JPH03145301A - Band filter for comb line filter type microwave - Google Patents

Abstract

PURPOSE: To widen a passing frequency band by including a common low impedance transmission line in a comb filter and specifying the length and the width of this low impedance transmission line. CONSTITUTION: This filter is formed by inserting the common low impedance transmission line 9 between the earth ends of five fingers 1 to 5 and an earth. Here, the length L of the line 9 is almost equal to the length of a filter, a width I is almost equal to the width of each of the fingers 1 to 5, and the transmission line 9 is fixed to the earth ends of the five fingers 1 to 5 by welding or soldering. Thus, a hitherto circuit has approximately 15MHz 17MHz of the passing frequency band of the comb filter, but here it becomes 36MHz. Thus, a passing frequency band is widened by one comb filter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a comb filter or a comb filter.
e) Relates to filter-type microwave bandpass filters.

Among microwave bandpass filters, the comb filter is a lumped constant filter that can achieve the best balance between insertion loss and response with a small volume.

Although this filter is constructed in microstrip or three-plate technology and can be directly applied to 8 old C integrated circuits, the response is accompanied by some problems with respect to F-waves.

FIG. 1 shows an example of a known tB tooth-shaped filter.

The filter is a triode filter with five parallel transmission line sections 1-5, each length equal to 178 of the central operating wavelength of its band. Each of these transmission lines or "fingers" is shorted to ground at one end and connected to ground via a tuning capacitor 6 at the other, free end. The tuning capacitor is for adjusting the resonant frequency of each resonator, such as resonator 1. Coupling capacitors 7 and 8 constitute the input and output elements of the filter, respectively.

This type of filter has the disadvantage that the pass frequency band is fixed depending on the specific physical structure. Therefore, especially in satellite communication systems, two comb filters of significantly different sizes must be provided, since two bandwidths are usually required (typically 36 MHz and 72 MHz). Nevertheless, comb filters are used in frequency transponders (transp) used in bands C and Ku.
There is an extremely strong desire to use this because it satisfies the requirement that it be small enough to be integrated with OSILions.

The purpose of the invention is to eliminate the drawbacks of this type of filter.

Accordingly, the present invention provides a comb filter type microwave bandpass filter including a plurality of parallel transmission line sections of equal length. Each transmission line section has a first end shorted to ground along a first line perpendicular to the length of the transmission line section. The characteristics of this filter are that the second end, which is the free end of the transmission line portion, is both connected to the ground via a tuning capacitor, the input element and the output element of the filter are constituted by a coupling capacitor, and the filter is Furthermore, we have three common low-impedance transmission lines, and this common transmission line is
a first end of the transmission line portion to a second line parallel to the seventh spin such that the green of the common transmission line furthest from the first line is at a predetermined distance from the first line; They are interconnected along the lines.

Hereinafter, the present invention will be explained in more detail by way of non-limiting examples based on the accompanying drawings.

1. The filter shown in Fig. 2 is obtained by modifying the comb-shaped filter shown in Fig. 1 and inserting a common low impedance transmission line 9 between the ground ends of the five fingers 1 to 5 and the ground. It is composed of In this example, the length L of &19 is approximately equal to the length of the filter, and the width l is approximately equal to the width of each finger 1-5. In this embodiment, the transmission line 9 is connected to five fingers by welding or soldering.
~5 is fixed to the ground end. Therefore, the pass frequency band of the comb filter, which was approximately 15 MHz to 17 MHz in the circuit shown in Figure 1, is approximately 36 MHz in the circuit shown in Figure 2.
become. With this new finger (FIG. 2), the access matching performance is maintained, but the characteristic impedance of fingers 1 to 5 is reduced, so readjustment of the tuning capacitor 6 is necessary.

The filter in FIG. 3 also has a similar structure to that in FIG. 2, but in this case, the low impedance transmission line 10 has the same length as the low impedance transmission line 9 in FIG.
° has doubled. Therefore, the new filter of FIG. 3 has a wider pass frequency band, extending to about 72 MHz.

If the width l is further widened, the passing frequency band will also be wider,
In this way, the pass frequency band can be varied in the range of 1 to 10.

