This paper presents a high efficiency and low profile quad‐beam circularly polarised transmitarray antenna using metasurface. In order to improve the aperture efficiency, the small unit cell is employed to obtain the beam forming since the gain of multi‐beam is higher and the feed antenna suitable for low profile transmitarray is selected. To further improve the aperture efficiency, the cells with high transmittance are located at the centre of metasurface to increase the transmission efficiency since the electric fields of the low profile transmitarray are more concentrated on the centre of metasurface than those of the high profile transmitarray. The unit cell of metasurface is stacked by optimising with equivalent circuit analysis and generalised sheet transition conditions that can confirm a multi‐layer performance easily. The principle of superposition was used to easily calculate the phase set required for quad‐beam forming. The designed metasurface is 17 × 17 array of four‐layer unit cells of 0.25λ0 × 0.25λ0 size at 5.8 GHz. The finally designed antenna with circularly polarised quad‐beam has the peak gain of 12.1 dBic at 5.72 GHz, and the aperture efficiency and 1 dB gain bandwidth were found to be 30.7% and 3.5%∼5.5% at four beams, respectively.
A wide-angle reconfigurable reflectarray antenna (RRA) was designed and experimentally verified utilizing a miniaturized ring patch efficiently controllable with a single bit. Based on the merits of the miniaturization of the radiating element and an elaborate study of the quantization efficiencies of the asymmetric phase differences between the on/off states of the unit cell by optimizing a reference phase on the metasurface, highly directive beam scanning is achieved in a wide ±60˚ range in both the H-and Eplanes. Furthermore, the illumination and spillover efficiencies and focal diameter ratio (F/D) are carefully optimized, resulting in a low profile configuration with F/D=0.36. The fabricated RRA prototype was measured at 9.85 GHz (X-band) with the highest aperture efficiency of 28% and a 1 dB gain bandwidth of 530 MHz, respectively.
This article presents design methods for a transmissive metasurface antenna composed of four layers of meta-structures based on the deep neural network (DNN). Owing to the structural complexity as well as side effects such as couplings among the adjacent meta-structures, the conventional design of metasurface unit cell strongly relies on the researcher’s intuition as well as time-consuming iterative simulations. A design method for a metasurface antenna unit cell with a size of a quarter wavelength operating at a frequency of 5.8GHz is presented. We describe two unique implementations for designing the target metasurfaces: 1) utilizing the inverse network 2) data augmentation by the forward network and a random search algorithm. With the usage of the two DNNs, the average transmittance of the unit cells is improved by about 0.024 than that of the unit cells designed by the conventional approach. This research invokes the application of DNN in designing antennas and other structures operating at radio frequency.
The development of biomedical devices benefits patients by offering real-time healthcare. In particular, pacemakers have gained a great deal of attention because they offer opportunities for monitoring the patient’s vitals and biological statics in real time. One of the important factors in realizing real-time body-centric sensing is to establish a robust wireless communication link among the medical devices. In this paper, radio transmission and the optimal characteristics for impedance matching the medical telemetry of an implant are investigated. For radio transmission, an integral coupling formula based on 3D vector far-field patterns was firstly applied to compute the antenna coupling between two antennas placed inside and outside of the body. The formula provides the capability for computing the antenna coupling in the near-field and far-field region. In order to include the effects of human implantation, the far-field pattern was characterized taking into account a sphere enclosing an antenna made of human tissue. Furthermore, the characteristics of impedance matching inside the human body were studied by means of inherent wave impedances of electrical and magnetic dipoles. Here, we demonstrate that the implantation of a magnetic dipole is advantageous because it provides similar impedance characteristics to those of the human body.
A miniaturized dual-band reflective metasurface unit cell is presented based on a square fractal copper-ring patch combined with a PIN diode. Its structure is optimally designed via the genetic algorithm to achieve ∘ 180 phase differences of the reflection coefficients between on and off states of the PIN diode at both C-and X-bands center frequencies. The accuracy of the proposed dual-band metasurface unit cell is verified by comparing simulations with measurements inside the C-and X-bands rectangular waveguides. The proposed miniaturized metasurface unit cell could improve the radiation efficiency of the dual-band reflective metasurface antenna by enabling fine quantization of the phase distribution and mitigating the mutual couplings among different states of the unit cells.
A phased array radar has been developed toward an effective means for integrating multiple functionalities into one radar platform. The radar system necessitates the ability to operate at multiple frequencies simultaneously. In this paper, a triple-band uniform radial sub-array using a shared aperture antenna is proposed for a multi-functional radar system. An efficient placement of different radiating elements is realized based on the radial displacement of the circular array. In addition, multi-layer feed networks are used to reduce the intricacy of integrating several feed networks into one antenna. The reasonable matching characteristics and far-field gain are acquired at the S-band, C-band, and X-band. The measured results of the prototype are presented, and the results are compared to the simulation, which showed a good agreement.
Electromagnetic (EM) metamaterial absorbers are new types of EM absorbers that can absorb the EM waves via conductive patterns. The performances of the EM metamaterial absorbers can be guaranteed when the unit cells of them are connected periodically. Therefore, the absorbing performances based on square unit cells may be degraded significantly when they are applied to a polygonal area or a corner that do not allow the periodic connection. In this paper, an optimization method is proposed for hexagonal EM metamaterial absorber unit cells that can be connected periodically for the c orners of which the interior angles are 60° or 120°. To achieve optimal hexagonal patterns, a tiling method is proposed based on an adaptive genetic algorithm. By minimizing the reflectances for both the transverse electric (TE) and transverse magnetic (TM) polarizations, the −10 dB reflectances were confirmed in the X band for the two polarizations simultaneously. Based on the finalized axially symmetric pattern along six axes, the −8 dB reflectances were confirmed in the same band for the oblique incidence with the vertical angle up to 45°. By comparing simulation results calculated by two different commercialized simulators based on the finite element method, the accuracy of the design was verified.
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