An Iterative Technique for the Synthesis of Active Antenna Oscillator Arrays

A design procedure for the synthesis of a coupled active antenna oscillator array is presented. Such an array is synthesized by deriving two sets of parameters: the radiators' positions and the oscillators' outputs. The outputs are used to excite the radiators. Minimization of the mean square error between the desired pattern and the resulting one is made. Synthesis starts from an initial array, which is perturbed iteratively by varying simultaneously the element excitations and positions. In the iteration, the first variation of the cost function is set equal to zero. The final array results from the last iteration, where the stopping criteria are met. The procedure designs simultaneously both the antenna and the attached coupled oscillator array providing viable solutions. The second by properly configuring the tuning parameters through the use of closed-form formulas. The resulting arrays are shown to comply with the desired pattern and the nonlinear dynamics thus proving the validity of our method

Transtelephonic Electrocardiographic Transmission in the Preparticipation Screening of Athletes

Transtelephonic electrocardiographic transmission (TET) is the most widespread form of telecardiology since it enables clinicians to assess patients at a distance. The purpose of this study was to assess the efficacy and effectiveness of TET either by fixed telephone line (POTS) or by mobile phone in the preparticipation screening of young athletes. A total of 506 players, aged 20.5 ± 6.2 years, from 23 soccer clubs in the prefecture of Thessaloniki, Greece, were physically examined in their playfields by a general practitioner (GP) and had their ECG recorded. In 142 cases, and on the judgment of the GP, the ECG was transmitted via POTS and/or global system for mobile communications (GSM) to a specialised medical centre where it was evaluated by a cardiologist. The mean total time for recording, storing, and transmitting the ECG was four minutes per subject. It was found that the success rate for transmission at first attempt was similar for both fixed and mobile networks, that is, 93% and 91%, respectively. The failure rate in the GSM network was correlated to the reception level at the site of transmission. Only in about half (n = 74) of the transmitted ECGs did the cardiologist confirm “abnormal” findings, although in 16, they were considered to be clinically insignificant. Consequently, 58 athletes were referred for further medical examination. Our results indicate that TET (either by fixed telephone line or by mobile phone) can ensure valid, reliable, and objective measurements, and significantly contribute to the application of medical screening in a great number of athletes. Therefore, it is recommended as an alternative diagnostic tool for the preparticipation screening of athletes living in remote areas

Procjena smjera dolaska vala primjenom neuralnih mreža za sustave D-CDMA s preklapanjem snopa

A Neural Network (NN) methodology is presented for the Direction of Arrival (DoA) estimation of the desired mobile user, namely the Signal of Interest (SoI), in the asynchronous Direct Sequence Code Division Multiple Access (DS-CDMA) scheme. In DS-CDMA the SoI DoA should be estimated in the presence of a group of interfering users that constitute the Multiple Access Interference (MAI). In this paper a NN algorithm follows the MAI suppression done by the code-matched filters, to achieve the DoA finding goal for a Switched-Beam System (SBS). The proposed method is developed, while DoA estimation simulation tests show accurate results for a varying number of mobile users.Prikazana je metodologija procjene smjera dolaska signala željenog pokretnog korisnika uz primjenu neuralnih mreža za sustave s višestrukim pristupom po kodnoj osnovi s asinkronom izravnom sekvencijom (DS-CDMA). U sustavima DS-CDMA, valja procijeniti smjer dolaska signala željenog korisnika u nazočnosti više korisnika koji stvaraju interferencije (smetnje) što vodi do interferencije višestrukog pristupa. U ovom se radu rabi algoritam neuralnih mreža za potiskivanje interferencije uz primjenu kodno prilagodenih filtara kako bi se mogao odrediti smjer dolaska signala u sustavu s preklapanjem antenskog snopa. Razvijena je predložena metoda, a simulacijski pokusi s procjenom smjera dolaska signala pokazali su točne rezultate za različit broj pokretnih korisnika

Lowering the Sidelobe Level of a Two-Way Pattern in Shared Aperture Radar Arrays

A study of lowering the peak SLL of shared aperture radar arrays is presented. A two-weight amplitude distribution for the elements of transmit and receive arrays is used. Imposing certain conditions, the relation of the number of elements of the arrays was found. One condition imposes the appearance of a minor lobe position of transmit or receive array pattern at a certain null of receive or transmit array pattern. A second condition imposes the equal sidelobe level of two consecutive minor lobes either near the main beam of the two-way array pattern or at certain positions of receive or transmit array pattern. The resulting peak SLL of the two-way radar array pattern depending on the conditions reaches from −47 dB up to less than −50 dB

Design of Large Thinned Arrays Using Different Biogeography-Based Optimization Migration Models

Array thinning is a common discrete-valued combinatorial optimization problem. Evolutionary algorithms are suitable techniques for above-mentioned problem. Biogeography-Based Optimization (BBO), which is inspired by the science of biogeography, is a stochastic population-based evolutionary algorithm (EA). The original BBO uses a linear migration model to describe how species migrate from one island to another. Other nonlinear migration models have been proposed in the literature. In this paper, we apply BBO with four different migration models to five different large array design cases. Additionally we compare results with five other popular algorithms. The problems dimensions range from 150 to 300. The results show that BBO with sinusoidal migration model generally performs better than the other algorithms. However, these results are considered to be indicative and do not generally apply to all optimization problems in antenna design

An Iterative Technique for the Synthesis of Active Antenna Oscillator Arrays

A design procedure for the synthesis of a coupled active antenna oscillator array is presented. Such an array is synthesized by deriving two sets of parameters: the radiators' positions and the oscillators' outputs. The outputs are used to excite the radiators. Minimization of the mean square error between the desired pattern and the resulting one is made. Synthesis starts from an initial array, which is perturbed iteratively by varying simultaneously the element excitations and positions. In the iteration, the first variation of the cost function is set equal to zero. The final array results from the last iteration, where the stopping criteria are met. The procedure designs simultaneously both the antenna and the attached coupled oscillator array providing viable solutions. The second by properly configuring the tuning parameters through the use of closed-form formulas. The resulting arrays are shown to comply with the desired pattern and the nonlinear dynamics thus proving the validity of our method