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In this paper, two element multiple input–multiple output (MIMO) meander line antenna systems with improved isolation performance and compact size are proposed and fabricated in WLAN frequency band. To increase isolation among antenna elements, a novel metamaterial spiral S-shaped resonator is embedded between two radiating elements. The proposed resonator has planar configuration and miniaturized size and is capable of blocking electromagnetic propagation between antenna elements by exhibiting negative effective permeability in the desired frequency band. To illustrate and evaluate the design process, two design samples are fabricated and tested in WLAN frequency band and the agreement among measurement and simulation results approves the design method. In the frequency range of 2.38–2.48 GHz, some MIMO communication system requirements like total active reflection coefficient, envelope correlation coefficient and capacity loss are tested on design samples which show satisfactory results, so this method can be employed in designing array antennas for small mobile communication systems. The designed MIMO antenna systems separated by 13.8 mm (less than λ/9), has better than ??40 dB isolation coefficient and near zero correlation coefficient and capacity loss at the operating frequency (2.4 GHz).
相似文献In case there is a communication contrary to the system security policies, a covert channel has been created. The attacker can easily disclosure information from the victim’s system with just one public access permission. Covert timing channels, unlike covert storage channels, do not have memory storage and they draw less attention. Different methods have been proposed for their identification, which generally benefit from the shape of traffic and the channel’s regularity. The application nature of HTTP protocol allows the creation of a covert timing channel based on different features of this protocol (or different levels) that has not been addressed in previous researches. This research tries to study the effect of using different features (or levels) of HTTP protocol on identifying the covert channel. The amount of channel’s entropy could be manipulated by changing the channel’s level or adding intentional noise on the channel to protect from the analyzer’s detection. The difference in the placement of the covert channel and the detector causes the amount of channel entropy to be far from the detection threshold. Therefore, we concluded that the analyzer must investigate traffic at all possible levels. Adding noise on the covert channel decrease its capacity, but as entropy increases, it would be harder to detect it.
相似文献This paper presents a wide frequency range three-stage voltage-controlled ring oscillator in CNTFET technology. The advantages of CNTFETs are the high speed of charge carriers, high signal to noise ratio, small size and ballistic transport. Therefore in comparison with MOSFETs, they have a higher frequency, and can operate at a wide frequency range with a very low phase noise if forward bulk bias and active inductor techniques are simultaneously used in the oscillators that employ CNTFETs. In this paper, the Stanford CNTFET model is implemented in Verilog-A, and the proposed CNT ring oscillator is simulated using ADS software over the 50–500 GHz frequency range. The phase noise of the oscillator is ? 136 dBc/Hz at 1 MHz offset, which is suitable for PLL applications.
相似文献In this paper, the vibration analysis of a Silicon Biological Nano-sensor (SBNS) with full coverage of Myosin as biologically adsorbent layer is investigated based on modified nonlocal Euler–Bernoulli beam model. This SBNS works based on calculating the shift of resonant frequency in the presence of Myosin layer and adsorbed viruses and bacteria. For this end, the effects of surface stresses, nonlocal parameter, and rotary inertia as well as the mass and stiffness of the adsorbent layer are taken into account, which can play a major role in changing the resonant frequency and the precision of SBNSs at nano-scale. The results illustrate that the effects of adsorbent layer, surface stresses, nonlocal parameter and rotary inertia may reduce resonant frequency of SBNS, which is significant especially at nano-scale. Finally, for the purpose of verification assessment, the numerical results were compared with the results of other studies and showed complete agreement. The present study can provide helpful insights for the design and characterization of accurate biological Nano-sensors.
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