Novel microstrip left-handed resonator with dual notched bands and its application in miniaturized triple-band 3-dB power divider

A novel microstrip left-handed resonator (LHR) is proposed in this paper by embedding narrow central symmetric spiral lines in the rectangular gap of the main microstrip line. According to the EM simulated results, the proposed LHR has two narrow notched bands, which is produced by the magnetic resonance and sudden change of the effective permeability and effective permittivity; the phase characteristics of the proposed LHR show that there are two frequency points with −90-degree phase shift and one frequency point with +90-degree phase shift in the passbands. According to the electromagnetic characteristics of the proposed LHR, we use it to replace the 70.7 Ω transmission line of conventional Wilkinson power divider, and a compact triple-band 3-dB power divider is presented. After fabrication, the presented triple-band power divider is measured by using Anritsu ME7808A vector network analyzer, the measured and simulated results are in good agreement with each other, showing that, the fabricated power divider operating at 2.20, 3.40, and 7.50 GHz with bandwidths of 84.5, 35.8, and 15.2%; in the passbands, the return loss is better than 15 dB, the insertion loss is between 3.4 ± 0.2 dB, and the isolation between port 2 and 3 is better than 20 dB. Moreover, the out-of-band rejection among three operating bands is also very good, which benefits from the two narrow notched bands. Simultaneously, the effective area of the fabricated power divider is 0.121 λg by 0.116 λg (where λg is the guided wavelength at 2.20 GHz), about 55.2% relative to that of conventional one operating at 2.20 GHz. Besides, the presented power divider is uniplanar, and there is no defected ground structure or lumped element.