A novel low profile and dual-band antenna for terrestrial digital multimedia broadcasting (T-DMB) and ultra high frequency (UHF) applications is proposed in this paper. The proposed antenna consists of a folded inverted-L antenna and two open stubs. The designed low profile antenna occupies an antenna volume of 1484911 mm3. The length of the folded radiating element is about 0.09λ at the resonant frequency of T-DMB application (180-210 MHz). The parasitic open stubs are utilized to obtain the wide bandwidth (50%) for UHF application (470-740 MHz). The maximum gains at the frequencies of T-DMB and DTV applications were -5 and +5 dBi, respectively. The radiation patterns are near omni-directional at frequency of interest.

In this paper, class DE inverter with second order constant K band-pass filter is proposed. In the proposed inverter, the band-pass filter is used instead of the resonant filter in class DE inverter presented at the previous papers. By using band-pass filter, two important results can be gotten. One is the sensitivity of the output voltage to the operating frequency is suppressed by using band-pass filter. The other is that zero voltage switching operation appears when the operating frequency is lower than the nominal frequency. Moreover, it keeps the advantage of class DE inverter with resonant filter, that is, high power conversion efficiency under high frequency operation because of class E switching. The laboratory experiments achieve 90.4% power conversion efficiency under 1.98 W output power and 1.0 MHz operation.

It has been widely observed that high-bandwidth traffic aggregates often occur by flooding-based distributed denial-of-service (DDoS) attacks. Several congestion control methods have been proposed for bandwidth controls. These methods are also considered to be important in order to avoid collapse of network services by DDoS attacks. We perform simulation studies of these well-known crowd management methods in order to minimize the damage caused by DDoS attacks with bandwidth control. Internet topologies have many facets in terms of the focus of the observation. Therefore, we need to conduct simulation of DDoS attacks in different Internet topologies, including the tiers model, the transit-stub model, and the Barabasi-Albert model. Using RED, CHOKe, and pushback with ACC as congestion control methods, we evaluate network resistance against DDoS attacks and similar overflow problems.

We present a low-cost UWB-based radiolocation system complying with the IEEE 802.15.4a specifications. To significantly reduce the required analog-to-digital converter speed, we employ the sampling down conversion technique. The matching pursuit algorithm combined with a lost sample restoration algorithm is derived for the UWB time of arrival (TOA) estimation. The simulation results of the proposed algorithm show that the TOA estimation accuracy approaches the multipath resolution under the NLOS channel.

This paper presents a model for the variation in height of the subscriber station (SS) antenna with respect to the path loss for microwave-band wireless access systems. The propagation mechanism that causes the dependency of the height variation characteristics of the received level at an SS on the SS location and operating frequency is clarified in terms of geometrical optics (GO) using the uniform geometrical theory of diffraction (UTD). The height variation characteristics strongly depend on whether or not regular reflected waves that have a higher level than that of the diffracted wave arrive at the SS. A representation of the model is shown. The model is validated using measured data at 2.2, 5.2, and 25.15 GHz and the validity of the model is shown. This model is useful in the radio zone design of microwave-band broadband wireless access (BWA) systems operating in a non-line-of-sight environment, and in estimating the height gain at a mobile station antenna for mobile communications.

Recently we proposed a new waveband MUX/DEMUX that uses two concatenated cyclic AWGs. We analyse and formulate connection arrangements of the waveguides connecting the two AWGs. The port utilization of the device is shown to be 100% with bi-directional input fibers.

This paper clarifies the sideband suppression ratio (SSR) value needed for multi-carrier signal modulation in an optical single sideband (SSB) modulator. An SSR value of about 25 dB is found to be sufficient for broadcast satellite (BS) multi-carrier signal modulation. For FM converted CATV signal modulation, an SSR value of about 10 dB is sufficient. In addition, the properties of cascaded lithium niobate Mach-Zehndar (LN MZ) optical SSB modulators are clarified to be better than those of the conventional single LN MZ optical SSB modulator with nearly the same SSR value of 27 dB.

