![]() ![]() Generally, the insertion loss of a circulator/isolator (or any microwave device for that matter) becomes more significant at higher frequency, namely because loss increases with frequency and higher frequency power sources are considerably more expensive. If the match on port 3 is poor, you can expected isolation below 10 dB, but if the match is improved to 1.10: 1 by using a good termination device in the circuit, then the isolation would improve to over 20 dB.Īnother important consideration when specifying a circulators and isolators is to ensure the device has minimal insertion loss when inserted in a transmission path. The amount of isolation is directly affected by the VSWR presented at port 3 of the isolator. The greater the isolation value, less interference from a signal on one port is present at the other. ![]() Isolation is a unit of measure (in dB) that states the separation of signal levels on adjacent ports of a device. ![]() As you will note, it makes no difference which port is the input of the circulator because the relationship at the outputs remains the same as these devices are electrically and mechanically symmetrical.Īn important consideration when specifying an isolator or circulator is to ensure the device has adequate isolation for your given application. If there is a mismatch at port B, the reflected signal from port B will be directed to port C. Example: If a signal is placed at port A, and port B is well matched, the signal will exit at port B with very little loss (typically 0.4dB). The arrows represent the direction of the magnetic fields and the signal when applied to any port of these devices. Notice how an isolator is a circulator with the third port terminated. The rotary field is very strong and will cause any RF/microwave signals in the frequency band of interest at one port to follow the magnetic flow to the adjacent port and not in the opposite direction.įigure 1 Shows the schematics for a circulator and an isolator. The interaction of the magnetic field to the ferrite material inside isolators and circulators create magnetic fields similar to the water flow in the cup. You can also see that it would be impossible for the pepper to move in a counterclockwise direction because the water motion is just too strong. If you sprinkle some pepper into the cup and continue to stir, you will notice that the pepper easily follows the circular motion of the water. To understand how these components control the signal flow, think of a cup of water into which you place a spoon and stir in a clockwise motion. Examples of both applications will be covered later in this article. An RF circulator is a three-port ferromagnetic passive device used to control the direction of signal flow in a circuit and is a very effective, low-cost alternative to expensive cavity duplexers in base station and in-building mesh networks. Isolators are commonplace in laboratory applications to separate a device under test (DUT) from sensitive signal sources. An RF isolator is a twoport ferromagnetic passive device which is used to protect other RF components from excessive signal reflection. ![]()
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