A new method to suppress harmonics using /spl lambda//4 bias line combined by defected ground structure in power amplifiers

A new /spl lambda//4 bias line combined by a dumb-bell shaped defected ground structure (DGS) is proposed to suppress harmonics in power amplifiers. The proposed DGS bias line maintains the required high impedance even after DGS is inserted, while the width and length of the /spl lambda//4 bias line are broader and shorter than those of conventional bias lines. When the DGS bias line is used in power amplifiers, the third harmonic components as well as the second harmonic are reduced, because of the increased slow-wave effect over wide harmonic band. It is shown that the reduction of the third harmonic component, the improvement of 1 dB compression point, and power added efficiency are 26.5 dB, 0.45 dB, and 9.1%, respectively.     

A novel phase noise reduction technique in oscillators usingdefected ground structure

A new technique to reduce the phase noise in microwave oscillators is developed using the resonant characteristic of the defected ground structure (DGS). Two kinds of oscillators have been designed and measured for the examination of the reduction of phase noise by the DGS. The first adopts the DGS section under the microstrip line at the gate circuit, while the second has only the conventional microstrip line. Measurement shows reduced phase noise by 10-15 dB in the oscillator with the DGS compared to the conventional one     

Computation of the average power pattern of a reflector antennawith random surface errors and misalignment errors

To specify manufacturing tolerances of a reflector antenna, various errors such as random surface errors and misalignment errors must be considered at one time because superposition of the effects of those errors may not hold. Based on the Rahmat-Samii's formulation (1983), a method for computing efficiently the average power pattern of a reflector antenna with those errors is presented. Simulation results show that superposition of the effects of errors does not generally hold and demonstrate how those errors degrade the peak-gain and sidelobe levels     

A novel high-efficiency linear transmitter using injection-locked pulsed oscillator

This letter presents a novel high-efficiency linear transmitter using pulse-width modulation (PWM). An envelope of radio frequency (RF) input signal is modulated by the PWM. The modulated signal is applied to the gate bias of a class F injection-locked power oscillator and switches it on and off. By filtering the pulsed oscillating output signal of the injection-locked oscillator using high-Q bandpass filter, the input signal is restored. This technique enables the transmitter to have high efficiency with good linearity. Also, there is little distortion near saturation point of an active device. The measured results show efficiency of 54.6% and very good linearity in PCS band at 26.4-dBm output power.     

The moderation effects of mobile technology advancement and system barrier on m-commerce channel preference behavior

Information Systems and e-Business Management - Mobile commerce, or m-commerce, has quickly become a powerful, indispensable approach for diverse business to consumer (B2C) industries to secure...     

Effect of Oxygen Partial Pressure During Liquid-Phase Sintering on the Dielectric Properties of 0.9MgTiO3–0.1CaTiO3

Microstructural evolution and microwave dielectric properties of liquid-phase-sintered 0.9MgTiO₃–0.1CaTiO₃ dielectric ceramic material have been investigated as a function of oxygen partial pressure (     ) during sintering. Sintering in a weakly reducing atmosphere (     =10⁻¹⁴ atm) generally increased the density, permittivity, quality factor ( Q × f ), and the temperature coefficient of resonance frequency (τ_f), but further reducing atmosphere down to     of 10⁻¹⁴ atm generally decreased Q × f and τ_f. When the 5 wt% lithium borosilicate glass-added specimen was sintered at 950°C and     =10⁻¹⁴ atm, it demonstrated a permittivity of 18.8, Q × f of 19 000 GHz, and τ_f of 10 × 10⁻⁶ K⁻¹.     

High-Efficiency Power Amplifier Using Novel Dynamic Bias Switching

A novel bias-switching scheme for a high-efficiency power amplifier is proposed. Two voltage levels for the drain bias of the RF power amplifier are generated using a combination of a class E dc/ac inverter and a class E rectifier with offset voltage. When signal peaks occur, the output of the class E dc/ac inverter is rectified and the rectified dc is added to the offset voltage by the class E rectifier, which boosts the drain bias of the RF power amplifier. Except during peaks, the drain bias of the RF power amplifier is connected to the offset voltage directly. Since the efficiency when there are no peaks is very high due to the direct connection between the offset voltage and drain bias, the overall efficiency of the RF power amplifier can be improved dramatically in high peak-to-average power ratio (PAPR) systems. The measured results show that the drain bias of the RF power amplifier is boosted up to approximately 1.8 times the offset voltage when the RF peaks generate. The overall efficiency of the proposed bias-switching amplifier is improved by 62% compared to that of the fixed bias amplifier in high PAPR systems     

Prediction of a CDMA output spectrum based on intermodulationproducts of two-tone test

A prediction method of a code-division multiple-access (CDMA) output spectrum based on intermodulation (IM) products of a two-tone test is proposed in this paper. An RF power amplifier is mathematically modeled by a complex envelope transfer function and, using this model, analytical expressions of IM products and a CDMA output spectrum are derived, respectively. By combining these two expressions, we finally derive an analytical expression that relates IM products to a CDMA output spectrum. It is shown in this expression that not only AM-AM, but also AM-PM distortion affects the CDMA output spectrum. Comparison between the measured and predicted results shows that the output spectrum predicted by this method agrees well with the measured spectrum     

A vertically periodic defected ground structure and its application in reducing the size of microwave circuits

The microstrip and coplanar waveguide transmission lines combined by a vertically periodic defected ground structure (VPDGS) are proposed. The slow-wave effect, equivalent circuit, and the performances are shown. As an application example, VPDGS is adopted in the matching networks of an amplifier for size-reduction. Two series microstrip lines in input and output matching networks of the amplifier are reduced to 38.5% and 44.4% of the original lengths, respectively, due to the increased slow-wave effects, while the amplifier performances are preserved.     

Analysis of electromagnetic wave transmission through a choke usingFE-BIM with arbitrary incident angle/polarization

The performance of a microwave choke is analyzed by the finite element-boundary integral method (FE-BIM) for an incident wave with arbitrary angle/polarization. The equivalence principle is used to divide the whole region into three subregions: incident region, choke region, and transmitted region. The functional in the choke region is derived with an appropriate boundary condition between subregions. The choke region is discretized by rectangular meshes. Vector edge elements are used for the representation of the cross-sectional electric field, while node elements are used for the axial-directional electric field. The electric fields in the cross section of the choke are determined by the Rayleigh-Ritz procedure. The performance of a microwave choke is analyzed by investigating the transmission characteristics of the choke for a plane wave with varying incident angle and polarization. Experiments have been done using a rectangular waveguide with the choke structure inside. The results agree very well with the theoretical prediction