MICROWAVE FILTERS DESIGN

COURSE NOTES

Dr. Kawthar Zaki

Dr. Kawthar Zaki 2

INTRODUCTION

• DEFINITIONS & CLASIFICATIONS OF MICROWAVE FILTERS

• FREQUENCY RANGE : 200MHZ TO 90 GHZ

• LOW FREQUENCY TECHNIQUES & THEIR LIMTATIONS

• AT HIGHER FREQUENCIES OPTICAL TECHNIQUES & THEIR LIMITATIONS

• CLASIFICATION BY TYPE: (LP, HP, BP, BS)

• CLASIFICATION BY FRACTIONAL B.W.

• CLASIFICATION BY TRANSIMISSION MEDIUM

Dr. Kawthar Zaki 3

LOWER FREQUENCY TECHNIQUES LIMITATIONS

• LOW FREQUENCIES ARE DEFINED TO BE BELOW @ 200 MHZ

• LUMPED ELEMENT SIZES (R, L, C) BECOME COMPARABLE TO WAVELENGTH

• RADIATION FROM ELEMENTS CAUSES UNDESIRABLE EFFECTS

• INCREASED LOSSES

• WIRE CONNECTIONS BETWEEN ELEMENTS BECOME PART OF CIRCUIT (PARASETICS)

• SOURCES & MEASUREMENT TECHNIQUES ARE UNSUITABLE AT HIGHER FREQUENCY

Dr. Kawthar Zaki 4

CLASIFICATION OF FILTERS BY PASS BAND TYPES

Attenuation

Freq.

Attenuation

Freq.Attenuation

Freq.

Attenuation

Freq.

L. P. F H. P. F.

B. P. F.B. S. F.

0

0

0

0

fc fc

fofo

b.w.

b. w.

Dr. Kawthar Zaki 5

CLASIFICATION OF FILTERS (ctd.)

• BY FREQUENCY BANDS:BAND DESIGNATION FREQ. RANGE GHZ.

P 0.225 - 0.39 LOWER

L 0.39 - 1.55 R.F. BAND

S 1.55 - 3.90

C 3.90 - 6.20 MICROWAVE

X 6.20 - 10.9 BANDS

K 10.9 - 36.0

Q 36.0 - 46.0 MILLIMETER

V 46.0 - 56.0 WAVE

W 56.0 - 100.0 BANDS

Dr. Kawthar Zaki 6

CLASIFICATIONS BY RESPONSE TYPE (INSERTION LOSS FUNCTION)

• BUTTERWORTH OR MAXIMALY FLATE T( n

• TCHEBYCHEFF OR EQUAL RIPPLE PASS BAND: T(2 Tn(

• INVERSE TCHBYCHEFF MAXIMALLY FLATE PASS BAND & EQUAL RIPPLE STOP BAND T(2 Tn(

• ELLIPTIC FUNCTION OR QUASIELLIPTIC FUNCTION (EQUAL RIPPLE IN BOTH PASS BAND AND STOP BAND)

• BESSEL THOMPSON (FLATE GROUP DELAY)

Dr. Kawthar Zaki 7

CLASSIFICATION BY FRACTIONAL BAND WIDTH

• NARROW BAND FILTERS : RELATIVE (bw/fo) BANDWIDTHS LESS THAN @ 5%

• MODERATE BAND WIDTH : RELATIVE BANDWIDTHS BETWEEN @ 5% TO 25%

• WIDE BAND FILTERS : RELATIVE BANDWIDTHS GREATER THAN 25%

• TECHNIQUES USED FOR DESIGN OF EACH TYPE DIFFER SIGNIFICANTLY

Dr. Kawthar Zaki 8

CLASSIFICATION BY TRANSMISSION MEDIUM

• LUMPED & QUASI LUMPED ELEMENTS

• COAXIAL TRANSMISSION LINES

• MICROSTRIP LINES

• SUSPENDED SUBSTRATE LINES

• STRIP LINES

• RECTANGULAR OR CYLENDRICAL WAVEGUIDES

• HIGH DIELECTRIC CONSATANT FILLED (OR PARTIALLY LOADED) COAXIAL LINES OR WAVEGUIDES

Dr. Kawthar Zaki 9

FILTERS TRANSMISSION MEDIA

FREQUENCY BAND DESIGNATION

P L S C X K Q V W

RE

LA

TIV

E B

.W.

