Volume 68, Issue 5-6

A wideband circularly polarized (CP) slot antenna array is presented by employing cavity-backed CP multi-feed slot antenna as the element. The antenna element consists of four microstrip-fed circular stubs that excite the circular slot to generate circular polarization, a circular back cavity and a separate corporate feed network layer. The measured 3-dB axial-ratio (AR) bandwidth of the element is 38.6% (4.6–6.8 GHz) in which the reflection coefficient (|S11|) is below −10 dB. The investigation is extended to a 2 × 2 antenna array by using sequentially rotated technique. Wilkinson power dividers are applied to design the feed network of the array. The fabricated antenna array can provide a 1-dB AR bandwidth of 55.7% (4.4–7.8 GHz). In the 1-dB AR bandwidth, the |S11| is below −10 dB and the gain is more than 10.0 dBic. The 3-dB gain bandwidth is about 40.0% (4.8–7.2 GHz) with the maximum gain 15.1 dBic.

A notch-etched circular patch antenna with dual polarized characteristic is presented in this paper. By loading metamaterial structures under the circular patch with four curved branches, two monopole modes with omnidirectional radiation patterns in the azimutal plane and one patch mode with patch-like radiation pattern in the vertical plane are excited. Despite the circular polarization (CP) realized by the four curved branches, it is obtained by introducing perturbations on the circular radiating patch as well. Besides, linear polarization (LP) for the second monopole mode stays unchangeable. To validate the analysis mentioned above, the antenna is fabricated and measured. The measured results show a good agreement with the simulated ones.

A novel technique to introduce an additional low frequency band to compact ultra wideband (UWB) slot antennas is proposed in this paper. To get an additional Bluetooth band, a parasitic strip is mounted on the back side of the slot edge. Because of the interaction of the strip and the slot edge, the Bluetooth band can be obtained while a notch band between the Bluetooth band and UWB band also appears. Two types of feeding, coplanar waveguide and microstrip line, are investigated. The proposed antennas are both fabricated on a low-cost FR4 substrate and have compact size (24 mm × 28 mm × 1 mm). The good agreement between measured and simulated results verifies our design.

This paper presents a triple-band bandpass filter for applications of GSM, WiMAX, and WLAN systems. The proposed filter comprises of the tri-section step-impedance and capacitively loaded step-impedance resonators, which are combined using the cross coupling technique. Additionally, tapered lines are used to connect at both ports of the filter in order to enhance matching for the tri-band resonant frequencies. The filter can operate at the resonant frequencies of 1.8 GHz, 3.7 GHz, and 5.5 GHz. At resonant frequencies, the measured values of S 11 are −17.2 dB, −33.6 dB, and −17.9 dB, while the measured values of S 21 are −2.23 dB, −2.98 dB, and −3.31 dB, respectively. Moreover, the presented filter has compact size compared with the conventional open-loop cross coupling triple band bandpass filters

A linearized differential common-gate CMOS low noise amplifier is proposed. The linearity is improved by a cross-coupled post distortion technique, employing auxiliary PMOS transistors in weak inversion region to cancel the third-order nonlinear currents of common-gate LNA and impair the second-order nonlinear currents of that. The negative conductance characteristic of cross-coupled auxiliary PMOS transistors improves the gain while the resulted NF is little affected. Furthermore, noise contribution and linearity deterioration from the cascode stage is eliminated by an inductor resonating with the parasitic capacitance observed at the source net of the cascode transistor. The LNA implemented in a 0.18 μm CMOS technology demonstrates that IIP3 and gain have about 8.2 dB and 1.4 dB improvements in the designed frequency band, respectively. The noise figure of 3.4 dB is obtained with a power dissipation of 6.8 mW under a 1.8 V power supply.

An improved wideband common-gate (CG) and common-source (CS) CMOS LNA with noise cancellation is proposed. The cross-coupled feedback between the CG input transistor and the cascode transistor of CS input stage is used to increase the input transconductance of the LNA. And the bulk effect of CS input transistors is utilized to enhance g m -boosting coefficient. Thus, comparable gain and noise are achieved by reduced bias currents of the LNA while the resulted additional NF degradation is negligible. Fabricated in a 0.13 μm RF CMOS process, the LNA achieves a flat voltage gain of 18 dB, an NF of 2.7~3.2 dB, and an IIP3 of −4.5~−7.4 dBm over a 3 dB bandwidth of 0.1~4.4 GHz. It consumes only 4.1 mA from a 1 V supply and occupies an area of 520 × 490 um 2 . In contrast to those of reported wideband LNAs, the proposed LNA has the merit of lower power consumption and lower supply voltage.

Mobile users today expect wide range of multimedia services to be available in different mobility scenarios, and among the others is mobile TV service. The Digital Video Broadcasting – Satellite services to Handheld (DVB-SH) is designed to provide mobile TV services, supporting a wide range of mobile multimedia services, like audio and data broadcasting as well as file downloading services. In this paper we present our simulation model for the performance evaluation of the DVB-SH system following the ETSI standard EN 302 583. Simulation model includes complete DVB-SH system, supporting all standardized system modes and parameters. From transmitter to receiver, the information may be sent over different channel models, thus simulating real case scenarios. To the best of authors' knowledge, this is the first complete model of DVB-SH system that includes all standardized system parameters and may be used for examining real DVB-SH communication as well as for educational purposes.

Wireless networks experience deficient transmission bandwidth and varying conditions in radio-link. Various technologies are combined to accomplish high data rate and quality of communication. This article describes the features of the proposed system based on 802.16 standard and orthogonal frequency division multiple access (OFDMA) with synergy of other advanced technologies. The system enables dynamic subcarriers allocation to users. Signal-to-noise ratio (SNR) per subcarriers is separately calculated for each user from the preambles. The resources are then allotted to users based on resource allocation algorithm (RAA) and required Quality of Service (QoS), defined for each type of data traffic. The proposed method performs adaptive modulation and coding with frequency hopping (FH). The results are compared to the existing RAA and subcarrier permutations. They show a more equitable allocation of available bandwidth among the users and greater system transmission capacity at lower bit error rate (BER).

In this paper, we first prove the optimality of ordered subcarrier pairing (OSP) in two-way orthogonal frequency division multiplexing (OFDM) relay systems. The probability distribution function (PDF) and the cumulative distribution function (CDF) of the signal-to-noise ratio (SNR) is then derived for each subcarrier pair of the two-way links over Rayleigh fading channels. Furthermore, we analyze the performance of the systems including outage probability, symbol error rate (SER) and capacity. Monte Carlo simulations validate our analysis.

The problem of power allocation for device-to-device (D2D) underlay communication to improve physical layer security is addressed. Specifically, to improve the secure communication of the cellular users, we introduce a Stackelberg game for allocating the power of the D2D link under a total power constraint and a rate constraint at the D2D pair. In the introduced Stackelberg game the D2D pair works as a seller and the cellular UEs work as buyers. Firstly, because the interference signals from D2D pair are unknown to both the legitimate receiver and the illegitimate eavesdropper, it is possible that a cellular UE decline to participate in the introduced Stackelberg game. So the condition under which a legitimate user will participate in the introduced Stackelberg game is discussed. Then, based on the Stackelberg game, we propose a semi-distributed power allocation algorithm, which is proved to conclude after finite-time iterations. In the end, some simulations are presented to verify the performance improvement in the physical layer security of cellular UEs using the proposed power allocation algorithm. We can determine that with the proposed algorithm, while the D2D pair's communication demand is met, the physical layer security of cellular UEs can be improved.