Showing papers by "He Zhu published in 2021"

A Highly Efficient Spherical Luneburg Lens for Low Microwave Frequencies Realized With a Metal-Based Artificial Medium

Abstract: This article describes a novel spherical lens antenna constructed of planar layers of lightweight foam with equally spaced conducting inclusions of varying sizes on an orthogonal grid. This construction largely overcomes the problems of weight and cost that have tended to make larger low-frequency Luneburg lenses impractical. A penalty for this type of design is that some anisotropy exists in the lens’s dielectric. This effect is examined using both ray-tracing techniques and full-wave simulation, and it is found that the principal consequence is that the focal length of the lens varies in different directions. Methods for mitigating the effect are proposed. A prototype lens antenna intended for cellular use in the band 3.3–3.8 GHz with dual-linear slant polarized feeds was designed and constructed to confirm the findings. The measured results show a peak gain of 23 dBi, which is less than 1 dB lower than the maximum possible directivity from the lens’s cross-sectional area. Scanning loss is less than 0.8 dB over the whole sphere. The simulated and measured performances show excellent agreement over the whole sphere. The overall performance of the prototype lens antenna demonstrates that this type of lens should be very suitable for use in high-gain multibeam antennas at lower microwave frequencies.

Dual-Band and Tri-Band Balanced-to-Single Ended Power Dividers With Wideband Common-Mode Suppression

Abstract: A new design approach of developing multi-band balanced-to-single-ended (BTSE) power dividers is presented in this brief. The design is based on flexible coupling schemes which can guide designing multi-band balanced-to-single-ended power dividers with arbitrary number of bands and controllable bandwidth. Microstrip-to-slotline transitions are used to suppress the transmission of common-mode signals at all frequencies, which lead to an ultra-wide bandwidth of common-mode suppression. Slotlines play a critical role for they have two functions, one is to control the external coupling between ports and resonators, and the other one is to prohibit the propagation of common-mode signals. Based on the design approach, a dual-band and a tri-band balanced-to-single-ended power divider are modeled and simulated in the full-wave simulation environment. Prototypes are fabricated and tested, and the experimental results demonstrate that dual-band and tri-band filtering responses are realized in BTSE power dividers successfully. Moreover, the common-mode suppression and mode conversion levels of both designs are less than −29.5 dB at all frequencies (common-mode suppression fractional bandwidth is 200%), which is extremely desired in balanced circuits and systems.