Design and characterization of planar traveling wave dipole antennas using resistive and reactive loading

Date of Completion

January 1992


Engineering, Electronics and Electrical|Physics, Electricity and Magnetism




It is well known that the current distribution on dipole antennas exists primarily as standing waves. For this reason, the input impedance of a dipole antenna is a strong function of frequency. In contrast, a traveling wave antenna possesses an input impedance that is comparatively frequency independent. An important result of this reduced frequency dependence is the decrease in VSWR and an increase in bandwidth for a given antenna. In the past, free standing, traveling wave dipoles have been realized by the incorporation of distributed resistive loading along the length of the antenna. This type of loading permits the rapid attenuation of a traveling wave current as it proceeds toward the feed point. These experiments were performed at frequencies of several hundred megahertz. Resistive loading, however, reduces the radiation efficiency of the antennas by dissipating some of the input power as heat. This dissipative power loss may be overcome by utilizing reactive loading.^ This work discusses the design and characterization of planar traveling wave dipole antennas in the frequency range of X-through Ku-band. All of the dipole antennas treated were characterized with the aid of a small loop magnetic field probe constructed for that purpose. The magnetic field probe was used to quantitatively measure the surface current magnitude and phase distributions along the lengths of the dipoles. The planar antennas considered include printed microstrip dipoles that incorporate either resistive or reactive loading schemes along their lengths. These printed metal dipoles range in length from one quarter of a wavelength to over five wavelengths at 20 GHz. In addition, silicon traveling wave dipoles obtained via conductivity modulation are also evaluated. ^