Unidirectional filter, also known as unidirectional isolator, is a non reciprocal dual port microwave ferrite device mainly used for unidirectional transmission of electromagnetic waves. The following are several key features and applications of a unidirectional device:
1. Working principle:
The unidirectional device utilizes the rotational magnetic effect of ferrite, which causes the ferrite to have different magnetic permeabilities for electromagnetic waves propagating in different directions under an external magnetic field, thus exhibiting non reciprocity. When electromagnetic waves propagate in the forward direction, they can pass through without damage; During reverse transmission, electromagnetic waves are absorbed and converted into heat energy, which is then dissipated.
2. Structural composition:
The unidirectional device is mainly composed of permanent magnets, ferrite sheets, and coating layers. Ferrite sheets are precisely sintered and ground to form coupling, resonant, and filtering circuits with microstrip inductors, capacitors, resistors, cavities, and other components.
3. Technical specifications:
Forward insertion loss: After adding a monochromator to the transmitter, the power loss will be 0.3~0.5dB, which is about 7~10W for a 100W transmission power. Reverse isolation degree and reverse isolation bandwidth: The Class II standard of the National Radio and Television Commission requires that the center frequency within ± 10MHz bandwidth should be better than 25dB, and within ± 5MHz bandwidth, it should be better than 30dB. Standing wave ratio: As an important indicator for evaluating the matching of unidirectional interfaces, a good standing wave ratio of a unidirectional device should be less than 1:1:1, and the reflected power should not exceed 0.8W at a transmission power of 100W.
4. Function:
As an irreversible attenuator, the unidirectional device attenuates the forward wave less and the backward wave more. It mainly serves as an isolation function, which can improve the standing wave ratio and ensure that each component and unit can work stably without affecting each other.
5. Application areas:
Unidirectional sensors are widely used in systems such as electric F countermeasures, phased array radar, and communication satellites, serving as fundamental components. They are also used in the design of wireless paging transmitters to absorb external interference signals entering the transmitter through the antenna system, protect the transmitter, and reduce the failure rate.
The above is a brief introduction to the unidirectional device.
