# Characterization of Tiled Architecture for C-Band 1-Bit Beam-Steering Transmitarray
## 4 Beam Steering by the Tiled Transmitarray
Figure 5: Measured (solid lines) and simulated with the patch antenna feed (dashed lines) beampatterns for different beam-scanning angles (viz., 0\({}^{\circ}\), 15\({}^{\circ}\), and 30\({}^{\circ}\)): (**a**) assembled transmitarray with the patch-antenna focal source visible; (**b**) binary phase distribution for different beam-scanning angles; (**c**) H-plane single-panel transmitarray beampatterns; (**d**) H-plane tiled transmitarray beampatterns; (**e**) E-plane tiled transmitarray beampatterns. Figure 6 shows the measured beam patterns in orthogonal polarization (cross-polarization) in the principal E and H planes and diagonal D-plane. All patterns exhibit a prominent peak at boresight with respective cross-polarization ratio (CPR) \(\sim\)14.5 dB. The shape of the cross-polarization beampattern is typical for dual-polarization transmitarrays, c.f., [17], and indicates polarization leakage due to coupling between the orthogonal feeds and between the patches on the opposite sides of the unit cell, as indicated by our equivalent-circuit characterisation. The measured figure agrees well with the data reported elsewhere, c.f. [17]. Table 2 shows the performance comparison of the reference single-panel transmitarray discussed in this paper against a selection of published C-band transmitarray implementations, including the theoretical ('theor. '), measured ('meas.') and simulated ('sim.') data, [17; 18; 19; 20]. Apart from one passive two-layer frequency-selective surface (FSS) lens, [20], the other transmitarrays adopt the conventional receiver-transmitter architecture with electronic control of the array functional (i.e., beam-steering, beam-forming or polarization conversion). As our design advances, it will integrate electronic control and provide wider bandwidth and better beam pointing accuracy. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **[17]** & **[18]** & **[19]** & **[20]** & **This Work (Tiled)** \\ \hline \multirow{4}{*}{Unit-cell} & Two-layer stacked patches (Rx), a patch with O-slot (Tx), reflective phase shifter, vias & Patches, proximity coupled diff. feeds, balanced bridged-T phase shifters & Five stacked layers of square slot FSS and feeding networks & Passive two-layer double split-ring slot until cells of varying size & Square-ring patch with positively coupled -shaped resonators, vias \\ \hline Array size & \(8\times 8\) & \(6\times 6\) & \(5\times 5\) & \(7\times 7\) & \(10\times 10\) \\ \hline Polarization & LP-to-LP/CP & LP & LP & LP & LP \\ \hline \(\theta\), GHz & 5.4 & 5 & 52 & 6 & 5.75 GHz \\ (\(\Delta\)/f) & (8.5\%) AR-3 dB) & (10\% by GO-2 dB) & (1.4\% by UC21-3 dB) & (15\% by GO-3 dB) & (2.5\% by GO-3 dB) \\ \hline Boresight antenna gain, dBi & \(17\) (meas.) & 20.5 (theor.) & 18.6 (sim.) & 16.7 (meas.) & 14 (meas.) \\ \hline HPBW, deg. (meas.) & \(13.5\) (E) & 20.4 (E) & 14 (E) & 12 & 12 \\  & & 18.4 (H) & 16 (H) & \(-\)9.7 & \(-\)10 & \(-\)12 \\ \hline SLL, dB (meas.) & \(-\)10 & \(-\)14.9 (H) & \(-\)9.7 & \(-\)10 & \(-\)12 \\ \hline CPR, dB (meas.) & 20 & 35 & N/A & N/A & 14.5 \\ \hline Scan loss (scan angle), dB & 0.9 (20 degree) & N/A & 1.4 (15 degree) & N/A & 2 (30 degree) \\  & 2.1 (30 degree) & & 7.8 (25 degree) & & \\ \hline \multirow{4}{*}{Beam pointing error (H), degree} & \multirow{4}{*}{N/A} & \multirow{4}{*}{N/A} & \multirow{4}{*}{N/A} & 0 (0 degree) & \multirow{4}{*}{N/A} & \multirow{4}{*}{N/A} \\  & & & 8 (0 degree) & & & \\ \cline{1-1}  & & & 16 (45 degree) & & & \\ \hline Control & Varactors & Varactors & Varactors & None & None \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of some existing C-band transmitarrays. Figure 6: Measured cross-polarization patterns of the tiled transmitarray radiating at boresight plotted in the principal (E and H) and diagonal (D) planes.