Electrical Balance Duplexers (EBDs) in modern communication systems provide Transmit (TX)-Receive (RX) isolation to implement a form of self-interference (SI) cancellation to facilitates simultaneous transmission and reception from single antenna. EBD works by coupling transmitter, receiver, antenna, and balancing impedance using a hybrid junction where the balancing impedance needs to be equal to the antenna impedance to achieve a high isolation. Variations in antenna impedance with respect to frequency significantly reduces the isolation bandwidth and is dominant factor in limiting the isolation. A method based on Sample Standard Deviation is firstly introduced to quantify impedance stability in the frequency domain. Then a frequency independent antenna with a core structure of equiangular Archimedean spiral is designed to achieve impedance stability in frequency domain. The antenna impedance at an ultra-wideband (UWB) frequency range of 1.5GHz to 4GHz is more smoothened in some design steps using electromagnetic absorbers, capacitive impedance tuning and modification techniques whilst this electrically small antenna also has circular polarization, electromagnetic compatibility, and suitable radiation efficiency. In comparison with the literature, using this antenna in the EBD stage along with a simpler balancing impedance has resulted to about six times wider 20 dB EBD isolation bandwidth.
|Number of pages||597|
|Journal||International Journal of Microwave and Optical Technology|
|Publication status||Published - 1 Nov 2021|