Radiofrequency (RF) waves, also known as microwaves, are electromagnetic waves in the frequency range 3 MHz – 300 GHz. They are used in telecommunications systems because of their ability to propagate both in conductive environments and in space.
What are radiofrequency systems used for?
RF systems are used to process analogue signals containing the data to be transmitted and received. These systems are called transceivers, a contraction of the terms transmitter and receiver.
Figure 1 shows the basic architecture of an RF receiver and transmitter.
There are many variants of this architecture, depending on the type of communication intended.
How a transceiver works
In transmission (Fig. 1a), the information to be transmitted is carried by analogue baseband signals (fBB). They are converted into radio frequency (fRF) by an up-converter mixer and a local oscillator:
fRF = fLO ± fBB
The RF signal is then amplified by a power amplifier (PA) and transmitted by the antenna.
The objective of this transmitter is to propagate a signal as clean as possible, with a high power to ensure the transmission of data by the RF waves.
At the receiving end (Fig. 1.b), the signal carrying the information is received by the antenna with relatively low power.
It is then amplified by a Low Noise Amplifier (LNA) before being mixed with the fLO frequency and converted back to baseband.
The signal can then be processed analoguically and then digitally to extract the data.
The objective of a receiver is to amplify the signal while adding very little noise so that the information, coming from a low-power signal, is not drowned out by the noise.
Radiofrequency in NV magnetometers
For NV magnetometers, an RF transmitter similar to the one shown in Figure 1a is required to emit microwaves at 2.87 GHz around the diamond to excite the NV centers.
This transmitter typically consists of a microwave generating block and an antenna (or resonator) designed to operate around 2.87 GHz and to emit the most homogeneous and intense magnetic field possible at the diamond surface.