JPH03218101A - interdigital filter - Google Patents

Abstract

PURPOSE:To facilitate the connection with an active component such as a transistor(TR) or a diode and to reduce the effect of a stray impedance of a capacitor by connecting a ground terminal of an input stage and an output stage of plural strip lines to the ground via the capacitor. CONSTITUTION:Strip line conductors 15-19 are selected to be a length equivalent to 1/4 wavelength of the center frequency of a transmission signal band and one terminal is connected to a ground conductor formed on the rear side of a dielectric board through throughholes 21-23 penetrating through the dielectric board plated with a conductor. One terminal of strip line conductors 15, 19 connected to the leadout electrodes 10, 11 for an external circuit are connected to a ground conductor via capacitors 12, 13 for DC blocking respectively. Thus, a DC block capacitor inserted between an interdigital filter and an input or output of an active element is not required and the increase in the transmission loss due to the capacitor is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to direct current blocking of an interdigital filter composed of microstrip lines, and facilitates connection with active elements such as transistors. [Prior Art] When using active elements such as transistors and diodes in microwave amplification circuits for satellite broadcasting, etc., it is necessary to supply direct current to the active elements. The interdigital filter used in connection with the active element is used by grounding one end of a strip line with a length corresponding to the wavelength of the microwave signal to be transmitted, so there is no connection between the active element and the interdigital filter. A DC blocking capacitor was inserted. [Problem to be solved by the invention] When the transmission frequency is low in the VHF or UHF band, there is no problem even if it is a lumped constant capacitor as a DC blocking capacitor, but at frequencies in the microwave region, the wavelength of the same frequency For this reason, the size of the elements used could no longer be ignored, and a lumped constant capacitor no longer functioned as a capacitor, increasing transmission loss. However, it has been necessary to accept an increase in transmission loss due to the direct current blocking capacitor inserted between the active element and the interdigital filter in an amplifier in the microwave region.

[Means to solve the problem]

The ground end of each strip line constituting the interdigital filter is grounded via a lumped capacitor or a coupling capacitance between the ground end and a conductor placed facing each other with a predetermined gap, and the interdigital filter and active A DC blocking capacitor inserted between the input or output of the element is not required.

[Function] Figures 1 and 2 are explanatory diagrams of an interdigital filter constructed using a strip line according to the present invention, and the figure is a plan view of the filter circuit viewed from the side of the main surface on which the strip line conductor is formed. (substrate not shown).

In the stripline filter circuit shown in FIGS. 1 and 2, each of the stripline conductors 15 to I9 has a length equivalent to the wavelength of the center frequency of the signal band to be transmitted, and one end thereof has a hole passing through the dielectric substrate. Through holes 21 to 23 having a conductor plated around them are connected to a ground conductor (not shown) formed on the back surface of the dielectric substrate.

One ends of the strip line conductors 15 and 19, which connect the lead-out electrodes 10 and 11 to the external circuit, are connected to the ground conductor via capacitors 12 and 13 for DC blocking, respectively.

In the embodiment of FIG. 2, the stripline conductor l
A conductor 29 facing each other is arranged with gaps 27 to 28 between the ground ends of 5 and 19, and the opposite conductor 29 is connected to the through hole 2.
5 to 26 are connected to the ground conductor, and grounded via the coupling capacitance generated between the ground ends of the strip line conductors 15 and 19 and the opposing conductor 29.

One end of each of the strip line conductors 15 to 19 is grounded, and the other end of each of the strip line conductors 15 to 19 is left open. Nos. 5 to 19 operate as electrodes that resonate at a frequency with a wavelength approximately four times as long as the length.

These strip line conductors 15 to 19 are arranged in parallel so that the grounded ends and open ends thereof are alternately arranged, and each strip line conductor 1
5 to 19 are combined to obtain multistage filter characteristics. A circuit example of a microwave amplifier using the interdigital filter of the present invention is shown in FIG.

The microwave transistor 35 has its source grounded, and the bias voltage 33 is supplied from the grounded end of the X-wavelength strip line conductor 4 through a low-pass filter consisting of a resistor 55 and capacitors 45 to 46 with a capacitor 45. The other end of the strip line conductor 4l, which has a high impedance, is connected to the transmission line 37 for signal input, and the transistor 3 is connected to the transmission line 37 for signal input.
Apply to gate 5. A bias voltage 33 applied to the gate of the transistor 35 is supplied from the end grounded by the capacitor 47 of the strip line conductor 42 of a certain wavelength through a low-pass filter composed of a resistor 56 and capacitors 47 to 48. The other end of the strip line conductor 42 serving as an impedance is connected to the transmission line 38 for signal output, and a current is supplied from the DC power supply 34 to the drain of the transistor 35.

