Fig.1 Traditional butterfly antenna L, Total arm length of antenna; θ0, Angle of spread.

Fig.2 Schematic diagram of antenna structure in this paper A, Schematic diagram of the three-dimensional structure; B, Single antenna bottom view; C, Side view of single antenna; D, Side view of chokes; E, Overall structural view of antenna. Ws, Lower width of the dorsal cavity; Wp, Upper width of the dorsal cavity; L1, L2and L3, Butterfly oscillator size; Hg, Coaxial feeding and distance from the top of the back cavity; Hs, Back cavity slope height; Hp, The distance between the upper back cavity and the oscillator height; Hq, Height of choke groove; La, Width of choke groove; Lb, Lcand Ld, The overall size of the ground penetrating radar antenna.

Fig.3 Back cavity evolution and 3D radiation pattern A, No dorsal cavity model; B, Two sided folding back cavity model; C, Four sided folding back cavity model.

Fig.4 Performance comparison of three models L3, Model without a dorsal cavity; L4, Double-sided folded dorsal cavity model; L5, Four fold back cavity model.

Fig.5 Effect of Hp on antenna performance

Fig.6 Influence of Ws on antenna performance

Fig.7 Effect of Wp on antenna performance

Fig.8 The structure and principle of the choke groove A, Choke groove structure diagram; B, Schematic diagram of the suppression of surface waves by a choke groove; C, The principle of choke groove for suppressing refractive and diffractive waves.

Fig.9 Impact of choke groove on isolation of antenna transceiver

Fig.10 Effect of choke groove on antenna gain

Fig.11 Physical object and test scenario

Fig.12 Antenna simulation and measured S-parameter curve

Fig.13 Gain pattern of antenna

Fig.14 Field test scenarios

Fig.15 Comparison of power spectral density under different soil moisture contents A, B, C and D are comparisons of power spectral density at soil moisture contents of 10%, 15%, 20% and 25%, respectively.