RF匹配设计——英文

Lecture 3 Richard Li, 2008 1

Lecture 3 : Impedance matching in narrowband case

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1. Introduction

2. Impedance Matching by Means of Return Loss Adjustment

o Return Loss Circles on Smith Chart

o Relationship between Return Loss and Impedance Matching

o Value of Parts

o Selection of Topology

5. Impedance Matching Network Built by Three Parts

o “Π” and “T” Types

o Recommended Topologies

6. Impedance Matching when Z

or Z

is not 50 Ω Parts in an

Impedance Matching Network

Lecture 3 Richard Li, 2008 2

Figure 1 A trace displayed in Smith Chart from RL (S

V

U

LH

Lecture 3 Richard Li, 2008 3

such as, γ =1, RL=0 dB, γ=0.79, RL=-1 dB, γ=0.63, RL=-2 dB, and so on.

Note 2: Normalized resistance, r, is bold-marked with values around the biggest circle,

Such as, 0, 0.1, 0.2, 0.5, 1, 1.5, 2, 3, 5, 10, ∞, -10, -5, -3, -2, -1.5, -1, -0.5, -0.2, -0.1.

Note 3: Normalized reactance, x, is bold-marked with values along the horizontal axis U,

Such as, 0, 0.2, 0.5, 1, 2, 5, ∞.

Figure 2 Constant return loss S

11, dB

or S

22, dB

circles on Smith Chart

V

U

∞

ã=0.79, RL=-1 dB

ã=0.63, RL=-2 dB

ã=0.50, RL=-3 dB

ã=0.40, RL=-4 dB

ã=0.32, RL=-5 dB

ã=0.25, RL=-6 dB

ã=0.20, RL=-7 dB

ã=0.10, RL=-10 dB

ã=0.03, RL=-15 dB

Lecture 3 Richard Li, 2008 4

RL = S

11

or S

22

= - 15 dB,

Table 1 Variation of return loss RL along with U axis (V=0)

Resistance, Reference Normalized Power Ref. Return loss,RL

Lecture 3 Richard Li, 2008 5