Jia-n Li

Novel Design of Wilkinson Power Dividers With Arbitrary Power Division Ratios

In this paper, a stub-loaded transmission line that is used to design Wilkinson power dividers with arbitrary power division ratios is discussed in depth. Power division is always required in most wireless/wireline communications such as industrial systems and consumer electronics. However, the design of an unequal Wilkinson power divider, particularly with a large division ratio, becomes a challenge in engineering because of the impractical realization of the high- or low-impedance transmission lines on a dielectric substrate. In this paper, we first introduce a transmission-line structure and perform theoretical analysis. The derivations reveal that the studied structure can be utilized to design Wilkinson power dividers with equal or unequal power divisions. For demonstration purposes, two power dividers with division ratios of 1 : 1 and 1 : 9, respectively, and operating in the popular industrial, scientific, and radio-frequency identification frequency bands are implemented by loading distributed transmission-line elements, namely, open- or short-circuited stubs. The demonstrators are also fabricated and validated by measurements, and good agreement between the experimental results and the simulated responses is observed.

DESIGN AND OPTIMIZATION OF LOW RCS PATCH ANTENNAS BASED ON A GENETIC ALGORITHM

In this article, a genetic algorithm (GA) is employed to the design of low radar cross section (RCS) patch antennas. Combined with the high frequency simulation software (HFSS) for antenna simulations, the GA performs the optimization of geometric parameters. In order to reduce the RCS while holding the satisfying radiation performance of antennas, the radiation model and scattering model are respectively calculated. The combination of proportionate selection and elitist model for the selection strategy is used to speed up the convergence of the GA. Two-point crossover is adopted to accelerate the converging speed and results in more flt individuals. Moreover, the whole design procedure is auto-controlled by programming the VBScript in the HFSS. Two examples of low RCS slot antennas are provided to verify the accuracy and e-ciency of the proposed method.

Numerical Dispersion Analysis and Key Parameter Selection in Laguerre-FDTD Method

In this letter, a theoretical analysis of the numerical dispersion and key parameter selection of the finite-difference time-domain (FDTD) method with weighted Laguerre polynomials is presented. Different from the conventional FDTD method, the numerical dispersion relation is relevant not only to sampling point density in space domain but also to time-scale factor. For a fixed relative error of phase velocity, the suitable sampling point density and time-scale factor can be determined. In addition, the selection of the number of Laguerre functions is derived using the theoretical time-scale factor, and is verified in a numerical example.

Compact Microstrip UWB Bandpass Filter With Dual Notched Bands Using E-Shaped Resonator

A new microstrip ultra-wideband (UWB) bandpass filter (BPF) with two sharp notches using E-shaped resonator is proposed in this letter. The circuit topology and its corresponding electrical parameters of the initial microstrip UWB BPF are achieved by a variation of genetic algorithm (GA). Then, the resonance properties of the E-shaped resonator are studied. Results reveal that the multiple-mode property of the E-shaped resonator can be utilized in the UWB BPF design to achieve dual band-notched performance. To validate the design concept, a microstrip UWB BPF with two notched bands respectively centered at frequencies of 5.9 GHz and 8.0 GHz is designed and fabricated. Both simulation and experimental results are provided with good agreement.

Design of Miniaturized Microstrip Dual-Mode Filter With Source-Load Coupling

A miniaturized microstrip dual-mode filter with different responses is developed in this letter. A coupling and routing scheme is presented to model the operations of this filter. The new filter reduces the occupied area up to 33% compared with the conventional one at 1.89 GHz. Meanwhile, the proposed circuit enables the second harmonic response to be effectively suppressed. A demonstrator filter is designed and validated with good agreement between the full-wave electromagnetic simulations and measurements.

A Compact Frequency Reconfigurable Rectenna for 5.2- and 5.8-GHz Wireless Power Transmission

A compact reconfigurable rectifying antenna (rectenna) has been proposed for 5.2- and 5.8-GHz microwave power transmission. The proposed rectenna consists of a frequency reconfigurable microstrip antenna and a frequency reconfigurable rectifying circuit. Here, the use of the odd-symmetry mode has significantly cut down the antenna size by half. By controlling the switches installed in the antenna and the rectifying circuit, the rectenna is able to switch operation between 5.2 and 5.8 GHz. Simulated conversion efficiencies of 70.5% and 69.4% are achievable at the operating frequencies of 5.2 and 5.8 GHz, respectively, when the rectenna is given with an input power of 16.5 dBm. Experiment has been conducted to verify the design idea. Due to fabrication tolerances and parametric deviation of the actual diode, the resonant frequencies of the rectenna are measured to be 4.9 and 5.9 GHz. When supplied with input powers of 16 and 15 dBm, the measured maximum conversion efficiencies of the proposed rectenna are found to be 65.2% and 64.8% at 4.9 and 5.9 GHz, respectively, which are higher than its contemporary counterparts.

