Antenna Design Aspects for mmWave Massive MIMO
By Hany A. Raouf, PhD February 2020
The antenna design for the mmWave massive MIMO has the following important aspects: the beamforming and synthesizing the array, designing the antenna elements; designing the feeding network, the effect of the coupling between the adjacent antenna elements, and the effect of surrounded materials on the radiation characteristics of the antennas.
The beamform is designed in order to maximize each user’s received signal power while minimizing the interference signal power from the other users.
The beamforming techniques are introduced in our previous blog.
The antenna design for mmWave massive MIMO include design antennas for smart phones, indoor small-cell networks, and the base stations.
The antenna design for the above problems focuses on design of ultrawideband (UWB), wide scanning, and dual-polarized phased arrays that shall scan the beam electronically. Examples of this design are arrays of patch antennas (Figure 1), planar dipoles, or bowtie antennas with two orthogonal feeding mechanisms to excite horizontal and vertical modes for each element. In addition matching networks should be designed to improve the impedance matching. The distances between the patches are λ/2 center to center which are 5 mm at 30 GHz and 2.14 mm at 70 GHz.
Figure 1: Example of planar patch array with orthogonal feedings (Feeding 1 and Feeding 2). Note that the boxes of “Feeding 1” and “Feeding 2” are just block diagrams that take different shapes and locations based on the design.
Implementing this design for the orthogonal modes is challenging because the difficulty of integrating the orthogonal feeds and the existence of resonance modes from the conductors surrounding the antennas.
Reconfigurable antenna design is used in order to switch between different 3D radiation patterns of the antenna and different polarization settings.
The reflection coefficient should be simulated when the antenna excited by the practical feeding structure over a wide range of frequencies, e.g. 20-80 GHz. The radiation pattern and the directivity level should be simulated and the stability of the radiation pattern should be tested over the operating frequency band and the symmetry in co-polar and cross-polar components should be inspected.
Over the air testing (OTA) requirements, such as the size of the chamber and the positioner choice, should be determined based on the size of the antenna structure and the radiation pattern characteristics. If the size or the position of antenna is unknown then we use white box dimensions which is a box include the electronic circuits with the antenna to determine the chamber size. In addition, we decide whether we use direct far field measurements or compact antenna test. In the direct far field measurements, the measurements of the field magnitude are performed in the far-field zone of the antenna while in the compact antenna test the measurements of the complex field are performed in the radiated near-field and then a near-field to far-field transform software is used.
HASystem Tech can choose which method/software is the best for your design.
Simulation of massive array of tightly coupled antennas with the feeding network over an UWB, e.g. 20 – 50 GHz is challenging. HAsystem Tech solve such kind of problems using techniques that we had developed such as domain decomposition.
For any consultations or questions, please contact us .