Also known as a one-way one-way filter
Also known as a one-way one-way filters, one-way isolator. It is from the microwave device - on the principle of developing the circulator up specifically for radio paging transmitter design, with energy absorption from outside interference signals enter the transmitter through the antenna system, as well as protect the transmitter to reduce the failure rate Features.
Unidirectional filter by a precision sintered and ground gyromagnetic constant magnetic decorated with microstrip inductors, capacitors, resistors, and other components coupled to the cavity resonance, the filter circuit. The rotating magnetic field, the electromagnetic wave signal having a one-way transfer of properties. Signal rotate 120 degrees almost no damage from the output terminal out; the external signal from the output terminal to enter, with the direction of rotation of 120 degrees into the absorbent end turns into heat energy dissipated (see Figure 4).
Unidirectional filter electrical characteristics: Requires forward insertion loss is very small, less than 0.3∽0.5dB; and the reverse feature requires greater the energy absorbed, the more bandwidth the better the frequency required in the 20MHz bandwidth and can reduce energy than 25dB . So, there is a one-way filter to absorb an interference signal at the transmitter frequency around the main entry from outside intrusion, as well as suppression of intermodulation products function.
Check the technical indicators are mainly three:
(1) Forward Insertion Loss
Plus one-way transmitter, it will lose power 0.3∽0.5dB (for 100W transmit power for about 7∽10W).
(2) reverse isolation and reverse isolation Bandwidth
This indicator refers to the ability to absorb external interference signals, SRRC of Ⅱ class standards should be better than the center frequency fo ± 10MHz bandwidth within 25dB, within fo ± 5MHz bandwidth is better than 30dB.
Ⅲ class one-way dual ends (ie, the composite made of two one-way), which can be done within the index fo ± 10MHz bandwidth than 40dB, and fo within ± 5MHz bandwidth than 50dB. Because of the relatively large insertion loss (insertion loss of two one-way), users do not want to accept.
(3) VSWR
VSWR is to evaluate whether the matching unidirectional interface to an important indicator. Less than 1: 2: 1, well less than 1: 1: 1. That is when the 100W transmit power, reflected power less than 0.8W.