Filter‒antennas and RF front‒end sensing receiver for cognitive radio applications -

Abstract

Cognitive radio antennas for spectrum overlay are usually dual‒port antenna systems. Such antenna systems integrate a wideband antenna, used for sensing, with a frequency‒reconfigurable antenna for communication. However, it is of a great importance to consider both mutual coupling reduction and polarization alignment between the two antennas in order to avoid any performance degradation. Another important issue to take into consideration is the limitations of wideband antennas when it comes to spectrum sensing. Wideband antennas present an inherent gain‒bandwidth product limitation, they also exhibit fluctuations resulting in a low signal to noise ratio. Wideband antennas require high‒speed ADCs, which are power intensive and have higher quantization errors. The design for wideband operation leads to compromise in the transceiver performance, caused by limitations in the RF front‒end components such as amplifiers, oscillators and mixers. As a solution to all the aforementioned issues in wideband antennas, tunable filter‒antenna appears as a suitable solution for spectrum sensing. This is due to the fact that tunable built‒in bandpass filtering provides flexible frequency discrimination, wideband suppression of unwanted interference, gain flatness over the operating frequency band, less disruption of the antenna’s radiation characteristics, better processing of down‒converted signals, and ease of implementation. Hence, a new cognitive radio antenna, for overlay spectrum operation, may be a single-port antenna system, which can be appropriately controlled to either sense or communicate. In this dissertation, frequency‒tunable microstrip antennas, for cognitive radio applications, are proposed. The approach is based on electrically tuning the antenna’s operating frequency by integrating reconfigurable bandpass filters into wideband antenna structures. The design of an open loop resonator (OLR)‒based bandstop filter, and its transformation to