New S-band Power Combiner

With primary radar operation short pulses are usually emitted with very high power. Reflection echoes are identified during the pulse intervals in receive mode. Objects that find themselves in the radar beam can be detected and identified using this.

The pulse power is increased accordingly to reach large ranges. This high pulse power can no longer be generated using individual amplifiers on a semiconductor basis. Here you have to opt for combining several individual amplifiers with low power so that the power can be added up. Different power combiner technologies can be used to combine the powers. However, same phase and amplitude control is required at the combiner input ports. If one of these conditions is not met, part of the energy remains in the integrated absorbers of the combiner, which heat it up. If this heat energy is not sufficiently dissipated it may lead to the combiner unit being damaged.

We received the order to replace an existing combiner unit, because a breakdown of the amplifier units caused an overload of the absorbers in the combiner. The radar system therefore automatically switched off and air surveillance was no longer possible.

To upgrade the existing radar systems, SPINNER has developed a fail-safe S-band combiner, which is also capable of working under the condition of up to four amplifier units failing and therefore enables air surveillance with reduced power and thus range. The power of each of the eight amplifiers generating 2kW pulse power is brought together in the combiner. The signals are fed to the coaxial inputs and added up in three stages. The total pulse power of 16kW is then available at an S-band waveguide at the combiners’ output.

Another challenge was to design the combiner so that the accumulated heat at integrated absorbers’ can be well dissipated even with asymmetrical load at the input ports. Due to the requirement of having to work perfectly in a temperature range of -30°C to +50°C, none of the standard components for absorbers available on the market could be used. SPINNER already has many years experience with this kind of specifications and has developed pulse resistant absorber elements specifically for such requirements.

These absorbers were used here in a slightly modified form. Optionally also the retrieval of a small part of the power is possible to enable monitoring of asymmetries at the combiner input ports. The planning of the new combiner unit began in March and the first two prototypes were supplied to the customer beginning of July. The combiners have been immediately integrated into a radar transmitter and have since proven to work very well. The availability of the radar system has been significantly increased thanks to the use of these new units.

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