Four-Port Orthogonal Circularly Polarized Dual-Band MIMO Antenna With Polarization and Spatial Diversity Using a Dual-Band Linear-to-Circular Polarization Converter

A dual-band circularly polarized (CP) four-port multiple-input-multiple-output (MIMO) antenna for K/Ka-bands fixed-satellite service is proposed in this communication. The single element of MIMO is composed of a cascade of two dipoles of different lengths resonating at around 20 and 30 GHz. An array of
$7 \times 7$
elements of the unit cell of the dual-band linear-to-circular polarization converter is placed at a distance of
$\lambda _{o}$
/4 (
$\lambda _{o}$
is calculated with respect to 19.51 GHz) in the endfire direction of MIMO antenna to obtain an orthogonal CP wave at the two frequency bands. The proposed CP antenna shows good MIMO performance with a correlation coefficient (CC) of less than 0.19 and diversity gain (DG) of better than 0.99 at both the frequency bands. The proposed MIMO also agrees with polarization and spatial diversity, and the CP nature at lower and upper frequency bands can be interchanged by exciting the orthogonal ports. A prototype of the MIMO antenna is fabricated, and the measured CP bandwidths of 11.51% and 3.69% are obtained in the lower (19.65–22.05 GHz) and upper (29.25–30.35 GHz) frequency bands, respectively. The proposed antenna can be used for the Ka-band: 29.5–30.0 and 19.7–20.2 GHz fixed satellite service as uplink and downlink frequencies, respectively.