With the arrival of the 5G era, the working frequencies of wireless devices are being transferred to a higher spectrum with a wider available bandwidth. However, conventional metal wire antennas used in 5G communication systems are often limited by their resonant structure, which inevitably leads to narrow operating bands and fixed sizes at integral multiples of λ/2 or λ/4. In this Letter, a ceramic inverted-L antenna with a non-resonant architecture is proposed to achieve a wide bandwidth and flexible size. Its leaky-wave radiation is based on the cutoff region of dielectric waveguides, which verifies that the working frequencies of the proposed antenna are related to the cross section rather than the length. Ceramic 3D printing technology is adopted for precise manufacturing of the proposed antenna, which covers the frequency range of 3.28-5.28 GHz, including the bands n77/n78/n79 of the sub-6 GHz spectrum.