Design and Optimization of High-Power UWB Combined Antenna Based on Klopfenstein Impedance Taper

In order to improve the operating bandwidth and achieve a compact design of the combined antenna, the Klopfenstein impedance taper method is adopted to implement the structure of the combined antenna in this paper. The effects of Klopfenstein taper with different parameters are compared and analyzed with simulation method. Also, the quantity of the magnetic moment of the combined antenna is optimized to improve the low-frequency performance. The relationship between the performance and the structural parameters for the combined antenna is concluded based on the research results. Finally, an optimized combined antenna with length of 30 cm is designed and measured. The impedance bandwidth [ voltage standing wave ratio (VSWR) <2] of the antenna is 180 MHz to 7 GHz, which means that the band ratio is about 40. The ratio between the antenna length and the wavelength of the lower cut-off frequency, L/lambda, is reduced to 0.18. The weighted radiation efficiency within 0-7 GHz is 93.7%. Both numerical and experimental results show that the antenna exhibits unidirectional patterns within the frequency range of 0.5-7 GHz. With a short ultra-wideband pulse excitation, gain of the antenna is measured and derived within the spectrum of the excitation, i.e., 0-3 GHz. The corner frequency of the antenna gain is about 200 MHz, which is close to that of VSWR. Moreover, the radiation efficiency is 76.1%, and the pulse fidelity factor is 0.82 with the applied excitation.