Extending Low-Frequency-Limit Boundary of Dual-Element Antipodal Vivaldi Antenna by Enhancing Both Impedance and Radiation Properties

In the low-operating-frequency regime of Vivaldi antennas, the traveling-wave operational mechanism hinders their further miniaturization. Moreover, attenuation of the slow-wave effect induces radiation pattern distortion at low frequencies. To overcome these limitations, this work integrates standing-wave resonance modes with the intrinsic traveling-wave radiation mechanism and extends the lowest operating frequency from 2 GHz to 1 GHz without increasing the antenna dimension. Meanwhile, the radiation distortions at low frequencies are also restored, and a consistent end-fire pattern from 1 to 18 GHz is realized. Experimental results demonstrate that the proposed antenna exhibits a satisfactory impedance matching (178.9% fractional bandwidth for |S₁₁|<−10dB), while maintaining a compact dimension of 0.538λ₀×0.3λ₀×0.0025λ₀ (λ₀ at 1 GHz). Together with the measured consistent end-fire patterns, the proposed antenna shows great potential for applications such as phased array detection, microwave imaging, and ultra-wideband systems.