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isolator and circulator

Time:2025-01-02 Views:1

  Isolators and circulators are two passive microwave devices based on non-reciprocal materials (such as yttrium iron garnet (YIG) or gyromagnetic ferrite), which utilize the unidirectional transmission characteristics of these materials under the action of an external magnetic field. Although their working principles are similar, their respective application scenarios are different. The following is a more detailed introduction to these two devices:

  RF Isolator

  Working Principle

  An isolator is a two-input and one-output structure device that allows signals to be transmitted from the front port to the rear port, but prevents signals from being transmitted from the rear port to the front port in the reverse direction. This is mainly achieved by using non-reciprocal materials (such as yttrium iron garnet (YIG) or gyromagnetic ferrite) and applying an appropriate DC bias magnetic field. In this material, electromagnetic waves can propagate more easily in a certain direction, while being suppressed in the opposite direction.

  Main Features

  Unidirectional signal path:

  The signal can be transmitted from the input port to the output port, but cannot be transmitted from the output port to the input port in the reverse direction.

  High Isolation:

  Provides high isolation from the output to the input to prevent reflected signals from returning to the source, thereby protecting sensitive RF components (such as amplifiers) from damage.

  Low Insertion Loss:

  Keeps the attenuation of the signal to a minimum to maintain high efficiency and signal strength.

  Temperature Stability:

  Maintains stable performance under different temperature conditions to ensure long-term reliable operation.

  Compact Design:

  Minimizes size and weight to facilitate integration into various devices without affecting its electrical performance.

  Multiple Connection Options:

  Equipped with standardized RF connectors (such as SMA, N-type, etc.) for easy docking with other devices.

  Wide Frequency Range:

  Supports a wide operating frequency range and is suitable for a variety of different application requirements.

  Application Areas

  RF Power Amplifier Protection: Prevents reflected signals caused by load mismatch or other reasons from damaging the amplifier.

  Transmitter System: Ensures that the transmitted signal does not affect the stability and performance of the system due to reflection.

  Test and Measurement Equipment: Used to build a stable test environment to avoid the influence of reflected signals on the measurement results.

  Medical equipment: Protect expensive and sensitive RF components, such as RF transmit/receive modules in MRI machines.

  RF Circulator

  How it works

  Circulators usually have three or four ports, and the signal is transmitted from one port to the next in a predetermined order without returning to the previous port. For example, in a three-port circulator, the signal can be transmitted from port 1 to port 2, then from port 2 to port 3, and so on. This behavior also relies on the effect of non-reciprocal materials and external bias magnetic fields.

  Main Features

  Multi-port unidirectional transmission:

  The signal is transmitted from one port to the next in a predetermined order without returning to the previous port.

  High isolation:

  The high isolation between the ports reduces the interference between different signals, which is especially important when operating in multiple channels or multiple frequency bands.

  Low insertion loss:

  Keep the attenuation of the signal to a minimum to maintain high efficiency and signal strength.

  Temperature stability:

  Maintain stable performance under different temperature conditions to ensure long-term reliable operation.

  Compact design:

  Minimize size and weight to facilitate integration into various devices without affecting its electrical performance.

  Multiple connection options:

  Equipped with standardized RF connectors (such as SMA, N-type, etc.), it is easy to connect with other devices.

  Wide frequency range:

  Supports a wide operating frequency range and is suitable for a variety of different application requirements.

  Application areas

  Radar system: used to protect the receiver from the strong signal of the transmitter while allowing antenna sharing.

  Wireless communication base station: Prevent the transmission signal from being fed back to the receiving link when the transmission and reception share the same antenna.

  RF front-end module: As an isolation element, it ensures that the signal can only flow in the specified direction to avoid problems such as self-excited oscillation.

  Test and measurement equipment: such as spectrum analyzers, network analyzers, etc., used to build complex signal paths without introducing unnecessary reflections.

  Satellite communication: Provides isolation between uplink and downlink to ensure the correct routing of signals.

  Design and Construction

  Common Features

  Non-reciprocal Materials:

  The core is made of non-reciprocal materials, such as yttrium iron garnet (YIG) or gyromagnetic ferrite, which can change the propagation characteristics of electromagnetic waves under the action of an external magnetic field and achieve unidirectional transmission.

  Permanent Magnets:

  The permanent magnets surrounding the non-reciprocal materials generate the necessary bias magnetic field to activate the non-reciprocal effect of the material.

  Microwave Transmission Lines:

  The microwave transmission lines connecting the various ports, usually coaxial cables or microstrip lines, are responsible for guiding the signals to the correct ports.

  Housing and Protective Covers:

  Provide physical protection to prevent external factors (such as moisture, dust, impact, etc.) from damaging the internal components without affecting their RF performance.

  Connectors:

  Equipped with standardized RF connectors (such as SMA, N-type, etc.), it is convenient to connect with other devices, and also considers waterproof and dustproof functions.

  Example of technical parameters (specific models may vary)

  Frequency range: e.g. 0.5 GHz to 6 GHz

  Insertion loss: < 0.5 dB

  Isolation: > 20 dB

  Maximum input power: +30 dBm (1 W)

  Connector type: SMA, N-type, etc.

  Size: Compact design for easy installation

  Selection considerations

  Operating frequency range: Confirming whether the device supports the required operating frequency is critical, especially for multi-band or multi-protocol applications.

  Gain level and insertion loss: Select the appropriate gain value and the lowest possible insertion loss according to the application scenario to ensure signal quality.

  Physical size and installation location: Considering the space constraints of the actual application environment, select a device of appropriate size and shape, and evaluate the best installation location.

  Environmental adaptability: If the device will be installed outdoors or exposed to harsh environments, its weather resistance and protection level should be evaluated.

  Price and cost-effectiveness: Balance performance and budget, and select the most cost-effective product while meeting technical requirements.

  Compatibility and integration difficulty: Ensure that the selected device is easy to integrate into the existing system and does not cause problems such as electromagnetic interference.

  Technical challenges and solutions

  Broadband design: In order to cover a wider frequency range, researchers are exploring new materials and technologies, such as using high-Q ceramic materials and developing new multilayer structures.

  Miniaturization and performance balance: As devices become smaller and smaller, how to achieve further miniaturization while maintaining high performance is an ongoing research topic. This involves the selection of new materials, the application of new manufacturing processes, and innovative design concepts.

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