Zoran Blazevic

Some notes on transmission line representations of Tesla’s transmitters

In this paper, we present a transmission line representation of various Teslapsilas oscillating transmitters and of propagation based on ldquotrue conductionrdquo, a Teslapsilas concept of non-Hertzian wireless transmission. We follow bits of Teslapsilas papers, mainly ldquoThe True Wirelessrdquo, from which is obvious that his theory is in essence compatible to the transmission line theory, and compare results obtained by the model and those given by Tesla, as well as predict some theoretical characteristics of his resonating coils. Although his conception of a more efficient radio transmission by ldquonon-Hertzian wavesrdquo has never been recognized exactly what he claimed it to be, his concept of radio apparatus prevailed as they were the first patented true radio systems.

Comparing Theoretical and Experimental Results in Gen2 RFID Throughput

Radio frequency identification (RFID) technology, based on wireless communication between a reader and tags, is the most popular technology for indoor item identification and tracking. Among competing RFID technologies, Gen2 has emerged as the most popular one, due to the best price/performance ratio. In order to communicate with multiple tags, Gen2 RFID systems use dynamic frame slotted ALOHA (DFSA) as a medium access control (MAC) mechanism. To maximize DFSA throughput simple calculations show that the number of tags should equal the DFSA frame size. However, the number of tags in an environment is usually unknown and has to be estimated. So far, significant effort has been invested in estimating the correct number of tags. However, to the best of our knowledge, no one has explored the estimator performance in a real RFID measuring scenario. In this paper, we evaluate the throughput of a real RFID system by using the Software Defined Radio (SDR) technology. Our results show that phenomena related to radio waves propagation and reception have a significantly bigger influence on Gen2 RFID throughput than traditional approaches take into account.

Wideband measurements and analysis of the single-floor indoor radio channel at 2.4 GHz

In this paper we present analysis of radio measurements at 2.4 GHz conducted in an indoor environment of out- faculty building. A significant correlation between coherence bandwidth and delay-spread is noticed, which is in accordance to previous results. Correlation noticed by certain authors between delay-spread and antenna separation could not be confirmed in this scenario. The analysis and comparison with other references show that different indoor radio channels may have certain common features in sense of power-distance law and delay-spread characteristics.

Gen2 RFID as IoT Enabler: Characterization and Performance Improvement

RFID has become an enabling technology for IoT implementation. In dynamic RFID scenarios, such as smart shops or industrial surroundings, it is crucial to identify every good, with an applied RFID tag, before it leaves the interrogation area. Currently, commercial reader solutions adopt DFSA protocol as a simple MAC that manages the communication between a reader and multiple tags. To increase DFSA throughput (the number of read tags in the unit of time) and thus speed up tag identification, simple calculations show that the number of tags should equal the frame size. However, the literature exhibiting RFID performance shows that tag responsiveness is stochastic, while this has been often neglected when considering the throughput. To investigate the influence and to define related research challenges in the RFID domain, this work provides the idea of the required measurements by using SDR technology, while arguing that PHY and MAC layers should be looked at integrally. If not, tag identification will be delayed, while at the same time unnecessary energy waste will occur. In the measurement campaigns, the metric of TRP is employed, given as tag response probability distribution, which can be used for modeling the MAC layer.

Impact of Tag Responsiveness on Gen2 RFID Throughput

It is well known in the research community that the throughput of dynamic frame slotted ALOHA (DFSA) in a radio frequency identification (RFID) system can be maximized when DFSA frame size is set to the number of tags. However, related works often neglect the fact that tag responsiveness is of a stochastic nature, depending on the tag hardware performance in the wireless channel. Therefore, as number of tag responses may not be equal to the number of tags located in the interrogation area, corrections to the standard simulation models should be applied. In this letter, we provide the corrections that are based on tag read probability (TRP) metrics. At first, numerically, TRP was retrieved by the usage of fully configurable open-source software defined radio RFID reader in an indoor nonfading radio channel at the single frequency and constant output power, while considering reliable communication parameters in the environment of single and a pair of commercial Gen2 RFID tags. Then, TRP is statistically modeled, and the implications to the throughput are shown.

Helical Antennas in Satellite Radio Channel

Monofilar and multifilar helical antennas are the most widely proposed antennas in satellite communications systems. The main reason why these antennas constitute an asset in applications concerning satellite and space communications generally is circular polarization. Good axial ratio provides precise measurement of the polarization of the received signal due to immunity of the circularly polarized wave to Faraday rotation of the signal propagating through the ionosphere. In addition to circular polarization, monofilar helical antennas offer the advantage of high gain in axial direction over a wide range of frequencies which makes them suitable for applications in broadband satellite communications.

Helical antenna performance in wideband communications

In this paper, we employed the electromagnetic theory to the design of a 2.4-GHz wideband helix antenna. The designed antenna was first simulated across wide bandwidth using 4NEC2 software, and then two identical antennas were made from available materials and finally measured using a vector network analyzer. The measured and simulated results are found to be in a quite agreement. Moderate discrepancies among measured and simulated resonant frequencies noted are contributed chiefly to the use of a high-loss PVC pipe as the drums for the coils and, to a smaller degree, to the loss in the copper at microwave frequencies and to the influence of the wire insulation.

Estimation of Channel Parameters for " Saleh-Valenzuela" Model Simulation

The paper presents application of channel simulation according to statistical Saleh-Valenzuela model for a typical university building architecture. Estimation of parameters is based on analyze of measured power delay profiles, obtained in measuring campaign inside the same building. The vector network analyzer method of measuring was applied, inside 1600 - 2000 MHz frequency band. All measurements were done on single-floor. The first assessment of cluster arrival rate, ray arrival rate, cluster decaying factor and ray decaying factor was gained from spatial-averaged measured power delay profiles. The simulated cumulative distribution function of effective time delay was compared with measured one in order to optimize mentioned channel parameters. The final result is a great deal of agreement between the simulated and measured CDFs

Interaction Between Human and Near-Field of Wireless Power Transfer System

In this paper we provide new recommendations for a type of antenna design in applications where a human is present in the vicinity of a wireless power transfer (WPT) system by means of power transfer efficiency (PTE) and specific absorption rate (SAR). The interaction between a homogenous human model and different WPT systems is investigated at 13.56 MHz using spherical mode theory antenna model (SMT-AM) and full-wave numerical analysis. The human model exposure and the performance of the proposed WPT system are analyzed further for some typical scenarios. It is shown that the position in which the human model is closer to the receiver is favorable over the position closer to the transmitter, concerning both PTE and SAR. Also, the consideration of variable receiver load indicates that different levels of SAR coupled by degraded PTE can be expected. The proposed antennas are designed, and proof of concept WPT measurements are carried out.

2.4 GHz micro-strip patch antenna array with suppressed sidelobes

In this paper, we present the design and simulated results for a patch antenna array at 2.4 GHz. The antenna consists of one linear array with six series-fed patch antennas. In radar and smart-antenna applications it is very important to use antennas with high gain and low sidelobes in order to avoid the interference and to increase the gain of antenna array. The aim of this research is to design an antenna array that has suppressed sidelobes as much as possible in azimuth by using Kaiser-Bessel amplitude coefficients. Our designed antenna has a gain of 15.1 dB with an angular width of 14.6° at a frequency of 2.4 GHz. The measured 10 dB return loss bandwidth equals 18.7 MHz. Patch antenna array is analyzed using CST MICROWAVE STUDIO 2014.