JPH03218102A - Interdigital filter - Google Patents

Abstract

PURPOSE:To facilitate the connection to an active element such as a transistor(TR) or a diode without use of a DC blocking capacitor by selecting the length of a strip line of an input stage and an output stage to be a length equivalent to 1/2 wavelength of the center frequency of a transmission signal band and leaving the end of the line open. 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. The length of strip line conductors 15, 19 connected to leadout electrodes 10, 11 for an external circuit is selected to be a length equivalent to 1/2 wavelength of the center frequency of a transmission signal band and the end of the strip line conductors 15, 19 is life opened. 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 active elements such as transistors and diodes are used in microwave amplification circuits for satellite broadcasting and the like, 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 X 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 bands, there is no problem even if it is a lumped constant capacitor as a DC blocking capacitor, but at frequencies in the microwave range, the size of the element used for the wavelength of the same frequency is ignored. Therefore, the lumped constant capacitor no longer functions 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 length of each strip line that makes up the interdigital filter is approximately a quarter wavelength of the transmission frequency, one end is open, the other end is grounded, and the strip line is placed outside and parallel to each strip line. However, only the strip line of the input/output stage connected to the external lead-out electrode is set to have a length approximately half the wavelength of the transmission frequency, and the end of the strip line is left open.

[Function] FIGS. 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. Name shown (board not shown).

In the stripline filter circuit shown in FIGS. 1 and 2, each of the stripline conductors 15 to 19 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.

The strip line conductors 15 and 19 connecting the extraction electrodes 10 and 11 to the external circuit have a length equivalent to two wavelengths of the center frequency of the signal band to be transmitted, and the ends of the strip line conductors 15 and 19 are Leave it open.

The strip line conductors 15 and 19 having a length corresponding to two wavelengths with the ends open exhibit high impedance at the same end, and low impedance at a central portion having a length equivalent to X wavelength from the same end. , the same operation as when the center part is grounded.

Moreover, since the strip line conductors 15 and 19 are not grounded for direct current, the lead electrodes 10 and 11 connected to the strip line conductors 15 and 19 to the external circuit must be connected via a DC blocking capacitor. It is possible to connect to an active element to which a DC voltage is applied.

The strip line conductors 16 to I8, which have one end grounded and the other end open, operate as electrodes that resonate at a frequency of about four times the wavelength of the strip line conductors 16 to I8, which have one end grounded and the other end open. l5 and l9 operate as electrodes that resonate at a frequency of approximately twice the wavelength of their 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 a bias voltage 33 is supplied from the end grounded by the capacitor 45 of the strip line conductor 41 of the wavelength range through a low-pass filter composed of a resistor 55 and capacitors 45 to 46. , the other end of the strip line conductor 4, which has a high impedance, is connected to the transmission line 37 for signal input, and the transistor 3 is connected to the signal input transmission line 37.
5 gate.

Bias voltage 3 applied to the gate of the transistor 35
3, the strip line conductor 4 at the wavelength of
The other end of the strip line conductor 42, which has a high impedance, is connected to the signal output transmission line 38, and current is supplied to the drain of the transistor 35 from the DC power supply 34. .

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 1 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 49-50 and a strip line conductor 4 of X wavelength.
A bias voltage 33 is applied via 3.

〔Example〕

In the embodiment of the present invention shown in FIG. 1, one end is open and the other end is connected to a lead-out electrode to an external circuit, and the lead-out electrode is used as an input terminal 10 and an output terminal 1, respectively, for a transmission signal band. Strip line conductors 15 and 19 having a length corresponding to two wavelengths of the center frequency are arranged parallel to each other in the length direction with their ends aligned.

A strip line conductor 1 having a length corresponding to the wavelength of the center frequency of the transmission signal band is installed between the strip line conductors 15 and I9 in parallel with the strip line conductors 15 and I9.
6 to I8 are arranged so that the ends of the strip line conductors 16 to 18 are aligned in a straight line with the ends of the strip line conductors 15 and 19 to which the extraction electrodes are connected. Arrange them so that the open ends and grounded ends alternate.

The strip line conductors 15 to 9 are arranged in parallel at intervals that provide a desired coupling capacity between adjacent strip line conductors.

Said stripline conductor! Items 5 to 9 are formed on the main surface of a dielectric substrate made of a material with a small dielectric loss and a high relative dielectric constant in the frequency band of the transmission signal, and a ground conductor is formed on the entire back surface of the dielectric substrate.

The ground ends of the strip line conductors 16 to I8 are grounded conductors (not shown) formed on the back surface of the dielectric substrate through holes 21 to 23 that penetrate the dielectric substrate and have a conductor plated around the periphery. Connect with.

The grounding at one end of the stripline conductors 16 to 18 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 connected to the ground end side of the strip line conductor 16 adjacent to the strip line conductor 5 of the strip line conductor 15.

Similarly to the strip line conductor I5, the strip line conductor 19 has an output terminal 1 at the ground end side of the strip line conductor I8 adjacent to the strip line conductor l9.
Connect the

The external extraction electrodes connected to the strip line conductors No. 5 and 19 are connected to the strip line conductors No. 5 and 19.
It can also be connected at a position where the impedance matches the external circuit, between the center in the length direction and one end with both ends open.

〔Effect of the invention〕

As in the present invention, the input stage and output stage strip lines constituting the interdigital filter are made to have a length equivalent to two wavelengths of the center frequency of the signal band to be transmitted, and by opening the ends, they are open to direct current. The state and transmission frequency are equivalently grounded to facilitate connection with active elements such as transistors and diodes without using capacitors of DC elements.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the interdigital filter of the present invention, Fig. 2 is an example of a circuit of a microwave amplifier using the interdigital filter of the present invention, Fig. 3 is an explanatory diagram of a conventional interdigital filter, and Fig. 4 is an example of the main circuit of a microwave amplifier using a conventional interdigital filter. In the figure, 10 is an input terminal, II is an output terminal, 45 to 54 are capacitors, 13 to 19 and 37 to 44 are strip line conductors, 20 to 24 are through holes, 30 is an interdigital filter of the present invention, and 3 is an amplifier. input terminal, 3
2 is an output terminal of an amplifier, 33 is a bias voltage, 34 is a DC power supply, 35 to 36 are transistors, 55 to 58 are resistors 60 is a conventional interdigital filter.

Claims (1)

[Claims] A full-surface ground conductor is formed on one surface of the dielectric substrate, and a plurality of stop lines each having a length of about a quarter wavelength of the microwave to be transmitted are provided on the other surface of the dielectric substrate, and a desired line is formed between adjacent strip lines. In an interdigital filter in which a plurality of strip lines are formed in parallel at predetermined intervals to generate coupling capacitance, one end of which is alternately grounded and the other end is open, and only one end of the same strip line is grounded, the external circuit The length of the input stage and output stage strip lines connected to the extraction electrodes of the input and output stages is approximately half a wavelength, and approximately a quarter wavelength is parallel to the strip lines between the input stage and output stage strip lines. An interdigital filter characterized by having a plurality of stop lines having a length of .