ELEC 412 - Lecture 14 1

ELEC 412 RF

& Microwave Engineering

Fall 2004

Lecture 14

ELEC 412 - Lecture 14 2

Lumped Parameter Band-Pass Filter Design

Design an N=3 band-pass maximally flat (Butterworth) filter with a center frequency of 900 MHz. The Bandwidth of the filter is 20% ; That is, BW = (0.20)(900 MHz) = 1.8 MHz or 0.9 MHz.

From the Maximally Flat Low Pass Prototype Table 5-2,

g0 = g4 = 1, g1 = g3 = 1, g2 = 2

ELEC 412 - Lecture 14 3

Low Pass Prototype Filter

RSg0=1

L1g1=1

C2g1=2

L3g3=1

RLg4=1

Where the normalized center frequency is

c = 1, L = 1.1(2·900 MHz), and

U = 0.9(2·900 MHz)

So that U - L = 1.13Grad/s and Grad/s627.5 ULo

ELEC 412 - Lecture 14 4

Finding the Filter Components

nH4450 131

LU

gLL

pF713.050

1

1231

gCC

o

LU

nH892.0502

22

gL

o

LU

pF2.3550

1 22

LU

gC

ELEC 412 - Lecture 14 5

Filter Simulation with Ansoft Designer

ELEC 412 - Lecture 14 6

Filter Simulation with Ansoft Designer

ELEC 412 - Lecture 14 7

Some Observations On The Results

• Values of components are unreasonable

• Some other method for implementing the filter design goals must be found

• Solution: Use distributed filters using waveguides

• Richardson Transforms and Kuroda’s Identities

ELEC 412 - Lecture 14 8

Richards Transformation: Lumped to Distributed Circuit Design

jXL

jBC

L

C

l/ 8 at c

l/ 8 at c

Zo = 1/(j C)

Zo = j L

ELEC 412 - Lecture 14 9

Kuroda Transforms