A very small focal-to-diameter (F/D) ratio transmitarray for compact antenna test range (CATR) application is proposed in this article. The transmitarray comprises a feed antenna, a metasurface for phase modulation (MPM), and another one for amplitude modification (MAM). MPM and MAM are implemented using the same metasurface cell but with different cell selections and arrangements. A holistic phase-only design method determines whether the metasurface is for amplitude modification or phase modulation. A CATR collimator with an overall low profile is realized through the joint design of MAM and MPM. The proposed technique overcomes the limits of the ordinary metasurface lenses and enables plane wave generation with a short focal length and sizeable quiet zone. The resulting CATR demonstrates a 50% quiet zone of the aperture size with ±0.5-dB amplitude and ±5° phase errors by full-wave simulation. For further verification, a prototype is fabricated, and its experimental results confirm the simulations.

This paper proposes a planar magneto-electric resonator (PMER) as the element of broadband dual-polarized (DP) and circularly-polarized (CP) reflectarray antennas (RAs). The PMER is realized by introducing a split in dual rhombic rings, which flats the vertical structure for magnetic resonance in common ME element. Owing to the isolated magnetic and electric resonant modes of the PMER, anisotropic characteristic is achieved to independently manipulate the reflection phase among two orthogonal polarizations and reflect CP incident wave in a wide bandwidth. Moreover, a simple modification method is presented for further expanding the operating band of CP element. For proof, a DP-RA and CP-RA prototype is fabricated and measured. The measured results reveal that 1-dB gain bandwidths of 17.5% / 22.2% and 25.6% are observed for DP- and CP-RA respectively, while maintaining low profiles and high aperture efficiencies. Especially, the measured axial ratio (AR) bandwidth of the PMER-based CP-RA reaches 66.7%.

An uncertainty model of total radiated power (TRP) measurements in a reverberation chamber (RC) has been proposed in a previous work, where it was hypothesized that the signal bandwidth had no effect on measurement uncertainty. However, our recent experiments indicate that the signal bandwidth of a long-term evolution (LTE) device indeed affects TRP’s measurement uncertainty. In this article, we investigate the effect of signal bandwidth on TRP tests and improve the uncertainty model to include this effect. It is shown that a larger LTE signal bandwidth helps reducing TRP uncertainty. This phenomenon can be well-captured by the improved uncertainty model, which is further validated by two sets of TRP measurements with different signal bandwidths.

A novel mode-stirred reverberation chamber (RC) is designed and analyzed for millimeter wave bands. The size of the proposed RC with dimensions of 0.9 m $\times0.9$ m $\times1.1$ m is suitable for user equipment (UE) tests. Two Z-shaped mode-stirrers are applied to generate a uniform field. To fulfill the communication and test requirements for user equipment, reference, measurement and link antennas with a large bandwidth are utilized, which can support both the frequency range (FR) 1 and FR2 bands of the 5G spectrum. The lowest usable frequency (LUF) and mode density were first calculated and examined. Then, the power transfer function (PTF) from 2 GHz to 40 GHz was obtained to verify the path loss. Three measurement campaigns were carried out to verify the accuracy of the RC. Firstly, the transmission power of the passive antenna for a conductive test was compared with the RC over the air (OTA) total radiated power (TRP) for single-tone signals. Then, signals with bandwidths of 100 MHz and 400 MHz were applied. A maximum power difference of only 0.8 dB was found in the above two experiments. Furthermore, the TRP for the same commercial 5G UE in both RC and compact antenna test range (CATR) systems was measured and compared. To the best of the authors’ knowledge, this is the first work to provide TRP results for 5G millimeter wave bands in a RC. The test results show that the TRP values for the two systems are almost the same with a maximum deviation of 0.5 dB, while the time required to carry out tests using the RC is lower than that for the CATR system.

A novel method for antenna far-field (FF) pattern reconstruction using sparse spherical near-field (SNF) measurements is presented. A conditional generative adversarial network (CGAN) is employed to significantly reduce the sampling density while maintaining high accuracy in FF prediction. The near-field (NF) data sampling is close to one-ninth of the Nyquist rate, converted to the initial FF patterns by fast Fourier transform (FFT). These initial patterns are utilized to train the neural network, which eventually reconstructs FF patterns closely approximating those obtained from full Nyquist-sampled measurements. This method avoids the use of super-resolution networks, which can introduce artifacts and struggle with phase reconstruction in complex electromagnetic environments. Simulation and measurement results demonstrate substantial reduction in measurement time and data acquisition while preserving accuracy, offering an efficient solution for antenna characterizations.

With the development of communication technology has come several measurement applications requiring plane-wave conditions for wireless-device characterizations in anechoic chambers. In this paper, a metasurface lens with a 2 × 2 feeding-antenna array is proposed and characterized to synthesize a plane wave in a near field for a fifth-generation (5G) millimeter-wave radio-frequency (RF) devices test. The metasurface lens, based on Jerusalem-cross elements printed on a printed circuit board (PCB) substrate, is used for controlling the phase-shift distribution of incident spherical waves. The lens has a size of 0.4 × 0.4 m and is designed to operate at a range from 24.25 GHz to 27.5 GHz, and its feeding-antenna array is located at a focal plane of the lens, which is parallel to the metasurface lens. The lens is studied and verified through simulations and experiments, and a uniform amplitude and phase-field distribution at a reduced distance of 1.2 m generated by the metasurface lens throughout a QZ are achieved. The worst-case amplitude and phase variation of the designed metasurface lens are ±0.75 dB and ±7.5°, respectively. The results show a plane-wave condition can be achieved in 5G millimeter bands through the proposed compact and effective metasurface lens. Moreover, the proposed metasurface lens is shown to be capable of reducing the plane-wave synthesizing distance compared to the compact antenna test range (CATR) with a significantly reduced system cost, making it an attractive alternative to antenna testing in 5G millimeter-wave frequency bands.