The output end of the transmission line 38 is directly connected to the interdigital filter 3 of the present invention without passing through a DC blocking capacitor.
The output terminal 11 of the interdigital filter 30 is connected via a transmission line 39 to the gate of a transistor 36 to which a bias voltage 33 is supplied.

The gate of the transistor 36 is connected to the transistor 3
5, a low-pass filter consisting of a resistor 57 and capacitors 49 to 50 and a strip line conductor 4 of different wavelengths.
A bias voltage 33 is applied via 3. [Example] Figure 1 is an explanatory diagram of an example of the present invention. In the figure, 15 to 19 are strip line conductors each having a length equivalent to the division wavelength of the center frequency of the signal frequency to be transmitted. The strip line conductors are arranged in parallel at intervals that provide the desired coupling capacitance. The strip line conductors 15 to 19 are formed on the main surface of a dielectric substrate made of a material that has a small dielectric loss in the frequency band of the transmission signal and a high ratio gt4, and a ground conductor is provided on the entire back surface of the dielectric substrate. Form. The strip line conductors 15 to 19 have one end thereof penetrated through the dielectric substrate and have a conductor plated around the L, that is, through holes 21 to 23.
The strip line conductors 15 to 19 are connected to a ground conductor (not shown) formed on the back surface of the dielectric substrate, and the other ends of the strip line conductors 15 to 19 are left open, and the ground ends and open ends are arranged alternately. The grounding at one end of the stripline conductors 15 to 19 may be directly connected to a grounding conductor formed on the main surface which is connected to the grounding conductor on the back surface of the dielectric substrate.

An input terminal 10, which is an external lead electrode, is provided at the ground end of the strip line conductor 16 adjacent to the strip line conductor 15 of the strip line conductor I5, and the other end of the strip line conductor 15 is connected to the ground end of the strip line conductor 15 through the capacitor 2. Connect to the ground conductor. Similarly to the strip line conductor I5, the strip line conductor 19 also has an output terminal 1 on the ground end side of the strip line conductor 18 adjacent to the strip line conductor l9.
1, and the other end of the strip line conductor l9 is connected to the ground conductor via a capacitor l3.

FIG. 2 is an explanatory diagram of another embodiment, and parts equivalent to those in FIG. 1 are given the same numbers. In the figure, 29 is a ground conductor formed on the main surface of the dielectric substrate, and the end of the ground conductor 29 is arranged opposite to the ground ends of the strip line conductors 5 and 19 with gaps 27 to 28 in between, Connect via coupling capacitance between conductors placed opposite each other. In the embodiments shown in FIGS. 1 and 2, only the strip line conductors l5 and l9, which connect the lead-out electrodes to the external circuit, are grounded via capacitors, but the other strip line conductors 16 to l8 are grounded. It is possible to have a structure in which the end is grounded via a capacitor instead of being directly grounded through a through hole.

The end of the ground conductor 29 facing the ground ends of the strip line conductors I5 and 19 is provided with through holes 25 to 26.
It is connected to the ground conductor on the back side of the dielectric board.

A plurality of through holes similar to the through holes 25 to 26 may be formed in the ground conductor 29 to make the grounding more effective.

〔Effect of the invention〕

As in the present invention, by grounding the ground terminals of the input stage and output stage of the strip line constituting the interdigital filter via a capacitor, connection with active elements such as transistors and diodes is facilitated, and low impedance Since a capacitor is used in the circuit, the effect of the stray impedance of the capacitor can be reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the interdigital filter of the present invention, Fig. 2 is an explanatory diagram of another embodiment, Fig. 3 is a circuit example of a microwave amplifier using the interdigital filter of the present invention, and Fig. 4 is a conventional diagram. An explanatory diagram of the interdigital filter,
Figure 5 shows an example of the main circuit of a microwave amplifier using a conventional interdigital filter.

Claims (2)

[Claims] (1) A full-surface ground conductor is formed on one surface of a dielectric substrate, and multiple strip lines each having a length of approximately a quarter wavelength of the microwave to be transmitted are provided on the other surface of the same substrate, and between adjacent strip lines, In an interdigital filter, a plurality of strip lines are formed in parallel at predetermined intervals to generate a desired coupling capacitance, and one end of the same strip line is alternately grounded and the other end is left open, and only one end of the same strip line is grounded. . An interdigital filter, characterized in that a ground end side of at least one of the plurality of strip lines relating to input/output is connected to the ground conductor via a capacitor. (2) A claim characterized in that an opposing conductor formed facing the ground end of the strip line at a predetermined interval is connected to the ground conductor, and the capacitor is a coupling capacitance generated between the opposing conductor and the ground end of the strip line. The interdigital filter according to item (1).