Volume 67, Issue 1-2 -

A novel technique to add an extra Bluetooth band and triple notch bands simultaneously to a compact ultra-wideband (UWB) monopole antenna is presented. This scissors-shaped UWB antenna, covering 2.9 GHz–12.5 GHz, is fed by a special microstrip line. To create an extra Bluetooth band centered at 2.45 GHz, an arc-shaped stub is attached to the high concentrated current area right of the feed line and a rectangular slot is etched in the radiation patch. Besides, a notch band for WLAN (5.6 GHz–6.15 GHz) is also obtained. In addition, by connecting two asymmetric stubs to the feed line, two other notch bands in 3.28 GHz–3.8 GHz for WiMAX and 7.1 GHz–7.76 GHz for downlink of X-band satellite communication systems are achieved. The proposed antenna with compact size of 20 mm × 26 mm is fabricated and measured, showing stable antenna gain and good omni-directional radiation patterns in H-plane.

A practical, easily manufactured multiport bicone antenna suitable for many receiving tasks such as direction finding systems can be made by using sharp-edged metal fins on the feeding coax center conductor to provide a tapered transition and connection path to coaxial probes. This construction resembles an arrow's tail. Already four mutually orthogonal fins can give full 360 degree azimuth coverage with suitable −3 dB port pattern overlap. Five experimental constructions working at Ku and Ka bands, each with fractional bandwidths of 23 to 31 per cent, are shown with full dimensional details. Suitable fin tapering is close to the full air gap in the coax and fin thickness should be less than 1/16th of the outer conductor diameter.

A novel microstrip lowpass filter based on a T-shaped resonator is proposed in this paper that presents wide stopband and compact size. A method of scaling is applied to and studied on the proposed resonator in order to tune its response parameters. To achieve wide stopband, a suppressing cell is designed and connected in series form to the resonator. The resulting filter is then fabricated and measured. Simulated and measured results of the proposed filter verify its advantages over those presented in the references in terms of stopband-width and physical size.

Thermal coupling in AlGaN/GaN transistors is investigated by means of thermal FEM (finite element method) simulation. The results are combined with electrical network simulation using an electro-thermal model. From the FEM analysis the thermal coupling matrix is established, describing the thermal interaction between the different cells of a power transistor. The matrix allows to extract an equivalent circuit for the thermal coupling in a straightforward way. The electrical transistor model is complemented by thermal ports to connect the cells via the thermal coupling network. The electro-thermal model developed yields information on the distribution of temperature and currents within a powerbar and thus is an important tool in transistor design.

This paper presents the design of a single-ended input, differential output low noise amplifier for GPS applications in 0.18 µm CMOS technology. This Low Noise Amplifier (LNA) is composed of a common source (CS) amplifier adopted with a common gate, common source (CGCS) balun load. Instead of spiral on-chip inductor, a differential active inductor circuit (DAI) is used as an active load of balun and also g m -boosting technique is used to decrease the noise figure (NF) of Single-to-Differential Low Noise Amplifier (S-to-D LNA). The LNA is simulated with Cadence Spectra which shows the S21 of 22.94 dB at 1.57 GHz, S11 of −13.1 dB, NF min of 2.66 dB and power dissipation of 2.5 mw from 1.8 V dc power supply. By adding an external capacitor to the DAI circuit, it is possible to reconfigure the LNA to use in multi frequency range. For using the LNA in frequency range of 1.22 GHz, the external capacitor is set to 121 fF. The result shows the S21 of 20.4 dB, S11 of −12.4 dB and NF min of 2.4 dB.

This paper presents the design of 28 GHz, 200 kW gyrotron for Indian TOKAMAK system. The paper reports the designs of interaction cavity, magnetron injection gun and RF window. EGUN code is used for the optimization of electron gun parameters. TE 03 mode is selected as the operating mode by using the in-house developed code GCOMS. The simulation and optimization of the cavity parameters are carried out by using the Particle-in-cell, three dimensional (3-D)-electromagnetic simulation code MAGIC. The output power more than 250 kW is achieved.

Byzantine attacks in collaborative spectrum sensing (CSS) systems of cognitive radio networks (CRNs) is a critical threat and has attracted considerable attention. However, in existing works, attacking strategies are generally modeled in a simple way, i.e., Single-Strategy, and the attackers can be detected easily. In practical CRNs, Byzantine attackers could be more sophisticated, and they could adjust their malicious actions according to the actions of normal nodes. In this paper, we propose a new type of attacks, i.e., Hybrid-Strategy attacks (HSAs), which are more flexible and destructive than Single-Strategy attacks. We analyze the properties of proposed HSAs and the limitations of existing attacker-detection methods when they encounter HSAs. Furthermore, we prove that the HSAs can avoid being detected by existing distance based detection algorithms when they evolve into stealthy attacks.

In this paper, we study the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch and stay combining receiver over Nakagami- m fading/gamma shadowing channels with arbitrary parameters. The average BER of quaternary phase shift keying is evaluated under the assumption that the reference carrier signal is extracted from the received modulated signal. We compute numerical results illustrating simultaneous influence of average signal-to-noise ratio per bit, fading severity, shadowing, phase-locked loop bandwidth-bit duration ( B L T b ) product, and switching threshold on BER performance. The effects of B L T b on receiver performance under different channel conditions are emphasized. Optimal switching threshold is determined which minimizes BER performance under given channel and receiver parameters.

In this paper, puncturing technique is used to establish variable-rate ring convolutional coded continuous phase modulation (CPM) systems. Maximum likelihood sequence detectors over both AWGN channels and Rayleigh flat-fading channels are considered. The suggested system provides us with different rates and performance when simple adjustment is taken to the puncturing matrix. Since the performance of the first error event of this system is represented by normalized minimum squared Euclidean distance (NMSED), some typical codes with maximum NMSED are searched and given. The performance of symbol error rate for the suggested system is simulated using computer software, and the results show that this system provides good performance of symbol error rate with variable-rate capabilities in time varying channels. Furthermore, simulation results also prove that the transmission efficiency increases when code rate is decreasing.