Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1998-10-05
2001-10-23
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S083000, C370S902000, C370S902000, C333S207000
Reexamination Certificate
active
06308051
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna duplexer, more specifically, the antenna duplexer to be used for a microwave band communication equipment or the like.
2. Description of the Related Art
For example, there is a portable telephone system having a plurality of passing bands of a transmitting circuit and a receiving circuit such as NTACS-CDMA. In the case of NTACS-CDMA, the frequency is allotted to 887-901 MHz and 915-925 MHz for the transmission side, and 832-846 MHz and 860-870 MHz for the reception side, having two kinds of passing bands, respectively. Thus, the transmission frequency bandwidth to be required for the transmitting circuit of the antenna duplexer to be used for NTACS-CDMA is 887-925 MHz while the reception frequency bandwidth to be required for the receiving circuit is 832-870 MHz, and both the transmitting circuit and the receiving circuit are required to have the wide passing band of 38 MHz. On the other hand, the separation to be secured to separate the transmission frequency bandwidth from the reception frequency bandwidth is 17 MHz, and the separation between the two becomes extremely small.
The antenna duplexer synthesizes the phase of the transmitting circuit with the phase of the receiving circuit. In the case of NTACS-CDMA, the transmitting circuit is set to be of high impedance (open) at the reception frequency bandwidth of 832-870 MHz, and the receiving circuit is set to be of high impedance (open) at the transmission frequency bandwidth of 887-925 MHz to ideally synthesize the phase of the transmitting circuit with the phase of the receiving circuit.
FIG. 11
is an example of the circuit of a conventional antenna duplexer
81
. In
FIG. 11
, Tx denotes a transmitting terminal, Rx denotes a receiving terminal, ANT denotes an antenna terminal, 82-85 denote resonators of a transmitting circuit
100
, C
31
-C
34
denote coupling capacitors to determine the magnitude of the attenuation in the blocking bandwidth, C
35
-C
39
denote capacitors, L
31
-L
34
denote coupling coils,
86
-
90
denote resonators of a receiving circuit
101
, and C
40
-C
45
denote coupling capacitors.
In the conventional antenna duplexer
81
, however, the transmission frequency bandwidth and the reception frequency bandwidth are wide, respective in the case of NTACS-CDMA, and the separation between the two is extremely small, and it is practically difficult to set the transmitting circuit
100
to be of high impedance in the reception frequency bandwidth and to set the receiving circuit
101
to be of high impedance in the transmission frequency bandwidth.
FIG. 12
is a Smith chart of the antenna duplexer
81
. In
FIG. 12
, P
1
, P
2
, P
3
and P
4
respectively indicates the impedance at the frequency of 832 MHz, 870 MHz, 887 MHz, and 925 MHz of the receiving circuit
101
viewed from a branch point A in FIG.
11
. The frequency 832 MHz is the frequency at a low frequency side end part of the passing band of the receiving circuit
101
while the frequency 870 MHz is the frequency at a high frequency side end part of the passing band of the receiving circuit
101
. The frequency 887 MHz is the frequency at a low frequency side end part of the passing band of the transmitting circuit
100
while the frequency 925 MHz is the frequency at a high frequency side end part of the passing band of the transmitting circuit
100
.
FIG. 12
shows that the impedance of the receiving circuit
101
at P
3
of the frequency of 887 MHz is low, and the insertion loss of the antenna duplexer
81
in transmission is increased. To cope with the problem, Q
0
is increased by increasing the size of the dielectric resonator of the transmitting circuit and the receiving circuit in order to obtain the steep attenuation curve, but there raises another problem that the size of the antenna duplexer
81
is increased.
As a method for miniaturizing the antenna duplexer, a proposal is made that the dielectric resonator is used in the transmitting circuit and the surface acoustic wave filter element is used in the receiving circuit. (For example, refer to Japanese Unexamined Patent Publication No. 5-95204.) However, it is difficult to set the transmitting circuit to be of high impedance at the reception frequency bandwidth or to set the receiving circuit to be of high impedance at the transmission frequency bandwidth though the antenna duplexer can be miniaturized by using the surface acoustic wave filter element, and the insertion loss in the transmission and reception can not be improved. It is more rather superior in the characteristic aspect to compose the transmitting circuit and the receiving circuit of the dielectric resonator.
Also, as the method to set the transmitting circuit to be of high impedance at the reception frequency bandwidth and to set the receiving circuit to be of high impedance at the transmission frequency bandwidth, an antenna duplexer
121
illustrated in
FIG. 13
capable of switching two kinds of the passing bands of a transmitting circuit
130
and a receiving circuit
131
is proposed. In
FIG. 13
, Tx denotes a transmitting terminal, Rx denotes a receiving terminal, ANT denotes an antenna terminal, CONT denotes a voltage control terminal,
122
and
123
denote resonators of the transmitting circuit
130
,
124
-
127
denote resonators of the receiving circuit
131
, L
35
and L
44
denote coupling coils, C
50
and C
51
denote coupling capacitors to determine the magnitude of the attenuation of the blocking region, C
52
and C
53
denote capacitors, C
54
-C
59
denote frequency variable bandwidth capacitors, D
11
-D
16
denote PIN diodes, L
36
-L
41
denote choke coils. R
11
, R
12
and C
60
, C
61
denote resistors and capacitors for supplying the control voltage, respectively, L
42
, L
43
and C
62
denote coils and a capacitor to constitute the phase shifter, respectively, C
63
-C
65
denote coupling capacitors, and C
66
and C
67
denote a multi-pass capacitors to polarize the receiving circuit
131
. The transmitting circuit
130
constitutes a variable bandwidth blocking circuit while the receiving circuit
131
constitutes the variable band passing circuit.
The antenna duplexer
121
can apparently set the transmission frequency bandwidth and the reception frequency bandwidth to be small, and to increase the separation between the two. However, there is a problem that the antenna duplexer
121
is not suitable for miniaturization because it requires one of the PIN diodes D
11
-D
16
and one of the choke coils L
36
-L
41
for each of the resonators
122
-
127
. In addition, degradation of the resonance system Q
0
(Q
0
is the Q at the center frequency) is not avoided because the PIN diodes D
11
-D
16
and the capacitors C
54
-C
59
are connected to a large number of resonators
122
-
127
in parallel. In particular, the insertion loss of the receiving circuit
131
to constitute the band passing circuit is dependent on the resonance system Q
0
, and electric degradation of the receiving circuit
131
is remarkable.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an antenna duplexer which is small in degradation of Q
0
of the resonance system, small in insertion loss and compact in size.
A preferred embodiment of the present invention provides an antenna duplexer, comprising: a transmitting terminal; a receiving terminal; an antenna terminal; a transmitting circuit electrically connected between said transmitting terminal and said antenna terminal, said transmitting circuit comprising at least one first resonator and a first element electrically connected to said first resonator and electrically changing the capacitance by the control voltage; and a receiving circuit electrically connected between said receiving terminal and said antenna terminal, said receiving circuit comprising at least one second resonator, a second element electrically connected to said second resonator and electrically changing the capacitance by the control voltage, and a surface acoustic wave filter eleme
Hunter Daniel
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Tran Pablo
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