A Circularly Polarized Broadband Printed Array With a Bud-Shape Feedline Network

This letter develops a printed two-element parallel array consisted of dual rhombic loops and a reflecting plate for broadband, high-gain, and circular polarization (CP) operation. An improved mixed feedline network of bud-shape junction is suggested for the parallel antenna array design. The bud-shape junction not only converts the coplanar stripline to the microstrip line, but also expands the impedance-match bandwidth. The dual parasitic rhombic loops are applied to broaden the CP operation bandwidth. The antenna array is simulated and fabricated with good agreement obtained between the simulation and experimental results. The fabricated prototype shows that the bandwidth of
${\rm AR}< 3~$
dB,
${ S}_{11}< -10~$
dB, and
${\hbox{gain}}> 12~$
dB is 18.1%, 18.8%, and 12.1%, respectively. A 2
$\,\times\,$
4-array structure is also presented using this bud-shape junction, and it is easy to be expanded to large arrays for high-gain applications.