Fundamentals of direction finding

All you need to know about direction finding and radiolocation techniques

What is direction finding and radiolocation?

Detecting emissions is always the first step. But often not only the existence of a signal of interest but also the location of the emitter.

The task of a radio direction finder is to estimate the direction to an emitter by measuring and evaluating electromagnetic field parameters. Usually, the azimuth angle to the emitter of interest is sufficient; the measurement of elevation is of interest for emitters installed on airborne platforms and especially for the direction finding of shortwave signals. Direction finding is therefore an indispensable first step in radiomonitoring, particularly since the content of such emissions is usually inaccessible.

Radiolocation of emitters is often a multistage process. Countrywide direction finders allow an emitter to be located to within a few hundred meters by means of triangulation. The emitter location can be determined more precisely with the aid of direction finders installed in vehicles. Moreover, portable direction finders allow searching within the last 100 m, for instance in buildings.

Typical applications for direction finding and radiolocation

Radiomonitoring in line with ITU guidelines

This application mainly concerns searching for interference sources and localizing non-authorized transmitters.

COMINT/CESM – military intelligence

The main objectives of this application are the detection of activities of potential enemies and the acquisition of information on an enemy's communications order of battle (COB).

Critical infrastructure security - Coast guarding applications

Coastal emergency radiomonitoring clearly demonstrates the importance of direction finding and radiolocation. It has saved the lives of many seafarers in distress.

Critical infrastructure security - ATC air traffic control

Air traffic control DF system solutions provide accurate and reliable direction finding for both civil and military airports. It enables air traffic controllers to accurately determine the direction to the aircraft on the basis of its radio transmissions. This helps reduce call-sign confusion and identify responses from wrong aircraft. The increased safety makes it possible to handle more flights per hour by reducing the time gaps between consecutive flights.

Counter UAS – swift detection and neutralization of drones

Protective measures can only be taken after a threat is detected. To effectively counter the threat, early warning is critical – every second counts. This solution detects commercial drone activity, it automatically classifies the type of drone signal and determines the direction of the drone and its pilot.

Direction finding and radiolocation webcasts

What is direction finding?

The direction of the emitter is identical to the direction of the radio wave incidence only in the event of undisturbed wave propagation. Usually, a large number of partial waves arrive from different directions, creating a more or less scattered field. The direction finder takes spatial and temporal samples from this wave front and estimates azimuth and elevation values for the most probable direction of the emitter.

Understanding the factors that influence direction finding is important. This includes basic knowledge of signal reflection and polarization. Of course, DF accuracy and DF sensitivity are also vital performance parameters. DF site selection and DF correction possibilities also need to be considered.

What are the most important requirements for direction finding antennas?

DF system performance is strongly linked to the connected DF antenna(s), especially for DF accuracy, sensitivity and immunity to strong signals. The DF antenna design is often decisive for a successful mission.

In this webcast you will learn more about this and answers to questions, such as ...

How does the DF antenna design contribute to DF system performance?
How does antennal element design affect immunity to strong signals?
What are the most important DF antenna requirements?

What are the main principles of direction finding?

The classic direction finding methods are

Beam steering
Watson-Watt
Correlative Interferometer (vector matching)
Super resolution

It is important to understand how direction finding methods function along with their advantages and disadvantages when choosing the best application method. This webcast gives an overview of the main principles of direction finding.

Introduction to direction finding systems webcast

What are the direction finding systems?

A typical direction finding system has several components, including a DF antenna, one or more receiving channels, a DF processing unit and a graphical user interface (GUI). Direction finding can be done either with a single receive channel or with multiple receive channels. To find the best solution for your application, you need to understand the advantages, disadvantages and restrictions.

In this webcast you will learn more about them and the following important questions, such as...

What is a scanning direction finder?
What is wideband direction finding?
What are further important DF performance parameters?

What is radiolocation?

Radio direction finders enable the direction to a transmitter to be estimated. This is sufficient in some applications such as traffic control. In all other applications listed above, the location of the transmitter of interest must be known.

There are various methods of finding a transmitter of interest:

Triangulation (AOA)
Time difference on arrival (TDOA)
Power difference on arrival (PDOA)
Homing/running fix

In order to find the best radiolocation solution for your application, it is important to understand the advantages, disadvantages and limits of each of these methods.

Learn more about radiolocation methods in this webcast.

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