Journal of Communication Engineering
Volume:3 Issue: 2, Autumn 2014

A new wideband Wilkinson Power Divider which use the nonuniform substrate integrated waveguide (NSIW) method is presented in this paper. This structure utilizes NSIWs instead of the uniform quarter wavelength SIWs in conventional Wilkinson power divider. The proposed structure is analyzed by odd and even mode analysis. The proper NSIW section widths can be extracted by using even mode while the divider resistances are achieved by odd mode analysis. Moreover using of half mode structure in the NSIW and two output ports reduces the overall size of the proposed divider. Finally a wideband Wilkinson power divider is designed and simulated to verify the proposed design method. A good return loss (S11, S22) and insertion loss (S21) across a very wideband width from 10 GHz to 20 GHz is achieved. Also, the isolation (S23) is better than -10 dB from 9.5 GHz to 21.5 GHz for the designed NSIW divider.

It is known that if a conductor resides in the neighboring of an antenna with a small distance relative to the wavelength, it induces a reverse current on the conductor. This paper involves the unavoidable coupling effects on some common types of LF antennas, due to the large wavelength in this frequency band. In particular, after some discussions about top-loaded antennas, the coupling effect of wire supports is studied for these antennas. In addition, the effect of support masts on the radiation resistance is shown for three kinds of Loran transmitter antennas with four masts. Furthermore, some formulas for the impedance of small monopole antennas with neighboring masts are proposed and some simulation results of practical antennas are reported. Finally it is indicated that the coupling effect is more destructive for sectional Loran transmitter antenna compared with square top loaded antenna.

In this paper, we study the impact of low-quality node on the performance of incremental least mean square (ILMS) adaptive networks. Adaptive networks involve many nodes with adaptation and learning capabilities. Low-quality mode in the performance of a node in a practical sensor network is modeled by the observation of pure noise (its observation noise) that leads to an unreliable measurement. Specifically, we consider ILMS networks with different number of low-quality nodes and compare their performance in two different cases including (i) ideal and (ii) noisy links in homogeneous and inhomogeneous environments. We show that in the case of ideal links among nodes, one node with low-quality mode degrades the estimation performance significantly and increasing the variance of observation noise does not degrade the performance anymore. Even with increasing node numbers with low-quality mode in network, estimation performance does not divergence. On the other hand, in the presence of noisy links, different behavior is observed and degradation is dependent on variance of noisy links and it may go unstable. Simulation results are provided to illustrate the discussions.

The high Peak to Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) and MIMO-OFDM systems reduces the system efficiency. In this paper, an extension of Tone Reservation (TR) method is introduced for PAPR reduction in Space Frequency Block Coded OFDM (SFBC-OFDM) systems. The proposed algorithm is based on a time domain kernel which is added to the signal of the antenna with maximum PAPR to reduce its peak power. The time domain kernel has been designed such that the location of the reserved tones is compatible with the structure of the space frequency code. Simulation results show that the proposed method has a very close PAPR reduction performance to that of the well-known RC-PII method, but its complexity is much less than of RC-PII.

This paper describes the design of an X-band balanced low noise amplifier (LNA) using an available HJFET device. The balanced LNA consists of a pair of electrically similar transistors whose input and output signals are divided or combined by 3 dB two-stage Wilkinson power dividers. The proposed balanced LNA is fabricated and measured. The measured results show that the noise figure is 1.30 dB at 10 GHz, the input and output return loss are more than 15 dB and 10 dB, respectively. Also, the gain of 12 dB and gain flatness of ±0.5 dB over the 9-11 GHz frequency range are associated to the balanced LNA. In addition, 15-element small signal equivalent model parameters of the HJFET device used in amplifier design are extracted with an analytical and optimization approache such as Particle Swarm Optimization (PSO) to achieve accurate values. The small-signal model parameters evaluated with the PSO attain 5.9% error compared to the measured data. The validity of the proposed approach is shown by comparing the modeled S-parameter and measured results over 2-18GHz. Simulation results indicate that the PSO approach accurately extracts the small signal model parameters of the HJFET.

In this paper, inference model is proposed so as to analyze nonlinearly loaded dipole antenna. In modeling process, linear and nonlinear behavior of the problem is saved as simple and unchanged membership functions and the effect of incident wave on the induced voltage at different harmonies are then extracted easily. Consequently the model achieved is more efficient than previous studies using neural networks.