%

.01

.1

1.0

10.

100 LUMPEDLC

COAXIALDIELECTRICRESONATORS WAVEGUIDES

PRINTED CIRCUITSAND SUSPENDED SUBSTRATES

Dr. Kawthar Zaki 10

A:Coaxial Resonators, Ceramic DielectricB:Coaxial Resonators, Air DielectricC: Single Mode Cavity ResonatorsD: Single Mode Cavity Resonators, Delectrically LoadedE: HTS Planar Resonators

UNLOADED Q’S FOR BASESTATION FILTERS

100K

10K

1K

Qu

Cost

Size

A B

C

D

E

(Technology Drivers)

(Multiple Modes)

Technology Gap

Dual Mode, materials, etc.)

(MaterialsPlating)

Increased CircuitComplexity

Dr. Kawthar Zaki 11

IMPORTANCE OF MICROWAVE FILTERS

• FREQUENCY SPECTRUM ALLOCATION AND PRESERVATION

• INTERFERENCE REDUCTION OR ELIMINATION - RECEIVERS PROTECTION

• ELIMINATION OF UNWANTED HARMONICS & INTERMOD. PRODUCTS GENERATED FROM NONLINEAR DEVICES (MULTIPLIERS, MIXERS, POWER AMPLIFIERS)

• SIGNAL PROCESSING & SPECTRUM SHAPING

• FREQUENCY MULTIPLEXING

Dr. Kawthar Zaki 12

APPLICATIONS OF MICROWAVE FILTERS

• COMMUNICATION SYSTEMS: – TERRESTRIAL MICROWAVE LINKS: RECEIVERS

PROTECTION FILTERS, TRANSMITTER FILTERS, CHANNEL DROPPING FILTERS, TRANSMITTER HARMONIC FILTERS, LOCAL OSCILLATOR FILTERS, MIXERS IMAGE REJECT FILTERS

– SATELLITE SYSTEMS:

» SPACE CRAFT: FRONT END RECEIVE FILTERS, INPUT MULTIPLEXERS CHANNELIZATION FILTERS, OUTPUT MULTIPLEXERS FILTERS, TRANSMITTERS HARMONIC REJECTION FILTERS

» EARTH STATIONS : LNA’S TRANSMIT REJECT FILTERS, HPA’S HARMONIC REJECT FILTERS, UP & DOWN CONVERTERS FILTERS

Dr. Kawthar Zaki 13

APPLICATIONS (ctd.)

• MOBILE AND CELLULAR SYSTEMS :– BASE STATIONS RECEIVE PROTECTION

– BASE STATIONS TRANSMITTERS FILTERS

– SUBSCRIBERS HAND SETS DIPLEXERS

– SATELLITE MOBILE APPLICATIONS

» AERONAUTICAL TX/RX SYSTEMS

» MARITIME SATELLITE TERMINALS

» LAND MOBILE SATELLITE TERMINALS

• RADAR SYSTEMS

• HIGH POWER APPLICATIONS

Dr. Kawthar Zaki 14

TYPICAL COMMUNICATIONS REPEATER

Antenna

Tx RejectFilter

LNA

LO

Up ConverterInput

Multiplexer

Power Amplifiers

OutputMultiplexer

Dr. Kawthar Zaki 15

HOW TO SPECIFY FILTERS

• FREQUENCY SPECS: f0 & BW (FOR B.P. OR B.S.), fc (FOR L.P. OR H.P.)

• PASS BAND INSERTION LOSS, RETURN LOSS AND FLATNESS (RIPPLE LEVEL)

• PASS BAND GROUP DELAY VARIATION

• SELECTIVITY OR SKIRT SHARPNESS

• OUT OF BAND REJECTION LEVELS

• SPURIOUS OUT OF BAND RESPONSE

• SPECIFICATIONS MASK

Dr. Kawthar Zaki 16

HOW TO SPECIFY FILTERS(ctd.)

