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Technology Explained

When choosing a radio frequency (RF) instrument, it is easy to get lost in the many specifications used to characterize an instrument's performance. We will explain some of the key terms to help you understand the specifications of RF instruments.

Radio Frequency

The oscillation rate of an alternating electromagnetic field in the frequency range from approx. twenty thousand times per second (20 kHz) to approx. three hundred billion times per second (300 GHz). The frequencies for automotive radar systems start at 20 GHz and go beyond 80 GHz. The higher the frequency of a radar system, the more it is affected by weather conditions, such as rain or clouds. However, the higher the transmitted frequency, the better the accuracy of the radar system.

Frequency Band

A group of frequencies in the electromagnetic spectrum that are assigned by regulatory agencies for a particular purpose. Automotive radar sensors typically operate in the K band (23 to 26 GHz) or E band (75 GHz to 85 GHz).

Frequency Range

The upper and lower frequency limits in which an instrument is able to process a signal. Within this range, the instrument is considered to provide satisfactory performance, such as a useful level of signal with acceptable distortion characteristics.

Intermediate Frequency

An intermediate frequency (IF) is a frequency to which an RF carrier wave is shifted as an intermediate processing step. The lower intermediate frequencies are easier and less expensive to handle.

RF Front End

In a radio receiver circuit, the RF front end is a generic term for the circuitry between a receiver's antenna input and the mixer stage. It consists of all the components in the receiver that process the signal at the original incoming radio frequency (RF) before it is converted to a lower intermediate frequency (IF).

Bandwidth

The difference between the lowest and highest frequency contained in an RF signal that an instrument is able to handle within a certain error tolerance.

Instantaneous Bandwidth

The bandwidth in which the output power remains constant within 3 dB without any adjustment of other operating parameters.

Dynamic Range

The ratio between the largest and smallest possible values that a changeable quantity can assume. In the context of radar signals, the power ratio between the echo signals from nearby objects and objects at a very large distance can be greater than 80 dB. Processing signals with power differences of this scale can be very difficult. This is particularly true if the echo signals are to be converted to a digital data format later on.

Range Accuracy

A radars degree of veracity regarding range. i.e., how close its measured distance comes to a reference value.

Range Steps

The smallest increment an instrument can detect, process, or output. 

Range Resolution

The minimum difference in distance, that a radar can distinguish between two objects.

Doppler Effect

The change in frequency caused by motion of the source. Radar systems can use the Doppler effect to measure the velocity of detected objects. For example, a car driving at 200 km/h shifts the frequency of a 77 GHz radar by approx. 28.5 kHz.

Bistatic Radar

A bistatic radar consists of separately located transmitting and receiving antennas.

Monostatic Radar

A radar system in which the transmitter and receiver share one antenna.

Quasi Monostatic Radar

A radar system that uses separate receive and transmit antennas that antennas are collocated. 

Maximum Range

The maximum distance at which echoes can be simulated.

Minimum Range

The minimum distance at which echoes can be simulated.

Radar Cross Section (RCS)

A quantity describing the amount of RF power an object reflects if hit by an electromagnetic wave. The RCS depends on the size, geometric form, material and orientation of the object.

MIMO

Multiple input multiple output (MIMO) is a method for multiplying the capacity of a radio link by using multiple transmit and receive antennas to exploit multipath propagation. Multiple transmit antennas send signals simultaneously. Multiple receive antennas process the same incoming signal. In terms of radar MIMO is used to enhance the angular resolution.