Analytical Calibration Scheme Suitable for Modern Mobile Communication Systems

Sammanfattning: Modern systems utilize multiple transceiver modules to enhance capacity by directing the energy of the basestation only at the desired directions using beamforming algorithms. To accurately control the beam patterns, the phase and amplitude at each antenna port must be manipulated to follow the desired beam weight response. In a real system electrical, mechanical, and thermal variations for each antenna port path introduces different amplitude and phase errors. To ensure the desired performance, calibration at the antenna ports must be performed. The distinct transmit and receive frequencies in FDD systems poses the limitation that the sensing of the system must happen at the port of the antenna with a directional coupler or alter the antenna with a probe, but a traditional mutual coupling calibration can be used . In this work, a mutual coupling calibration scheme exploiting edge elements on the periphery of the array in tandem with array symmetry suitable to overcome this limit is proposed. To enable the scheme, the edge element frame must be able to receive and transmit in both frequency bands to facilitate transmitter or receiver calibration. This is achieved by connecting the edge element to a transmit/receive module that is in turn connected to a single-pole-dual-through switch and a bandpass filter that covers both uplink and downlink frequency bands. The single-pole-dual-through switch has a single input/output which is connected to and can be switched between two outputs/inputs. The array symmetry enables a larger array size when utilising a particular mutual coupling order. This is achieved by dividing a rectangular array across its breadth symmetry line and assigning the antenna element columns to their nearest edge element column. The division across the line of symmetry enables a particular mutual coupling order to be used in calibrating the column that corresponds to it in each half, thus, enabling a larger array. The full array calibration is then achieved by utilising a row of edge elements to calibrate the columns. The collective use of array symmetry and an edge element frame enables the analytical calibration methodology derived in this work. The scheme was then further verified numerically by using 2nd order mutual coupling to calibrate a 6 X 6 patch antenna array.