JPH04332210A - Band selective type ultra-high frequency band pass filter - Google Patents

Abstract

PURPOSE:To prepare a compact, high performance band pass filter that permits an amount of attenuation in correspondence with the pass band width of the band pass filter in conformity with the intensity of the receiving field in an ultra-high frequency band and that can switch arbitrarily and selectively. CONSTITUTION:Between stages of cascaded resonators RES1-RES5 each of which is grounded to input/output terminals of transmission lines, inductive coupling elements L1-L4 are connected, between the first resonator at the input terminal side and each hot point of resonators at the output side that hold resonators placed at even numbered stages counting from the first stage resonator, parallelly connected capacitors CC1-CC3 that are different in capacitor are laid in parallel in conformity with band width, and connected capacitors are selectively switched corresponding to a desired band by a single multiple changeover switch.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive, compact, and high-performance filter that can selectively switch the passband width of a bandpass filter used in the ultra-high frequency field such as a satellite broadcasting receiver.

0002

[Prior Art] Receivers for ultra-high frequency bands such as those used for satellite broadcasting use bandpass filters whose passband widths vary in width and narrowness in order to suppress noise, depending on the strength of the received electric field. In band-pass filters used in such ultra-high frequency bands, obtaining a steep change in attenuation is approximately determined by the number of cascaded filter stages, and the number of stages in the signal passband is proportional to the number of stages. Since the loss increases, the no-load Q of the resonator itself is increased to avoid this problem. However, this unloaded Q increases in proportion to the volume of the resonator, so in the end, in order to reduce the passing loss and obtain a steep attenuation amount, there is no choice but to increase the number of cascaded resonators and increase the shape of the filter. This would lead to a result that goes against the trend of miniaturization.

Therefore, in order to eliminate the above-mentioned drawbacks, an even number of stages (usually 4 stages or more) of band-pass filters as the main transmission line and a sub-transmission line coupled in parallel with the resonators at the input and output ends of the band-pass filter are provided. By providing attenuation poles on both sides of the band, the sub-transmission line is weakly coupled to the main transmission line, and in the passband, it has almost no effect on the main transmission line, and the propagation signal wave to the output side of the main transmission line and It is known that the propagation signals reaching the output side via the sub-transmission line have opposite phases to each other, so that if their amplitudes are equal, they cancel each other out.

There is also an example as shown in FIG. 3 in which the pass band of a high frequency band pass filter is switched according to wide/narrow selection. A high frequency band pass filter 12 having a narrow pass band width is provided in parallel via changeover switches SW1 and SW2 linked to the respective input and output sides, and the high frequency band pass filters are connected in parallel according to the number of switching of the pass band width. It is configured to increase the number of filters.

[0005]

[Problems with the Prior Art] By the way, in an example in which a resonator at the input/output end and a sub-transmission line are arranged in parallel to the conventional even-stage passband filter as the main transmission line, at least four or more even-stage filters are used. Not only can this method be applied only when a resonator is provided, but also the branch circuit that couples the resonators becomes complicated, and furthermore, it is difficult to control the attenuation pole with good reproducibility.

Furthermore, in an example in which a plurality of band-pass filters are arranged in parallel according to the width and narrowness of the passband and are selectively switched by interlocking switches provided at the input and output terminals, it is necessary to sequentially increase the number of high-performance and expensive band-pass filters. However, it is unavoidable that the filter is large, uneconomical, and occupies a large space for installing the filter.

[0007]

[Means for Solving the Problems] Thus, the present invention provides an inexpensive, high-performance, and compact structure in which a plurality of capacitors having capacitances corresponding to the passband width can be selectively switched by a single changeover switch. .

[0008]

[Embodiment] An embodiment of the present invention will be explained in detail below with reference to FIGS. 1 and 2. First, FIG. 1 is a circuit diagram of a band-selective ultra-high frequency band-pass filter according to the present invention, in which a transmission path from an input terminal I to an output terminal O includes a plurality of resonators RE, each of which is grounded.
S1 to RES5 are inter-stage coupled by inductive coupling elements L1 to L4, and each hot point is straddled between the input end side resonator RES1 and the resonator RES4 sandwiching the next even-numbered stage, that is, RES3. Therefore, a plurality of coupling capacitors CC1 to CC3, etc. having capacitances corresponding to the passband width are commonly connected in parallel to the hot point on the output end side, and a high frequency switch SW having a fixed contact at each open end is connected to the high frequency switch SW with its movable contact. It is arranged so as to be in contact with the hot point on the input end side.

Here, the above-mentioned parallel coupling capacitor has been changed to a capacitance of around 0.1 picofarad, and several tens of
It uses a NanoHenry inductive coupling element. The high frequency band pass filter may be of any type, such as a lumped constant type, a helical type, a dielectric type, or a strip line type.

FIG. 2 shows the relationship between the bandpass frequency and its attenuation based on the above configuration. In the figure, A is the characteristic when no coupling capacitor is inserted, and as the capacitance is increased from small to medium to large, the characteristics change as B, C, and D. From this, the center frequency remains almost unchanged and the passband width It is clearly seen that the curve becomes narrower as the capacitance of the coupling capacitor increases.

[0011]

[Effects of the Invention] As described above, in order to obtain a steep attenuation amount as an ultra-high frequency band-pass filter and to suppress the area occupied by the filter, each stage of the resonator is inductively coupled, and even number Coupling capacitors with different capacitances are configured to be selectively switched depending on the bandwidth between the hot points of the input and output side resonators sandwiching the resonator of the stage, and can be used as a passband filter. Since the desired bandwidth and attenuation can be reliably obtained without changing the center frequency, there is no need to use an expensive ultra-high frequency band-pass filter, and as a result, an inexpensive, compact, and high-performance filter can be obtained. .

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a band-selective ultra-high frequency band-pass filter of the present invention.

FIG. 2 is a characteristic graph showing the relationship between passband frequency and attenuation amount depending on the presence or absence of the coupling capacitor in FIG. 1;

FIG. 3 is a block configuration diagram showing a conventional example of a parallel filter switching type.

[Explanation of symbols]

I input terminal O
Output end RE
S1~RES5 resonator

Claims (1)

[Claims] 1. An ultra-high frequency band-pass filter in which each stage is grounded, the stages are cascade-connected by inductive coupling elements, and polarized capacitors are arranged in parallel across the input and output resonators, Inserting at least two or more even stage resonators,
having different capacitance between each hot point of the output side resonator, and having the output side commonly connected to the hot point,
A band-selective ultra-high frequency band-pass filter comprising a plurality of parallel coupled capacitors, each of which has a fixed switching contact at its open end, and a multiple switch that selectively switches the fixed switching contact. .