JPH0758520A - Dielectric duplexer - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce mutual interference caused by parallel connection. A first terminal of each of a plurality of dielectric filters having a first terminal and a second terminal is connected in parallel with each other to form a common terminal, and each second terminal serves as an individual terminal. A distributed constant line DTL is provided between the common terminal and the first terminal of at least one of the dielectric filters.
1, DTL2 is interveningly connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric duplexer used for mobile communication such as mobile phones and car phones.

[0002]

2. Description of the Related Art As a conventional dielectric duplexer, as shown in FIG. 6, the first terminals of a plurality of dielectric filters 21 and 22 each having a first terminal and a second terminal are mutually connected. A configuration is used in which the terminals are directly connected in parallel to form a common terminal 23 and the second terminals of the common terminals 23 are used as individual terminals 24 of the dielectric filters 21 and 22.

Generally, in a mobile communication system, an antenna of a portable device is commonly used for transmission and reception, so that a demultiplexer for separating signals of the transmission and reception is required. In such mobile communication, a frequency of several hundred MHz to 3 GHz is usually used, but a dielectric filter is optimal as a filter in this frequency band.

Therefore, as the demultiplexer, a plurality of dielectric filters having the respective transmission and reception frequency bands as pass bands are prepared, and terminals on one side of these dielectric filters are connected in parallel with each other. Then, a duplexer is used in which the common side terminal 23 is used and the other side terminal is used as the individual side terminal 24.

FIG. 7 shows an example of mutual interference of characteristics when the frequency interval between the sending and receiving is relatively narrow. 1, in the figure
Reference numerals 2, 3 and 4 show the individual and parallel characteristics of the sending side dielectric filter and the individual and parallel characteristics of the receiving side filter, respectively.

[0006]

One of the problems in realizing such a duplexer is the problem of mutual interference between dielectric filters due to parallel connection. That is, when the dielectric filters 21 and 22 shown in FIG. 6 are connected in parallel, the input admittance of the receiving dielectric filter has a bad influence on the pass band characteristic of the feed, and the pass band characteristic of the receiving has a negative effect. The input admittance of the feed dielectric filter is adversely affected.

A unique frequency band is assigned to each of the transmission and reception frequency bands for each mobile communication system. In particular, in the case of a system in which the frequency interval between the transmission and reception frequency bands is narrow, the dielectric demultiplexing is performed. Realization of a vessel becomes very difficult.

For example, as is clear from FIG. 7, both the sending and receiving dielectric filters have flat passband characteristics as independent characteristics, but when connected in parallel, the sending dielectric filter has a low frequency. Results in a large loss, and the receiving dielectric filter has a loss of more than ten dB in the pass band, which is not practical.

This is due to the admittance characteristic outside the pass band of the dielectric filter of each of the transmitter and the receiver. In particular, in this example, there is a large change in the admittance outside the pass band of the dielectric filter on the sending side, and the admittance becomes maximum. In other words, since the point where the impedance is close to the short circuit exists in the pass band on the partner side, the influence on the pass band characteristic on the receiver side is extremely large. Moreover, the admittance characteristic outside the pass band cannot be selected independently of the characteristic inside the pass band, which is a very difficult problem.

Therefore, an object of the present invention is to provide a dielectric duplexer that reduces mutual interference caused by parallel connection.

[0011]

According to the present invention, the first terminals of a plurality of dielectric filters each having a first terminal and a second terminal are connected in parallel to each other to form a common terminal. In the dielectric duplexer using the second terminal as an individual terminal, a distributed constant line is interposed between the common terminal and the first terminal of at least one of the dielectric filters. The characteristic dielectric duplexer is obtained.

[0012]

[Operation] A distributed constant line having a characteristic impedance equal to the terminating impedance of the dielectric filter is used as the distributed constant circuit, and by connecting this to the input side of the dielectric filter in a cascaded manner, the loss characteristics of the filter are not changed. Only the input admittance can be changed.

Therefore, by selecting the value of the input admittance so as to be suitable for the parallel connection, it is possible to perform the parallel connection without deteriorating the pass band characteristic even in the application where the frequency interval is relatively narrow.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the dielectric duplexer of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an equivalent circuit of the dielectric duplexer.

In the dielectric duplexer, the first terminals of a plurality of dielectric filters each having a first terminal and a second terminal are connected in parallel to each other to form a common terminal, and each second terminal is Use separate terminals. A distributed constant line is interposed between the common terminal and the first terminal of at least one dielectric filter.

Referring to FIG. 1, Tx is a dielectric filter portion (Tx filter) that allows a sending signal to pass therethrough, and Rx is a dielectric filter portion (Rx filter) that allows a receiving signal to pass therethrough. The parallel resonant circuits R1, R2, R3, R4, and R5 are equivalent circuits of dielectric resonators that are coaxial resonators each having a quarter wavelength. The parallel resonant circuits R1 and R2 are Tx
It constitutes a filter, and R3, R4 and R5 constitute an Rx filter.

L and C are coils and capacitors as circuit elements. ANT is an antenna terminal commonly used for transmission and reception. A dielectric filter is composed of the dielectric resonator and the circuit element. Also, DTL1 and DTL
Reference numeral 2 is a distributed constant circuit connected to the common terminal side of the Tx filter and the Rx filter, respectively.

