JPH0374522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a dielectric filter used in radio equipment, particularly mobile radio equipment.

(2) Background of the Technology Filters used in in-vehicle radios and portable radio devices, generally called mobile radios, are required to be small, lightweight, and low in price. Hitherto, helical filters and microstripline type filters have been used as such filters, but high performance filters have the drawback of being large and expensive.

Recently, low-loss dielectrics with high conductivity and excellent frequency temperature coefficients have been developed, and it has become possible to obtain small, lightweight, and low-cost dielectric filters. VHF,
In the UHF band, coaxial dielectric filters are mainly used. However, the conventional structure has problems as described below, and countermeasures are desired.

(3) Prior art and problems Figures 1 and 2 show the basic configuration of a coaxial dielectric filter. In the figure, numeral 1 indicates a metal casing;
Reference numeral 1a indicates the lid. Also, code 2 is the housing 1
A rectangular parallelepiped-shaped dielectric block is shown housed within. A plurality of holes are drilled in the dielectric block 2, and the inner surface of the hole 3 and both side and bottom surfaces of the block are coated (metallized) with a conductive film (indicated by cross hatching in the figure) by a method such as thick film coating. It has been done. The metallized surface of the hole 3 constitutes a 1/4 wavelength resonant element that resonates at a frequency where the depth of the hole is 1/4 wavelength. That is, the dielectric block 2 constitutes a 1/4 wavelength coaxial resonator in which the metallized surface of the hole 3 serves as an inner conductor (resonant element) and the outer metallized surface of the block (side and bottom surfaces) serves as an outer conductor. be. By connecting an external circuit (not shown) to the resonant elements at both ends of this dielectric block via a suitable exciter 4, the dielectric block operates as a band pass filter (BPF). Note that a non-metalized hole 5 is formed between the metalized holes 3 (resonant elements) of the dielectric block 2, and by inserting a metal screw or the like into this hole, the coupling band between the resonant elements can be increased. It is adjustable. In FIG. 1, reference numeral 6 indicates this coupling band adjustment screw. In addition, code 7 indicates a frequency adjustment screw,
Reference numeral 8 indicates an input/output connector.

As mentioned above, the dielectric block 2 is housed in the casing 1, but at this time, a gap inevitably occurs between the casing and the dielectric block due to dimensional tolerances and the like. If such a gap exists, the contact between the housing and the outer metallized surface of the block will be poor, and radio waves will propagate through this gap, so BPF
electrical characteristics deteriorate. FIG. 10 is a graph showing the amount of attenuation outside the band of the above-mentioned dielectric filter, where the solid line shows the actual measured value of a conventional example, and the dotted line shows the theoretical value. As you can see from this graph, if the contact between the housing and the outer metallized surface of the block is poor, the BPF
The amount of attenuation outside the band becomes extremely poor.

For this reason, conventional methods have been used to improve the dimensional accuracy of the casing and dielectric block, to solder the casing and the dielectric block, or to fill the gaps with conductive paste. This improves contact between blocks and prevents deterioration of damping characteristics. However, these methods require a large number of man-hours such as machining and soldering, which is one of the causes of increased costs. In particular, the dielectric block is an integral part, and the casing essentially only has to serve as a shield, and its dimensional accuracy may be quite poor. On the other hand, aluminum casings are commonly used to reduce weight. In this case, there are problems with workability, such as difficulty in soldering and poor solder flow.

Therefore, as another method, a method has been proposed in which the dielectric block is fixed from the side surface of the casing with metal screws to increase the contact area and prevent radio wave propagation during the gap. However, this method requires a fairly large number of screws to prevent radio wave propagation through the gap. For this reason, the number of man-hours involved in drilling screw holes in the casing and screwing them together becomes a factor in increasing the cost of the filter.

(4) Purpose of the Invention The present invention solves the above-mentioned conventional problems in dielectric filters, that is, it is possible to bring the dielectric block into good contact with the casing,
Moreover, it is an object of the present invention to provide a simple and inexpensive fixing structure for dielectric blocks.

(5) Structure of the invention The dielectric filter according to the present invention generally includes:
This structure has a structure in which a metal having spring properties is inserted between the outer metallized surface of the dielectric block and the casing in a direction perpendicular to the metallized surface.

(6) Embodiments of the invention Hereinafter, embodiments of the invention will be described in detail with reference to the drawings.

