Retrodirective Array Research Articles

An HF-Band Linear Retrodirective Array With Scale Model RCS Measurements

An HF-Band Linear Retrodirective Array With Scale Model RCS Measurements

Channel estimation for backscatter communication systems with retrodirective arrays

AbstractBackscatter communications, which originated from World War II, have been widely applied in the logistics domain, and recently attract emerging interest from both academic and industrial circles. Here, the backscatter communication systems equipped with retrodirective arrays that can re‐transmit the impinging signals back toward the direction of incidence are studied so as to reduce the power loss of the signals. Specifically, the authors consider the tag is equipped with retrodirective arrays to improve reliability and enhance communication range. The probability density function of channel coefficients is then derived. Next, a channel estimator based on Bayesian theory is proposed to acquire the modulus values of channel parameters and calculate its Bayesian Cramer–Rao Lower Bound. Finally, simulation results are provided to corroborate these theoretical studies.

Solar microwave fabric paper on the key technology for making our future satellite and skin surfaces for aircraft, eliminating APU’s

Solar-Microwave Fabric (SMF) is a mass-produced, thin, flexible membrane upon which is imprinted various combinations of solar cells, microwave patch antennas, and analog control devices. This is for applications such as solar power collection, power transmission, communication, and defense. It can be folded into a compact volume for transport and then unfurled for its operation. In its most sophisticated form, the SMF features the full complement of printed devices: solar cells, patch antennas, transceivers, and retro-directive phased array capability. This most mature capability can be applied to the Power-Star in section 1.6 (Figure 46) space solar power satellite, and to ground installations for combined solar power and air defense. The SMF has various modes of operation of, Solar Power Collection, Communications, Distribution & Defensive systems. Ultimately the Power/ Comm/Defense has one side printed as an “active” mode of power transmission whereby radiation is broadcast to a non-cooperative target and the return from the target is used as the beacon for the direction of a high-power density beam with focusing (vaporization). This could be applied for both ground-based power collection and air/space defense. World’s 1st exposure to: US Patent 11,251,658, Japan Patent 6,987,935.

Age of information for short-packet covert communication with time modulated retrodirective array

Age of information for short-packet covert communication with time modulated retrodirective array

NOMA-based retrodirective frequency diverse array for multi-user communication

Frequency Diverse Array (FDA) and retrodirective array have found applications in wireless communication networks, offering cost-effective and efficient beamforming capabilities. In this paper, a novel concept of the retrodirective frequency diverse array (RFDA) is introduced, which empowers each array element to handle multiple communication channels, thereby enabling support for multiple users. This is made possible by utilizing the non-orthogonal multiple access (NOMA) scheme. The antenna elements are organized in a uniform circular array configuration. The system supports the multitude of users by assigning them into distinct clusters based on the serving antenna and then allocating transmit power to each user based on their respective channel conditions and distances from the base station. Consequently, efficient schemes for user clustering and power allocation tailored to the NOMA-RFDA system are developed. As a result, multi-user connectivity is achieved while maintaining low design costs. The simulation outcomes affirm that the proposed system attains superior performance in terms of both data rate and energy efficiency when compared to similar reference schemes.

Covert Communication Using Time Modulated Retrodirective Array

Covert Communication Using Time Modulated Retrodirective Array

Antenna Array Design With Self-Adaptive In-Band Radar-Cross-Section Reduction and Beam Scanning

In this article, a novel antenna array with self-adaptive radar-cross-section (RCS) reduction has been proposed for the first time. The design mechanism of the proposed array is based on Van Atta retrodirective array and orbital angular momentum (OAM) vortex wave. By inheriting the adaptive beam tracking ability of the Van Atta array, the scattering beam of the proposed antenna can be automatically steered toward the incident wave direction without any prior knowledge of the incident wave. By reasonably designing the connection line lengths in the Van Atta array, the OAM scattering beam with null amplitude along the arbitrary incident direction is generated for the RCS reduction. As the demonstration, a dual-ring array with dual-polarization characteristic has been designed. By choosing a part of the antenna elements as the Van Atta array and the remaining part of the antenna elements as the radiation array, the designed antenna array can simultaneously achieve the beam steering and the low in-band RCS performance without the increase in the antenna array size. The prototype of the proposed array is fabricated, and good agreement between the simulation and the measurement verifies the proposed design.

