Richard W. Ziolkowski

Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications


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(AiP) solutions. In addition to managing the radiation performance of the antenna elements and arrays, one must consider several issues for AiP designs. These include, for instance, the materials; process selection and control; power and heat management; and new testing techniques. As an example, Figure 1.1 shows a 64‐element AiP system at 28 GHz. It has four flip‐chip‐mounted transceiver ICs that support its dual‐polarized operation [8]. For clarity, the heat sink below the ball‐grid‐array (BGA) interface is not shown.

Schematic illustration of a 64-element antenna-in-package (AiP) assembly breakout.

      Source: From [8] / with permission of IEEE.

      One particular new challenge associated with highly integrated 5G antenna arrays is obtaining accurate antenna beam patterns. Depending on their actual implementation, methods for testing active antennas vary. Current examples include the following [4]:

       a) Sample Testing

      This approach involves the fabrication of a number of fixed analog beamforming circuits that provide the requisite amplitude and phase excitations to the antenna array to produce the desired beams including narrow beams for user traffic and broad beams for user management. Each circuit produces one specific beam. This allows one to sample each of the desired beam types and steering directions. For practical reasons, it is difficult to perform a comprehensive test of all of the possible beams generated by a large array. Therefore, only those beams of greatest interest are likely to be tested.

       b) Element‐by‐Element Testing

      The far‐field vectorial pattern of each element, i.e., the amplitude and phase distribution in the far‐field of the array, can be measured with respect to a common reference. Any beamforming pattern can then be synthesized numerically by adding all the element patterns with the corresponding appropriate complex weights. This approach is the most flexible method since all possible patterns can be tested. Nevertheless, one can argue realistically that the synthesized beam patterns may differ from the real ones to a certain extent because all of the actual interactions are not explicitly included.

       c) Employ Beam Testers

      It must be recognized that when active electronics are added to a radiating aperture to form a MIMO antenna, the antenna ports are now embedded in the system. As a result, it becomes much more difficult to measure the true gain and antenna efficiency. Because a massive MIMO antenna has a large number of antenna elements and its radiating aperture can be excited in many ways to create different beams, both narrow and broad, it is truly difficult to fully test and validate beam performance in terms of conventional figures of merit, e.g., pattern characteristics, beam shapes, beam steering, side lobe levels, and null locations. Testing is further complicated because measurements for both the transmit case and the receive case must be performed to understand the operating characteristics of both RF chains.

Schematic illustration of three levels of AiP implementation by TMYTECH.

      Source: From [9] / with permission of TMY Technology Inc.

Schematic illustration of a potential ISTN architecture for 6G and beyond.

      Source: From [10] / with permission of IEEE.

      Airborne networks have a number of unique characteristics. First, most of their nodes would have multiple links to achieve network reliability, high capacity, and low latency. Second, most of them will be mobile. Therefore, both their network links and topologies will vary with time, some faster than others. Third, the distances between any two adjacent nodes will vary significantly, from hundreds of meters to tens of kilometers. Fourth, the power supplied to any node would be limited. Consequently, as in the case for terrestrial networks, the energy efficiency of each node not only impacts the operation