Enhancing the Bandwidth in Transmitarray Antennas Using Tapered Transmission Line Matching Approach

Beam Scanning Capabilities of a 3D-Printed Perforated Dielectric Transmitarray

“…The dimension of the tapered section changes linearly with z, and, as a consequence, the characteristic impedance Z * tap (z) follows the same linear law. As discussed in [10], a good matching can be realized choosing the lengths l 1 and l 3 of the tapered lines at least equal to λ g /2, where λ g is the effective wavelength in the tapered section. The unit-cell was designed to work in Ka-band, at a frequency f 0 = 30 GHz.…”

“…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.…”

“…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. This cell element was firstly introduced in [10][11][12][13], 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. This cell element was firstly introduced in [10], where its wideband behavior was tested only with numerical simulations of a medium size TA, designed using a conventional dielectric material and without considering the possible limitations introduced by the manufacturing process.…”

“…This cell element was firstly introduced in [10][11][12][13], 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. This cell element was firstly introduced in [10], where its wideband behavior was tested only with numerical simulations of a medium size TA, designed using a conventional dielectric material and without considering the possible limitations introduced by the manufacturing process. In [11], the enhanced performances of the same unit-cell were compared with those of a conventional unit-cell having just a single layer with a square hole; in this case, a material usable for the realization of the TA with an Additive Manufacturing (AM) technique was considered, since this seemed to be the only adoptable method for the TA fabrication, but also in that work the designed antenna was only numerically analyzed, neglecting the constraints imposed by the AM process.…”

“…The unit-cell was instead experimentally validated in [12]: firstly, several numerical tests were conducted to find the optimum geometric parameters and transmitarray configuration at Ka-band; then, the unit-cell was modified to make it 3D-printable in view of the limitations introduced by AM techniques; finally, a 15.6λ 0 × 15.6λ 0 antenna was designed, manufactured with 3D-printing techniques and experimentally characterized in the anechoic chamber. All of the configurations considered in [10][11][12], were designed neglecting the effect of the direction of arrival of the incident field on the unit-cell and they are only center-fed transmitarrays that generate a main beam in the broadside direction. In [13], some very preliminary considerations on the possibility to realize a mechanically steerable transmitarray are summarized: two different unit-cells are considered, one of which is the dielectric one; small size TAs working at 5.6 GHz were designed without taking into account any manufacturing limitations and considering the possibility to design a bifocal configuration or to use a global optimizer, and then characterized numerically.…”