Liang-Feng Qiu

A Four-Way Microstrip Filtering Power Divider With Frequency-Dependent Couplings

A four-way microstrip power divider is designed with bandpass filtering response. The synthesized inline filter has a generalized Chebyshev response, where frequency-dependent couplings are utilized. All of the critical parameters, including the characteristic impedances and electrical lengths, can be determined by our derived closed-form formulas. By extending the inline filter, the configuration of four-way power divider is obtained. Then, three isolation resistors are properly selected according to the even-/odd-mode analysis. The proposed four-way filtering power divider has low in-band insertion loss and high frequency selectivity. It can provide the in-band return loss and isolation between outputs better than 16.7 and 17.5 dB, respectively .

Novel Bandpass Filters by Using Cavity-Loaded Dielectric Resonators in a Substrate Integrated Waveguide

This paper presents novel bandpass filters by using a triple-mode dielectric resonator (DR) implemented in a substrate integrated waveguide (SIW). The resonant frequency and unloaded Q-factor of the DR were first calculated and simulated by Ansoft HFSS. The dimensions of the DR were then determined. A single triple-mode SIW loaded with a DR filter with tuning elements was designed, simulated, and measured. Spurious suppression with source and load couplings, as well as fabrication tolerance, was analyzed. A six-mode filter that uses two DRs was also proposed and measured. These filters exhibit close agreements between the simulation and measurement results and have the advantages of low insertion loss, compact configuration, and easy integration with other planar circuits. The proposed concept is very attractive for designing low cost, low insertion loss, and miniaturized filters for wireless communication systems.

A new balanced-to-single-ended (BTSE) power divider

A balanced-to-single-ended (BTSE) power divider is proposed in this paper. Its input is a differential pair while both the outputs are single-ended ports. It can replace the cascade of a balun and a conventional power divider. The characteristics requirements of a two-way BTSE power divider with equal power division are first derived, and then a prototype is designed for 2.0 GHz. In order to construct the component compactly, a short-ended four-wire coupled line and T-shaped sections are utilized to realize a -90° transmission line and a phase inverter, respectively. The developed prototype occupies an area of 0.077 λg2, where λg is the guided wavelength of central frequency. It provides all the desired performances within the operating bandwidth of 25%, with low insertion loss and good balance also achieved.

A Flat-Passband Microstrip Filter With Nonuniform-

A compact lossy microstrip bandpass filter is realized with flat passband and high selectivity, using the method of nonuniform Q. Two dual-mode resonators are utilized. The Q-factor of odd mode can be properly reduced by loading resistors over the symmetric plane of each resonator, with the even-mode Q unchanged. The geometric and resistance parameters are determined by the derived formulas and optimization. The 0.2 dB bandwidth of the fabricated prototype is improved by 62% when compared with the uniform-Q counterpart. The equivalent Q-factor is as high as 970, which is extracted from measurement.

Q

An improved spectral-domain exponential matrix technique is proposed for investigating on the interaction of a THz wave with planar structures consisting of multilayer graphene sheets and bianisotropic slabs. Hybrid effects of different parameters, such as THz wave incident direction, its frequency and polarization, chemical potentials of the graphene sheets and constitutive tensors of the bianisotropic media, on the co- and cross-polarized reflection and transmission coefficients are characterized numerically, with their bandpass properties captured and compared. It is shown that there are more freedoms provided by layered graphene sheets and bianisotropic media at the same time, which can be exploited for effectively controlling the THz wave propagation.

Dual-Mode Resonators

An absorptive bandstop filter is proposed and synthesized with prescribed negative group delay (NGD) and negative group delay bandwidth (NBW). It is realized with resistor-loaded coupled-line structures where the NGD can be controlled by the Q-factors of resonators. The resistor of the first section is determined for impedance matching, also providing a negative delay. A prototype is developed, following the proposed design procedure, with NGD = −6.5 ns and NBW= 105 MHz obtained. The proposed method is experimentally validated by the good agreement between the synthesized and measured results.

THz wave interaction with planar structures consisting of multilayer graphene sheets and bianisotropic slabs

A new synthesis method is proposed for the design of high-performance parallel connected lossy filters. Compared with the nonuniform Q method, where the Q distribution is determined by the sensitivities of a preset coupling matrix, our method can provide a flat passband with flexible combination of nonuniform Q resonators by utilizing the predistortion technique with an adaptive offset. Two generalized Chebyshev filters with different specific Q-factors are designed with the negative and positive distortion offsets. The proposed hybrid method has been validated by the perfect passband flatness achieved with both of them.

Absorptive Bandstop Filter With Prescribed Negative Group Delay and Bandwidth

A new method is proposed for tunable negative group delay (NGD) circuit in this paper. The tuner is based on a transmission line resonator loaded on a λ/4 stub, and a lumped resistor and two varactors are mounted on it. By properly biasing the two varactors, the susceptance slope parameter and unloaded Q-factor are significantly tuned while the resonant frequency and input admittance are almost unchanged. In the measured results of the tuner prototype designed at 1.0 GHz, when NGD is tuned from 0.2 to 1.9 ns, the stable insertion loss is only changed from 3.4 to 2.5 dB.

A hybrid method for flat-passband filter with nonuniform Q resonators and predistortion

A general method is proposed in this paper to extract the two-port coupling matrix of filtering antennas. By using the passivity and the realizability properties of a filter network, the rational polynomial forms of S-parameters can be obtained from the reflection and realized radiation efficiency of a filtering antenna. The coupling matrix is then obtained with transformation and optimization. After the coupling matrix is reestablished, the diagnosis and tuning of filtering antenna can easily be carried out. Our method has been validated with the successful tuning of a stacked patch antenna.