Multibeam Generation and Measurement of a DDS-Based Digital Beamforming Array Transmitter at Ka-Band

In this paper, a Ka-band digital beamforming array transmitter (DBFAT) using direct digital synthesizer (DDS) for millimeter-wave (mmW) applications is proposed. The system architecture, realization, generation, and measurement process of multiple beams are introduced. The array element consists of two kinds of tapered slot antennas with opposite fin orientations. They are placed in the side-by-side configuration such that the undesirable orthogonal electrical field is suppressed, thereby decreasing the cross-polarization level at the majority of the scanning angles. Different sets of weighting coefficients are synthesized by the DDS module, which generates various types of multibeam patterns simultaneously. Compared with the existing realized DBFAT systems, the radiation patterns of various multibeam scenarios are investigated and measured. Also, all of the mmW channels are placed on a single board, making the overall system much more compact. In addition, compared to DBFAT, which consists of identical array elements, the cross-polarization performance of the proposed DBFAT is improved within a wide range of scanning angles. As a proof-of-concept example, a 15-element linear DBFAT system prototype is fabricated and measured, confirming the validity of the presented technology, which can be utilized as a simple and low-cost alternative for evaluating the radiation performance of mmW DBFATs.