# Beam Scanning Capabilities of a 3D-Printed Perforated Dielectric Transmitarray
## 1 Introduction  
The next generation of high performing radar and satellite communication systems is requiring the development of enhanced technologies for the design and realization of its components. For what concerns antennas, the main constraints are related to the frequency bands, moving from microwave to millimeter or sub-THz frequencies, the high gain and the multibeam or beam scanning capabilities. To generate wide scanning antennas with good performances in all the pointing directions, the use of active arrays is the most straightforward solution, even if they are characterized by high complexity, that increase dramatically with the number of array elements; moreover, at the higher frequencies, the poor performances of the feeding network represent a limitation to this type of antenna. An alternative is that of using a mechanical beam-steering mechanism, easily implementable in reflector-type antennas. To reduce the antenna volume, recently, solutions where Reflectarray (RA) or Transmitarray (TA) antennas substitute the reflector are taken into account, since they represent a convenient and efficient alternative for obtaining high gain and low cost antennas [1; 2]. A transmitarray is typically composed of a feed source that illuminates a single or multilayer quasi-periodic array, whose unit-cells are characterized by one or more variable geometrical parameters, through which it is possible to control the transmission coefficient phase of each cell and to obtain the desired radiation pattern [2]. The TA unit-cell can consist in metallic elements printed on different dielectric layers [3; 4; 5], in completely metallic slot-based layers separated by air gaps [6; 7] or even in a dielectric structure perforated by one or several holes, as implemented in [8; 9; 10; 11; 12; 13]. In comparison with reflectarrays, TAs present the advantage to not suffer for blockage, which require the use of off-set feeds in RA, and this increases the difficulty to implement efficiently the beam scanning. In view of their features, transmitarrays have been widely considered for the realization of multibeam [14; 15] or beam scanning antennas [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27]. The most straightforward way to obtain the beam steering is that of integrating active elements in the unit-cell, such as p-i-n diodes [16; 17; 18; 19; 20] or-vaxator diodes [21; 22; 23; 24; 25; 26; 27]: the resulting radiation features are good, but the same considerations already done for active arrays apply. An alternative solution can be the use of a passive TA illuminated by a moving feed or by a feed array, generating beams that impinge on the TA surface with different incident angles and are therefore focused by the TA itself in different directions [14; 15; 16; 17; 18]. The main limitation of this solution is its reduced scanning capabilities: in [16], a small size configuration shows a reduction of the gain of approximately 4 dB on a scanning range from \(-30^{\circ}\) to \(30^{\circ}\). Some improvements can be obtained using a larger TA, so that just one part of it is illuminated by each incident field [15; 17], or designing the TA so that it acts as a bifocal lens [18], even if in this case a degradation of the beam in the broadside direction occurs. In this paper, the design of the 3D-printable dielectric transmitarray with beam-scanning capabilities is discussed. It adopts the wideband dielectric unit-cell already introduced in [12] are investigated which consists of three perforated layers: the central presents a square hole, which is used to control the phase of the transmission coefficient, while the external layers are equal and have a truncated pyramid hole, which allow for improving the bandwidth and the efficiency.