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Multiple electric resonators loaded with lumped resistors are usually constructed in a unit cell to design broadband metamaterial absorbers. In this paper, we propose a simple way to achieve ultrabroadband microwave absorption. Only one split ring resonator loaded with one lumped resistor in the absorber's unit cell in our design. Its measured reflection coefficient is lower than −10 dB in the frequency range 14.20 GHz to 32.98 GHz. Its bandwidth is 18.78 GHz, and its absorption frequency covers the Ku-, K-, and Ka-bands. The absorber has a 1.524 mm dielectric layer, and the thickness of the copper foil on both sides of the dielectric layer is 0.035 mm. Therefore, the total thickness of the absorber is only 1.594 mm. The edge length of its unit cell is 1.8 mm, which is about 1/4 of the wavelength of 40 GHz, so the oblique incidence of electromagnetic waves will not excite higher-order modes below 40 GHz. In addition, we study its absorption mechanism in detail. It is discovered that besides selecting a suitable lumped resistance value, the construction of two magnetic resonances and an electric resonance between them is necessary to achieve broadband absorption.