of the composite metamaterial can be modulated over a given frequency band as a function of bias voltage. We demonstrate a quantitative understanding of the composite device through the application of numerical approaches that simultaneously treat the semiconductor junction physics as well as wave propagation.

Frequency and Radiation Pattern Reconfigurability of a Multi-Size Pixel Antenna

Pixel reconfigurable apertures constitute one of the most adaptable structures regarding antenna reconfiguration, being capable to achieve frequency and pattern compound reconfiguration. However, pixel antennas require a large amount of switches (typically above 100) that severely impact the antenna efficiency, complexity, cost and reconfiguration time. This paper presents a novel technique to mitigate the inherent complexity of pixel antennas by including multiple sized pixels divided over driven and parasitic regions. The technique has been applied to a planar monopole architecture leading to a low-complexity prototype of small dimensions and requiring only 12 switches. Its reconfiguration properties have been fully characterized through exhaustive measurements. Frequency reconfiguration is achieved from 1 GHz to 6 GHz with simultaneous beam-steering capabilities, being capable of synthesizing at each frequency an omnidirectional pattern and up to 5 directive patterns steered towards directions covering an angular range of almost 180°.

A Wideband Reconfigurable Transmitarray Element

Transmitarrays have been shown to be viable architectures for achieving high-directivity reconfigurable apertures. Two reconfigurable transmitarray elements, using single and stacked patches, based on proximity-coupled feeding and two balanced reconfigurable bridged-T phase shifters are presented. Both designs achieve over 400 of phase range and achieve average insertion losses of 3.6 dB. Compared to existing proposed transmitarray elements, the stacked-patch element has a much smaller physical profile, with a lens thickness of only 0.17 λ in free-space, while achieving a large bandwidth of 500 MHz at 5 GHz (10%). Other considerations such as the mutual coupling and beam squint of an array using the stacked-patch element are also discussed.

MIMO Capacity Enhancement Using Parasitic Reconfigurable Aperture Antennas (RECAPs)

The capacity of multiple-input multiple-output (MIMO) systems employing reconfigurable apertures (RECAPs) is carefully analyzed with a realistic thermal noise model for three different power constraints: average receive signal-to-noise ratio (SNR), maximum effective isotropic radiated power (EIRP), and average transmit power. Performance is studied not only for a noise-limited single link, but also in the presence of interference and multiple RECAP-equipped users. The impact of loss and finite bandwidth on the operation of the RECAP is also considered. For the practical EIRP constraint, results show that a compact MIMO RECAP (1λ×1λ) provides 30%-50% capacity improvement for a single link. It is also found that RECAPs are even more beneficial in interference-limited and multiuser scenarios, where capacity is increased by 50% to 800% depending on the severity of the interference, indicating that RECAPs are an attractive solution for future wireless systems employing aggressive spectral reuse.

Investigation of the S-PIN Diodes for Silicon Monolithic Antennas With Reconfigurable Aperture

Investigations of surface p-i-n (S-PIN) diodes developed for silicon monolithic antennas with reconfigurable aperture have been described. The main criteria for choosing a suitable substrate for the S-PIN diodes have been extensively discussed. Based on this analysis, it has been found that dedicated silicon-on-insulator (SOI) substrates meet the requirements of efficient and lossless wave propagation. Experimental results shown in this paper confirm the applicability of SOI substrates for manufacturing of electrically reconfigurable slot apertures. The results show that S-PIN diodes realized on SOI substrates are suitable for various microwave and millimeter-wave applications.

Frequency-selective surfaces to enhance performance of broad-band reconfigurable arrays

We present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs on the basis of the reflection coefficient amplitude and were intended for radome applications rather than substrates. Designing FSSs subject to phase requirements is seen to require some compromise in the magnitude. Broad-band requirements also present us with a need for noncommensurate FSS designs.

MEMS and Si micromachined circuits for high-frequency applications

RF micromachining and microelectromechanical structure (MEMS) technology promise to provide an innovative approach in the development of effective and low-cost circuits and systems. This technology is expected to have significant application in the development of low-cost antenna arrays and reconfigurable apertures, due to its potential to support novel systems architectures. This paper presents a brief history and the state-of-the-art in the development of RF MEMS devices, with primary emphasis on switches and Si-micromachined circuit components for use in high-performance high-density on-wafer packaged circuits.