This paper presents a novel dual-band comb-line filter using a pair of hybrid resonators. The resonator consists of a half-wavelength stripline resonator short-circuited at both ends and a quarter-wavelength resonator of coplanar waveguide that is nested in the half-wavelength resonator. Numerical calculations by an electromagnetic simulator clarify the characteristics of dual-frequency resonance of the hybrid resonator when the structural parameters are changed. The surface current density on the resonator is also investigated at the resonant frequencies. A typical model of the resonator is fabricated and its resonance frequency characteristics are measured.

This paper presents an ultra-wideband (UWB) bandpass filter using a combination of broadside-coupled structure and lumped-capacitor-loaded shunt stub resonator. The broadside-coupled microstrip-to-coplanar waveguide structure provides an ultra-wide bandpass filtering operation and keeps a good stopband at lower frequencies from DC at the same time. The lumped-capacitor-loaded shunt stub resonator creates two transmission zeros (attenuation poles which can be located at the outsides of the two bandedges of the UWB bandpass filter to improve the out-band performance by selecting a suitable combination of the length of the shunt stubs and the capacitance of the loaded chip capacitors. The filter was designed based on electromagnetic simulation for broadside-coupled structure, microwave circuit simulation and experiments for determining the transmission zeros. The filter was fabricated on a one-layer dielectric substrate. The measured results demonstrated that the developed UWB bandpass filter has good performance: low insertion loss about 0.46 dB and low group delay about 0.26 ns at the center of the passband and very flat over the whole passband, and less than -10 dB reflection over the passband. The implemented transmission zeros, particularly at the low frequency end, dramatically improved the out-band performance, leading the filter satisfy the FCC's spectrum mask not only for indoor but also for outdoor applications. These poles improved also the skirt performance at both bandedges of the filter. A lowpass filter has been also introduced and integrated with the proposed bandpass filter to have a further improvement of the out-band performance at the high frequency end. The filters integrated with lowpass section exhibit excellent filter performance: almost satisfying the FCC's spectrum mask from DC to 18 GHz. The developed UWB bandpass filter has a compact size of 4 cm1.5 cm, or 4.8 cm1.5 cm with lowpass section implemented.

A rectangular waveguide compatible NRD guide E-plane bandpass filter is proposed for 55 GHz band OFDM applications. The NRD guide E-plane bandpass filter is constructed by inserting a metal foil array in the E-plane of NRD guide. Simulation, fabrication, and handling of the filter are not difficult because each resonator is constructed by a couple of metal foils of a simple shape. A Chebyshev response 5-pole bandpass filter with a very narrow bandwidth of 550 MHz is designed and fabricated at 55 GHz band. Simulated and measured filter performances agree well with the design specifications. Insertion loss of the fabricated filter is found to be around 2.0 dB. Although temperature stability of the fabricated filter are found to be within manageable level, the adoption of cyclo olefin polymer can be one of solution for the temperature stability improvement.

Novel multiband circular microstrip antennas (C-MSAs) with multiple half-ring slots are presented in this paper. Two antenna-feeding systems, i.e. an embedded L-probe beneath the patch and a coplanar circular arc- shaped probe (T-probe), are used to feed the C-MSA with multiple half-ring slots. The embedded L-probe is used to excite the C-MSA with a double-layer dielectric substrate due to its tremendous performance to provide a wideband impedance matching. The coplanar T-probe is proposed to realize an excellent multiband C-MSA in a single-layer structure. The C-MSA with four half-ring slots fed by the embedded L-probe exhibits satisfactory radiation characteristics. Five frequencies with broadside radiation patterns and gains of at least 5.0 dBi are obtained. It is also confirmed by simulation that resonant frequency and gain can be easily controlled to meet the desired frequency requirements. Moreover, the C-MSA with three half-ring slots fed by the coplanar T-probe presents satisfactory performance over the four observed frequencies with good return losses (-10 dB reference). Broadside radiation patterns with acceptable cross-polarization level and gains in the range of 3.0-7.0 dBi are obtained. Couplings between the C-MSA and the coplanar T-probe have an important contribution to obtain good return losses. It can be controlled by adjusting the distance between them and the arc angle of the coplanar T-probe appropriately. Experiments of both types of antenna were conducted to verify the simulation results and good agreements are confirmed. Due to the performances, these two C-MSAs are considered to be an effective model as a multiband planar antenna.

