A Novel Nonlinear LPDA Design for HF Direction Finding

A novel design of log-periodic dipole array (LPDA) for high-frequency direction finding (DF) is presented. The traditional Carrel method employs fixed values of scale factor and spacing factors in LPDA designs. Here, we propose a design method which uses the continuous change of both the scale factor and the spacing factor so that the length of the dipoles and the space between dipoles vary nonlinearly. One advantage of our design is that the effective distance between the phase center position and the feed point of LPDA can be increased. So the effective radius of the circularly disposed antenna array (CDAA) composed of LPDA is extended, which is important for improving the accuracy of the DF system. Both the simulation and measurement results show that the proposed LPDA achieves larger effective distance and higher gain compared to that using the traditional Carrel method. The proposed LPDA also shows characteristics of wideband impedance matching. The antenna has been successfully applied to practical HF direction finding system.