Over The Horizon (OTH) Radar Basics

This page covers OTH Radar (Over The Horizon Radar) Basics. It also mentions the working operation of Over The Horizon Radar (OTH Radar).

There are different layers around the earth in the atmosphere viz. Troposphere (upto 12Km), Stratosphere (from 12 to 50Km), Mesosphere (From 50 to 80Km) and Thermosphere (above 80Km).

Thermosphere is further made of two layers viz. Ionosphere (from 80 to 400Km) and Exosphere (above 400Km). It is the Ionosphere which is used in OTH radar as radio frequency waves reflect back to earth from this layer. This layer helps in long range surveillance applications.

Working Operation of Over The Horizon Radar - OTH Radar

The figure depicts OTH radar used for long-range detection of aeroplanes and ships. The OTH radar can detect objects as far as 1000 to 3000 Km. As it detects the objects beyond the radar horizon range with the help of the ionosphere, it is known as Over-the-horizon or OTH radar.

The Over The Horizon Radar operates in the HF frequency range from 5 to 30 MHz. It is used as an early warning radar application. Let us understand how it works.

Like other radar systems, OTH radar transmits a powerful RF signal in the HF band using a large-size antenna. This signal reaches the target after reflecting from the ionosphere layer above the earth. This signal gets reflected from the target and returns back to the receiving antenna of the OTH radar using the same route. There are two separate antennas used in OTH radar: one for transmission and the other for reception.