Van Atta Arrays Research Articles

RCS Enhancement of Millimeter Wave LTCC Van Atta Arrays With 3-D Printed Lenses for Chipless RFID Applications

RCS Enhancement of Millimeter Wave LTCC Van Atta Arrays With 3-D Printed Lenses for Chipless RFID Applications

Simple Millimeter Wave Identification System Based on 60 GHz Van Atta Arrays.

The paper presents a proof-of-concept of a millimeter-wave identification system based on Van Atta array tags in the 60 GHz band. For interrogation of the tags, a vector network analyzer and a measurement transceiver were employed in alternative test configurations. The design, fabrication and measurements of co- and cross-polarized Van Atta arrays are presented in the paper. They can be treated as simple chipless RFID tags with frequency-response-based identification. Tags with various resonance frequencies are designed by scaling an optimized base model. The designed 57-67 GHz co-polarized and cross-polarized tags have small dimensions of approximately 23 mm × 21 mm and 40 mm × 25 mm, and they exhibit radar cross-section (RCS) levels of -16 dBsm and -21 dBsm, respectively. Owing to the retrodirective properties of Van Atta arrays, the RCS can be maintained at a high level within a broad range of angles of incidence. The system was validated in an anechoic chamber where the spectral responses of all the manufactured tags can be clearly distinguished from the environment, enabling their identification. Tests in a reflective environment were also performed, and they have shown that only the cross-polarized tags could be detected and identified in the presence of reflections from the tags' surroundings.

Metasurfaces for Reconfiguration of Multi-Polarization Antennas and Van Atta Reflector Arrays

This paper discusses the application of metasurfaces for three different classes of antennas: reconfiguration of surface-wave antenna arrays, realization of high-gain polarization-reconfigurable leaky-wave antennas (LWAs), and performance enhancement of van Atta retrodirective reflectors. The proposed surface-wave antenna is designed by embedding four square ring elements within a metasurface, which improves matching and enhances the gain when compared to conventional square-ring arrays. The design for linear polarization comprises of a 1 × 4 arrangement of ring elements, with a 0.56λ spacing, placed amidst periodic patches. A 2 × 2 arrangement of ring elements is utilized for reconfiguration from linear to circular polarization, where a similar peak gain with better port isolation is realized. A prototype of the 2 × 2 array is fabricated and measured; a good agreement is observed between simulations and measurements. In addition, the concepts of the design of polarization-diverse holographic metasurface LWAs that form a pencil beam in the desired direction with a reconfigurable polarization are discussed. Moreover, recent developments incorporating polarization-reconfigurability in metasurface LWAs are briefly reviewed. In the end, the theory of van Atta arrays is outlined and their monostatic RCS is reviewed. A conventional retrodirective array is designed using aperture-coupled patch antennas with a microstrip-line feeding network, where the scattering from the structure itself degrades the performance of the reflector. This is followed by the integration of judiciously synthesized metasurfaces to reconfigure and improve the performance of retrodirective reflectarrays by removing the above-mentioned undesired scattering from the structure.

Radiative Wireless Power-Transfer System Using Wideband, Wide-Angle Slot Arrays

This paper analyzes the benefits of using wideband, wide-angle arrays in radiative wireless power-transfer systems. A physical optics (PO) code is used to investigate the focusing capabilities and operating range of two 2-D antennas: Van Atta arrays and phase-conjugate/time-reversal arrays. In the PO analysis, the antennas are assumed to be ideal mirrors, which do not backscatter the impinging energy but rather completely absorb and reemit it. Sources located in both the near and far field of the antennas are considered. It is shown that for distances larger than the mirror size, the two antennas have similar focusing capabilities. In such scenarios, a Van Atta approach is preferred over a phase-conjugate approach due to its ease of implementation. Antenna elements used to realize these arrays/mirrors are typically resonant and exhibit strong backscatter, a limited field of view, and small bandwidth. To overcome these limitations, we propose an array/mirror consisting of long slots fed by parallel plate waveguides. A spectral Green’s function approach is used to derive the scattering performance of the infinite array in reception. It is shown that the array can collect the total power impinging from a remote source over a large field of view and bandwidth. The conclusions arrived at for the infinite case are extended to the finite case through full-wave simulations. It is shown that the array can refocus the energy impinging from a close source over a large bandwidth. An infinite magnetic line source is considered as an example. An accurate expression is provided for the voltage distribution across the feed lines of the array. The proposed solution paves the way toward the practical implementation of ideal Van Atta and time-reversal/phase-conjugate mirrors. The wideband behavior of the array may enable high-power, pulsed retrodirective arrays.

A novel bi-directional amplifier with applications in active van atta retrodirective arrays

A novel two-port bi-directional amplifier, which may simultaneously amplify the waves coming from both ports, is proposed and demonstrated in this paper. Using this amplifier, a two-element active Van Atta retrodirective array is implemented and compared to a four-element passive array. The bi-directional amplifier is constructed by two identical one-port reflection-type amplifiers and a 3-dB 90/spl deg/ hybrid. The reflection-type amplifier is designed using an FET with a single-power-supply configuration. A quarter-wavelength microstrip radial stub is connected to the device's source terminal to narrow down the negative-resistance frequency range so as to avoid oscillation at undesired frequencies. The fabricated bi-directional amplifier provides the transmission gain over the frequency band from 5.76 to 6.88 GHz, with a peak value of 9.1 dB at 6.04 GHz. Printed Yagi antennas with four directors are adopted to build both the active and passive Van Atta arrays. The 3-dB back-scattering beamwidth of the active array is measured as wide as 74/spl deg/. Finally, it is observed from the measurements that, although only half of the antenna elements are used, the active Van Atta array produces a back-scattering field level 4.5 dB, on average, higher than the passive one does. This verifies the performance of the bi-directional amplifier.

In defense of dipole Van Atta arrays

In defense of dipole Van Atta arrays

Discussion on “Some properties of Van Atta arrays and the use of 2-way amplification in the delay paths”

Discussion on “Some properties of Van Atta arrays and the use of 2-way amplification in the delay paths”

Some properties of Van Atta arrays and the use of 2-way amplification in the delay paths

The paper describes how the principle of a Van Atta linear array may be extended to circular arrays, which can act as corner reflectors over 360°. It is also shown that several methods are available for varying the direction of the reflected signal relative to the incident wave. The properties of such arrays with 2-way amplification in the delay paths is discussed, and some possible applications are suggested in the field of responder beacons and satellite communication.

Communications Satellites Using Arrays

Passive reflectors require large ground antennas and powers but permit use of unstabilized reflectors. Active systems, on the other hand, offer attractive performance through high directivity antennas but generally require stabilized vehicles. Further, the reliability of a satellite repeater amplifier is a critical factor. Automatic angle return arrays are investigated for both passive and active systems. These arrays, called Van Atta arrays, return a signal in the direction of incidence and are effective over at least ±45°. Thus only partial stabilization or single axis (spin) stabilization need be used, greatly simplifying the station-keeping orbit control problem. An active Van Atta (AVA) scheme has inherently high reliability since many of the distributed amplifiers can fail without serious performance degradation. The distributed structure also allows use of low-power solid-state amplifiers. This paper points up the salient advantages of the AVA system, and de'ineates the major areas where further work is indicated.