# A Four-Port Dual-Band Dual-Polarized Antenna for Ku-Band Satellite Communications
## 2 Antenna Design and Working Mechanism  
### Antenna Configuration  
The geometry of the proposed four-port shared-aperture DBDP antenna and its side view are shown in Figure 1a,b, respectively. The antenna is designed with a multilayer PCB process. It has six substrate layers (\(sub\)-\(1\)-\(sub\)-\(6\)), five prepreg layers (prepreg 1-5), and seven copper layers (\(M1\)-\(M7\)). The substrates are Taconic TLE-95 (\(\epsilon_{1}\) = 2.95 and tan\(\delta_{1}\) = 0.0028). The prepreg materials have the same thickness of \(h_{p}\) and are based on Rogers RO4450T material (\(\epsilon_{2}\) = 3.23 and tan\(\delta_{2}\) = 0.0039).  
The dual-band operation of the proposed antenna is achieved by two separate antennas, one LB antenna and one HB antenna, sharing a common radiating aperture. The LB antenna consists of a square-ring radiator with four chamfered corners printed on the copper layer \(M1\). Two \(L\)-probe feeds, each comprising a stripline embedded in copper layer \(M2\) and an LB feed, are implemented and positioned in the \(x\)- and \(y\)-directions to excite the square ring for dual polarization at the low band. In order to improve the impedance matching of the LB antenna, three protruding stubs are attached directly to the corners of the square ring. The HB antenna is a stacked-patch radiator, consisting of two identical plus-shaped parasitic patches printed on the copper layers \(M2\) and \(M3\) and a plus-shaped driven patch printed on the copper layer \(M4\). Two capacitive feeds are used and positioned in the \(x\)- and \(y\)-directions to excite the driven patch for dual polarization at the high band. Four identical open rectangular slots are etched symmetrically on each parasitic patch to lower the operational frequency band of the HB antenna. In addition, four identical arc-shaped slots are etched symmetrically on the driven patch to improve the impedance matching. Due to the inherently poor isolation of the capacitive feeding, the HB antenna is equipped with a shorting pin to improve the isolation between two orthogonal polarizations. The proposed antenna is excited by four excitation ports **P1-P4** through four 50-coaxial cables. Each coaxial cable is connected to a feed via a grounded coplanar waveguide (GCPW) consisting of a feedline and a bottom ground plane on the copper layer _M7_, a top ground plane on the copper layer _M6_, and a series of orange blind vias penetrating through the substrate layer _sub_-6. A cavity formed by a square ring printed on the copper layer _M5_ and a series of green blind vias surrounding the antenna is used to define the array lattice size for array construction. The size of the cavity is 10.3 mm \(\times\) 10.3 mm. This corresponds to an array with spacing of 0.43\(\lambda_{12.75\mathrm{GHz}}\) and 0.50\(\lambda_{14.5\mathrm{GHz}}\) between elements at 12.75 and 14.5 GHz, respectively, allowing a maximum achievable scan angle of \(\pm 70^{\circ}\) for both operating bands. The detailed configurations of each copper layer are shown in Figure 2, with the optimized design parameters summarized in the caption. The antenna was optimized using Ansys HFSS 2020 R2.  
Figure 1: Geometry of the proposed four-port shared-aperture DBDP antenna. (**a**) 3D exploded view. (**b**) Side view. (\(h_{1}=0.13\) mm, \(h_{2}=0.25\) mm, \(h_{3}=1.58\) mm, \(h_{4}=h_{5}=0.51\) mm, \(h_{6}=0.25\) mm, and \(h_{p}=0.076\) mm).