## 4 Measurement Results
Figure 10: Theoretical and measured scattering parameters: (**a**) magnitude for S\({}_{11}\), S\({}_{22}\), and S\({}_{21}\); (**b**) measured phase difference, corresponding to states I and II. to obtain the independent control of each element in the transmitarray. The design uses surface mount connectors (24 pins) to control each transmitarray cell independently. The 24-pins connectors adopted in the entire bias line network are evenly distributed on the left- and right-hand sides of the surface of the transmit array. These details are illustrated in Figure 14a,b with a complete fabrication scheme for the transmitarray. Metal through-holes connect each front surface mount connector pin with the corresponding bias line at the back. The theoretical ad hoc simulator and full-wave simulation CST E-plane and H-plane radiation pattern are presented in Figure 10. The higher side-lobe level (SLL) in the full-wave simulation is due to spillover radiation losses that are not part of the numerical  
Figure 14: The 20 \(\times\) 20 hexagonal meander-shaped transmitarray: (**a**) 24 pin connectors for biasing, (**b**) full scheme of the bias line. Figure 12: Three-dimensional and side view of proposed 20 \(\times\) 20 transmitarray. Figure 13: The 20 \(\times\) 20 frequency versus gain graph. simulations. The maximum gain is 24.4 dBi with a side-lobe level of \(-19.7\) dB and an aperture efficiency of 74.4% at 16 GHz. The results of the full-wave simulations to understand the array's beam-scanning characteristics in the E-plane are presented in Figure 15a,b at 16.5 GHz. The maximum gain reduces from 24.4 dBi to 20.8 dBi to a 60\({}^{\circ}\) scan angle. The simulated gain and directivity at 16.5 GHz are 24.4 dBi and 25.5i dB, respectively, for the 20 \(\times\) 20 transmitarray. Thus, the radiation efficiency gain over the directivity ratio is 95.5%. The HPBW are 6.70 degrees and 6.76 degrees in the E plane and H plane, respectively. The side-lobe level (SLL) and cross-polarization level (CPL) are \(-19.7\) dB and \(-22.4\) dB, respectively. The aperture efficiency is obtained using the formula \(e_{ap}=\frac{G}{D_{max}}\) where \(D_{max}=\frac{4\pi A}{{\lambda_{0}}^{2}}\) which is approximately 29.1%. It is noted that the E-plane and H-plane radiation patterns are almost symmetrical due to the similar E- and H-plane oblique incidence performance of the unit cell. Figure 8.0 _Cont._  
The phase distribution and focal distance (F) were selected for maximum aperture efficiency. Ad hoc simulator and full-wave simulations in CST compare the radiation patterns and characteristics of the reconfigurable transmitarray is shown in Figure 8.1 The 3 dB gain bandwidth lies between 15 GHz and 18.6 GHz, associated with an overall fractional bandwidth of 19.18% at 16.5 GHz. Several designs were investigated to reduce the one-bit phase quantization for two-bit or three-bit fixed beam (passive) transmitarrays. A 2-bit reconfigurable transmitarray requires at least 4 diodes to achieve a 90-degree phase shift for each phase state which makes a multi-bit design challenging in transmitarrays. It is not easy to control the reverse direction of the current in a unit cell by just applying all four diodes on the receiver or transmitter sides. Two diodes can be installed on the receiver side; on the other hand, two diodes can be installed on the transmitter side with different polarization. Four diodes are required for biasing two circuits to control the phase shift independently. The current reversal control of both sides provides us four states and can produce a two-bit reconfigurable transmitarray unit cell. Figure 8.2 Wideband hexagonal unit cell: (**a**) E-plane phase distribution and gain spectrum, (**b**) H-plane phase distribution and gain spectrum.