An RF and microwave Isolator is a two-port RF device used in the RF circuit to protect the RF system from excessive RF signal reflection from the load side.
RF isolator ensures that it will pass signal from the input port to the output port and absorb any RF power incident at its output port when it is connected to an RF system. An RF isolator connected at the output port of a sensitive Rx/Tx system helps the designers to avoid unwanted signals reflected back to the system and causing damage to the sensitive components in it.
RF Isolators are designed using ferrite materials and it is covered with a magnets material to determine the direction of signal flow through the material. In general RF isolators offer an isolation range between 12 and 20 dB from port 1 to port 2 and have only very lower insertion loss.
There are many RF isolator manufacturers who offer RF connectors isolators like SMA, N, etc type, SMD package types, and also the waveguide type RF Isolator.
This article will cover follow information about RF and Microwave isolators.
An RF isolator is a two-port ferromagnetic passive RF component used to protect RF systems from excessive reflected signals. Isolators are mainly used in RF testing to separate DUT from sensitive signal sources.
The generated rotary field inside the RF isolator, due to electromagnetic interference is very strong and will cause any RF and microwave signals to enter into port 1 circulate to port 2, and if any signal reflected from port 2 will circulate to port 3. Due to the strong field, RF and microwave signals will not flow in the opposite direction.
As in the case of the Isolator, port 3 is terminated with a suitable RF terminator and so no signal will flow from port 3 to port 1, hence the signal will flow only from port 1 to port 2.
Isolation of the RF isolators is measured in the unit of dB value, It represents the level of separation of RF signal levels from the output port to the input port. The greater the isolation level, the less RF signal will enter from the output port to the input port, ( Port which is connected to the source).
RF isolator is mainly used to transmit the signal only in one direction and provide high isolation in the reverse direction using a transversely magnetized ferrite channel.
RF isolator comes with a directional arrow in its body to indicate the direction of the RF signal flow. An RF signal experiences very low loss in the direction of signal flow ( arrow) and very high loss on the base of the VSWR match of the isolated port ( port 3) in the reverse direction.
RF isolators are manufactured using a stripline circuit sandwiched between two magnetic ferrite discs, on both sides (upper and lower side). The frequency of operation and input power handling rating of the RF isolators are based on the ferrite materials and magnets used for the manufacturing. In the RF Circulator, the magnetic field is applied Y-axis of this isolator assembly which results in a clockwise circulation of the RF energy from one port to the adjacent port.
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RF Isolators are classified on the basis of the structure and type of the material used.
RF isolators use strip-line printed circuit boards and are enclosed with a metal box with RF connectors or use surface mount interface technology. In addition to strip line isolators, waveguide isolators are used for high-frequency applications. The type of interface for the RF isolators is based on the RF circuit design and the application of the RF system.
Basically, RF isolators can be classified into 3 types on the base of the package structure.
Depending on the materials used in the construction of the RF isolators, it is classified into two main categories: Ferrite RF Isolators and Non-ferrite RF isolators.
In Ferrite RF isolators, magnetized microwave ferrite materials are used to create the isolator. They are classified into 2 classes:
In both types of RF isolators, when waves propagating over two different paths will get canceled inside the magnetized ferrite material.
For better isolation, two or more junction isolators can be combined to make a single isolator by terminating the reflected ports.
Even though ferrite isolators provide good forward circulation of RF signal, they are the bulky sizes for the lower frequency and also can offer only the narrow bandwidths.
Non-Ferrite RF isolators are designed by using transistors that are non-reciprocal in nature. As transistors are active devices, the operation of the non-ferrite transistors requires power.
In April 2016 non-ferrite transistor with smaller dimensions than conventional devices is designed using an integrated circuit based on an N-path filter for full-duplex communication.
RF and Microwave isolators are used for the following applications in RF and Microwave circuits, system, and test and measurement applications.
Following are some of the industrial field's applications of an RF isolator -
RF isolator is a passive component to protect sensitive RF components from excessive power reflection. RF isolators are available in connectors packages like SMA, 2.92mm, Type-N, and also with SMD and waveguide type which offer isolation up to 20 dB, with power ratings up to 1K Watts with lower insertion loss as low as 0.3 dB.
For RF testing applications RF isolator is placed between a signal source and the device under test (DUT) to avoid any reflections due to mismatches at DUT input and cause wrong measurements. For the testing applications, the RF tester should use an RF isolator that can handle 100 % of the reflected power.
When a designer needs to connect a source to a device with an unknown impedance, the isolator will protect the source from any unexpected refection by absorbing the reflected signal, and protecting the expensive signal source hence it works as an impedance match circuit when connected to the device with unknown impedance.
This feature of the RF isolator helps the RF power amplifiers to operate with different loads that have poor impedance matches.
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Below are the few parameters that need to know and specify in the selection of RF and Microwave isolators in the design of the RF and microwave systems.
The frequency range of operation of the RF and microwave isolator need to cover the full range of frequency of operation, with suitable isolation.
The level of Isolation offered between the output port to the input port is the important parameter need to consider in the selection. The higher the isolation of the RF isolator the better the protection.
Insertion loss of the RF isolator indicates the level of signal loss from port 1 to port 2. RF and Microwave Isolator with lower Insertion loss, when inserted in a transmission path, is better for the design.
In higher frequency, insertion loss of isolator will increase, hence for the wideband operation, need to select an isolator that offers the flat insertion loss response over the band of operation. If the insertion loss of the RF isolator is lower it will help to prevent the power loss in the RF chain.
RF power level of an RF isolator indicates the level of power handled by maintaining its electrical characteristics when it is in the RF chain. Power handling needs to define for both forwarding power handling and reverse power handling.
In General, an RF isolator with higher forward and reverse power handling is good for the RF and microwave chain design.
The input impedance of the RF and Microwave isolator must match with the remaining circuit to minimize any internal reflection. Need to choose as per the source impedance.
The operating range of the RF isolator shows the temperature over which the RF isolator will operate without any variation in electrical specifications. For industrial RF isolator, -40ºC to +85ºC is acceptable for most of the RF and Microwave systems.
RF Isolators are available in any size and shape packages like surface mount, Drop-In Packages, connectors modules with different connector options, and also with waveguide connectors. The physical size and the type of the RF isolator need to select as per the requirement of the RF circuit design.
RF isolators are widely used in many RF and microwave circuit design applications like Radio communications equipment to high power Radar systems to protect the source from varying loads.
RF and microwave isolators are passive components, which are available in different packages from many manufacturers from different parts of the world. The RF isolators are available with different connector interfaces and gender options for establishing the suitable connection in the RF systems as per the requirement of the customer’s design needs.
We hope this article about RF and Microwave isolators will help system designers to understand the Function, Application, and Selection specification of the RF and microwave isolators, in the communication system. If you would like to add any further details we are happy to hear from you over the comment box or through the article submission button above.
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