JPH04239202A - Micro wave circuit - Google Patents

Abstract

PURPOSE:To improve image disturbance suppression ratio. CONSTITUTION:A wave absorber 1 made up of foamed body is constructed incorporating carbon with taking polyethylene as a base. An aluminum foil 2 is stuck on the surface of the wave absorber 1 opposite to a dielectric substrate 3. The wave absorber 1 with this aluminum foil 2 is arranged inside a case 4 so as to be faced with the pattern of the band-pass filter of the dielectric substrate 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave circuit including a filter used in satellite broadcasting and communication satellite receivers, microwave communication equipment, and the like.

0002

[Prior art] LNB (Low N
oise Block down convert
When configuring a frequency-selective bandpass filter 5 in a microwave circuit typified by R), a pattern like the one shown in FIG. A structured microstrip filter is common.

[0003] Furthermore, the above-mentioned microwave circuit is housed in a metal case 4 mainly made of die-cast aluminum, as shown in FIG. 7, in order to ensure weather resistance and shielding properties. Here, the characteristics of the bandpass filter 5 change under the influence of the metal case 4 and deviate from desired characteristics. To counter this, metal partitions are added or radio wave absorbers 1 are placed at appropriate locations.

0004

Desirable characteristics of a bandpass filter include low transmission loss in the passband and good selectivity (transmission loss is large outside the passband). In the case of a bandpass filter used inside the LNB, the frequencies for evaluating its selectivity include a local oscillation frequency point and an image frequency band. The function of LNB is to reduce the frequency of the input signal to an intermediate frequency band, which is the difference frequency between the signal frequency band and the local oscillation frequency, but it also lowers the frequency of the input signal to an intermediate frequency band, which is the difference frequency between the signal frequency band and the local oscillation frequency. Even if a disturbance wave of

[0005] As a characteristic indicating the strength against this interference wave, there is a characteristic of image interference suppression ratio. The present invention has been provided in view of the above-mentioned points, and provides a microwave circuit aimed at improving the image interference suppression ratio.

[0006]

[Means for Solving the Problems] In the present invention, a radio wave absorber whose surface is coated with metal is disposed on the inner surface of the case facing the filter pattern and on the side facing the dielectric substrate.

[0007]

[Operation] Metal is provided on the surface of the radio wave absorber, and the image interference suppression ratio is improved by spatial processing within the metal case.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. The pattern of the bandpass filter on the dielectric substrate 3 shown in FIG. 1 is similar to that of the conventional example, and the dielectric substrate 3 is surrounded by a metal case 4. Here, the internal distance h between the upper and lower cases 4 is 10 mm, and the radio wave absorber 1 made of foam is made of polyethylene containing carbon, and its surface resistance value is 10 6 Ω or less. The width is about 10mm, the length is about 20mm (thickness is 2mm)
), and the surface facing the dielectric substrate 3 has a thickness of 40~
60 μm (in terms of characteristics, it may be outside this range, but 100 μm
, 60 μm. In addition, the thickness is such that it does not cause waves. ) of aluminum foil 2 is pasted as shown in FIGS. 1 and 2. Furthermore, as a processing issue, the aluminum foil 2 is made to have a thickness that will not cause burrs or the like when punched out with a die.

[0009] Radio wave absorber 1 with aluminum foil 2 pasted on it
is arranged on the inner surface of the case 4 so as to face the bandpass filter pattern of the dielectric substrate 3. Figure 3 shows data on the image interference suppression ratio. A is the RF signal (-70d
Bm) indicates the IF output level at the time of input, B indicates the IF output level at the input of the image frequency band (-40 dBm) in the conventional configuration shown in FIG. 7, and C indicates the IF output level at the input of the image frequency band (-40 dBm), This shows the IF output level when the image frequency is input. Therefore, it can be seen that in the case of the present invention, the IF output level when the image frequency is input is lower, that is, the image interference suppression ratio is improved. In other words, it is considered that the selectivity of the bandpass filter is improved.

FIGS. 4 and 5 show another embodiment, in which a radio wave absorber 1 made of a foam to which aluminum foil 2 is pasted is doubled. Moreover, it is good also as multilayered with two or more layers.

[0011]

[Effects of the Invention] As described above, the present invention has a radio wave absorber having a metal surface on the inner surface of the case facing the filter pattern and the side facing the dielectric substrate. It is possible to improve the image interference suppression ratio by providing metal on the surface of the body and spatial processing inside the metal case. It is possible to obtain the desired filter characteristics with the filter housed in the case without changing the shape, and it can be configured at low cost.Also, the position of the filter can be changed by changing the layout of the pattern on the dielectric substrate. This also has the effect of being flexible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a microwave circuit according to an embodiment of the present invention.

FIG. 2 is a perspective view of a radio wave absorber and aluminum foil.

FIG. 3 is a characteristic diagram showing measurement data of image interference suppression ratio of LNB.

FIG. 4 is a sectional view of another embodiment.

FIG. 5 is a perspective view of a radio wave absorber and aluminum foil.

FIG. 6 is a pattern diagram of a microwave bandpass filter.

FIG. 7 is a cross-sectional view of a conventional microwave circuit.

[Explanation of symbols]

1 Radio wave absorber 2 Aluminum foil 3 Dielectric substrate 4 Case 5 Bandpass filter

Claims (1)

[Claims] 1. A microwave circuit having a pattern formed as a filter on a dielectric substrate, the dielectric substrate being surrounded by a metal case, wherein a dielectric is provided on the inner surface of the case facing the filter pattern. A microwave circuit characterized in that a radio wave absorber having a metal surface is arranged on the side facing the body substrate.