JPS5811045Y2 - high frequency filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency filter that has excellent attenuation and absorption characteristics in a high frequency band and is capable of supplying direct current.

Conventionally, in active circuits in high frequency bands, it is necessary to cut off the high frequency circuit section and the DC bias circuit section at high frequencies, so a method has been developed that can supply direct current through a shielding chassis and short-circuit the high frequency. A feedthrough capacitor as shown in Figure 1 was used.

This feedthrough capacitor consists of a disc-shaped dielectric 1 with electrodes 2 and 2' on both sides, a center conductor 3 soldered to the electrode 2 via a ring 9, and a center conductor 3 soldered to the other electrode 2'. The grounding external conductor 5 is provided with a mounting screw part 11, and an insulating filler is provided between the two to prevent moisture from dielectric material and fix the center conductor. 4,4' are filled.

When using a feedthrough capacitor as described above in a high frequency band active circuit, the feedthrough capacitor is screwed into the chassis 14, as seen in the cross-sectional view of the panel in FIG.

Wiring is provided between one end 3b of the center conductor 3 and the active element 12 in the high frequency circuit section, and the DC bias circuit section 1
3 to the electrode-side end 3a of the center conductor is applied to the active element 12.

Usually, the end 3b of the center conductor and the high-frequency circuit are connected with a quarter-wave thin wire or an air-core coil, but the impedance when the feed-through capacitor is viewed from the high-frequency circuit side is as shown in Figure 3. Impedance 50. As can be seen from the measured example shown in the Smith diagram normalized by Q, there is a complete reflection state within the range of 1 to 12 GHz, and the phase rotation with respect to frequency is large.

Therefore, due to the coupling with the impedance of the connected high-frequency circuit side, resonance occurs at any frequency within this frequency range, causing unstable operation of the active element, such as oscillation of the amplifier.

In addition, when this feedthrough capacitor is used to supply power to active circuits that generate high frequencies, such as oscillators, modulators, and multipliers, the oscillation of the oscillator is interrupted because the high frequencies are almost completely reflected as described above. There were drawbacks such as frequency jumps and deterioration of the modulation characteristics of the modulator.

The purpose of this invention is to solve the above drawbacks, supply direct current,
Another object of the present invention is to provide a high-frequency filter that can operate stably even when used in a high-frequency active circuit by having excellent attenuation characteristics in a high-frequency band.

According to the present invention, electrodes are provided on both sides of a disc-shaped dielectric, one of the electrodes is connected to a central conductor passing through the center of the electrode, and the other electrode has an axially symmetrical chassis mounting portion. A high frequency filter is obtained in which a feedthrough capacitor having a coaxial structure is connected to an outer conductor, and a tubular radio wave absorber is inserted between the center conductor and the outer conductor.

Next, the high frequency filter of the present invention will be explained with reference to the drawings.

FIG. 4 is a sectional view showing the structure of an embodiment of the present invention.

In FIG. 4, symbols that are the same as those shown in FIG. 1 represent the same functions and will not be described again.

As can be seen from this figure, a tubular radio wave absorber 6 made of epoxy and iron powder is inserted between the center conductor 3 and the outer conductor 5, and the gap is sealed with an insulating paint 15.

In the high frequency filter formed in this way, the impedance characteristics seen from the end 3b of the center conductor on the side where the radio wave absorber 6 is inserted are as shown in the measured example in FIG.
A return loss of 6 dB or more was obtained over the frequency range of 2 to 12 GHz.

As a result, it is possible to absorb not only the fundamental wave of 2 to 12 GHz, but also harmonics generated in a circuit of 2 to 6 GHz, so it is possible to absorb the harmonics generated in the circuit of 2 to 6 GHz. The problem of unstable operation can be easily solved.

In addition, the performance of blocking high frequency waves between the high frequency circuit section and the DC bias section, that is, the amount of passing attenuation, cannot be achieved even with conventional feed-through capacitors, with an input/output termination impedance of 50Q.
Approximately 40 dB was obtained over a range of 2 to 12 GHz, but according to the high frequency filter of the present invention, the attenuation due to the radio wave absorber is added, and this is improved to approximately 50 dB.

Note that the high frequency filter of the present invention can be manufactured with the same external dimensions as the conventional through-hole type capacitor, so it can be easily replaced.

As is clear from the above explanation, according to the high-frequency filter of the present invention, direct current is supplied to the high-frequency active circuit through the chassis that separates the high-frequency circuit section and the DC bias circuit section, resulting in large transmission attenuation. A large value of the return loss can provide great effects such as being able to block high frequencies and stably operating the active circuit due to the large value of the return loss.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the structure of a conventional feedthrough capacitor.
Figure 2 is a schematic cross-sectional view showing a panel mounting method for a conventional feedthrough capacitor used in high-frequency active circuits, Figure 3 is a Smith diagram showing an example of actual measurement of the impedance of a conventional feedthrough capacitor at high frequencies, and Figure 4 5 is a sectional view showing the structure of an embodiment of the high frequency filter according to the present invention, and FIG. 5 is a Smith diagram showing an example of actually measured impedance for high frequencies of the high frequency filter according to the present invention. In the figure, 1 is a dielectric, 2 and 2' are electrodes, 3 is a center conductor, 3a and 3b are respective ends of the center conductor, and 4.
4' is an insulating filler, 5 is a grounding external conductor, 6 is a radio wave absorber, 8 is a through hole, 9 is a ring, 11 is a mounting screw, 15
is an insulating paint.

Claims (1)

[Scope of utility model registration request] Electrodes are provided on both sides of a disc-shaped dielectric, one of the electrodes is connected to a central conductor that passes through the center of the electrode, and the other electrode is connected to an axially symmetrical outer conductor having a chassis attachment part. In the feedthrough capacitor with coaxial structure,
It includes a tubular radio wave absorber inserted between the center conductor and the outer conductor, and a circuit unit that handles radio waves to be blocked is connected to the center conductor on the side where the radio wave absorber is inserted. high frequency filter.