# Low-Profile High-Efficiency Transmitarray Antenna for Beamforming Applications
## 3 Beamforming Partial H-Plane Waveguide Slot Array Antenna
Figure 7 shows the photographs of the fabricated beamforming 8 \(\times\) 10 partial H-plane waveguide slot array antennas using an FSS. To verify the performance of the proposed beam-steering array antenna, we simulate and measure the reflection coefficient, far-field radiation pattern, peak gain, and aperture efficiency. The measured reflection coefficients at \(-40^{\circ}\), \(-20^{\circ}\), \(0^{\circ}\), +20\({}^{\circ}\), and +40\({}^{\circ}\) are \(-9.1\) dB, \(-8.2\) dB, \(-10.3\) dB, \(-7.7\) dB, and \(-9.3\) dB at the resonance frequency, respectively. The designed FSS does not have 100% transmittance performance and is located close to the slot array antenna. Thus, the impedance matching of a total beamforming antenna system is not sufficiently good. It is expected to improve the reflection coefficient by an FSS with a perfect transmittance. The far-field radiation pattern and peak gain are measured in the full anechoic chamber system. The anechoic chamber is composed of a shield enclosure (size: 4 m \(\times\) 2.5 m \(\times\) 2.5 m), 18-inch pyramidal absorber, network analyzer, wireless communication test set, positioner, turn table, and dual-polarized transmit antenna. Figure 8 shows the full-wave simulated and measured far-field radiation pattern in the \(x\)-\(z\) plane. The measured results are in good agreement with the simulated results. The measured peak gains at \(-40^{\circ}\), \(-20^{\circ}\), \(0^{\circ}\), \(+20^{\circ}\), and \(+40^{\circ}\) are 21.2 dBi, 23.6 dBi, 24.3 dBi, 23.6 dBi, and 21.3 dBi, respectively. The measured radiation patterns, including a forming angle, are well matched with the simulated results, even though the measured maximum peak gains are 1-1.5 dB lower than the simulated results. The discrepancy between both results is caused by the loss of a coaxial transition as a feeding structure. Moreover, the high aperture efficiencies at \(-40^{\circ}\), \(-20^{\circ}\), \(0^{\circ}\), \(+20^{\circ}\), and \(+40^{\circ}\) are measured as 44.2%, 62.7%, 69.2%, 62.2%, and 45.4%, respectively. Table 4 shows the comparison of the performances between the previously published TAs and the proposed antenna. The single-source TA cannot \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline _pw\({}_{1}\)_ & 0.5 & 1 & 1.5 & 2 & 2.5 & 3 & 3.5 & 4 \\ \hline _pw\({}_{2}\)_ & 0.5 & 1 & 1.5 & 2 & 2.5 & 3 & 3.5 & 4 \\ \hline Transmittance (Linear) & 0.91 & 0.9 & 0.91 & 0.93 & 0.95 & 0.97 & 0.99 & 0.99 \\ \hline Transmission phase (Degree) & \(-73\) & \(-76.9\) & \(-77.5\) & \(-81.8\) & \(-88\) & \(-96.6\) & \(-106.3\) & \(-120.9\) \\ \hline _pw\({}_{1}\)_ & 4.5 & 5 & 5.5 & 6 & 6.5 & 6.6 & 6.9 & 7.3 \\ \hline _pw\({}_{2}\)_ & 4.5 & 5 & 5.5 & 6 & 6.5 & 7 & 7.5 & 7.7 \\ \hline Transmittance (Linear) & 0.99 & 0.97 & 0.95 & 0.98 & 0.99 & 0.97 & 0.9 \\ \hline Transmission phase (Degree) & \(-134.1\) & \(-150.6\) & \(-162.1\) & \(-170.8\) & \(-181.6\) & \(-252.6\) & \(-404.9\) & \(-604.5\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Transmittance responses of the designed FSS against patch dimensions (unit mm). achieve a low profile to obtain a relatively high aperture efficiency. However, the phase gradient FSS for the beamforming multi-source TA can be located close to multi-sources with a high taper and spillover efficiencies because of the uniform power distribution and the proximity of the FSS and sources, respectively. Therefore, using multi-sources rather than a single source is more appropriate to achieve an extremely low profile and a highly efficient beamforming TA.