# A Novel Metasurface Lens Design for Synthesizing Plane Waves in Millimeter-Wave Bands
## 4 Measurements and Discussion  
The proposed metasurface lens fed by the planar 2 \(\times\) 2 patch-antenna array was manufactured and measured to verify its design. A metasurface-lens prototype is exhibited in Figure 8a; the copper Jerusalem-cross patterns are etched onto one side of the Rogers RO4003C substrate with a thickness of 1.524 mm. As shown in Figure 8b, the planar 2 \(\times\) 2  
Figure 6: Performance of the 2 \(\times\) 2 square patch array: (**a**) \(S_{11}\) parameter and gain of the feeding antenna array and (**b**) magnitude and phase-variation distribution.  
Figure 7: Simulated electric-field intensity distribution of QZ center at 26 GHz: (**a**) amplitude distribution and (**b**) phase distribution.  
patch-antenna array located on the focal plane of the metasurface lens was designed as the feeding-antenna array, which was assembled with the metasurface lens using an acrylic supporting structure. The metasurface lens and feeding-antenna array prototypes were both fabricated with LDI technology, which could be printed on ordinary PCB in a modular form and assembled as a flat structure. Figure 9 presents the proposed metasurface lens fed by the planar 2 \(\times\) 2 patch-antenna array, to which a supporting structure was added to maintain the position of the focus. The distance between the metasurface lens and the feeding-antenna array was 0.4 mm, and the QZ was synthesized at a reduced distance 1.2 m from the feeding-antenna array with respect to the boresight direction.  
The amplitude and phase variation of the QZ are considered the dominant performance criteria of a given metasurface lens in the CATR. The field properties were generally characterized as part of a metasurface-lens design using a procedure based upon a field-probe scanner comprising a probe antenna mounted on a linear translation axis. The measured results are shown in Figure 10; due to the physical symmetry of the metasurface lens in the vertical and horizontal directions, the amplitude and phase of the designed QZ are shown along one principal cut over a range of 0.4 m in x direction, which is 1.2 m away from the feeding-antenna array. It can be seen that in the designed 0.2 m QZ, the amplitude taper fulfilled 1 dB and the peak-to-peak amplitude and phase ripples were \(\pm\)0.75 dB and \(\pm\)7.5\({}^{\circ}\), respectively. This corresponded to a QZ = 50% of the size of the metasurface lens. Meanwhile, as depicted in Figure 10a-d, probably due to misalignment errors, some slight dis-symmetry occurred in the axis center. In summary, the designed structure printed on a single layer of the Rogers substrate had a wide frequency coverage from 24.25 GHz to 27.5 GHz, which could be used as a practical alternative for RF millimeter user-equipment tests in band N258. This essentially shows that it is possible to generate a relatively large QZ using a metasurface lens fed by an antenna array. Furthermore, in this preliminary design, the metasurface lens was optimized for a 0.2 m \(\times\) 0.2 m QZ with a 0.4 m \(\times\) 0.4 m PCB substrate. It is expected that a larger QZ can be achieved with the enlargement of the metasurface lens. These topics should be subject to future investigations and research.  
Figure 8: Photographs of the fabricated prototype of the proposed metasurface lens and 2 \(\times\) 2 patch-antenna array: (**a**) metasurface lens and (**b**) 2 \(\times\) 2 patch-antenna array.