Compact multiple bandstop filter using integrated circuit of defected microstrip structure (DMS) and dual-mode resonator

Abstract

In this article, a compact bandstop filter (BSF) with desirable four attenuation narrow bands is developed for multiple wireless network systems. The developed filter composes of two microstrip circuits. In the first microstrip circuit, stepped-impedance and two open-circuit stubs in defected microstrip structure (DMS) are analyzed to generate the first and the second rejection bands. The third and the fourth stopbands are realized using a second microstrip circuit consist of two dual-mode resonators. This circuit are capacitively coupled to the DMS-circuit. The filter attitude is very well explained using a coupling mechanism diagram. To demonstrate the developed concept, dual and quad-bandstop filters are designed, fabricated, and measured to supress the frequencies of (2.4 GHz and 5 GHz WLAN) and (1.56 GHz GPS, 2.4 GHz WLAN, 3.5 GHz WiMax, and 5.25 GHz WLAN) respectively. The measured results agree with the predicted ones closely. The measured responses improved that the quad-BSF can apply 10 dB attenuation bandwidths of 81 MHz, 73 MHz, 60 MHz, and 129 MHz centred at 1.56 GHz, 2.4 GHz, 3.5 GHz, and 5.25 GHz respectively. The designed filter has overall circuit area of 125 mm2 excluding the feeding ports.