# Development of a Wideband Slotted Antenna Array with Low Profile and Low Sidelobe
## 3 Performance of the Proposed Antenna Array  
With the regularly arrayed subarrays along the \(x\)- and \(y\)-axis, the whole antenna, which is fed by a 1-64 ways network, is obtained. The overall size of the final slotted cavity antenna array is 169.6 \(\times\) 169.6 \(\times\) 7.23 mm\({}^{3}\). The FEM simulation results of the reflection coefficient and the total gain are plotted in Figure 9. As can be seen in Figure 9, the reflection coefficient within the frequency range from 17.9 GHz to 22.3 GHz is always smaller than \(-10\,\mathrm{dB}\), where the corresponding bandwidth is 21.9%. Several obvious ripples can be observed in the simulated reflection coefficient, which might be related to the multiple wave reflections in the long feeding network. Nevertheless, this has almost no effect on the radiation performance of the antenna array. Additionally, in the impedance bandwidth from 17.9 GHz to 22.3 GHz, the gain is always better than 28.1 dBi, and especially at the center frequency of 20 GHz, the peak gain is 29.1 dBi.  
Figure 8: Power ratio required to achieve a quarter of the Chebyshev distribution.  
The simulated normalized radiation patterns in both \(E\)- and \(H\)-planes at arbitrary three frequency points of 17.9 GHz, 20 GHz, and 22.3 GHz are presented in Figure 10. There is a slight difference in the SLLs and the 3 dB beam-widths at the presented three frequencies for both the \(E\)-plane and the \(H\)-plane. For readability, the first SLLs and the 3 dB beam-widths at the three frequencies are listed in detail in Table 2. It is seen that, as expected, the maximum beam-widths appear at 18 GHz, and the corresponding values for \(E\)-plane and the \(H\)-plane are 6.82\({}^{\circ}\) and 7.23\({}^{\circ}\), respectively. At the center frequency of 20 GHz, the 3 dB beam-widths for the \(E\)-plane and the \(H\)-plane are 5.46 deg and 5.74 deg, respectively.  
Obviously, the first SLLs in the \(E\)-plane at the three selected frequency points are close to the designed \(-\)30 dB, which demonstrates the good agreement between the simulated and theoretical results. Nevertheless, the first SLLs in the \(H\)-plane at the three frequency points are not as good as that in the \(E\)-plane, which might be related to the asymmetric distribution of the radiation slots in \"Layer1\" of Figure 1. Generally, at higher frequencies, both the first and the total SLLs are slightly larger. One reason is that with the decrease of the wavelength of the radiated waves, the grating lobes usually increase. Another reason is that at frequencies when the resonance cavity does not work at its resonant frequency, the phase difference of the radiated waves among the slots will increase, while at low frequencies, the phase difference can partly compensated by other modes, such as the \(TE_{120}\) mode and the \(TE_{210}\) mode of the resonance cavity. It can be further observed that there are two convex sidelobes at about \(\theta=\pm\)40\({}^{\circ}\) at the three frequencies, which might be related to the fact that the power distribution at the 16 \(\times\) 16 radiation slots is not a typical Chebyshev distribution. As mentioned above, the power at the 8 \(\times\) 8 coupling slots in \"Layer3\" is in Chebyshev distribution, while the waves at the four radiation slots of each subarray, which is supported by one coupling slot, are the same.  
Figure 10: Normalized radiation patterns in the \(E\)-plane and \(H\)-plane at (**a**) 17.9 GHz, (**b**) 20 GHz, and (**c**) 22.3 GHz, respectively.  
Figure 9: Reflection coefficient (black line) and gain (red line with symbols) for the proposed slotted cavity antenna array.