Establishing Multi-User MIMO Communications Automatically Using Retrodirective Arrays

Establishing Multi-User MIMO Communications Automatically Using Retrodirective Arrays

A Planar 2-D 8×8 Van Atta Retrodirective Array for RCS Enhancement in a Wide Angular Range

Large-scale 2-D Van Atta retrodirective arrays (RDAs) typically use coaxial lines to form feeding networks, resulting in a large 3-D structure. In this study, a planar 2-D Van Atta RDA with 64 antennas and 32 transmission lines is proposed. By adding an air layer between the feeding network and the antenna array, double-layer microstrip lines can be used to realize a planar feeding network. Different types of length compensation networks are designed in limited space to eliminate the length differences between the 32 microstrip lines. Based on measured results, the Van Atta RDA works at 8.9–10.4 GHz, and the −6 dB beamwidths of the monostatic radar cross section (RCS) at 9.65 GHz are 78° (E-plane) and 90° (H-plane). Compared with the same size metal plane, the proposed Van Atta RDA has RCS enhancement of about 10–20 dB in a wide angular range.

A Wide-Angle and Fully Polarimetric Retrodirective Array Based on Tri-Polarized Antennas With Pattern Complementation

A wide-angle and fully polarimetric Van Atta retrodirective array (RDA) based on tri-polarized antennas is proposed in this article. By leveraging the pattern complementary and polarization orthogonality of three resonant modes including a TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> monopole-like mode and two orthogonal TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> microstrip patch modes, the RDA could better sense and retrodirect the incident wave with arbitrary polarization over a large field of view. A prototype of the RDA consisting of four tri-polarized antenna elements is designed and fabricated, which works at 5.8 GHz and has a low-profile planar structure with a compact volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.93\times 0.56\times 0.059\,\,\lambda _{0}^{3}$ </tex-math></inline-formula> . The simulated and measured monostatic radar cross-section (RCS) results show that, compared with the RDA composed of dual-polarized microstrip patches, this tri-polarized RDA has a significant improvement of the retrodirective angle range for the transverse-magnetic (TM) incident wave. Specifically, for the tri-polarized RDA, the −3 dB monostatic RCS beamwidth is 132°, and the −7 dB monostatic RCS beamwidth can reach 180°; while for the dual-polarized RDA, the −3 and −7 dB monostatic RCS beamwidths are only 52° and 73°, respectively.

Differential Retrodirective Array With Integrated Circuits in Low-Cost 0.18 μm CMOS for Automatic Tracking

This communication presents a differential retrodirective array (RDA) for real-time tracking. The proposed differential RDA consists of three phase-conjugating chips and two circularly polarized antenna arrays. The phase-conjugating circuit chip which is in 0.18-um CMOS process, includes a differential low-noise amplifier, a double balanced mixer and a differential power amplifier. The specifically designed chip consumes 38.4 mW with a low voltage supply of 1.2 V. Experimental results of monostatic and bistatic cases show that, the RDA has a 3-dB beamwidth up to 77°. To the best knowledgement of the authors, the proposed RDA with circular polarization, which is promising for tracking free-moving targets, is the first differential RDA enabled by specifically designed low-cost CMOS chips.

