<p>This study used radio-frequency (RF) magnetron sputtering to produce NbMoTaW high-entropy-alloy thin films on silicon substrates and explored the composition, microstructure, hardness, and resistivity of these films. X-ray diffraction analysis indicated that polycrystalline alloy materials were present in the thin films fabricated under all process parameters. Moreover, an increase in substrate temperature and RF power resulted in improvements in the properties of the produced NbMoTaW thin films. Among all prepared films, a substrate temperature of 300°C and RF power of 200 W resulted in the lowest resistivity (57 μΩ·cm) but also the lowest hardness; however, the hardness value (12.425 GPa) was still sufficient. This film was then deposited on alumina substrate in the fabrication of a 24 GHz monopole antenna with good impedance matching for an automotive radar system. The maximum gain of this antenna was 7.05 dBi, and the antenna had a relatively stable temperature drift coefficient of the resonant frequency.</p>