Impedance transformation in a duplexer using a transmission line
View Patent ↗A duplexer having a filter and a transmission line that transforms an impedance of the filter to an impedance of an antenna.
1. A duplexer comprising a filter and a transmission line that transforms an impedance of the filter to an impedance of an antenna, wherein the transmission line has an impedance that is a geometric mean of the impedances of the filter and the antenna, wherein the geometric mean of the impedance is given by:
Z L =( Z RX *Z A ) 1/2
where Z L is the impedance of the transmission line, Z RX is the impedance of the filter, and Z A is the impedance of the antenna.
2. The duplexer of claim 1 , wherein the transmission line is a quarter wave transmission line at a frequency of a transmit filter of the duplexer.
3. The duplexer of claim 1 , wherein the filter is a receive filter.
4. The duplexer of claim 1 , wherein a length of the transmission line is selected to provide a 90 degree phase shift in a transmit band of a transmit filter of the duplexer.
5. The duplexer of claim 1 , wherein the impedance transformation provided by the transmission line enables the use of higher impedance structures on a receive side of the duplexer.
6. A method for impedance matching in a duplexer, the method comprising: transforming an impedance of a filter in the duplexer to an impedance of an antenna, wherein the transforming comprises:
selecting an impedance of a transmission line to have a geometric mean of the impedance of the filter and the impedance of the antenna, wherein the geometric mean is given by:
Z L =( Z RX *Z A ) 1/2
where Z L is the impedance of the transmission line, Z RX is the impedance of the filter, and Z A is the impedance of the antenna.
7. The method of claim 6 , wherein transforming comprises transforming using a quarter wave transmission line at a frequency of a transmit filter of the duplexer.
8. The method of claim 6 , wherein transforming comprises transforming an impedance of a receive filter in the duplexer to the impedance of the antenna.
9. The method of claim 6 , further comprising selecting a length of the transmission line to provide a 90 degree phase shift in a transmit band of a transmit filter of the duplexer.
10. A cellular communication station, comprising:
an antenna;
a filter; and
a duplexer having a transmission line that transforms an impedance of the filter to an impedance of the antenna, wherein the transmission line has an impedance that is a geometric mean of the impedance of the filter and the impedance of the antenna, wherein the geometric mean is given by:
Z L =( Z RX *Z A ) 1/2
where Z L is the impedance of the transmission line, Z RX is the impedance of the filter, and Z A is the impedance of the antenna.
11. The cellular communication station of claim 10 , wherein the transmission line is a quarter wave transmission line at a frequency of a transmit filter of the duplexer.
12. The cellular communication station of claim 10 , wherein the filter is a receive filter.
13. The cellular communication station of claim 10 , wherein a length of the transmission line is selected to provide a 90 degree phase shift in a transmit band of a transmit filter of the duplexer.
14. The cellular communication station of claim 10 , further comprising a structure on a receive side of the duplexer having a higher impedance than the impedance of the antenna.