This paper presents the switched-beam slot antenna over the electromagnetic band-gap (EBG) reflector. This antenna is composed of two slot elements fed with a phase difference and the EBG reflector, which is used in order to realize a low profile structure. The radiation characteristics of this antenna are calculated using the FDTD method. Calculations show that the height of the antenna using the EBG reflector is 60 % lower than that of the antenna using a perfect electric conductor (PEC) reflector. The radiation characteristics at the center of the operating frequency band in the EBG reflector are equivalent to that in the PEC reflector. It is shown that the tilt angle of the main beam in the elevation plane varies with the operating frequency, and the variation in the case of the EBG reflector is caused by its frequency-dependent reflection phase. Moreover, the radiation pattern of the fabricated antenna is measured. The results demonstrate that the low profile design can be achieved by using the EBG reflector, and reveal the influence of the EBG reflector on the antenna efficiency.

Basic microwave properties of magnetic photonic (MPC) and degenerate band edge (DBE) crystals are investigated mathematically and experimentally. Two dimensional and three dimensional models are considered demonstrating the very high sensitivity and field growth associated with these crystals. A major part of the paper deals with the development of realistic anisotropic periodic structures using a combination of layers constructed from thin film frequency selective surfaces, alumina, titanate and calcium vanadium garnet (CVG) materials. Measurements for antenna applications demonstrate and validate the theoretical performance of the MPC and DBE crystals. The latter part of the paper will present an exciting and promising development relating to microwave circuit applications. Specifically, a novel dual-line printed circuit is presented to emulate propagation in anisotropic media. As such, the MPC and DBE phenomena can be realized using very simple printed circuits (coupled lines). Lastly, physically small printed antennas and arrays based on the coupled transmission lines are presented.

In this paper, we propose a PON-based access network based on conventional TDM-PON architecture for the smooth, economical and effective transition to the future optical access network. We also propose a dynamic MAC protocol for wavelength channel and bandwidth allocation in the TDM-PON subscriber networks, which can provide enhanced network scalability and flexibility, and greater adaptability to the increasing number of subscribers in TDM-PON. In the proposed dynamic MAC protocol, several key functions are manifested, such as multiple wavelength channel utilization and dynamic allocation of multiple time-slots to a user depending on SLA between OLT and ONUs to meet QoS requirements. A dedicated control channel is used for delivering the request and status information between OLT and ONUs. We evaluate the performances of the proposed MAC protocol thru a statistical queuing analysis and numerical simulations. In addition, through simulations using various traffic models we verify the superior performance of the proposed approach by comparing it with conventional TDM-PONs.

A double square loop antenna with fractal geometry that supports for multiband operation is proposed. The antenna has multiband operation in that the generator model, which is an initial model to create a fractal loop antenna to operate at the first and second resonant frequencies, is inserted at each center side of a big square loop antenna. It also has a small square loop to operate at the third resonant frequency. The proposed antenna is implemented and shown to effectively support the global system for mobile communication (880-960 MHz), digital communication system (1710-1880 MHz), personal communication system (1850-1990 MHz), universal mobile telecommunication system (1920-2170 MHz), and wireless local area network (2400-2483 MHz) bands. The radiation patterns of the proposed antenna are still similar to a bidirectional radiation pattern. The properties of the antenna such as return losses, radiation patterns and gain are determined via numerical simulation and measurement.

