# A Critical Examination of the Beam-Squinting Effect in Broadband Mobile Communication: Review Paper
## 3 Studies Related to the Beam Squint Effects  
Since the 1990s, beam squint phenomena in antenna attracted much attention; in [43], the authors drew a comparison between prime focus beam squint and offset fed of microstrip reflect arrays. Results from an examination of a linear reflectarray are presented, and a straightforward criterion for decreasing beam squint with frequency is discussed. The author in [44] describes the design of a tri-mode matched feed horn in order to counteract the effects of beam squinting in a circularly polarized offset parabolic reflector antenna. Three modes--TE11, TM1, and TE21--are merged in a conical horn at the correct amplitude and phase ratio to provide a tri-mode matched feed arrangement. The circularly polarized offset parabolic reflector antenna is then lit using the suggested tri-mode horn as the primary feed mechanism. The radiation parameters of the offset reflector are simulated, the amount of beam squinting is calculated, and the results are compared with those of a conventional offset reflector fed by a potter horn. The study also includes the experimental findings regarding the secondary radiation pattern. In [45], in order to calculate beam squinting in a phased array antenna system, a general formula was created. This formula is especially useful for estimating wide band beam squinting (time-delay) in phased array antenna systems. To determine beam squinting, the authors calculated the criterion (f\(\phi\) = 0, cell) from the delay cell's phase-transfer function, then used (f\(\phi\) = 0, cell) as a parameter in the beam-squinting formula. In radar communications, the beam squint phenomena were studied in [46]. By employing phase shifters as opposed to time-delay, [PERSON] was able to construct a formula for beam squint and demonstrated how the array factor varies. In order to address the beam squint issue, true temporal delay (TTD) beam steering was applied using two different techniques, the first of which was dubbed optical delay lines, and the second, electronic delay lines. In the first technique, an RF signal was used to modulate a laser diode's bias current. A length of optical fiber delays the light, which is subsequently transformed by a photodetector back into an electronic signal. The main drawback of optical time delay was the modulator's and detector's subpar RF performances, particularly insertion loss. Traditional microstrip lines or coax wire was employed in electronic technologies to delay the signal. Overall, the results demonstrated that TTD beam steering outperforms phase shifters; however, this implementation came at a considerable cost and complexity of the system. [PERSON] and [PERSON] in [47] implemented a novel design for a serially fed antenna array using a negative group delay (NGD) in their study of the beam squint problem in mobile communication [48]. Each active antenna unit included an amplifier, a T-junction  
Figure 8: Example of MLE channel estimate using the receiver’s beam squint. There is no beam squint in the transmitter and only one path. No more noise exists. The number of antennas N = 16 [41]. power divider, and an antenna in the array of series-fed active antennas that composed the design (see Figure 9). Beam squinting was a significant problem with the conventional series-fed antenna array. To solve this issue, the phase shift among the antennas should be frequency-independent. In other words, there cannot be a delay in the group. To achieve zero-group delay between the adjacent antennas, a negative group delay (NGD) circuit was added to the feed line. The variance of phase shift with frequency was decreased and the beam squint was minimized by fusing the NGD circuit with the connecting line. With no additional losses, this method significantly reduced the beam squint problem by a factor of six. In [49], the authors investigated the 60 GHz mmwave wireless communication beamforming process's beam squint issues in 2013.