Shilong Qian

Dual-Band Differential Filter Using Broadband Common-Mode Rejection Artificial Transmission Line

A new balanced dual-band bandpass fllter with strong common-mode rejection is presented in this paper. Common-mode rejection is provided by a section of a periodic microstrip difierential line that behaves as a low-pass fllter under common-mode operation. In contrast, the difierential line exhibits very good all-pass behavior under difierential mode operation. This structure is combined with a difierential dual-band bandpass fllter based on embedded resonators. Simulations and experiments conflrm that the combined structure has good common-mode rejection within the passbands of the dual-band difierential fllter.

Miniature Quasi-Lumped-Element Wideband Bandpass Filter at 0.5–2-GHz Band Using Multilayer Liquid Crystal Polymer Technology

Miniature wideband bandpass filters are proposed using multilayer liquid crystal polymer (LCP) technology to cover the very low-frequency band of 0.5-2 GHz. To reduce the filter size at such low frequencies, lumped-element theory is used for the filter design and a value extraction process is developed to accurately get the capacitive or inductive values of different multilayer microstrip quasi-lumped elements. These elements are used to produce the required filter response, and thus the overall design process relies less on the time-consuming EM optimization. A filter with the size 0.058 λ_g ×0.026 λ_g ×0.004 λ_g is demonstrated as an initial design. To further improve the stopband performance, an improved design is then developed while still maintaining the compact sizes within 0.065 λ_g ×0.026 λ_g ×0.004 λ_g. Both filters are fabricated on a five-metal layer LCP construction, which has not been done before, with robust via connections using the newly developed laser-aided fabrication technique. Good agreements between simulation and fabrication are observed, which has proven both the success of the design methodology, as well as the fabrication technique.

The Design of Miniature Multilayer Bandpass Filters With Mixed Couplings

This paper introduces a new design process for miniature coupled resonator filters with mixed couplings, which can better preserve wideband response matching with coupling matrix prototype. A special type of matrix transformation is introduced in this paper to transform the coupling matrix into a configuration that consists of an equal number of capacitive and inductive main couplings. Based on this, lumped-element circuit models can be produced. Then, by using π to T transformations for some parts of the circuit, all the elements have realizable values. A miniature bandpass filter with a fractional bandwidth of 20% of this type based on N×N coupling matrix is demonstrated with both simulated and measured response. The filter is implemented using multilayer liquid crystal polymer circuit technology and has a compact size of 0.0294λg × 0.0303λg ×0.00052λg, where λg is the guided wavelength at the center frequency of 250 MHz.