JPS59112702A - Branching filter - Google Patents

Abstract

PURPOSE:To omit a combining part and to reduce the overall size of a branching filter by using capacitors as exciters for dielectric filters which are used as a transmitting and a receiving filter. CONSTITUTION:The filter 2 for transmission and filter 7 for reception are both dielectric filters. The capacitor 22 is used as an exciter for those filters 2 and 7. This capacitor 22 is a parallel flat plate type and has upper and lower metallic plates 22a and 22b interposing a dielectric 22c in-between. Transmission and reception systems are coupled together on the capacitor 22-1 of the transmitting filter 2, but the exciter (capacitor) is a direct coupling part in this case, so shielding is unnecessary and the combining part is therefore unnecessary, reducing the overall size of the branching filter.

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a transmitter/receiver duplexer using a dielectric filter, and particularly aims to improve the combining section and reduce the size thereof.Prior art and problems 1 In order to use a real antenna for both transmission and reception, a duplexer is required to separate the transmitted and received waves. Figure 1 shows an example of the configuration of a general wireless transceiver. 1 is an antenna, 2 is a transmitting filter, 3 is a circulator, 4 is a power amplifier, 5 is a transmitter, 6 is a receiver, and 7 is a receiving filter. be. The duplexer 8 is constituted by these filters 2 and 7.

FIG. 2 is a plan view showing a specific structural example of the duplexer 8.
11 is a metal housing having a partition wall 10, and 11 is a filter 2.
, 7 and the antenna 1. In the combining section 11, the output cable 12 of the transmission filter 2 and the long cable 13 of the reception filter are combined into one and connected to the antenna 1. The partition wall 10 divides the inside of the casing 9 into three rooms, and each room accommodates the transmission filter 2, the reception filter 7, and the combining section 11. The combining section 11 includes a cable 12.
13 into one cable leading to the antenna 1, the cables 12 and 13 are relatively long, for example, 40 mm and 60 fins, and therefore require processing such as winding to fit, making it difficult to miniaturize. Since the characteristics of the duplexer are adjusted by the cable length from the filter terminals of the transmitting filter 2 and the receiving filter to the antenna terminal, the cables (coaxial or pipe type) 12 and 13 should be shortened simply from the viewpoint of miniaturization. That cannot be said. In other words, it is necessary to make the impedance of the output terminal of the transmission filter 2 infinite when viewed from the cable synthesis section at the receiving frequency, and the impedance of the input terminal of the reception filter 7 when viewed from the transmission frequency. Therefore, the cables 12 and 13 have the lengths described above.

Furthermore, if the cables 12 and 13 are not shielded from each of the filters 2 and 7, there will be problems such as poor isolation, so the combining section 11 requires a shielded and isolated space. In order to form this space, a T-shaped partition wall 10 is provided in the example shown in FIG. 2, which increases the size of the coupling section 11. Therefore, the transmitting and receiving filter sections are made smaller by using dielectric filters. However, the duplexer as a whole becomes large.

In particular, in-vehicle and portable wireless devices are required to be miniaturized, so the coupling portion must also be miniaturized.

OBJECTS OF THE INVENTION The present invention aims to reduce the size of the entire duplexer by using a capacitor in the exciter of each filter and making it possible to omit the combining section.

Structure of the Invention The present invention uses a dielectric filter, which is formed by forming a plurality of holes in a dielectric block at predetermined intervals and forming a conductive film on the inner surface of each hole and the surface of the block, for transmission and reception. In a duplexer in which these transmitting filters and receiving filters are housed in a metal casing with a common partition wall, a capacitor is used as the exciter of each filter, and the output side capacitor of the transmitting filter and It is characterized in that the input side capacitors of the reception filter are connected by a synthesis cable, and the output side or input side capacitor is connected to a common antenna. will be explained in detail.

Embodiment of the invention Connector 30T for transmitter, connector 30R for receiver
is established.

When the capacitors 22 are classified into 22-1 to 22-4, the capacitors 22-1, 22-3, 22-4 and the connectors 30A, 30T, '30R (7) are connected by cables 23, respectively. Since this cable 23 is not necessary for phase adjustment, it can be omitted depending on the structure. What is important in the configuration of the duplexer is the capacitor 2
A coaxial or pipe type cable 24 connects between 2-1 and 22-2. In the illustrated example, the cable 24 is bent and laid along the wall of the housing 9, but the required length is short (about 20 mm), so the capacitor 22-1°22-2
It may be something that connects them in a straight line.

