Studies on antenna arrays: Advanced manufacturing methods and integration of microwave components

Radars, electronic warfare devices, and telecommunication systems use antenna arrays to transmit and receive radio frequency (RF) signals. Compared to single antennas, antenna arrays can electrically adjust their radiation patterns. New frequency bands have constantly been allocated to these systems, and the bandwidth of the RF signals has been increasing. For example, typical military radars use frequencies from 150 MHz to 18 GHz, depending on the specific radar. Furthermore, the current fifth-generation (5G) mobile networks can use frequency bands from 410 MHz to 71 GHz. The constant evolution of these systems has led to stricter demands for antenna arrays. Better electrical performance, smaller size, and lower price are expected by the industry, and the antenna arrays should also be compatible with various platforms. This thesis proposes solutions for these challenges by focusing on two aspects: new manufacturing methods and novel integration techniques of microwave components into antenna arrays. The first part of this thesis presents new manufacturing techniques for making lightweight antenna arrays without compromising electrical performance. The antenna arrays designed have been manufactured using an unconventional method, in which the antenna elements are metalized cavities in foam or plastic material instead of solid metal. This so-called inverted manufacturing technique provides a material-efficient manner to fabricate antenna arrays, resulting in up to 73% mass reduction compared with conventional, all-metal arrays. The designed antenna arrays operate at 2–6 GHz and 6–18 GHz frequency ranges, and they can steer the beam ±50° in both planes. The second part of this thesis concentrates on the integration of microwave components into antenna arrays. The thesis presents two antenna arrays, where wideband band-pass filters and lowpass filters are incorporated into Vivaldi antenna elements. The filters are based on corrugated slotlines, which are strongly dispersive. The designed antenna arrays operate at 1.3–3.1 GHz and 6–18.5 GHz frequency ranges, and their out-of-band suppression is 20–40 dB. The performance metrics of the filters, namely their attenuation and cut-off frequency, are independent of the beamsteering angle, which is a desirable property for phased arrays. In addition to filtering antenna arrays, the thesis investigates the integration of wideband push–pull amplifiers into an antenna array. The active antenna array is designed employing an antenna–amplifier codesign methodology, where the antenna array is designed to provide a suitable load impedance for the amplifier without a separate matching network. Because both the antenna and amplifier are differential, a balun is not needed in the antenna–amplifier interface. The advantages of the proposed design are its small size, simple structure, and large 2–5 GHz bandwidth. Every active antenna element can produce up to 12 W power, and thus the array is suitable for high-power applications such as multi-static radar transmitters.