Dual-frequency and broad-band antennas with stacked quarter wavelength elements

Original lightweight, low-cost, and compact air-filled planar antennas with short-circuited elements, fed by a coaxial probe, for dual-frequency (S-antenna) and wide-band applications (E-antenna) are investigated. The two-band frequency antenna is formed of two stacked quarter-wavelength elements, short-circuited along diametrically opposed planes. This structure offers two modes with different radiation characteristics. The ratio between the two frequencies can be closely controlled within a range varying from 1.3-2. A bandwidth of 30% for a VSWR <2 is demonstrated using two stacked quarter-wavelength elements short-circuited along the same plane. Numerical simulation results are compared with experiments and a very good agreement is observed. Radiation patterns and input impedance of both structures are measured and the effects of various physical parameters are presented.