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Advantages of Isolator | disadvantages of Isolator

This page covers advantages and disadvantages of RF Isolator. It mentions RF Isolator advantages or benefits and RF Isolator disadvantages or drawbacks. It provides links on various topics on RF Isolators.

What is Isolator?

It is a non-reciprocal device made using ferromagnetic materials such as ferrites (Mg +Mn) and (Ni+Zn) alloys. When these materials are placed in the DC magnetic field, EM wave propagation becomes non-reciprocal. This property is used in the design of RF Isolators.

The ideal RF isolator absorbs the signal power in one direction and supports the propagation in the other direction. Hence it is a uni-directional device. Due to this, reflections from the opposite directions are blocked by it. This property is used in test and measurement domain which is shown in the figure-1 below.

rf isolator application note-2, in protecting test and measurement equipments

In this setup, reflections from DUT (Device Under Test) towards signal source can be blocked. This helps in preventing any damage to the equipment. Moreover, this helps in improving the frequency stability of the microwave signal generator or source. Refer RF Isolator basics and types>> and RF Isolator Application notes>>.

Following are the types of Isolators.
• Faraday Rotation Isolator
• Microstrip Isolator

Benefits or advantages of Isolator

Following are the benefits or advantages of Isolator:
➨As mentioned it is two port non-reciprocal device used to pass signal in one direction with minimum of attenuation and blocks the signal in the opposite direction with high attenuation. When it is connected between source and load, Isolator helps to eliminate variations in output power from the source as it blocks any reflections going towards source from the load. Moreover it avoids frequency pulling due to changing loads.
➨RF Isolator has many uses in Test and Measurement to protect the T&M equipment from damage while performing testing and measurements due to overload or high reflected power.
➨RF Isolator can be used in RF circuit design as depicted in the figure-2 below. In this design it passes all the fequencies from its input port to the output port and blocks all the frequencies in the other directions. This way it protects small miniaturized RF components such as amplifiers, mixers etc.

Drawbacks or disadvantages of Isolator

rf isolator application note-1, in RF circuit design

Following are the disadvantages of Isolator:
➨The major consideration in the above RF circuit is that as RF isolator passes all the frequencies in the forward direction within its band of interest, often it passes undesired frequencies also along with desired ones. Hence appropriate RF filters are used after RF isolator to selectively pass frequencies of interest.
➨Maximum power handing capability of the RF isolator is limited due to the fact that reverse power is absorbed in the ferrite material used in the isolator and dissipated as heat. In order to increase capacity of heat dissipation, two ferrite slabs are used instead of one.
➨Waveguide resonance isolator requires very high steady magnetic field at higher frequencies.

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