Nonlinear characterisation of reconfigurable antennas

[摘要] The lack of references on nonlinearity issue faced in reconfigurable antennas has motivated the work described in this thesis. The nonlinear behaviour is caused by active switches introduced on the radiating structure of the reconfigurable antennas. Depending on the type of active switches deployed on the antenna, the nonlinearity could be severe, which could have serious implications for antenna operation. Thus, the issue of nonlinearity in reconfigurable antennas should not be ignored and nonlinearity measurements should be performed to ensure the nonlinear performance is within an acceptable level. A set of nonlinearity measurements has been identified and performed on the proposed reconfigurable PIFAs. Prototypes are presented with PIN diode and E-PHEMT switches. For the purpose of comparison, measurements were also made with the active switch replaced with a copper bridge for linear interconnection. The nonlinearity performance can be evaluated from the measurement values of third-order intermodulation distortion (IMD3) products, ratio of IMD3 products to carrier, IMD3 products asymmetry, third-order input intercept point (IIP3) and 1-dB gain compression point (P\(_1\)\(_-\)\(_d\)\(_B\)). The measurements are performed when the antenna is transmitting signals. All measurements are performed on the state-of-the-art, 4-port ZVA67 Rohde & Schwarz VNA. Based on the nonlinearity measurements, it can be concluded that the presence of active switches has compromised the nonlinearity of the reconfigurable antennas. This is evident from the appearance of strong IMD3 products at the frequency of interest. In addition, the power-series-based approximation of 10 dB difference between the measured P\(_1\)\(_-\)\(_d\)\(_B\) and IIP3 is shown to be reasonable. Moreover, this work has demonstrated that the ratio of the IMD3 products to carrier does not vary significantly with radiation angles.

[发布机构] University:University of Birmingham;Department:School of Engineering, Department of Electronic, Electrical and Systems Engineering

[关键词] T Technology;TK Electrical engineering. Electronics Nuclear engineering