# Tilted Beam Fabry-Perot Antenna with Enhanced Gain and Broadband Low Backscattering
## 3 Simulation Results and Experimental Validation
### Scattering Results  
Next, monostatic backscattering performance of the F-P antenna is presented. The focus of this work is on monostatic RCS reduction, as in most real-world applications, such as surveillance/reconnaissance radars, the transmitter and receiver are co-located. The simulated monostatic RCS frequency response for a normally incident x-polarized (x-pol) wave is shown in Figure 16a; also included in this plot is the simulated reference RCS of a patch antenna, and calculated RCS of a perfect electric conductor (PEC) plate of similar size. It can be observed that the RCS of reference patch antenna is identical to that of a PEC plate. The radar cross section of the PEC plate can be calculated using the following Equation (3):  
\[\sigma_{PEC}=4\pi S^{2}/\lambda^{2} \tag{3}\]  
where \(\sigma_{PEC}\) represents radar cross section of PEC plate (m\({}^{2}\)), \(S\) is the surface area of the PEC plate (m\({}^{2}\)), and \(\lambda\) is wavelength. For the proposed antenna, as is evident from Figure 16a, wideband RCS reduction including in-band frequencies is achieved spanning 5.6-16 GHz, equaling 96.3% bandwidth. The maximum reduction is 31 dB, occurring at 8.8 GHz. Over the entire band, the average RCS reduction is 13 dB. Around operating frequency, the RCS reduction degradation is as expected, and still 5 dB of reduction, from the reference  
Figure 14: Principal plane patterns. (**a**) E-plane; (**b**) H-plane. Figure 15: Radiation pattern plotted at various frequencies (f). antenna, is achieved. Likewise, for y-pol normally incident wave, simulated frequency response of monostatic RCS is shown in Figure 16b. The RCS reduction performance is almost symmetric to Figure 16a. In this case also, wideband RCS reduction from 5.6 GHz to 16 GHz (96.3% BW) is achieved. The in-band RCS reduction is more than 3 dB. About 30 dB of maximum RCS reduction occurs and appears at 8.9 GHz. The average RCS reduction is 13 dB for y-pol incident wave. The scattering performance for the reference and proposed antennas are shown for the matched impedance case. Referring back to Figure 4, some peaks can be observed around 14 GHz and slightly higher. In fact, there are two sets of such peaks, one at roughly 13.8 GHz, and the second around 15 GHz. For the first set, if we observe Figure 4a, it can be seen that these peaks have a dynamic range of about 37 dB. At the same frequency, the peaks shown in Figure 4b have an almost insignificant dynamic range, and hence Figure 4a would primarily dictate the way the wave would interact with the top surface at this frequency. Figure 4a indicates the reflection response of a wave incident towards the negative \(z\)-axis. The response is shown for different patch sizes (\(v\) values), and their combined effect in the full structure would in fact increase the overall reflection. This implies that the RCS reduction should deteriorate at this frequency. This sudden RCS deterioration can clearly be observed at exactly the same frequency in Figure 16a,b. The results in Figure 4 have been obtained from unit cell simulations (periodic boundary conditions and Floquet ports), whereas the results in Figure 15 have been obtained from the actual structure simulation (using perfectly matched layer (PML) boundary setup). Therefore, it can be inferred that the sudden peaks observed in Figure 4a are not a simulation artifact; rather, these represent the actual resonance of the structure. For the second set  
Figure 16: Monostatic radar cross section (RCS) frequency response. (**a**) x-Polarized incident wave; (**b**) y-Polarized incident wave. of peaks, their dynamic range is not significant enough to be easily identifiable in Figure 16, although a corresponding little impact can still be observed. In order to validate the measured RCS frequency response performance, two pairs of in-house fabricated parabolic reflector antennas, with half wave dipole sources, were utilized to determine the scattering performance. Six discrete frequency points, spread over the frequency range of interest, could be measured.