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Isolators, also known as a one-way filter

Isolators, also known as a one-way filter

* : * : admin * : 2014-11-13 * : 76
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     Isolators, also known as a one-way filter, unidirectional isolator. It is from microwave devices - Development circulator principle on up specifically for radio paging transmitter design with energy absorbed from outside interference signals enter the transmitter through the antenna system, as well as the protection of the transmitter, reducing the failure rate, etc. function.
     Unidirectional filter by sintering and precision grinding gyromagnetic constant magnetic decorated with microstrip inductors, capacitors, resistors, and other components coupled cavity resonator, filter circuit. In the rotating magnetic field, the electromagnetic wave signal having a unidirectional transfer characteristics. Almost no signal is 120 degrees rotation from the output terminal out of injury; external signal from the output terminal to enter into the same direction of rotation of 120 degrees of heat dissipated into the absorption edge (Figure 4).
     Unidirectional filter electrical characteristics: Requires forward insertion loss is very small, less than 0.3∽0.5dB; and the reverse feature requires the greater absorption of energy, the better the wider frequency bandwidth required in the 20MHz bandwidth, can reduce energy than 25dB . Therefore, a unidirectional filter is to absorb the primary interference signal at the transmitter frequency is about to enter from outside intrusion, as well as the function of suppressing the intermodulation products.
     Check the technical indicators are mainly three:
     (1) Forward insertion loss
     The transmitter coupled isolators, it will lose power 0.3∽0.5dB (100W transmit power for speaking about 7∽10W).
     (2) reverse isolation and reverse isolation bandwidth
This indicator refers to the ability to absorb external interference signals, SRRC's Class Ⅱ standard should be better than in the center frequency fo ± 10MHz bandwidth 25dB, within fo ± 5MHz bandwidth is better than 30dB.
     Ⅲ class dual junction isolators way (ie the composite made of two one-way), which can be done within the indicators fo ± 10MHz bandwidth than 40dB, and fo within ± 5MHz bandwidth is better than 50dB. Since the insertion loss is relatively large (two-way device's insertion loss), users do not want to accept.
     (3) VSWR
VSWR is to evaluate whether the match-way interface to an important indicator. Less than 1: 2: 1, well less than 1: 1: 1. That is, when the transmission power 100W, the reflected power is not more than 0.8W.
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