Research on epoxy resin decomposition under microwave heating by using ReaxFF molecular dynamics simulations

To investigate the effects of microwave heating on decomposing epoxy resin, ReaxFF molecular dynamics simulations are performed. As one of its special effects, the thermal runaway phenomenon is studied and compared under microwave heating and under conventional heating. This study shows that this phenomenon results from the enhancement of system absorption of microwave energy, which is caused by the increasing number of small size polar species generated during the pyrolysis of epoxy resin under microwave heating. Meanwhile, non-thermal effects are investigated under microwave heating. Simulations indicate that, at the early stage of decomposition, average generating rates of H2O and H2 obtained under microwave heating are always, or partly, lower than that obtained under conventional heating. To analyze the influence of microwave heating on reaction rates, collision theory is introduced. Further, several simplified collision models are constructed and formulated to study the effectiveness of collision orientations under microwave heating. Analyses illustrate that external microwave heating reduces the effectiveness of collision orientations between polar hydric fragments as well as hydroxyl radicals and polar hydric fragments, thus, decreasing relevant reaction rates.

COMPACT MICROSTRIP UWB BANDPASS FILTER WITH TRIPLE-NOTCHED BANDS

A new microstrip ultra-wideband (UWB) bandpass fllter (BPF) with triple-notched bands is presented in this paper. The circuit topology and its corresponding electrical parameters of the initial microstrip UWB BPF are desired by a variation of genetic algorithm (VGA). Then, triple-notched bands inside the UWB passband are implemented by coupling a square ring short stub loaded resonator (SRSSLR) to the main transmission line of the initial microstrip UWB BPF. The triple-notched bands can be easily generated and set at any desired frequencies by varying the designed parameters of SRSSLR. For veriflcation, a microstrip UWB BPF with triple-notched bands respectively centered at frequencies of 4.3GHz, 5.8GHz, and 8.1GHz is designed and fabricated. Simulated and experimental results are in good agreement.

Flexible Design of a Compact Coupled-Line Power Divider

Studies indicate that the size reduction of a conventional coupled-line power divider can be implemented with the introduction of reactive elements at the output ends of the pair of coupled-line sections. A theoretical analysis of such a kind of power dividers is performed, and simple design equations are presented in this paper. By choosing the electrical length of the coupled-line section as 30°, a very compact coupled-line power divider is demonstrated. Centered at 1.5 GHz, a validation circuit is optimally designed, built and experimentally verified. Measurements, which match the predictions, confirm the proposed compact divider topology and design procedures.

NOVEL UNIDIRECTIONAL SLOT ANTENNA WITH A VERTICAL WALL

A novel slot antenna that consists of an H-shaped slot encompassed by a rectangular metallic wall and a pair of C-shaped slots outside the wall is proposed. It features a unidirectional pattern, small electrical dimensions and medium gain. The H-shaped slot radiates as an inductively loaded magnetic dipole while the induced electric currents on the vertical wall radiates as electric dipoles. The front-to-back ratio (FBR) of the antenna can be controlled by proper constructive and destructive interferences of radiating fields of the magnetic and electric dipoles. The size of the ground plane can be reduced by the use of the C-shaped slots that confine the currents to the proximity of the metallic wall. Two prototype antennas operating at 2.4 GHz were designed. By adjusting the structure parameters, the front-to-back ratio of the antenna can be conveniently altered. The first prototype has an impedance bandwidth (BW) of 3.8% for SWR ≤ 2, a 4.6 dBi gain, a 10-dB FBR and a ground size of 0.84λ0 × 0.64λ0 where λ0 is the free-space wavelength at the center frequency. The corresponding figures of the second prototype are 1.83%, 4.1 dBi, over 20 dB and 0.64λ0 × 0.64λ0. Both antennas have a height of 0.128λ0.