Zhewang Ma

Novel Compact Microstrip Dual-Mode Ring Resonator Wideband Bandpass Filter with Significantly Improved Stopband Property

A novel wideband bandpass filter with improved stopband characteristics is presented in this paper. Dual-mode square ring resonator is used in the proposed filter. New formulas based on the even- and odd-mode analysis are derived to facilitate the design of transmission zeros of the square ring resonator. A short-circuited stub and a piece of aperture-enhanced parallel-coupled lines are introduced to the input and output of the resonator to lower the passband return loss and widen the stopband of the filter significantly. The filter has a 50% fractional bandwidth, is compact in configuration, and shows remarkably improved performance compared with previously reported filters of the same kind. The measured filtering response shows a good agreement with the simulated result.

Microstrip Lowpass Filters with Reduced Size and Improved Stopband Characteristics

Novel microstrip lowpass filters are developed with reduced size and significantly improved stopband characteristics. After introducing quarter-wavelength open stubs, we get one or two transmission zeros in the stopband. By folding the high impedance microstrip lines, we reduce the size of the filter. Three-pole and five-pole lowpass filters are designed, and their measured frequency responses agree well with theoretical predictions.

Synthesizing Microstrip Dual-Band Bandpass Filters Using Frequency Transformation and Circuit Conversion Technique

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype lowpass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series or shunt resonators, and is thereby easy to be realized by using conventional distributed elements. A microstrip dual-band BPF with central frequencies of 1.8 GHz and 2.4 GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate thereby the proposed theory.

Miniaturized High-Temperature Superconducting Microstrip and Coplanar Waveguide Filters

Two types of miniaturized high-temperature superconducting filters are described in this paper. The first type is developed by using small-sized microstrip spiral resonators, and the second type by coplanar waveguide quarter-wavelength resonators. The filters have significantly reduced size compared with many previous HTS filters. They are designed by employing an electromagnetic simulator in combination with appropriately chosen equivalent circuits. Their measured frequency responses agree well with theoretical predictions, and show low insertion losses in spite of their small sizes.

Miniaturized High-Temperature Superconductor Bandpass Filters Using Microstrip S-Type Spiral Resonators

At frequencies currently used by mobile communications, many of the microstrip half-wavelength resonators are too large to realize miniaturized filters. For this reason, very small-sized microstrip spiral resonators and filters, using high-temperature superconductors (HTS), have been studied recently. In this paper, the resonant and coupling characteristics of microstrip G-type and S-type spiral resonators are investigated first by using an electromagnetic simulator. Then small-sized 4-pole, 8-pole. and 16-pole Chebyshev bandpass filters using S-type spirals are designed, respectively, with a midband frequency f 0 = 1.93 GHz. The frequency responses of the filters satisfy well the desired specifications, and the measured frequency response of the 8-pole HTS filter agrees well with the theoretical prediction.

Dual-Mode Bandpass Filters Using Microstrip Slotted Equilateral Triangular Patch Resonators

SUMMARY Two compact and low loss dual-mode filters are proposed by using degenerate modes of slotted triangular microstrip patch resonators. The geometrical size and radiation loss of the triangular patch are reduced simultaneously by loading both horizontal and vertical slots. The resonant frequencies of two degenerate modes can be easily controlled by varying the dimensions and positions of the slots. A two-pole dualmode filter operating at 3.94 GHz with a fractional bandwidth of 4.3% is designed, fabricated, and measured. The measured results verify well the

Design and Measurement of a Miniaturized HTS Filter Using Microstrip Spiral Resonators

A high temperature superconductor (HTS) filter is designed and measured at 1.93 GHz, using microstrip half-wavelength spiral resonators. Resonant and coupling characteristics of miniaturized microstrip spiral resonators are investigated first. Then a 4-pole Chebyshev bandpass filter with a very narrow passband (4.1 MHz) is designed and realized using microstrip spiral resonators. The filter is fabricated using HTS YBCO films deposited on a LaAlO 3 substrate. The measured frequency response of the filter agrees reasonably with the specifications, and shows that the filter owns excellent property of spurious resonance rejection over a wide frequency range.

Further Study on Coaxial-Probe-Based Two-Thickness-Method for Nondestructive and Broadband Measurement of Complex EM-parameters of Absorbing Material

Two-Thickness-Method (TTM) based on an open-ended coaxial probe was investigated with an emphasis on uncertainty analysis to perfect this technique. Uncertainty equations in differential forms are established for the simultaneous measurement of complex electromagnetic (EM) parameters in the systematical consideration of various error factors in measurement. Worst-case differential uncertainty equations were defined while the implicit partial derivation techniques were used to find the coefficients in formulation. The relations between the uncertainties and test samples thicknesses were depicted via 3D figures, while the influence of the coaxial lines dimension on the measurement accuracy is also included based on the same analysis method. The comparisons between the measured errors and theoretical uncertainty prediction are given for several samples, which validate the effectiveness of our analysis.

A Novel Compact HTS Interdigital Bandpass Filter Using CPW Quarter-Wavelength Resonators

A novel high temperature superconducting interdigital bandpass filter is proposed by using coplanar waveguide quarter-wavelength resonators. The CPW resonators are arranged in parallel, and consequently the filter becomes very compact. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0 GHz and an equal-ripple fractional bandwidth of 3.2%. It is fabricated using a YBCO film deposited on an MgO substrate. The measured filtering characteristics agree well with EM simulations and show a low insertion loss in spite of the small size of the filter.