When the exciter of each filter 2.7 is a capacitor, the phase of the filter 2.7 coupled by these capacitors is near the open plane. In reality, there is a slight deviation due to the influence of the capacitor electrodes, etc., and one filter has an almost open surface. FIG. 4 is a Smith chart showing the state of this impedance, and FIG. 3 is a diagram showing an embodiment of the present invention.
(Al is a plan view, (bl is a cross-sectional view.) The transmitting filter 2 and the receiving filter 7 are both dielectric filters.

This dielectric filter 2 (same as 7) has a plurality of holes 21 formed in a dielectric block 2o as shown in (bl), a conductive film is formed on the inner surface of each hole and the surface of the block, and the holes 21 are connected to a resonant element. Details are given in Japanese Patent Application Laid-open No. 57-172.
As stated in No. 01, etc., in short, the resonant frequency is determined by the depth of each hole 21, and the dielectric around the hole constitutes a filter in which these resonant elements are coupled in multiple stages (in this example, five stages). do. For example, it resonates at a frequency where the depth of the hole 21 is λ/4.

In the present invention, a capacitor 22 is used as an exciter for these filters 2.7. This capacitor 22 is a parallel plate type,
Metal plates (Meklais, etc.) 22a and 22b are placed on the top and bottom, and a dielectric material 22c is interposed between them. The metal housing 9 is a partition wall 1o that separately accommodates the filter 2.7.
There is also a connector 3QA for the antenna on the outer wall.

be. In this figure, the impedance characteristics of filters 2 and 7 are also shown. C1 is the characteristic of the transmitting filter, C2 is the characteristic of the receiving filter, Pl is the impedance of the transmitting filter at the receiving frequency, and P2 is the receiving at the transmitting 1 control frequency. is the impedance of the filter. Here, the receiving frequency is assumed to be higher than the transmitting frequency. When coupled using a capacitor in this way, the capacitor section 22-1 of the transmission filter 2
The impedance Z when viewed at the reception frequency is approximately 0], that is, it is open, and there is no need to rotate the phase of the transmission filter 2. On the other hand, in the receiving filter, since the impedance at the point P2 is not infinite, it is necessary to move the point P2 to the vicinity of the point Z=ω, and this is accomplished by rotating the phase using the cable 24 as in the conventional method. sending,
The receiving system is coupled on the capacitor 22-1 of the transmitting filter 2, but in this case, the excitation body (capacitor) is the direct coupling part, so there is no need for shielding, and therefore, as shown in Figure 2, there is no need for shielding. The synthesis section 11 is no longer necessary.

The capacitance of the capacitor 22 is determined by the characteristics of the filter.

However, in the vicinity of Z-ω, the influence of the capacitance value is much weaker than in the vicinity of Z-0, so the capacitance value of the capacitor 22 may vary slightly.

If the receiving frequency is lower than the transmitting frequency, the antenna output 130A may be connected to the receiving filter capacitor 22-2 with the cable 23.

Effects of the Invention As described above, according to the present invention, since a capacitor is used as the excitation body of the dielectric filter used as the transmitting and receiving filter, there is no need to house the coupling part in an isolated shielded space. In addition, the length of the cable whose length is selected for the purpose of impedance adjustment can be reduced to just one short cable, which has the advantage of simplifying the structure and reducing the size.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing an example of a wireless transmitting/receiving device;
Figure 2 is a plan view showing an example of a duplexer, and Figure 3 (al (
bl is a plan view and a sectional view showing an embodiment of the present invention, and FIG. 4 is a Smith chart showing filter characteristics. In the figure, 1 is an antenna, 2 is a transmission filter, 7 is a reception filter, 8 is a duplexer, 19 is a housing, 10 is a partition wall, 20 is a dielectric block, 21 is a resonant element (hole), and 22 is a capacitor , 24 is a composite cable. Applicant Fujitsu Limited Representative Patent Attorney Minoru Aoyagi

Claims (1)

[Claims] A dielectric filter in which a plurality of holes are formed in a dielectric block at predetermined intervals and a conductive film is formed on the inner surface of each hole and the surface of the block is used for transmission and reception, and these transmission filters and In a duplexer in which reception filters are housed in a metal housing with a common partition wall, a capacitor is used as the exciter of each filter, and the output side capacitor of the transmission filter and the input side capacitor of the reception filter A duplexer characterized in that the output side or input side capacitor is connected to a common antenna.