Non-Foster impedance matching for electrically small antennas

Altuntaş, Orhun Tevfik
At low frequencies, non-Foster matching improves the performance of ESAs and overcomes the limitations imposed by the electrical size of antenna. Thus, the major objective of this thesis is to design and implement a non-Foster matching network in order to improve the bandwidth of an ESA beyond the levels that cannot be reached by conventional passive matching. Negative impedance converters (NICs), which are specific circuits to realize negative circuit elements, are used to design such non-Foster circuits. In this context, a systematical design procedure for a non-Foster matching network is presented and implemented to match a 10-cm monopole antenna between 150 MHz and 500 MHz. A BJT based NIC is built to generate a series combination of a negative inductor and a negative capacitor together with an inductive T-dualizer which is a circuit that is used to transform small radiation resistance of the ESA to a desired constant value. The performance of the overall network is measured between 100 MHz and 1 GHz with different input power levels and different loads. A bandwidth of 684 MHz from 127 MHz to 811 MHz is achieved with a VSWR that is better than 3.57 while the unmatched antenna has a VSWR that is no better than 8.72 until 850 MHz. Besides, the effects of input power and load changes on matching performance are examined and commented.
Citation Formats
O. T. Altuntaş, “Non-Foster impedance matching for electrically small antennas,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Electrical and Electronics Engineering., Middle East Technical University, 2019.