JPS6320042B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-reflection termination for strip lines used in microwave ICs and the like.

Currently, microwave equipment is becoming significantly smaller and more reliable by using ICs such as microstrip lines. Microwave IC like this
In a circuit, a non-reflection termination with very strict characteristics is required to convert a circulator into an isolator or to an isolation port of a directional coupler.

For example, in the case of a non-reflection termination when a circulator is converted into an isolator, the reflection characteristics of the non-reflection termination become the isolation characteristics as they are, and very good characteristics are required. For example, if the input VSWR of the non-reflection termination is 1.2, it is no longer possible to obtain isolation of 20 dB or more. Also, when measuring the characteristics of coaxial-stripline converters, it would be good to be able to use IC-based non-reflection terminations, but in that case, a non-reflection termination with a reflection VSWR of about 1.1 to 1.2 is required, which is much better than the reflection VSWR of these converters. It is.

Figure 1 shows a conventional thin film non-reflective termination.
A thin film resistor 4 having a resistance value equal to the characteristic impedance (usually 50Ω) is formed at the end of a microstrip line in which a grounding conductor film 2 and a line conductor film 3 are formed on the lower surface of a dielectric substrate 1, and a short circuit is established. Grounding was performed using a conductor 5. In this case, the shape of the thin film resistor is designed without regard to high frequency characteristics; it can be simplified by making it the same width as the microstrip conductor as in a, or it can be made into a mesh-like diamond shape to improve power characteristics as in b. I was doing it. However, the resistive film itself has a small amount of inductance, and there is also a small amount of capacitance between it and the ground conductor. Therefore, at very low frequencies, these unnecessary reactances can be ignored, but at high frequencies such as microwaves, they can no longer be ignored with respect to the resistance value, causing unnecessary reflections, which is a problem.
Even at low frequencies such as the UHF band, high-power non-reflection terminations become larger in size, and their unnecessary inductance or capacitance cannot be ignored.

Conventionally, it has been unclear how to design non-reflection terminations including these, and it has not been possible to use non-reflection terminations for ICs with guaranteed characteristics that are sufficiently good in the microwave band. Therefore, the non-reflective termination shown in Figure 1 is used only in places where very strict characteristics are not required, and in places where strict characteristics are required, the coaxial type non-reflective termination is used after converting to coaxial using a connector. Termination was often used.

The purpose of this application is to provide a non-reflection termination with extremely good characteristics that can be applied to microwave ICs in terms of circuitry and manufacturing, based on a design method for a non-reflection termination that includes unnecessary reactance. It is in.

According to the present invention, the resistance value of the thin film resistor is adjusted to the characteristic impedance Z _p at the non-reflection termination in which the end of the strip line with the characteristic impedance Z _p is short-circuited through the thin film resistor, and in parallel with the thin film resistor section,
When the thin film resistor is replaced with a conductor film of the same shape, the inductance per unit length is L _p , the capacitance is C _p , and the length is l, approximately. A reflection-free termination for a strip line is obtained, which is characterized in that a capacitor C _a is inserted so that the following holds true.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view showing a non-reflective termination used to explain the present invention. In the figure, the non-reflective termination includes a dielectric substrate 1, a grounding conductor film 2, a line conductor film 3,
It consists of a thin film resistor 4 and a shorting conductor 5.

Now, consider a thin film resistor of length l as shown in diagram a as a lossy distributed constant line, and its input impedance Z _i
When calculated, Z _i =Z _R tanh γl (1). However, Z _R is the characteristic impedance of this resistance value, γ is its propagation constant, ω is the angular frequency, R _p is the resistance per unit length of the thin film resistor, L _p is the inductance, and C _p is the capacitance to ground. Ba γ=√ _p ( _p + _p ) (3). However, √-1=j.

If l is sufficiently small and the thin film resistance is considered to be a lumped constant, and γl≪1, then equation (1) can be transformed as follows using equations (2) and (3).

