Radar Front End Design
1 General Information
General information Since Radars use radio wave in the detection process, the Radar front ends are related to electronic circuits that operate with high-frequency signals. Depending on the purpose of applications, these frequencies range from hundreds of MHz up to hundreds of GHz, for example, defense systems of military radars and body scanners at airports. The design of Radar front ends involve with the designs and developments of radio-frequency (RF) electronic circuit building blocks such as amplifiers, mixers, oscillators and also some passive elements such as antennas.
2 Radar Front End Building Blocks
Radar front ends typically share a similar structure as shown in Figure 1. Some circuit building blocks used in Radar front ends are described here.
Amplifier: Amplifiers are used to amplify weak signals to higher power. On the transmitter (Tx), it plays a role to enlarge the signal to a sufficient level to be transmitted through the antenna. This amplifier is referred to as Power Amplifier (PA). On the receiver, since the signal reflected from an object and picked up by the antenna is in a very weak level, the amplifier on the receiver side has to amplify this signal by adding noise as less as possible to it. This amplifier is referred to as Low-Noise Amplifier (LNA).
Mixer: Mixers are used for blending the signal at different frequencies and format together. On the transmitter side, a mixer is used to mix a sinusoidal and high frequency signal from an oscillator to a modulation signal operating at a lower frequency and can be modulated. Then, this low-frequency signal is up-converted to a higher frequency and transmitted to the antenna. The mixer on the receiver side works in a reverse direction, i.e., to transform the high-frequency signal received at the antenna to a low-frequency signal for baseband processing.
Oscillator: Oscillators are used on the transmitter and the receiver. They are used to generate a reference signal that is stable in frequency, and if possible, in amplitude. The frequency can be tuned to cover the required bandwidth and shifts in temperature. Since the tuning is normally done by varying the control voltages, these oscillators are then referred to as Voltage-Controlled Oscillator (VCO).
Other blocks: Other circuits that can be found in Radar front ends may include a Variable-Gain Amplifier (VGA), which is used to amplify the low-frequency signal from the receive mixer before going out of the chip, a Frequency Divider or sometimes just a Divider which is used for dividing the high frequency signal from a VCO to a lower value in order to interface with an off-chip Phase-Locked Loop (PLL) for frequency stabilization and Baseband processors for interfacing between the Radar front end and a computational unit.