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Register a new userTransformation-Optics-Based Design of a Metamaterial Radome for Extending the Scanning Angle of a Phased Array Antenna
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We apply the transformation-optics approach to the design of a metamaterial radome that can extend the scanning angle of a phased-array antenna. For moderate enhancement of the scanning angle, via suitable parameterization and optimization of the coordinate transformation, we obtain a design that admits a technologically viable, robust and potentially broadband implementation in terms of thin-metallic-plate inclusions. Our results, validated via finite-element-based numerical simulations, indicate an alternative route to the design of metamaterial radomes which does not require negative-valued and/or extreme constitutive parameters.
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Based on rigorous scattering theory we establish a systematic methodology for research of metamaterial-modified current-carrying conductors, from which we mathematically demonstrate the explanation of transformation optics could be extended in metamaterial-modified wireless power transfer system, and based on that we could establish a equivalent model. More important, our demonstration reveals that the equivalent model will still be applicable even when TO could not give a direct explanation, as the requirements of complementary media is not satisfied. And numerical results from our methodology as well as COMSOL verified our findings. The demonstration is not under specific frequency, the conclusion could be extended to a broad range of wavelength, and expected to be applicable for active cloak etc.
Cavity array metamaterials (CAMs), composed of optical microcavities in a lattice coupled via tight-binding interactions, represent a novel architecture for engineering metamaterials. Since the size of the CAMs constituent elements are commensurate with the operating wavelength of the device, it cannot directly utilise classical transformation optics in the same way as traditional metamaterials. By directly transforming the internal geometry of the system, and locally tuning the permittivity between cavities, we provide an alternative framework suitable for tight-binding implementations of metamaterials. We develop a CAM-based cloak as the case study.
In this report we present a model for phased array feed (PAF) and compare the model predictions with measurements. A theory for loss-less PAF is presented first. To develop the theory we ask the question -- what is the best $T_{sys}/eta_{ap}$ that can be achieved when a PAF is used on a telescope to observe a source at an angle $theta_s, phi_s$ from the boresight direction ? We show that a characteristic matrix for the {em system} (i.e. PAF+telescope+receiver) can be constructed starting from the signal-to-noise ratio of the observations and the best $T_{sys}/eta_{ap}$ can be obtained from the maximum eigenvalue of the characteristic matrix. For constructing the characteristic matrix, we derive the open-circuit voltage at the output of the antenna elements in the PAF due to (a) radiation from source, (b) radiation from ground (spillover), (c) radiation from sky background and (d) noise due to the receiver. The characteristic matrix is then obtained from the correlation matrices of these voltages. We then describe a modeling program developed to implement the theory presented here. Finally the model predictions are compared with results from test observations made toward Virgo A with a prototype PAF (Kite array) on the GBT (Roshi et al. 2015).
In this paper, a single layer Coplanar Waveguide-fed microstrip patch antenna array is presented for biomedical applications. The proposed antenna array is realized on a transparent and flexible Polyethylene Terephthalate substrate, has 1x4 radiating elements and measures only 280 x 192 mm2. The antenna array resonates at 2.68 GHz and has a peak-simulated gain of 10 dBi. A prototype is also fabricated, and the conductive patterns are drawn using cost-efficient adhesive copper foils instead of conventional copper or silver nanoparticle ink. The corresponding measured results agree well with the simulated results. The proposed low profile and cost-efficient transmit antenna array has the potential for wearable born-worn applications, including wireless powering of implantable medical devices.
An intelligent radome utilizing composite metamaterial structures is presented and investigated in this article, which can realize energy isolation and asymmetric propagation of electromagnetic (EM) wave self-adaptively by controlling states of PIN diodes. The whole structure mainly consists of a broadband polarization-sensitive polarization converter (PC) and an active frequency selective rasorber (AFSR) switching between a transmission mode and absorption mode which is used as an energy-selective surface (ESS). Among them, the function of the PC is to make the EM waves transmit asymmetrically, and the purpose of AFSR is to make the high-power waves be reflected or absorbed, which depends on the polarization type of the wave. Thus, the radome can realize both asymmetric propagations of EM wave and electromagnetic shielding. The equivalent circuit models (ECM) and parametric studies are considered to explain the physical operating mechanism of PC and AFSR. The fabricated structure with 7*7 unit cells is experimentally demonstrated and the measured results agree with simulated results well. Considering the distinctive characteristic of self-actuation, the presented concept has the potential application in electromagnetic stealth and HPEMWs shielding to protect communication devices.
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