JPH0328562Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a bandpass filter (hereinafter abbreviated as BPF) used in a high frequency band above the UHF band.

[Prior art and its disadvantages] Generally, in the UHF band, a coaxial type where the electrical length of the resonant element is approximately λ/4 as shown in Figure 1 is used.
BPF is often used. In the same figure, 1
1 is an outer conductor housing. The inside of this outer conductor housing 11 is divided by partition plates 12 and 13, and resonance elements 14, 15, and 16 are arranged in each room, respectively. Coupling windows 17 are provided in the partition plates 12 and 13 to provide an appropriate degree of coupling between the resonant elements 14, 15 and 16, respectively. Also, 18
19 is the input (input) power connector, 2 is the output (input) power connector,
0,21 is the binding probe.

The frequency characteristics of this BPF are (2n+1) times the fundamental resonance frequency (n=1, 2,
3...), a higher-order resonance exists and a passband occurs. Therefore, if this BPF is inserted at the output end of the transmitter, among the harmonic output components of the transmitter as shown in Figure 3, the harmonic output components that are 2n times the fundamental wave can be removed, but the harmonic output components that are (2n + 1) times the fundamental wave can be removed. The harmonic output components of cannot be removed.

As a countermeasure against this, conventionally, resonant elements 14, 1
The load capacitance on the open end side of 5 and 16 is set to an appropriate value to shorten the resonant element length, and the frequency at which higher-order resonance occurs is set to (2n+1) of the fundamental wave, as shown in Figure 4.
A method was used to remove the harmonic components of the transmitter by shifting the frequency from the doubled frequency. Also,
Another method is to improve the attenuation characteristics in the harmonic region by configuring the resonant element by combining λ/4 resonant elements 14 and 16 and λ/2 resonant element 22, as shown in FIG. Ta.

However, in the former method, if the length of the resonant element is significantly shortened, the Q will deteriorate and the passage loss at the fundamental frequency will increase. Furthermore, if the degree of shortening is small, there is a drawback that the frequency at which high-order resonance occurs often cannot escape from (2n+1) times the fundamental frequency.

On the other hand, the latter method is a reliable method for improving the attenuation characteristics in the harmonic region without increasing the passage loss, but it has the drawback that it increases the size and price. .

[Purpose of the invention] The present invention was made in view of the above-mentioned circumstances, and its purpose is to reliably and easily improve the attenuation characteristics in the harmonic region without increasing the pass loss in the fundamental wave pass band. The object of the present invention is to provide a small and inexpensive bandpass filter that can improve the

[Key points of the invention] In other words, the present invention arranges, for example, a threaded rod protruding from the inner wall surface of the outer conductor casing near the center conductor of the input (output) connector of the λ/4 coaxial type BPF, and this threaded rod It is designed to operate as a notch filter having an attenuation pole at one of (2n+1) times the fundamental resonance wave of the BPF. Therefore,
Since the attenuation pole of the notch filter is added to the high-order passband generated by the high-order resonance of the resonant element in the BPF, overall, no high-order passband occurs and harmonics The attenuation characteristics in this region are improved.

[Embodiment of the invention] An embodiment of the invention will be described below with reference to the drawings. In FIGS. 6 and 7, 31 is an outer conductor housing. The inside of this outer conductor housing 31 is divided by partition plates 32 and 33, and resonance elements 34, 35, and 36 are arranged in each room. Resonant elements 34, 35, 3 are provided on the partition plates 32, 33, respectively.
A coupling window 37 is provided to provide an appropriate degree of coupling between the two. Further, 38 is an input connector, and 39 is an output connector, and from these input connectors 38 and output connectors 39, coupling probes 40, 41 are directed inside.
has been introduced. Further, from the side wall of the outer conductor housing 31, threaded rods 42 and 43 are arranged protruding from the center conductors 38a and 39a of the input connector 38 and the output connector 39, respectively.

FIG. 8 shows an equivalent circuit of the BPF having the above configuration. In the same figure, the series resonant circuits A and B indicated by broken lines are connected to the threaded rods 42 and 42 of FIGS. 6 and 7.
43, and forms a notch filter having an attenuation pole in the harmonic region of the BPF.

In the above BPF, the threaded rods 42, 43 are adjusted to determine the length of the portion protruding from the inner wall surface of the outer conductor housing 31, or the tip of the open end of the threaded rods 42, 43, and the input The inductance component (L) or capacitance component (C) of the series resonant circuits A and B shown in FIG. 8 can be changed by changing the distance between the connector 38 and the output connector 39 and the respective center conductors 38a and 39. Therefore, the frequency of the attenuation pole of the notch filter (resonant frequency of the notch filter) can be changed extremely easily. Therefore, for example, the attenuation pole frequency of the knob by the threaded rod 42 is set to three times the fundamental resonance frequency of the BPF, and the attenuation pole frequency of the knob by the threaded rod 43 is set to five times the fundamental resonance frequency of the BPF. If so, the attenuation characteristics of the BPF in the harmonic region will be greatly improved as shown in FIG.

Here, the notch switch using the added threaded rods 42 and 43 is used because the frequency interval between the attenuation pole frequency and the passband frequency (passband in the fundamental wave of BPF) is very far apart. The increase in BPF passing loss due to the addition of the notch filter is almost negligible.

In the above embodiment, the threaded rods 42 and 43 were used as elements to obtain attenuation poles in the harmonic region of the BPF, but the invention is not limited to this, and other shapes such as a flat plate may be used. It may also be a metal member.

In addition, in the above embodiment, the case where the number of stages of the resonant element is three, the input/output coupling means is a probe, and the shape of the resonant element is a round bar is explained as an example, but the present invention is applicable to other stages. , method and shape.

[Effect of the invention] As described above, according to the invention, it is possible to reliably and easily enter the harmonic region without increasing the size of the BPF and without increasing the transmission loss in the fundamental wave passband. Therefore, it is possible to provide an inexpensive bandpass filter that can improve the attenuation characteristics of the filter.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the structure of a conventional bandpass filter, Fig. 2 is a frequency characteristic diagram of the filter, and Fig. 3 is an output characteristic diagram of a transmitter to which the filter is applied. FIG. 4 is another frequency characteristic diagram of the same filter, FIG. 5 is a sectional view of yet another conventional band-pass filter, and FIG. 6 is a band-pass filter according to an embodiment of the present invention. Figure 7 is a cross-sectional view of the filter shown in Figure 6 taken along the line X-X', Figure 8 is an equivalent circuit diagram of the filter shown in Figure 6, and Figure 9 is a cross-sectional view of the filter shown in Figure 6. FIG. 3 is a frequency characteristic diagram of the device. 31... Outer conductor housing, 32, 33... Partition plate,
34, 35, 36...Resonance element, 37...Coupling window, 38...Input connector, 39...Output connector, 4
0,41...Coupling probe, 42,43...Threaded rod.

Claims (1)

[Scope of utility model registration request] an outer conductor casing, a plurality of resonant elements disposed within the outer conductor casing, mounted opposite to each other on a side wall of the outer conductor casing, each center conductor facing the resonant element; Threaded rods are arranged protruding from the inner wall surface of the set input and output connectors and the center conductors of the input and output connectors, respectively, and screws are attached to the concentric conductors. A bandpass filter characterized in that the open ends of the rods are capacitively coupled, and a notch filter for high frequency removal is formed depending on the coupling capacitance and the length of the threaded rod.