This letter presents a whole UWB band suppressed ring resonator bandpass filter with small LUCs (Lowpass filter unit cells) [Lee W‐K, Hwang H‐Y. J Electromagn Eng Sci. 2014;14:387–392.] based on artificial transmission lines [Martin F. Artificial Transmission Lines for RF and Microwave Applications. 1st ed. New York: Wiley; 2015]. Two LUCs are used as building blocks for miniaturization and harmonic suppression of the ring resonator of the filter. Design equations for proper characteristic impedances of the ring and for proper stopband transmission zeros of the LUCs are newly presented. Fabricated filter shows insertion loss of 2.3 dB at center frequency of 2.55 GHz, fractional bandwidth of 2.5%, and good harmonic suppression about 20 dB in whole ultra‐wide band, which agreed well with the simulation results. The ring area of the proposed bandpass filter has 36% of that of the conventional one.

In this paper, a coupled line directional coupler using an LUC(Low-pass filter Unit Cell) of artificial transmission line is presented. The conventional coupled line coupler is limited in length by the λ/4 transmission line while the proposed coupling structure is implemented smaller than 90° by inserting the phase delay line between two coupled line, reduced in physical size by configuring a phase delay line with an LUC having the characteristics of a typical transmission line in a particular frequency. A coupler having -10 dB coupling factor at the center frequency of 700 MHz is designed, fabricated. The measured result agrees well with that of conventional one. The length of the fabricated coupled line coupler has about 45 % in length compared to the conventional one.

This paper presents dual-mode ring-resonator bandpass filter using LUC of artificial-transmission-lines. The conventional ring-resonator bandpass filter has limitation in miniaturization because the conventional ring-resonator is based on a one wavelength operation, and problem due to undesire harmonics. The ring-resonator bandpass filter is miniaturized and show higher order mode rejection by configuring a ring-resonator with LUC of artificial-transmission-lines. The two-stage bandpass filter is designed and fabricated with a ring-resonator and input/output interdigital coupled line. A fabricated filter shows dual-mode, rejection of whole ultra wide band, sharp skirt characteristics and has ring area reduced by 60 % compared to the conventional ring-resonator bandpass filter.