A Near-Field-Based Gain and Pattern Measurement Technique for Probe-Fed Millimeter-Wave Antennas [Measurements Corner]

Driven by the perpetual demand for higher data rates, extensive research efforts have been devoted to millimeter-wave (mm-wave) 5G technologies in recent years. Highly integrated mm-wave antennas for 5G user equipment are considered one of the key components in the realization of mm-wave-based mobile networks. An accurate characterization of antennas is as important as antenna design. Despite great advances in measurement capabilities over the years, we are still facing many difficulties in probe-based mm-wave antenna measurements. This article presents a fast, simple, and accurate near-field (NF)-to-far-field (FF) technique for gain and radiation pattern measurements of probe-fed mm-wave antennas. A setup based on an electro-optical (EO) NF measurement system (NeoScan) is utilized to measure the NF of the antenna under test (AUT). The system uses a high-spatial-resolution nonintrusive probe to scan the NF in very close proximity to the antenna’s surface, which significantly alleviates multipath effects and reduces the required scan area. The radiation pattern of the AUT is computed using the NF-to-FF transformation. To obtain the gain of the AUT, a ground-backed dipole antenna is created and used as a gain standard. The absolute gain of the ground-backed dipole is characterized using the image method. Measurement accuracy is checked against the simulation. With the help of the standard gain antenna, the NF-to-FF method can be used to measure both the gain and radiation pattern of any type of probe-fed mm-wave antenna. For demonstration purposes, two test antennas, a horizontally polarized tapered slot antenna, and a dual-band vertically polarized hexagonal bridge antenna operating at 28 GHz are fabricated and characterized. Excellent agreement against full-wave simulation is achieved.