A MEMS-based adaptive downtilt antenna for cellular base stations

A scalable, wideband downtilt demonstrator has been realized on a single printed circuit board (PCB). The system improves the efficiency and reconfigurability of antennas in base transceiver stations (BTS) and meets adaptive downtilt requirements. The downtilt beamsteering system is implemented as a four-element phased array fed by a feed network that generates a power taper of 1 : 3 : 3 :1 over the elements. The concept allows for beamsteering by applying phase shifts in low power branches only, using a two-bit switched line implementation (30°/bit). A fractional bandwidth of 40% is realized around the center frequency of 2.0 GHz. Hard-wiring of the phase shifter bits is used to demonstrate the operation of the concept. The measured gain varies less than 1:76 dB over the total bandwidth and scan range and is in agreement with the expected values, calculated from individual building blocks. Simulation and measurement results for the co- and cross-polarization performance match well and are in line with state-of-the-art requirements.