FIG. 3 is a diagram showing one embodiment of the present invention in comparison with the basic configuration example shown in FIG. 2. Its feature, in short, is that a metal member 10 having spring properties is inserted between the casing 1 and the dielectric block 2. As shown in FIGS. 4 and 5, the metal plate 10 is a thin metal plate with a large number of protrusions 10a formed by cutting and bending, and these protrusions 10a provide spring properties. By bending such a metal plate 10 into a U-shape around the outer metallized surface (both sides and bottom surface) of the dielectric block 2 and inserting it between the casing 1 and the dielectric block 2, the protrusion 10a is formed. The housing 1 and the dielectric block 2 are in good contact with each other through the metal plate 10 due to the block metallized surface and the spring property in the vertical direction.

Furthermore, since the present invention is particularly intended for a filter for mobile radio equipment, the vibration of the dielectric block poses a problem, but in the present invention, the dielectric block 2 has a fairly good vibration due to the springiness of the metal plate 10. is maintained. In particular, since the protrusions 10a of the metal plate 10 are open upward, the holding force (deterrent force) against upward movement is large. However, in order to further ensure vibration prevention, the housing 1, the block 2, and the metal plate 10 may be fixed to each other with adhesive after assembly, as shown by the dotted line A in FIG. As shown by B, a spacer may be provided on the housing lid 1a to securely hold the block 2.

The metal plate 10 described above is suitable for mass production at low cost by sheet metal processing, and the filter assembly operation using this metal plate is easy.

6 and 7 show a second embodiment of the invention. In this example, a metal plate 11 formed into a corrugated shape to have spring properties is bent into a U-shape along the outer metallized surface of the block 2, as in the first embodiment.
, and substantially the same effect as in the first embodiment can be obtained. However, metal plate 11
It seems that the structure shown in FIG. 1 is inferior in holding power against vibrations compared to the metal plate 10 of the first embodiment, but this problem can be solved by using the above-described auxiliary means such as a contact agent and a spacer.

Note that various shapes of the metal plate having spring properties are conceivable in addition to the above embodiments.

Next, FIGS. 8 and 9 show an embodiment in which the present invention is applied to an antenna duplexer of a simultaneous transmitting/receiving radio device. As shown in FIG. 8, the antenna duplexer AS is located between the transmitter T, the receiver R, and the antenna AN.
It consists of a receiving filter TF, a transmitting filter RF, and a combining circuit S. FIG. 9 shows its specific configuration, in which dielectric blocks 21 and 22 constituting a transmitting filter and a receiving filter, respectively, are fixed to an H-shaped auxiliary housing 20 with adhesive or the like, and then the main housing 23 is fixed. A spring metal plate 24 as shown in FIG. 7 is inserted between the main housing 23 and the main housing 23. As a result, each metallized side surface of each dielectric block 21 and 22 is brought into good contact with the main housing 22. In this embodiment, it is also possible to hold the blocks 21 and 22 in the auxiliary housing 20 by interposing spacers in the upper spaces of the blocks instead of using adhesive.

(7) Effects of the Invention As described above, according to the present invention, good contact between the casing and the dielectric block can be obtained, the electrical characteristics are significantly improved, and the amount of attenuation outside the band is as shown in Fig. 10. It is very close to the theoretical value shown. Further, the structure according to the present invention is very simple and easy to assemble, so the processing time and assembly time are short, and it can be manufactured at an extremely low cost, making it extremely practical.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing the basic structure of a coaxial dielectric filter, FIG. 2 is a sectional view taken along the line - in FIG. 1, and FIG. 3 is a first embodiment of a dielectric filter according to the present invention. 4 is a partial plan view of the metal plate of the first embodiment, and FIG. 5 is a cross-sectional view of the example, and FIG.
6 is a sectional view of a second embodiment of the present invention, FIG. 7 is a perspective view of a metal plate of the second embodiment, FIG. 8 is a schematic configuration diagram of a simultaneous transmitting and receiving radio device, and FIG. FIG. 9 is a sectional view of the antenna duplexer according to the present invention, the first
Figure 0 is a graph showing the amount of attenuation outside the band of the dielectric filter. 1... Housing, 2... Dielectric block, 3... Hole (resonant element), 4... Exciter, 5... Coupling hole, 10, 11
...Metal plate, 20...Auxiliary case, 21, 22...Dielectric block, 23...Main case, 24...Metal plate.

Claims (1)

[Claims] 1 A dielectric block is provided with a plurality of holes, the inner surface of the holes and the required outer surface of the dielectric block are covered with a conductive film, and an external circuit is connected through the excitation parts at both ends of the dielectric block. In a dielectric filter comprising a coaxial resonator housed in a metal casing, the conductor film-coated surface and A dielectric filter characterized by inserting a metal with spring properties in the vertical direction.