Z _i = (R _p +jωL _p )l{1−jωC _p (R _p +jωL _p )l
² /3} (4) Furthermore, since the propagation constant value in equation (4) is small, it is transformed as follows.

Z _i = Rol + jωLol/1 + jωCol/3 (R _p 1 + jωL _p l) (5
) From the above equation, the thin film resistor section can be completely represented by an equivalent circuit as shown in FIG. 3 using lumped constant RLC elements. By the way, if we use the lumped constant condition ω ³ C _p L _p 1 ² <<1 assumed earlier, equation (4) becomes further as follows.

Z _i = R _p 1 + jωL _p l (1-C _p /L _p R _p ² l ² /3) The conditions for a good reflection-free termination without frequency characteristics are
Since Z _i =Z _p , R _p l=Z _p (6) If the relationship is maintained, a good reflection-free termination can be obtained. 50
When a thin film resistor coaxial with the Ω strip line conductor is used, unnecessary reactance occurs because the capacitance C _p l in this case is not large enough to satisfy equation (7).

Therefore, we added another parallel adjustment capacitor C _a to the thin film resistor section as shown by the dotted line in Figure 3 (6)
with the ceremony If the width of the thin film resistor section is set as follows, a good reflection-free termination can be obtained even if the width of the thin film resistor section is arbitrary.

FIG. 4a shows a first embodiment of the present invention based on the above principle, in which the width of the thin film resistor 4 is arbitrarily widened and the convex portion 9 provides the required capacitance C _a that satisfies equation (8). It is. b is another dielectric 10 on the thin film resistor 4
, and the required capacitance C _a is provided. c is the one in which the thin film resistor 4 is formed on this adjusting dielectric 10, and the thickness and relative dielectric constant of the dielectric 10 are adjusted.
If formula (8) is satisfied, it is easy to put it into practical use.

FIG. 5 is a diagram showing yet another second embodiment, in which an adjusting screw 1 is mounted on a thin film resistor 4 that satisfies equation (6).
1 and add the required capacitance C _a that satisfies equation (8). In this case, L _p l also varies, but it is practical because it is possible to provide the required amount C _a while observing the characteristics of the screw without having to strictly design the pattern. 55 is a short circuit terminal.

Although FIGS. 4 and 5 only show examples of either the microstrip type or the suspended triplate type, the principle of the present application can be applied to the triplate type and microstrip type, respectively, other than those shown. Needless to say, it can also be applied.

[Brief explanation of the drawing]

Figure 1 shows a conventional thin film non-reflective termination.
a, b are separate plan views, c is their center line
It is a cross-sectional view regarding AA'. 1 is a dielectric substrate, 2
3 is a conductor film for grounding, 3 is a line conductor film, 4 is a thin film resistor, and 5 is a conductor film for shorting. FIG. 2 is a perspective view showing a non-reflective termination used to explain the present invention. Components that are the same as those in FIG. 1 are indicated with the same symbols. (Similarly below) FIG. 3 is an explanatory equivalent circuit diagram. FIG. 4 is a diagram showing the first embodiment, in which a and b are a plan view and c is a sectional view. 9
1 is a line conductor convex portion, and 10 is a dielectric. FIG. 5 is a cross-sectional view showing the second embodiment.
6' is a grounding conductor, 11 is an adjustment screw, and 55 is a short-circuit terminal.

Claims (1)

[Scope of Claims] 1. A non-reflective termination in which the terminal end of a strip line with a characteristic impedance Z _p is short-circuited through a thin film resistor, the resistance value of the thin film resistor is adjusted to the characteristic impedance Z _p , and the thin film resistor is connected in parallel to the thin film resistor. When the resistor is replaced with a conductor film of the same shape, the inductance per unit length is L _p , the capacitance is C _p , and the length is l. A non-reflection termination for a strip line, characterized in that a capacitor C _a is inserted so that the following holds true.