in beam direction of the HBF is away from the is ABF limited. main beam direction, The the smaller the gain. Therefore, the coverage of the beams 3. 2. Users The HBF located at certain AoD 4 within the range of 84-96 degrees will observe that the designed for 90 degrees is actually the ABF with all antennas. HBF designed for direction P has the largest signal power. sensitivity of the antenna array beam steering to the phase differences tolerances between (see the Due antenna to the elements, each array must be calibrated for the following Fig. 5.31) [18]: Phase error can have a significant effect on the antenna beam depending the array, on then its statistical Phase: properties. If the phase error is uniformly distributed across often used to block the main beam direction does not change. Instead, the nulls that are Figure 5.31 Array calibration: static and dynamic tolerances in active antenna systems [18]. New Radio Access RF and Transceiver Design Considerations 741 interference are severely affected, resulting in 10-20 dB loss. If there is more determin- istic phase error distribution, this will steer the beam in a different direction. Phase error can be caused by manufacturing tolerances in the RF feeding network, thermal effects in the PAs and LNAs, and group delay variations in the filters. It is recommended to keep the phase error between antenna elements below +1 5 degrees (commercial specifi- cation for AAS). Amplitude: Amplitude error does not affect the direction of the beam, but rather the peak gain and the sidelobe levels and is generally due to the thermal effects on the active components (PA and LNA). Recommended error should be below + 0.5 dB (commercial specification for AAS). Timing/frequency: Depending on the circuit architecture, if a common LO network is not used between modules, there will be frequency drift in addition to the timing errors in the ADCs. Recommended level of frequency drift is 0.5 ppm (commercial specifica- tion for AAS). The different phases in active antenna array developm