Chapter 19Co-design of the Antenna with LNA forUltra-wideband Applications1




19.1. The interest in co-design

Antennas and low noise amplifiers (LNA) are generally interconnected by intermediate propagation lines. Typically, these lines have real standardized impedances of 50 Ω or 75 Ω. Firstly, working with real impedance facilitates the realization of propagation lines. In addition, capacitive effects become critical at high frequencies that prevent us from using propagation line with high impedance.

The classical approach consists of optimizing on one hand, the antenna so that it presents a characteristic impedance of 50 Ω, and separately, on the other hand optimizing the LNA so that its input impedance is equal to 50 Ω, in order to be able to achieve a perfect impedance matching in terms of gain or noise. This procedure imposes a limitation on the antenna’s design as well as on the amplifier.

In the context of ultra-wideband (UWB) where the useful signals have a very low power spectral density (limited to −41.3 dBm/MHz), these problems are of particular interest [PEL 06]. It is then a question of approaching the subject globally across the {low noise active reception} function. On the other hand, co-design also allows us to integrate the antenna as close as possible onto the printed circuit board (PCB). A better compromise may be found between the two blocks in order to improve performances with fixed consumption.

This chapter presents co-design and the measurements obtained ...

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