Methodology for calculating a low-pass filter based on dumbbell-shaped defected ground structure

Аuthors

Barannikov L. N.^*, Ishchenko E. A.^**, Proskurin D. K.^***, Pasternak Y. G.^****, Fedorov S. M.^*****

Voronezh State Technical University, VSTU, 14, Moskovsky prospect, Voronezh, 394026, Russia

*e-mail: ia.barannikov@yandex.ru
**e-mail: kursk1998@yandex.ru
***e-mail: rector@cchgeu.ru
****e-mail: pasternakyg@mail.ru
*****e-mail: zar36@yandex.ru

Abstract

Filtering unwanted frequencies is an important task in electronic devices designed to operate in the microwave range. Lumped-element filters are the most commonly used. They are simple to design but require assembly during manufacturing and impose specific requirements on the components used. An alternative is to use distributed-element filters. These are based on microstrip structures and are significantly more complex to design, as well as larger in size than lumped-element circuits. A relatively recent approach to filter design involves the use of defected ground structures, located beneath the microstrip line. Their main advantage is much smaller size, but they are also complex to design and can generate unwanted radiation at certain frequencies. The article considers the calculation methodology of a microstrip low-pass filter based on dumbbell-shaped defected ground structures, which allows to significantly reduce the design time of such filters due to simplified calculations and a reduction in the time of selecting the optimal dimensions of the structure geometry. It is based on the empirical calculation formulas obtained by means of regression analysis on the basis of modeling data of structures with various parameters and describing the relationships between the defect geometry, the substrate parameters and the attenuation pole and cutoff frequencies. The calculation accuracy of this technique is confirmed by the statistical characteristics of the obtained formulas: for the attenuation pole, the determination coefficient was 0.975, and the standard deviation was 0.0686; for the cutoff frequency, the same characteristics are 0.961 and 0.0376, respectively. The frequency limits of applicability of the technique lie from 1.33 GHz to 12.1 GHz for the attenuation pole and from 0.64 GHz to 6.87 GHz for the cutoff. The relationship between the obtained formulas and the capacitance and inductance values of the equivalent circuit is also presented, allowing for a quick evaluation of the filter’s performance. Finally, an example of calculating a 6 GHz filter design using the proposed method is presented to confirm its efficiency. The presented method can be applied to designing filters for various components of microwave electronic devices with dimensional constraints.

Keywords:

low-pass filer; defected ground structures; dumbbell-shaped defect; regression analysis.

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