# Compact Beam-Scanning Reflectarray Antenna with SLL Reduction Using In-Plane Panel Translations
## 4 Experimental Validation  
To validate the results from this work, a demonstrator is manufactured and measured. The optimized phase response from Figure 4b is implemented using the unit cell shown in Figure 5, consisting of three coplanar parallel dipoles of two different sizes. It is implemented on a thin, single-layer DiClad 880 substrate at 0.762 mm thickness, with a permittivity \(\epsilon_{r}=2.3\) and a loss tangent \(\tan\delta=0.005\). This cell has been introduced before in previous works [32,33]. The two dipole sizes resonate at two different frequencies, resulting in a smooth and highly linear phase response that can improve the bandwidth of the antenna. Its good angular stability is also particularly important for this phase-only design, as the angle from which each array element is excited depends on the position of the panel, and a stable cell response is desired. With the dimensions listed in Figure 5a, a full phase cycle (360 degrees) is covered while losses are kept below 0.5 dB. The manufactured demonstrator is shown in Figure 6. The panel slides along a 3D-printed rail, and it is fixed at multiple predefined positions for the measurements. The full 3D antenna gain pattern is measured at these positions. Figure 7 compares the gain cuts along the scanned plane between the measurements and the calculated predictions at the design frequency of 29.5 GHz. A good match is observed, with the prototype achieving a maximum gain of 31.6 dB with a scan loss of 1.1 dB for over 45 degrees of scanning range. Scanning outside the optimization range at \(d_{12}\) results in a 50-degree beam tilt with losses of 2.8 dB. Side lobes are kept below \(-9.9\) dB. Since the support structure is mostly 3D-printed and it contains moving parts, any discrepancies in the results may be attributed to minor alignment errors. The aperture efficiency at 29.5 GHz is 24.7%, which is calculated by comparing the antenna gain with that of an ideal, uniformly illuminated aperture of the same size [31]. This antenna design, however, is based on a partial aperture overlap among panel positions, meaning that only part of the RA aperture has a noticeable contribution to the radiated field at any given panel position. If we only consider the aperture area where the illumination taper is over \(-12\) dB, the aperture efficiency is increased to 34.6%. Figure 5: Reflectarray unit cell geometry (**a**) and its direct reflection coefficient \(\rho_{xx}\) at 29.5 GHz (**b**), simulated in Ansys HFSS under periodic boundary conditions. The measured in-band antenna performance is presented in Figure 8. The scanning range is most affected at highly obliquely radiating positions, and particularly below the design frequency. For a 45-degree scanning range, scan losses are kept below 2 dB, from 28.5 to over 32 GHz, and below 3 dB, starting at 28 GHz. To compare these measurements with the expected performance, the feeding horn and the RA layout are also simulated over a broad band, and the radiation pattern is calculated at multiple panel positions. Focusing exclusively on the set of measured positions that fall within the optimized translation range, the minimum and maximum beam levels among these positions are represented in Figure 9 for both measurements and simulations. The measured results show a good match with the simulations, and the variation in maximum gain of the measured prototype is only 0.83 dB between 28.5 GHz and 32.0 GHz (11.9% bandwidth). Figure 6: Manufactured demonstrator with a sliding rail **(left)** in our spherical range measurement facility **(right)**. Figure 7: Measured and calculated gain cuts at \(\varphi=0^{\circ}\) and 29.5 GHz, for different predefined panel positions, where \(p=4.07\) mm. For the calculation, the response of every cell in the array was simulated in HFSS. Compared to other beam-scanning reflectarray designs (see Table 2), the proposed antenna prioritizes mechanical simplicity by relying on a single stepper motor to achieve linear in-plane panel translations.