JPH05160602A - Strip line filter - Google Patents

Abstract

PURPOSE:To reduce insertion loss and to set the strip line width of a conductor line to such value that a strip line filter can be easily produced. CONSTITUTION:In the strip line filter where a conductor line 11 is arranged on a dielectric substrate 10 to form a strip line and there is at least one capacitor (inductor) 12 on the strip line, the line width of the strip line is widened, and a transforming circuit 13 for matching between the conductor line 11 and another circuit connected to this main line is provided, thus reducing the characteristic impedance of the conductor line 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stripline filter, and more particularly to a stripline filter composed of microstrip lines.

[0002]

2. Description of the Related Art Conventionally, in this type of stripline filter, as shown in FIG. 2, a conductor line (hereinafter referred to as "main line") 11 is formed on a dielectric substrate 10 made of ceramics or fused silica. Further, the capacitor (or inductor) 12 is arranged on the main line 11 in one or several stages.

[0003]

However, in the above filter, the design is made from the viewpoint of matching the characteristic impedance with other circuits, and the insertion loss is not considered so much. It is known that the insertion loss α is composed of a conductor loss α _C and a dielectric loss α _D, and is approximated by the following equation.

[0004]

[Equation 1]

Where R _S : Conductor resistance W: Stripline width Z ₀ : Stripline characteristic impedance ε _re : Equivalent permittivity of substrate ε _r : Relative permittivity of substrate h: Substrate thickness tan δ: Dielectric loss tangent of substrate λ: Free space wavelength of radio waves.

Here, for example, the relative permittivity ε _{r of the} substrate is 30,
Using a substrate with a substrate thickness h of 1 [mm], a frequency of 1 [GH
Z] (at frequency 1 [GHZ], the free space wavelength λ of the radio wave
When designing a one-stage stripline with 0.3 [m]),
When the characteristic impedance Z ₀ is 50 [Ω], the stripline width W is derived from equation (7), W = 0.237 [mm], and the conductor loss α _C is derived from equation (2),

[0007]

[Equation 2]

[0008] The equivalent dielectric constant ε _re of the substrate is
Derived from (4), ε _re = 18.019, and assuming that tan δ of the substrate is 10 ⁻³ , the dielectric loss α _D is
Derived from equation (3),

[0009]

[Equation 3]

The insertion loss α is derived from the equation (1), and α = α _C + α _D = 0.325 [NP / m]. Such insertion loss has a problem that the battery life of the telephone is shortened, and that the strip line width cannot withstand the production.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a stripline filter having a stripline width which can reduce insertion loss and can be easily manufactured.

[0012]

In order to solve the above-mentioned problems, according to the present invention, a conductor line is arranged on a dielectric substrate to form a strip line, and at least one capacitor and an inductor are provided on the strip line. In the stripline filter having, there is provided a stripline filter including a transformer for matching the characteristic impedance of a conductor line on the stripline.

[0013]

The characteristic impedance of the strip line can be matched, that is, the characteristic impedance can be lowered by the transformation means which is a transformation circuit. Therefore, the insertion loss can be reduced by reducing the characteristic impedance of the conductor line without reducing the stripline width of the conductor line.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawing of FIG. FIG. 1 is a configuration diagram showing a configuration of a stripline filter according to the present invention. In the figure, the same components as those in FIG. 2 are designated by the same reference numerals for convenience of description.

In FIG. 1, a transformer (transformer circuit) 13 is provided at the input / output portion of the main line 11 formed on the dielectric substrate 10 to match with other circuits connected to the stripline filter. There is. Here, as in FIG. 2, the relative permittivity ε _r of the substrate is 30 and the thickness h of the substrate is 1 [m
frequency 1 [GHZ] (frequency 1 [G
HZ] has a free space wavelength of radio waves λ = 0.3 [m]), a width of λg / 8 (λg is a wavelength on the dielectric substrate 10) or less, and a height from the center of the main line 11 to λg / 4. If the capacitor (or inductor) 12 is designed as a single-stage stripline, the characteristic impedance Z ₂ of the main line 11 is 14.8 [Ω].
In the case of, the stripline width W is W = 3.0 [mm] from the equation (8), and in order to realize the characteristic impedance Z ₀ = 50 [Ω] of the input / output section of the stripline filter as in FIG. Is the characteristic impedance Z ₁ of the transformer 13,

[0016]

[Equation 4]

Set to Also, Transformer 1
The line width of 3 is set to 1.09 [mm] from equation (8). Further, the conductor loss α _C of the main line 11 is derived from the equation (2), and α _C = 0.075 [NP / m]. Also, the equivalent permittivity ε _re of the substrate is derived from (4), and ε _re = 22.432, and assuming that tan δ of the substrate is 10 ⁻³ , the dielectric loss α _D is
Derived from equation (3),

[0018]

[Equation 5]

The insertion loss α is derived from the equation (1), and α = α _C + α _D = 0.125 [NP / m]. Similarly, the insertion loss of the transformer 13 part is derived as follows. α _C = 0.112 [NP / m] α _D = 0.0468 [NP / m] α = α _C + α _D = 0.159 [NP / m] As shown in Fig. 1, the lengths of the transformers 13 are λg / 4, respectively. , At frequency 1 [GHZ],

[0020]

[Equation 6]

Therefore, the insertion loss α _T of the transformers 13 at both ends is α _T = α · (λg / 4) · 2 = 0.159 × 0.06713 × 0.5 = 0.00534 [NP / m], and the total insertion loss is α = 0.0053 + 0.125 = 0.130 [NP / m].

Therefore, in this embodiment, since the transformer for matching with other circuits connected to the main line is provided in the input / output section of the main line, the main line is three times as large as the conventional example. The line width can be formed to facilitate manufacturing, and the characteristic impedance of the main line is 1/3 that of the conventional type.
The insertion loss can be reduced by lowering the insertion loss. As a result, it is possible to achieve matching with other circuits connected to the stripline filter.

[0023]

As described above, according to the present invention, a stripline filter having conductor lines arranged on a dielectric substrate to form a stripline and having at least one capacitor and an inductor on the stripline is provided. Since the transformation means for matching the characteristic impedance of the conductor line is provided on the strip line, the strip line width which can be easily manufactured can be formed and the insertion loss can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a stripline filter according to the present invention.

FIG. 2 is a configuration diagram showing a configuration of a conventional stripline filter.

[Explanation of symbols]

 10 Dielectric Substrate 11 Conductor Line (Main Line) 12 Capacitor (or Inductor) 13 Transformer (Transformer Circuit)

Claims (1)

[Claims] 1. A stripline filter having a conductor line on a dielectric substrate to form a stripline, and having at least one capacitor and an inductor on the stripline, the characteristic of the conductor line on the stripline. A stripline filter comprising a transformation means for matching impedance.