# Calibration of a Low-Cost 8\(\times\)8 Active Phased Array Antenna
## 4 Measurement Comparison  
After the calibration, shown in the previous section, the measured and simulated radiation pattern results are compared in this section. As described in the previous section, with phase calibration, the obtained result is similar to the obtained result using the REV calibration method; therefore, the radiation patterns simulated and measured within this section only take into account the phase calibration method.  
Figure 12 presents the comparison of the normalized radiation patterns (simulation vs. measurement) of the radiation pattern of the horizontal plane at the lower, center and upper frequency. The calibration at the center frequency also has excellent in-band performance for the lower and upper frequencies despite amplitude imbalance between the elements. The measured cross polar level is higher than the simulation because of the manufacturing misalignment. Figure 13 presents the radiation pattern at the lower, center and upper frequency of the extreme beam steering direction (\(-35^{\circ}\)). For this beam direction, the progressive phases of lineal array for this steering are applied to each column by adding the calibration states from the broadside steering. This figure shows that the calibration for broadside direction is valid for the extreme beam steering angle in the band.  
Once the calibration has been demonstrated to work for broadside in the entire working band, progressive phase shifting is applied to steer the beam from \(-35\) degrees to \(35\) degrees for the phased array. Since the discrete phase step of the beamformer is \(5.625\) degrees, there are certain states in which the closest phase state (previous or subsequent) should be selected. Figure 14 presents the comparison of radiation patterns of the antenna at the center frequency (\(18.95\) GHz). As Figures 12 and 13 show, the behavior of the phased array at the lower and upper frequencies is very similar.  
Finally, the realized active phased array antenna gain is measured by comparing with a calibrated standard gain horn antenna (SGH). Figure 15 shows the measured realized gain for all the beam steering directions; the highest gain of the phased array occurs in the broadside direction. The further you move away from the perpendicular axis of the array, the more the gain decreases. As can be seen in Figure 15, in the worst-case gain loss is \(4\) dB.  
Figure 12: (**a**) Comparison of radiation patterns at frequency = \(17.7\) GHz. (**b**) Comparison of radiation patterns at frequency = \(18.95\) GHz. (**c**) Comparison of radiation patterns at frequency = \(20.2\) GHz.  
Figure 13: (**a**) Comparison of radiation patterns at frequency = \(17.7\) GHz. (**b**) Comparison of radiation patterns at frequency = \(18.95\) GHz. (**c**) Comparison of radiation patterns at frequency = \(20.2\) GHz.  
The measured realized gain includes the losses of the cables, the additional lines that move the connectors away from the columns and the losses of the connectors.  
Figure 14: Simulated and measured copolar normalized radiation pattern at 18.95 GHz of the phased array antenna.  
Figure 15: Measured realized gain in band.