This letter proposes a sliding window method with iterative tuning for channel estimation of UWB signals. The iterative tuning scheme, which is based on multiple iterations of least mean square (LMS) algorithm, is utilized for modifying the output of the conventional sliding window channel estimator. By using this, the proposed method is more flexible due to the tradeoff between the processing time and accuracy, which makes it more suitable for practical UWB wireless communications. Simulations are also provided for demonstrating the validation of the proposed method.

In this paper, CPW-fed slot antennas using loading metallic strips and a widened tuning stub (CPW-FSLW) which provides wideband operation on the flat, a Λ-shape reflector with horizontal plate that prevents the back radiation and provides the uni-directional radiation are investigated. We observe that the size and shape of the reflector have significant impact on the impedance matching and radiation patterns. By fabricating the CPW-FSLW on the Λ-shape reflector with horizontal plate structure, noticeable enhancements in both radiation pattern and bandwidth are achieved. The antennas are verified both through numerical simulations and also measurements of the experimental prototypes and these confirm the good performance antennas. It is found that the proposed antenna can deliver a measured impedance bandwidth of 64% from 1.6 to 3.1 GHz for VSWR ≤ 2. The antennas are designed to have wideband operation suitable for applications in GSM1800, GSM1900, PCS, IMT-2000 and WLAN bands.

This paper presents data on a reconfigurable predistorter for compensating the nonlinearity of a power amplifier in a system supporting both multimode and multiband operations. For compensation, the magnitude and phase response of a predistorter should be easy to tune to match that of a nonlinear amplifier that is used in various standards. That is to say, the predistorter should show decreasing magnitude followed by increasing magnitude, and the phase must initially lag and then lead, or lead and then lag, as a function of the increasing power input. In doing so, the power turning point, gain & phase deviation, and phase lead & lag should easily be controlled by the proposed reconfigurable predistorter using a bias control and impedance transformer. These characteristics are provided by the nonlinearity of the FET and the movement of the bias point caused by negative current generation. This proposed predistorter can be adopted for a system that uses Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA) 800 MHz, and CDMA 1800 MHz. For example, by adopting this reconfigurable predistorter in a CDMA 1800 MHz, as much as 14 dB improvements in Adjacent Channel leakage Power Ratio (ACPR) at the 4 dB back off power level, can be achieved for the CDMA 1800 MHz signal.

Audio applications for mobile phone and portable devices are increasingly popular. To attract consumer interest, a multi-standard design on a single device is the trend of current audio decoder development. This paper presents a configurable common filterbank processor (CCFP) for AC-3, MP3 and AAC audio decoder. It is used as an accelerator for general purpose processors to improve performance. All the filterbank transforms are derived to even- or odd-point IFFT flows. In the architecture, a fully pipelined approach is developed which can be configured for different operation modes. This design is synthesized using UMC 0.18 µm library and takes about 26.7 K gates. By the fast algorithm and fully pipelined architecture, the operation cycles are greatly reduced. Therefore, it can be executed at a very low operation frequency with the range of 1.3 to 3.6 MHz. Besides, the power consumption is only 0.9 mW, 3.2 mW and 1 mW for AC-3, MP3 and AAC respectively. We further port our design on an ARM Integrator platform to make a real play system. On average, over 50% ARM performance loading can be saved and used for handling other applications.

FM converted CATV and super high frequency satellite TV signal transmission using lithium niobate Mach-Zehnder optical SSB modulator is proposed and demonstrated. Simultaneous FM-converted 40 CATV signal carriers (from 93 to 375 MHz) and 104 super high frequency satellite TV signal carriers (from 11.7 to 20.2 GHz) could be transmitted with good noise properties and distortion quality over 40 km of dispersive SMF with chromatic dispersion of 680 ps/nm. We clarify the required phase and power values by experiments on the relationship between sideband suppression ratio (SSR) and the phase/power to LN MZ optical SSB modulator. For instance, the absolute value of phase and power should be less than 5 degrees and 0.4 dB, respectively, to obtain SSR values above 35 dB.