Mode Compression Method for Wideband Dipole Antenna by Dual-Point Capacitive Loadings

In this communication, a dual-inode compression method is proposed for wideband applications of thin dipole antennas. In this method, only two points along the thin dipole antenna are properly found and loaded by two capacitors, lumped or distributed. At these two loading points, there are current nulls of the third mode of the dipole. With two capacitive loadings, an obvious upshifting of the first mode's resonant frequency is observed but with little effects on the third mode. By compressing the first and third modes. an enhancement of the antenna bandwidth is achieved. In addition, a parallel line is used as a transformer for impedance matching. A prototype of the design has been fabricated and tested. The measured results agree well with the simulated ones. In the thin structure of 1.01 x 0.09 lambda(0) (lambda(0) is the free space wavelength at the center frequency), a wide bandwidth from 1.88 to 3.18 GHz (51.4%) is achieved, performing an omnidirectional radiation pattern with gain of 2.0-4.0 dBi in azimuthal plane.