Why a good LNA is key to a viable antenna front-end
Written by Bill Schweber
One of the first lessons about RF and wireless links that any student learns is that antennas adhere to the reciprocity principle. This means that the transmit and receive characteristics of an antenna are identical, with no difference in attributes such as transmit or receive gain, beamwidth, or radiation patterns between the two modes. If you know the specifications of the
Reciprocity is certainly a simplifying design principle, but there is much more to transmit and receive-side antenna paths than the antenna. The transmit side has a fairly easy task as it is a deterministic function: it takes a known, relatively strong signal with defined attributes, which has passed through the power amplifier (PA), and “presents” it to the antenna. There are few unknowns
antenna in transmit mode, then you also know them in the receive mode. Of course, antennas for higher power transmission are often made of physically larger elements as needed to handle the power, but reciprocity still holds. There is some research into non-reciprocal antennas using metasurfaces and metalenses, but they are in the R&D stage and not a concern here.
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