FIG. 4 shows a highly advantageous filter embodiment having the same performance as the filter of FIG. The filter of this embodiment is formed by soldering (-t) a tin-plated wire 11 in line with the ground plane at a distance 11 from the ground end of fingers 1 to 5. From the crucible point it functions in place of the metal strip 9 of FIG.

FIG. 5 also shows a similar wire 11 connected at a distance AM(
It is shown that a filter having the same performance as the filter in FIG. 3 can be obtained by arranging the filter with a difference of 1'.

6 and 7 show filter embodiments corresponding to FIGS. 2 and 3 respectively, but in this case the low impedance transmission lines 9 and 10 are integrated entirely into the filter structure. Each low impedance transmission line and finger assembly, ie, fingers 1-5 and 1 transmission line 9 and fingers 1-5 and transmission line IO, are each constructed as a single block.

Filters of this type can also be manufactured in stripline technology, three-plate technology and integrated technology (suitable for MMrC). When the strips 9 and 10 are later installed, they can be fixed by soldering or by hot compression with screws.

Figures 8 and 9 illustrate a particular embodiment formed using a three-plate technique.

In these figures, the fingers 12 and the low-impedance transmission line 13 are constructed from a single metal member, which is threaded so that another plate can be screwed on if the filter's passband needs to be expanded. A hole 14 is provided. The casing 15 is normally used both for the comb filter itself and for the rest of the circuit (for example a group propagation delay corrector) on which it is integrated.

The comb filter itself is closed by a screw-on lid 16 (screws 17 and 18) [20 closes the casing 15 by screws 18 and 19].

The filter described above provides the following possibilities.

You can introduce a specific band of your choice.

The pass frequency band can be easily modified during the life of the product.

Over a very wide pass frequency band, an optimal balance can be achieved between the coupling sensitivity related to the positional accuracy of the finger pairs and the physical realization of a low impedance transmission line (for maximum capacitance values).

The stripline and three-plate technology manufacturing method is suitable for producing similar filters in the 100 MHz to 10 GIIz range.

Although other propagation media may be used, the present invention provides an integrated filter (with a pass frequency band of 500 MHz to 3 Gtlz).
) and future 3GIIz to 20Gtlz integrated filters.

Of course, the present invention is not limited to the embodiments described above, and may be modified in various ways within its scope.

[Brief explanation of the drawing]

FIG. 1 is a simple explanatory diagram showing an example of a prior art filter, FIGS. 2, 3, 4, 5, 6 and 7.
The figures are explanatory diagrams showing six embodiments of the filter of the present invention, FIG. 8 is a partially exploded perspective view of the three-plate type filter of the present invention, and FIG. 9 is a partial sectional view of the filter of FIG. 8. 1 to 5...Finger, 6...Tuning capacitor, 7,8...Coupling capacitor.

Claims (5)

[Claims] (1) A comb filter-type microwave bandpass filter including a plurality of parallel transmission line sections of equal length, the first end of each transmission line section being a first end perpendicular to the longitudinal direction of these transmission line sections. along the line, the second free end of each transmission line section is connected to ground through a respective tuning capacitor, and the input and output elements of the filter are connected to a coupling capacitor. It consists of
The filter further includes a common low-impedance transmission line, the common transmission line being connected to the transmission line such that the edge of the common transmission line furthest from the first line is a predetermined distance from the first line. A comb filter type microwave bandpass filter, characterized in that first ends of the sections are interconnected along a second line parallel to the first line. 2. The filter of claim 1, wherein the length of the common low impedance transmission line is substantially equal to the total length of the filter across the widths of the plurality of parallel transmission line sections. 3. The filter of claim 1, wherein a low impedance transmission line is attached to the ground end of the plurality of parallel transmission line sections. (4) A low impedance transmission line is formed by welding or soldering a tin-plated wire to a plurality of parallel transmission line sections parallel to the ground plane at a predetermined distance from the ground end of said transmission line section. The filter according to claim 1. (5) The low impedance transmission line is continuously integrated into the filter structure, and the plurality of parallel transmission line sections and the common transmission line are formed from a single conductive member. filter.