2022/2

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Multi-Spot Tracking System for Free-Space Optical Communication
(Společnost pro radioelektronické inženýrství, 2022-05) Skryja, Petr; Poliak, Juraj; Wilfert, Otakar
This article describes a multi-spot tracking system for free space optic communications systems suitable for tracking optical terminals observed within the field-of-view of a wide angle telescope. The article explains the conversion of the terminal position to the position in the plane of the tracking sensor and the subsequent recognition and tracking of terminals. In the first part of the article camera image processing is described. Then, basic projection of optical terminal into the tracking sensor plane (into the active surface of a camera) is expressed by using geometry and matrix optics. Afterwards, the angle resolution of optical terminal in plane of the receiver is obtained by using the Airy disk approximation. The basic projection is then extended to the calculation of the Earth-satellite system followed by spot tracking, where method for determining the optical terminal and the state machine is explained.
On Theoretical Accuracy of Meteorological Targets Measurement by Radar
(Společnost pro radioelektronické inženýrství, 2022-05) Fiser, Ondrej; Kovalchuk, Maria
We draw your attention to the fact that meteorological radar does not actually measure a commonly used quantity “radar reflectivity factor,” (which is not dependent on frequency) but a different quantity called “radar reflectivity.” We present the usual recalculation which is based on frequency dependency used by Rayleigh approximation of radar cross-sections (back scattering cross section of rain, cloud, fog drop). But this approximation is valid in Rayleigh region only. We concluded that for admitting error lower than 2 dB in the radar reflectivity factor determination we can use the “effective radar reflectivity factor” for frequencies up to 19 GHz only. Otherwise the error will increase. As we use (and present in this article) the Mie algorithm we can replace the Rayleigh frequency dependence estimation by more accurate radar reflectivity factor determination using the Mie scattering. The correction is presented in the form of “Correction function C” dependent on frequency and rain rate in the graphical form and polynomial approximation. Beside this we present the simplification of back scattering cross sections for Rayleigh and Optical regions and the borders values of size parameter for these regions. We added the meteorological radar equation derivation. This should support the radar measurement understanding.
A Simple Approach for Improving Bandwidth and Isolation of Wilkinson Power Divider
(Společnost pro radioelektronické inženýrství, 2022-05) Nguyen Minh Giang; Luong Duy Manh
A simple approach to improve both the bandwidth and isolation of the Wilkinson power divider for using in L-band satellite communications is presented in this paper. To enhance the bandwidth, a multi-section method based on the Chebychev impedance transformation is employed. In order to improve the isolation performance between output ports, the values of isolation resistors are carefully determined by using the iterative approximation method combined with an investigation procedure. In order to validate the proposed design, a two-way and eight-way power divider prototypes were fabricated and tested on a Rogers RO4003C material. Good agreements between simulations and measurements are obtained in a frequency range from 0.8 GHz to 2.2 GHz. The two-way power divider had a fractional bandwidth of 106% with an isolation of better than 30 dB. The eight-way power divider achieved the bandwidth and isolation of 109% and better than 24 dB, respectively. Both the power dividers exhibit the phase imbalance of less than 3 degrees, and amplitude imbalance of less than 0.02 dB. Compared with the other works, the proposed power dividers deliver broader bandwidth and improved isolation while still retaining good insertion loss, low phase and amplitude imbalance in the operation frequency range.
Object Tracking Based Surgical Incision Region Encoding using Scalable High Efficiency Video Coding for Surgical Telementoring Applications
(Společnost pro radioelektronické inženýrství, 2022-05) Sanagavarapu, Karthik Sairam; Pullakandam, Muralidhar
Surgical telementoring is an advanced tele-medicine concept where the expert surgeon guides the onsite novice present at the remote location. The efficient telementoring system requires the wireless transmission of high-quality surgical video with less bitrate in less time. The bit rate of the surgical video can be decreased by segmenting the surgical incision region and removing the background region. The High Efficiency Video Coding (HEVC) standard has provided promising results for surgical telementoring applications. But the Rate-Distortion Optimization (RDO) search process in HEVC increases the complexity that in turn increases the encoding time. We propose the method which involves the segmentation of the surgical incision region using the Kernelized Correlation Filter (KCF) object tracking technique. The segmented region is encoded by the complexity-efficient Scalable HEVC (SHVC) to meet the resolution of an end-user device. The complexity of SHVC is decreased by using the Convolutional Neural Network (CNN) and Long- and Short- Term Memory (LSTM) to predict the Coding Tree Unit (CTU) structure. The results show that the proposed method decreases the bitrate significantly for segmented surgical video sequences without degradation in Peak Signal-to-Noise Ratio (PSNR). These results are obtained for the surgical video sequences with slow-moving objects. Furthermore, the CNN+LSTM approach reduces the encoding time of standard SHVC by 51% with negligible Rate-Distortion (RD) performance loss.
A Wideband Wearable Antenna with AMC Ground Plane for WBAN Applications
(Společnost pro radioelektronické inženýrství, 2022-05) Bhattacharjee, Shankar; Midya, Manas; Bhadra Chaudhuri, Sekhar Ranjan; Mitra, Monojit
A flexible wearable antenna with wideband characteristics and having a conical radiation pattern which is suitable for ON body application is presented. To realize a compact antenna size, characteristic modal (CM) analysis is performed initially, and the ground plane of the antenna is utilized to generate one of the resonant modes. The quasi-current loop in the feed layer patch is used to generate another resonant mode. Combination of these two modes has resulted in the wideband performance of the antenna from 4.72 to 6.08 GHz. A planar wideband artificial magnetic conductor (AMC) is used beneath the antenna. This AMC surface compensates the undesired coupling taking place due to the ground radiator thereby reducing the specific absorption rate (SAR) to 76.4% and enhancing the gain of the antenna. The performance of the antenna in terms of return loss, gain, efficiency, SAR and bending sensitivity is studied.

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