In the European PANAMA project (Power Amplifiers aNd Antennas for Mobile Applications), the EM group has worked on two subjects.
We have developed a novel concept for down-tilt for a cellular base station antenna that consists of a power splitting network, a phase shifter and a 4-element antenna array. The design is integrated onto a single PCB of 1.5 mm Rogers 4003 substrate. The total system has a center frequency of 2.0 GHz and 40% fractional bandwidth (from 1.6 to 2.4 GHz). The power splitting network splits the power unequally over four branches, thereby reducing the power handling requirements on the phase shifter. By creating phase shift in low-power branches only, beamforming requirements of +/- 5° are still fulfilled. Furthermore, switchable power in the phase shifter is reduced, allowing for the ability of 'hot' switching, which will be crucial in future systems (LTE). In addition, in this way, the main losses are confined to the low power branches. The phase shifter is implemented using switchable delay lines (two bits of 30°). The antenna array consists of four wideband bow-tie elements. Its active impedance is matched in the operational band. Also, a balun has been included in the design for common-mode rejection and a director is used to optimize far-field patterns over the operational band. Specifications for gain, sidelobe level, and co- and cross-polarization are comparable of better than commercial state-of-the-art antenna solutions. A picture of the demonstrator is shown below in Figure 1, as well as simulated and measured results of the input return loss of the total system (Figure 2). The input matching for the total system is better than -10 dB for the operational band.
Integrated mm-wave antennas
We designed a 60 GHz Antenna-on-Chip (AoC), which was fabricated in NXP's Qubic4 technology. The measurement results confirm that its performance exceeds the one of previously reported AoC designs in similar standard silicon integrated circuit technologies, see Figure 3. During the characterization phase, however, several challenges were identified with respect to the measurement of highly integrated millimeter-wave (mm-wave) antennas. In order to overcome these challenges, a measurement package was developed that proved to enhance the measurement results significantly. Furthermore, an alternative characterization method ws investigated that eliminates the need for a physical connection between the antenna-under-test and the measurement equipment. An alternative integrated mm-wave antenna concept was developed based on standard wire-bond technology, see Figure 4. Measurement results were validated with an approximate model for computer-aided-design.