Efficient microwave power transfer system using retrodirective antenna array

ABSTRACT In this paper, we present a design method for a highly efficient retrodirective array (RDA)-based microwave power transfer (MPT) system for the mMTC scenario, and evaluate its characteristics through experiments. Long-range wireless power transfer is required to effectively support the mMTC situation. RDA-based MPT controls and tracks the power beam towards the device within a certain range and it enables efficient power transfer. The overall link budget analysis is examined first and the required antenna gain is calculated. The required antenna gain can be secured using multiple-antenna modules. So, it is possible to design an RDA-based MPT system. In this paper, we implement a reduced RDA-based MPT system and evaluate its characteristics to confirm the feasibility of this design method. Through experiments, it has been confirmed that additional gain can be secured by using multiple antenna modules, and the RDA function can be effectively operated to effectively make a power beam in the direction of the power receiver. Conclusively, the gain of about 2.2dB increased whenever the number of antennas is doubled. The experimental results also show that the RDA-based MPT system designed in this paper is capable of adaptive power beamforming from −30 degrees to 30 degrees.

Proof of Concept of a Low-Cost Beam-Steering Hybrid Reflectarray that Mixes Microstrip and Lens Elements Using Passive Demonstrators

In this article, a proof-of-concept study on the use of a hybrid design technique to reduce the number of phase shifters of a beam-scanning reflectarray (RA) is presented. An extended hemispherical lens antenna with feeds inspired by the retrodirective array is developed as a reflecting element, and the hybrid design technique mixes the lenses with the microstrip patch elements to realize a reflecting surface. Compared to the conventional designs that only use microstrip antennas to realize a reflecting surface, given a fixed aperture size the presented design uses 25 percent fewer array elements while shows comparable beam-steering performance. As a result of using fewer elements, the number of required phase shifters or other equivalent components such as RF switches and tunable materials is reduced by 25 percent, which leads to the reduction of the overall antenna system's complexity, cost, and power consumption. To verify the design concept, two passive prototypes with a center frequency at 12.5 GHz were designed and fabricated. The reflecting surface was fabricated by using standard PCB manufacturing and the lenses were fabricated using 3D printing. Good agreement between the simulation and measurement results is obtained. The presented design concept can be extended to the design of RAs operating at different frequency bands including millimetre-wave frequencies with similar radiation performances. The presented design method is not limited to the microstrip patch reflecting elements and can also be applied to the design of the hybrid RAs with different types of reflecting elements.

Passive 2-D Retro Directive Array Antenna with Adjustable Reflection Angle

Passive 2-D Retro Directive Array Antenna with Adjustable Reflection Angle

A Methodology for Remote Microwave Sterilization Applicable to the Coronavirus and Other Pathogens Using Retrodirective Antenna Arrays.

This paper describes an innovative remote surface sterilization approach applicable to the new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The process is based on the application of a liquid film on the surface or object under sterilization (OUS). A beacon signal is used to self-steer the transmitted power from the designed retrodirective antenna array (RDA) towards the OUS using circularly polarized fields; then, the sterilization is completed by raising and maintaining the required temperature for a certain time. Results suggest that the process takes 5 minutes or less for an angular coverage range over 60 degrees whilst abiding by the relevant safety protocols. This paper also models the power incident onto the OUS, providing consistent results with full-wave simulations. A practical RDA system is developed using a 2 × 1 microstrip patch array operating at 2.5 GHz and tested through the positioning of a representative target surface. Measurements, developed by sampling the power transmitted by the heterodyne RDA, are reported for various distances and angles, operating in the near-field of the system. To further validate the methodology, an additional experiment investigating virus deactivation through microwave heating was also developed. Measurements have been performed with an open cavity microwave oven on the Coronavirus (strain 229E) and egg white protein in a cuvette. This demonstrates that the temperature increases of aqueous films up to 70 n}{}^{circ }C by remote microwave-induced heat can denature proteins and deactivate viruses. Possible applications of the method include sterilization of ambulances, medical equipment, and internet of things (IoT) devices.

SOME METHODS OF CREATING SIGNS OF RADAR TARGETS THAT CAN BE USED TO DESIGN TRAINING TARGETS

Proposals for developing of radar training targets in decimeter and centimeter wave ranges in conditions of a previous uncertainty of radar signal parameters is developed. It based on the results of analysis and comparison of simple artificial reflectors and retrodirective antenna array characteristics. Targets for single-position radars are considered.

