In this paper, a new type of transmission line-based metamaterial resonator is proposed. The structure is based on a modified uniplanar series resonator bent to form a close square loop inclusion which contains a distributed capacitance and inductance. Many advantages of the proposed structure over conventional split ring resonators are discussed. Based on simple transmission line theory, the resonance frequency at which a deep rejection frequency band occurs with sharp cutoff rates beside the stopband, due to the presence of negative effective permeability in the dielectric slab of the host transmission line in the vicinity of resonance, is calculated and verified with simulated and measured results. Two prototype microwave devices are designed to illustrate the potentiality of the proposed inclusion. The first design represents a dual-band bandstop filter with designed center band frequencies at 1.6 and 2.2 GHz. The lumped element model of this filter contains four series-connected parallel LC resonators which are implemented using our high Q-factor artificial magnetic materials (AMMs) patterned on the backside of a coplanar waveguide (CPW) transmission line. The second device is a miniaturized hybrid branch line coupler operating at 2.4 GHz, based on a special loading technique that increases the electric length of transmission lines by patterning the ground plane under the conductor trace in microstrip lines with the complementary, dual-behavior, configuration of AMMs. A size reduction factor up to 16.95% is achieved compared to conventional couplers. For both design examples the measured and simulated responses are in very good agreement which validates our work.