# 3-D Printed Fabry-Perot Resonator Antenna with Paraboloid-Shape Superstrate for Wide Gain Bandwidth
## 4 Fabrication, Measurements, and Discussion  
To validate the proposed FPRA, a prototype antenna will be fabricated and tested. The complex structure, especially the paraboloid-shape superstrate, may make the fabrication very difficult. Hence 3-D printing technology is employed to fabricate the proposed antenna (see Figure 8). In this work, all components of the proposed antenna are printed using a laser to solidify liquid photopolymer resin which is then treated by the surface metallization including the following step: (1) the printing material of resin is treated by a sequence of chemicals to activate the material's surface; (2) 0.5 \(\upmu\)m of Ni is electrolessly plated on the surface, the Ni serves as a seed layer for the later process; (3) 1-2 \(\upmu\)m copper is elecrolessly plated above the surface of Ni; (4) 6 \(\upmu\)m of copper is electroplated to increase the thickness of the copper and guarantee the layer is much larger than the skin depth (the value is 0.84 \(\upmu\)m for copper at 6 GHz); (5) finally, 0.15 \(\upmu\)m of silver is plated on the surface of the copper to prevent oxidation.  
For the 3-D printed antenna, its input reflection coefficient was measured with an Agilent network analyzer N5230A. The simulated and measured \(|\)S\({}_{11}\)\(|\) are plotted and compared in Figure 9. The measured results are in good agreement with simulated ones, and indicate a \(|\)S\({}_{11}\)\(|\)\(<\) -10 dB impedance bandwidth of about 12.4% (from 5.8 GHz to 6.53 GHz).  
The radiation pattern of the 3-D printed antenna is measured in an anechoic chamber. Figure 10 plots the co-polarization and cross-polarization in E-plane and H-plane at 5.8, 6, 6.2, and 6.5 GHz respectively. It can be observed that the proposed FPRA performs good directive radiation patterns at all of those frequency points. The measured cross polarizations are also presented, which are less than -25 dB at the broadside. The polarization of the FPRA is consistent with that of the feeding antenna, which can be easily changed by employing a feeding antenna with a different polarization. With the increase of frequency, the side-lobe levels are also increased, this phenomenon has been observed with many wideband Fabry-Perot resonator antennas [25].  
Figure 8: Photograph of the proposed 3-D printed antenna. A waveguide to coaxial connector is used to feed the antenna.  
Figure 10: _Cont._  
Figure 9: Simulated and measured reflection coefficients for the proposed FPRA.  
The simulated gains against the frequency for the proposed FPRA with a paraboloid-shape superstrate and the FPRA with a traditional planar superstrates are presented and compared in Figure 11a. The 3-dB gain bandwidths for those two FPRAs are 22.2% (from 5.67 to 7 GHz) and 6% (from 5.81 to 6.17 GHz), respectively. It is obvious that the paraboloidal superstrate significantly improves the gain bandwidth in comparison with a traditional planar one. Figure 11b compares the simulated and measured gain-frequency response for the proposed FPRA, one can observe they are in good agreement.  
Table 1 lists 3-dB gain bandwidths of a few FPRAs designed in previous literatures, and are compared to that in this work. One can observe that the FPRA proposed in this work achieves a larger 3-dB gain bandwidth than those FPRAs in previous studies.  
Figure 10: Normalized radiation patterns of the proposed FPRA: (**a**) E-plane at 5.8 GHz; (**b**) H-plane at 5.8 GHz; (**c**) E-plane at 6 GHz; (**d**) H-plane at 6 GHz; (**e**) E-plane at 6.2 GHz; (**f**) H-plane at 6.2 GHz; (**g**) E-plane at 6.5 GHz; and (**h**) H-plane at 6.5 GHz.