Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1999-07-16
2003-01-14
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S126000, C455S271000, C455S282000, C455S284000, C455S304000
Reexamination Certificate
active
06507728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of preventing transmission spurious response in a radio transceiver, and in particular, to a method of preventing transmission spurious response in a receiver section and a radio transceiver.
2. Description of the Related Art
In a conventional transceiver using a time division duplexing (TDD) system, a transmission frequency is quite similar to or equal to a reception frequency.
Consequently, it is pretty difficult to attenuate sufficiently a component of the transmission signal which leaks into the reception signal by using only a band-pass filter.
Japanese Patent Laid-Open application No. 9-116459 describes a technology to remove such interference in a radio transceiver having an antenna used commonly for transmitting and receiving signals. According to the laid-open application, an apparatus to remove interference between transmission and reception signals operates as follows. In a transceiver in which, as shown in
FIG. 1
, a transmission signal fed from a transmitting section
31
via band-pass filter (BPF)
32
which limits bandwidth of transmitting signal is applied via first metallic path
41
to transmission and reception circulator
33
and guided into antenna
34
by circulator
33
, and reception signal fed from antenna
34
is delivered by circulator
33
to band-pass filter
35
which passes the reception signal via second metallic path
43
and transferred to receiver section
36
after filtering.
The transceiver further comprises circulator
45
which distributes transmission signal between transmitting section
31
and circulator
33
, receiver side directional coupler
44
between receiving section
36
and circulator
33
and third metallic path
42
including amplifier
51
and phase shifter
52
between circulator
45
and coupler
44
. The difference between a length of the path from circulator
45
via first and second paths
41
and
42
to coupler
44
and an associated length therefrom via third path
42
to coupler
44
is set to &lgr;/2 (&lgr;=wavelength) or an odd-number multiple thereof so as to cancel a leakage component of the transmission signal.
The leakage component of the transmission signal flows into an input port of receiving section
36
due to, for example, a reverse directional or directive distribution of circulator
33
. Using coupler
44
, a leak signal from circulator
45
is regulated in amplitude and phase by amplifier
51
and phase shifter
52
to be fed via third path
42
as a transmission signal component.
The signal component cancels interference caused by the leakage transmission signal via metallic path
43
through circulator
33
. This cancellation secures removal of interference between the transmission and reception signals even when these signals are similar in frequency to each other. Therefore, the radio frequency bandwidth can be efficiently used by minimizing the difference between the frequencies.
The technology of the laid-open application is effective in that the leakage transmission wave from circulator
45
is canceled through the matching operation with the path length, the amplitude, and the phase shift to resultantly suppress interference between transmission and reception. However, the laid-open application describes no measure to remove a transmission spurious response component having a frequency similar to the transmission frequency.
In the transceiver using the TDD system, when the transmission signal is transmitted, a high powered transmission signal is inputted into the receiving amplifier even if it is not supplied power yet, causing to generate a distortion due to non-linear characteristic of input stage of the receiving amplifier and generates not only expected receiving signal frequency but unexpected harmful frequencies so called as the spurious response.
Particularly, in a transceiver using two transmission frequencies at the same time, components of the two transmitting signals having different frequencies enter into a receiver thereof via unexpected routes. This causes intermodulation distortion and hence transmission spurious response.
SUMMARY OF THE INVENTION
An object of the present invention to provide a transmission spurious response preventing method in which a leakage signal due to a transmission signal sent from a transmitter with a high power is prevented by canceling the leakage signal with a signal having opposed phase and the same amplitude to the leakage transmission signal.
Another object of the invention is to provide a transceiver which operates in a time division duplex (TDD) system and has a receiving amplifier including an input port connected to an antenna system selected for a signal transmission.
The transceiver is also provided means for supplying a signal divided from the transmission signal and having the same amplitude and opposite phase to the amplitude and phase of the leakage transmission signal into the input port of the receiving amplifier which is connected to an antenna selected for the transmission, for canceling the leakage transmission signal.
The radio transceiver further includes a first circulator for separating a transmission and reception path, a transmitting amplifier, and a second circulator disposed in an outlet side of the transmitting amplifier. The transmission signal is supplied via the first circulator to the antenna, and the division of the transmission signal for use of canceling is fed via the second circulator to the receiving amplifier.
In accordance with the present invention, a radio transceiver operating in a time division duplex (TDD) transmission including: an antenna used commonly for transmitting and receiving signals; a first circulator of rotary insulating type connected to the antenna; a receiving section for receiving a signal via a first strip line and a receiving amplifier from said first circulator; a transmitting amplifier for high-frequency amplifying a transmission signal; a second circulator connected to an output port of said transmitting amplifier; a third strip line and a fourth strip line for establishing connection between a normal directivity outlet from said second circulator to said first circulator; and a sixth strip line and a seventh strip line for establishing connection between a reverse directivity outlet from said second circulator and an input port of said receiving amplifier of the receiving section.
In the transceiver, a transmission signal reached to the input port of the receiving amplifier via a first path including normal directivity outlet of the second circulator, said third strip line, said fourth strip line, reversed directivity outlet of said first circulator, said first strip line, and the input port of said receiving section, and a transmission signal reached to the input port of the receiving amplifier via a second path including the reverse directivity outlet of said second circulator, said sixth strip line, said seventh strip line, are equal in amplitude and reverse in phase to each other.
There is provided in accordance with the present invention a transmission spurious response preventing method used for a radio transceiver operating in a time division duplex (TDD) transmission, wherein the method includes the step of inputting a high-frequency signal delivered from a transmitting amplifier to an input port of a receiving amplifier of a receiving section connected to an antenna system selected for a signal transmission to cancel a leakage transmission signal by setting the amplitude of the delivered transmission signal the same to the leakage transmission signal and setting the phase of the delivered transmission signal to reversed relativity with the leakage transmission signal.
Conceptually, the transmission spurious response preventing method of the present invention is implemented in a radio transceiver operating in a TDD including a unit which supplies an input port of a receiving amplifier connected to an antenna system selected for transmission with a transmission signal having
Watanabe Nozomu
Yajima Yuji
Green Miguel D.
NEC Corporation
Sughrue & Mion, PLLC
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