FIGS. 2A and 2B show the input admittance of the Tx filter and the Rx filter, respectively, when the distributed constant circuits DTL1 and DTL2 are not provided. In the figure, 5 and 6 are the real and imaginary parts of the input admittance of the Tx filter, and 7 and 8 are the real and imaginary parts of the input admittance of the Rx filter. Here, the input admittance value is converted into a value when the terminating resistance is 1Ω.

In order that the input admittance value does not adversely affect the filter of the other party connected in parallel, it is desired that the imaginary part of the input admittance be as close to zero as possible within the pass band of the filter of the other party.

However, as is apparent from FIG. 2A, there is a peak value of admittance indicated as PTx for the input admittance imaginary part of the Tx filter. For this reason, as shown in FIG. 7 as a conventional example, the characteristic of the Rx filters connected in parallel has a large loss peak PRx in the pass band.

Further, the input admittance imaginary part of the Rx filter has a large negative value on the low frequency side as shown by the imaginary part 8 of FIG. 2 (b). The loss increases on the low frequency side of.

3A and 3B show a case where the distributed constant circuit DTL1 is connected as a distributed constant line to the common terminal side of the Tx filter, and the distributed constant circuit DTL2 is connected to the common terminal side of the Rx filter. It is admittance. In the figure, 5'and 6'represent the real and imaginary parts of the input admittance of the Tx filter, and 7'and 8'represent the real and imaginary part of the input admittance of the Rx filter. Here, the electrical lengths of the distributed constant circuits DTL1 and DTL2 are each 50 m.
m and 30 mm.

In FIGS. 3 (a) and 3 (b), as shown in FIG.
There is no peak of the input admittance as shown in FIG. 2B, and the imaginary part of the admittance outside the pass band is close to zero.

Therefore, as shown in FIG. 4, the Tx filter,
The pass band characteristics are good even after the Rx filters are connected in parallel. In FIG. 4, 2'and 4'indicate Tx filter and Rx filter characteristics when they are connected in parallel, respectively. The value of the input admittance is the distributed constant circuit DTL1.
And DTL2 are continuously changed by continuously changing the lengths of the distributed constant circuits DTL1 and DTL2.
The length of TL2 can be chosen to be the most suitable length.

As a means for realizing the distributed constant circuits DTL1 and DTL2, it is possible to employ a coaxial cable or a strip line. In either case, when the distributed constant circuits DTL1 and DTL2 having a predetermined electric length are realized, the actual length of the distributed constant circuit is shortened by the square root of the dielectric constant of the dielectric material forming the distributed constant circuits DTL1 and DTL2. You can For example, if the permittivity ε = 20, the shortening rate of the length is 1 / 4.5, and if ε = 40, the shortening rate is 1 / 6.3.

Therefore, in order to realize a predetermined electric length with a short length, it is advantageous that ε is large.

FIG. 5 shows distributed constant circuits DTL1 and DTL.
An example in which a stripline is adopted as a means for realizing 2 is shown. As the substrate material, a dielectric ceramic substrate 11 having a thickness of 1 mm and ε = 20 is used. The lower surface of the substrate 11 is metallized. A strip line 12 having a width of about 0.4 mm is formed on the upper surface of the substrate 11. As a result, the strip line 12 having the characteristic impedance of 50Ω can be formed. In this case electric length 5
A 0 mm stripline can be realized with a length of about 11 mm.

[0028]

According to the present invention, by interposing a distributed constant line having a predetermined electric length on the input side of dielectric filter terminals connected in parallel with each other, mutual interference caused by parallel connection is reduced. be able to.

Therefore, the problem of parallel connection of filters, which has been difficult to solve by the prior art, can be solved relatively easily, and the effect is extremely large.

[Brief description of drawings]

FIG. 1 shows an example of an equivalent circuit in a dielectric duplexer of the present invention.

2A and 2B are graphs showing frequency characteristics of input admittance when there is no distributed constant circuit.

3A and 3B are graphs showing frequency characteristics of input admittance when a distributed constant circuit is connected as a distributed constant line to the common terminal side of a filter.

FIG. 4 is a graph showing respective filter characteristics when connected in parallel.

FIG. 5 is a perspective view showing one form of a strip line which is an example of means for realizing a distributed constant line.

FIG. 6 is a simplified configuration diagram showing a conventional dielectric duplexer.

7 is a graph showing an example of characteristics of each filter alone and mutual interference due to parallel connection when a frequency interval between a feed and a receive of the dielectric duplexer of FIG. 6 is relatively narrow.

[Explanation of symbols]

 Tx Dielectric filter part that passes the sending signal Rx is a dielectric filter part that passes the receiving signal R1, R2, R3, R4, R5 Parallel resonance circuit L coil C capacitor DTL1 and DTL2 Distributed constant circuit PTx Admittance peak value PRx Peak in the pass band of filtering characteristics 5, 5'7 Real part 6, 6 ', 8 Imaginary part 21, 22 Dielectric filter 23 Common terminal 24 Individual terminal

Claims (1)

[Claims] 1. A plurality of dielectric filters each having a first terminal and a second terminal, wherein the first terminals of each of the plurality of dielectric filters are connected in parallel to each other to form a common terminal, and each second terminal of the dielectric filter is an individual terminal. In the dielectric duplexer, a distributed constant line is interveningly connected between the common terminal and the first terminal of at least one of the dielectric filters.