A Multi-Channel MAC Protocol With Retrodirective Array Antennas in Flying Ad Hoc Networks

In this paper, we propose a multi-channel medium access control (MMAC) protocol for the exploitation of retro-directive array antennas in Flying Ad Hoc Networks (named FA-MMAC). This FA-MMAC employs multiple channels and retro-directive array antennas to adjacent unmanned aerial vehicles (UAVs) to transmit simultaneously over the same channel without causing interference. The channel utilization characteristic of FA-MMAC increases the spatial reuse of channel and thus improve the system performance. The key idea is that UAVs first exchange control packets in control window to select data channels and to align beams before exchanging data packets in the data window. In this way, the hidden-terminal and deafness problems are reduced. UAVs can reserve channels and align beams through a circular directional transmission of control frames so that the protocol can take advantage of the benefits of retro-directive array antennas of spatial reuse and increased coverage without prior knowledge of the locations. We develop both antenna model and channel model for FA-MMAC protocol. Analysis and simulation results show that our proposed FA-MMAC can offer a significant performance gain for both static and mobile scenarios than the existing MMAC and 802.11-based protocols. Our findings reported in this paper provide some insights into the performance of multi-channel Flying Ad Hoc Networks which might help network researchers to contribute in the development of next generation UAVs.

Design of Rat-Race based Retrodirective Arrays for Backscatter Communications

Fast beaming tracking and security are important factors for the development of communication technology. A Retrodirective antenna (RDA) technique has been attenuated to one way of improving security. It has the interesting property of automatically responding to an incoming signal location without any prior knowledge of the direction of that source. The purpose of this paper is to design a Rat race coupler which acts as a Retrodirective mode in ANSYS. The resonant frequency of the coupler is 2.4 GHz. The Proposed Rat race couplers have been devised using the Glass Epoxy substrate (FR4) with dielectric constant (?r = 4.4). S parameters, radiation pattern, insertion and isolation losses are obtained from ANSYS software

Synthesis-free directional modulation for retrodirective frequency diverse array

Combination of directional modulation (DM) and frequency diverse array (FDA) provides a novel opportunity for enabling physical layer security because of the enhanced ability of distance resolution. However, in the existing studies, the time-varying nature of the FDA pattern is usually ignored. In this paper, a modified model of FDA-DM is proposed, in which the ignored time factor in the previous studies is taken into consideration for providing a new and more accurate perspective on evaluating the security of FDA-DM. Furthermore, we reveal that FDA-DM can achieve angle-dependent and directional-time-coupled-dependent security. After that, based on the retrodirective FDA (RFDA) with a new structure, a novel synthesis-free FDA-DM scheme is proposed for both overcoming the limitations of the FDA-DM scheme and allowing self-tracking the position of the pilot signal without any prior knowledge. Meanwhile, a new set of nonlinear frequency offsets, defined as rearranged linear frequency offsets (RLFOs), is also proposed for both combining the advantages of the linear/nonlinear frequency offsets and bringing conveniences to practical implementation. In addition, the closed-form expression of the average signal-to-artificial-noise-ratio (SANR) is given out for evaluating the security performance of the proposed scheme. Finally, numerical results are presented to verify both the accuracy of the proposed theoretical analysis and the superiority of the RFDA-DM scheme.

다중 사용자 마이크로웨이브 무선전력전송 시스템 설계와 전력전송 효율 평가

In this study, a wireless power transmission system supporting multiple users was built based on a power pilot. The power pilot transmits the authorization and power status information of the user to the power station. The power station first transmits power to the user in the lowest power state for the longest time. A code-division multiple access system was used for supporting multiple receiving users and a non-uniform time-division multiple access system, which allocates power charging time differently to each user, was employed. Consequently, power was transmitted according to the power priority of multiple users. Finally, the power efficiency of the retrodirective array antenna system based on a phase-locked loop was increased by conjugating the phase of the power pilot received from the user and transmitting it to the user. We designed these three systems and verified their performance through simulations to build a wireless power transmission system that supports multiple users.