1,721,131 research outputs found
Characteristic Modes Analysis of a Near-Field Polarization-Conversion Metasurface for the Design of a Wideband Circularly Polarized X-Band Antenna
Full text linkA metasurface (MS) based on loop elements operating in the near field of a linearly-polarized microstrip antenna is employed to realize a circularly polarized radiated field. The properties of the loop unit cell are highlighted with the help of the Characteristic Mode Analysis that is employed for investigating the achievable linear to circular polarization conversion bandwidth and providing the guidelines for the design of the final antenna. A finite structure comprising 4×4 unit cells is tailored for achieving a circularly polarized far field within the whole X-band adopted for satellite communications (7.25 GHz-7.75 GHz, 7.9 GHz-8.4 GHz). A simple but effective single-port excitation scheme is adopted, and the overall performance are assessed by measurements on the fabricated prototype. The good agreement between simulated and measured results confirms the reliability of the proposed approach as well as the meaningful insight provided by Characteristic Modes Theory
Penrose Tiling Subarrays Exploiting Mixed Antenna Element Factors for Large-Scanning Phased Arrays
No full textLow Profile Dielectric Transmitarray Based on Additive Manufacturing Technology
No full textA preliminary study concerning the possibility to exploit Additive Manufacturing (AM) technologies for the fabrication of a transmitarray (TA) is addressed. More in detail, dielectric unit cells are tailored to alter the phase profile of a TA panel operating at 30 GHz
A Chipless RFID Based on Multiresonant High-Impedance Surfaces
No full textA novel chipless RF identification based on a multiresonant high-impedance surface is proposed. The structure is based on a finite metallic frequency-selective surface (FSS) comprising 2× 2 (30 mm× 30 mm) or 3× 3 (45 mm× 45 mm) unit cells. The FSS unit cell is formed by several concentric square loop resonators. The thin structure performs deep absorptions of the impinging signal at several resonant frequencies related to the loop resonators. If one of the printed loops in the unit cell is removed, the corresponding absorption peak disappears from the reflected signal giving the possibility of encoding a desired bit sequence. The proposed structure exhibits some intrinsic advantages, such as scalability (bit number increase) without any size increase, polarization independence, large read range, and the capability of operating when mounted on metallic objects. A transmission line model is employed to illustrate the operation principle of the structure, whereas measurements on realized prototypes are provided to assess the reliability and effectiveness of the proposed desig
Double-loop antenna for wireless tyre pressure monitoring
No full textThe design of a double-loop antenna operating at two distinct frequencies is presented for wireless tyre pressure monitoring systems. The radiation properties of the printed antenna, placed inside the wheel and with the tyre rubber, are discussed as well as the performance in terms of gain and power handling
Normalization-Free Chipless RFIDs by Using Dual-Polarized Interrogation
Full text linkA reliable encoding/detection scheme for chipless radio frequency identification (RFID) tags, free from any normalization procedure, is presented. The key strategy of the present approach consists in storing the information in the difference between vertically and horizontally polarized reflection coefficients of a completely passive tag. The measured reflection coefficients are preemptively filtered in the time domain to remove most of harmful effects due to the antenna coupling and environment multipath, and finally they are subtracted to obtain the differential response. A couple of chipless tag configurations suitable for providing the desired spectral response are presented. The resonators consist of an artificial impedance surface comprising either concentric rectangular loop resonators or square loop resonators loaded with stubs. The presented approach is experimentally verified in a non-anechoic environment, and its robustness is proved. This calibration-free approach could pave the way to practical applicability of chipless RFID tags in realistic scenarios with unknown response
Compact Triple-Frequency Antenna for Sub-GHz Wireless Communications
No full textThe design of a compact printed antenna operating concurrently at three distinct frequencies is presented for sub-GHz wireless communications. The radiation properties of the antenna, realized by using a low-cost PCB process on FR4 substrate, have been measured, and the feasibility of a sub-GHz wireless sensors network in an industrial scenario has been evaluated
On the Bandwidth of High-Impedance Frequency Selective Surfaces
No full textIn this letter, the bandwidth of high-impedance surfaces (HISs) is discussed by an equivalent circuit approach. Even if these surfaces have been employed for almost 10 years, it is sometimes unclear how to choose the shape of the frequency selective surface (FSS) on the top of the grounded slab in order to achieve the largest possible bandwidth. Here, we will show that the conventional approach describing the HIS as a parallel connection between the inductance given by the grounded dielectric substrate and the capacitance of the FSS may induce inaccurate results in the determination of the operating bandwidth of the structure. Indeed, in order to derive a more complete model and to provide a more accurate estimate of the operating bandwidth, it is also necessary to introduce the series inductance of the FSS. We will present the explicit expression for defining the bandwidth of a HIS, and we will show that the reduction of the FSS inductance results in the best choice for achieving wide operating bandwidth in correspondence with a given frequency
Low-Profile Array With Reduced Radar Cross Section by Using Hybrid Frequency Selective Surfaces
No full textA solution for reducing the radar cross section (RCS) of amicrostrip antenna based on the use of frequency selective surfaces (FSSs) is described. The goal is accomplished by replacing the solid ground plane of the device with a hybrid structure comprising a suitable FSS. The behavior of the hybrid ground plane illuminated by a plane wave is analyzed by using a periodic method of moments (PMM), and it is modeled by resorting to a transmission- line equivalent circuit. Similarly, the propagation of the quasi-TEM mode along the modified feeding line of the array is represented by an equivalent circuit for surface waves. The two simplified analyses provide useful design criteria for the hybrid ground structure. The presented solution guarantees a decrease of the out-of-band radar signature of the target while preserving the desired in-band radiation characteristics of the low-profile array. A careful comparison to alternative configurations employing different ground planes has revealed the superior performance of the proposed design. Measurements on a realized prototype show a good agreement with simulations and prove the reliability of the design approach
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