A new green energy interface for telecommunications

Providing electricity to telecom tower can be realised by hybrid green energy systems than extending a power line from grid. For a hybrid energy system, it is important to develop a converter to integrate different power sources and storage elements. Conventional systems use an individual converter for individual source thus leading to a relatively complex configuration, larger component count and reduced system efficiency. To address these issues green energy interface (GEI) converter is used. In this paper, a detailed component wise analysis and performance comparison between conventional and GEI converter using Matlab/Simulink is presented. GEI converter has linear and non-linear components. So, small signal model based on state space averaged model of the GEI topology is obtained. A lab level prototype for the GEI converter with programmable interface controller is implemented and tested under various input conditions to study the performance of the converter during seasonal changes. The simulation and experimental results showed that effective operation and control strategy of the hybrid power supply system.

Abbreviations: BTS: base transceiver station; MSC: mobile switching centre; BSC: base station controller; CAPEX: capital expenditure; OPEX: operational expenditure; GEI: green energy interface     

Computationally efficient MUSIC based DOA estimation algorithm for FMCW radar

This paper proposes low-cost yet high-accuracy direction of arrival (DOA) estimation for the automotive frequency-modulated continuous-wave (FMCW) radar. The existing subspace-based DOA estimation algorithms suffer from either high computational costs or low accuracy. We aim to solve such contradictory relation between complexity and accuracy by using randomized matrix approximation. Specifically, we apply an easily-interpretable randomized low-rank approximation to the covariance matrix (CM) and approximately compute its subspaces. That is, we first approximate CM \begin{document}${\bf{R} }\in {\mathbb{C}}^{M\times M} $\end{document} through three sketch matrices, in the form of \begin{document}$\mathbf{R}\approx \mathbf{Q}\mathbf{B}{\mathbf{Q}}^{\mathrm{H}} $\end{document}. Here the matrix \begin{document}$\mathbf{Q}\in {\mathbb{C}}^{M\times z} $\end{document} contains the orthonormal basis for the range of the sketch matrix \begin{document}$\mathbf{C}\in {\mathbb{C}}^{M\times z} $\end{document} which is extracted from \begin{document}$ \mathbf{R} $\end{document} using randomized uniform column sampling and \begin{document}$ \mathbf{B}\in {\mathbb{C}}^{z\times z} $\end{document} is a weight-matrix reducing the approximation error. Relying on such approximation, we are able to accelerate the subspace computation by the orders of the magnitude without compromising estimation accuracy. Furthermore, we drive a theoretical error bound for the suggested scheme to ensure the accuracy of the approximation. As validated by the simulation results, the DOA estimation accuracy of the proposed algorithm, efficient multiple signal classification (E-MUSIC), is high, closely tracks standard MUSIC, and outperforms the well-known algorithms with tremendously reduced time complexity. Thus, the devised method can realize high-resolution real-time target detection in the emerging multiple input and multiple output (MIMO) automotive radar systems.     

Extended Continuous Tuning of a Single-Frequency Diode-Pumped Vertical-External-Cavity Surface-Emitting Laser at 2.3 $mu$m

We report on single-frequency operation and wide mode-hop-free tuning range of a diode laser-pumped vertical- external-cavity surface-emitting semiconductor laser producing up to 3 mW around 2.3 $mu$m. An optically stable external cavity of only 1.4 mm is formed using a concave dielectric mirror of 2-mm radius. The maximum continuous tuning is about 500 GHz wide, obtained by a synchronized ramp of external cavity length and of the gain medium temperature. We used this tunable source to record a direct absorption spectrum of methane, which is found to match well a simulated spectrum from the HITRAN (high-resolution transmission molecular absorption database http://www.cfa.harvard.edu/hitran) database.      

Taper transmission line UWB Wilkinson power divider analysis and design

This paper proposed, analysed and fabricated an ultra-wideband Wilkinson power divider. This proposed power divider contains two parts, namely the transmission lines with fixed characteristic impedance and the tapered transmission line.

The power divider has a fixed architecture with the ability to broaden for different bandwidths by changing its circuit parameters including resistors and impedances. It also can create a bandwidth of about 40 GHz with a smaller physical dimension and fewer numbers of resistors.

The proposed power divider is investigated using the even/odd analysis method in order to compute equations required for designing power divider.

The proposed power divider was designed and fabricated for the 3-11 GHz ultra-wideband range. Then, the results are compared with the simulated results and a good agreement is obtained consequently. Furthermore, input return loss better than 12dB, output return loss better than 15dB, insertion loss better than 4.8dB and output ports isolation less than 12 dB are achieved by measured results. The overall size of the proposed power divider is 14.2 × 4.8 mm².     

Measurement of an Electron Density Disturbance in a Positive Column with Magnetic Field

It is found that two columns of different luminosity which are separated by an intervened disc appear along a magnetic field, when a certain disc is inserted in a positive column with an axial magnetic field. These are a luminous column and a dark column which are extended from the disc toward the cathode and the anode side respectively. These deviations in luminosity decay from it in the direction of each side. Change in luminosity along the axis is confirmed by measurements of electron density distribution with movable probes.

An attempt to attribute this recovery toward the normal distribution to ambipolar diffusion of charged particles across the magnetic field is given.