• POWER HANDLING CAPABLITY– MULTIPACTOR EFFECTS & VOLTAGE BREAKDOWN

• ENVIRONMENTAL SPECIFICATIONS– OPERATIONAL TEMPERATUE LIMITS

– PRESSURE & HUMIDITY ENVIRONMENTS

– SHOCK & VIBRATION LEVELS

• MECHANICAL SPECIFICATIONS– SIZE, SHAPE & WEIGHT

– TYPE OF INPUT/OUTPUT CONNECTORS

– MECHANICAL MOUNTING INTERFACES

Dr. Kawthar Zaki 17

TYPICAL INSERTION LOSS SPECIFICATION MASK

FREQUENCYf0 (4000 MHz)

INSERTION LOSS0.6dB

BW36 MHz

= dB

40 dB

50dB60 dB

70 dB

Dr. Kawthar Zaki 18

TYPICAL GROUP DELAY SPECIFICATION MASK

FREQUENCYf0 (4000 MHz)

GROUP DELAY

Dr. Kawthar Zaki 19

METHODS OF FILTER DESIGN1. IMAGE PARAMETER METHOD (EARLY 1920’S)

•BASED ON A WAVE VIEWPOINT OF CIRCUITS

1 2

ZI2

2 1

ZI2 ZI1

1 12 2

ZI1 ZI2ZI2

Etc. toInfinity

Etc. toInfinity

• IMAGE IMPEDANCES ZI1, ZI2 AND IMAGE PROPAGATION FUNCTIONARE DEFINED BY:

ZI2

ZI2E2

I2

E1

ZI1

ZI1

I1

+

-

+

-Eg e = (E1/E2) (ZI2 / ZI1)1/2

Dr. Kawthar Zaki 20

CONSTANT K-HALF SECTIONS

L1 = 1

C2 = 1ZI2ZI1

ZI1, ZI2

RI2

RI1

j XI1

j XI2

Dr. Kawthar Zaki 21

M-DERIVED HALF SECTIONS

ZI1, ZI2

RI2

RI1

j XI1

j XI2

L1 = m

C2 = mZI2

ZI1

L=(1-m2 )/m

=1/(1-m2)1/2

Dr. Kawthar Zaki 22

IMAGE PARAMETER FILTERS DESIGN

• PIECE TOGETHER ‘ENOUGH’ CONSTANT-K & M-DERIVED SECTIONS TO MEET REQUIRED ATTENUATION

• TERMINATION WILL BE DIFFERENT FROM THE IMAGE IMPEDANCE

• END SECTIONS ARE DESIGNED TO IMPROVE MATCH

Dr. Kawthar Zaki 23

2. INSERTION LOSS THEORY SYNTHESIS (DARLINGTON, 1939)

• SPECIFY TRANSFER FUNCTION OF COMPLEX FREQ. SATISFYING REALIZABILITY CONDITIONS

• FIND INPUT IMPEDANCE OR REFLECTION COEFFICIENT FROM TRANSFER FUNCTION

• DECOMPOSE TRANSFER FUNCTION & REFL. COEEF. TO TWO CASCADED PARTS:

– A PART CORRESPONDING TO A SIMPLE SECTION OF KNOWN PARAMETRS

– A PART OF LOWER ORDER THAN THE ORIGINAL TRANSFER FUNCTION ALSO SATISFYING REALIZABILITY CONDITIONS

• REPEAT SYNTHESIS CYCLE UNTILL REMAINING SECTION IS OF ZERO ORDER (CONSTANT TERMINATION)

• COMMON METHODS ARE CASCADE SYNTHESIS, PARTIAL AND CONTINUOUS FRACTION EXPANSIONS.

Dr. Kawthar Zaki 24

EXAMPLE OF CASCADE SYNTHESIS CYCLE

FILTER TO BE SYNTHESIZED

(UNKNOWN)

T(s) = P(s)/Q(s)T(j) < 1 ; - <Q(s) Strictly Hurwitz

8 8

REMAINING UNKNOWNSECTION

T1(s) = P1(s)/Q1(s)

2

Extracted Sectionof Known Elements

and Values

T1(j) < 1 ; - <Q1(s) Strictly Hurwitz

8 8

2

PowerAvailMax

PowerOutputjT

. .

2

Dr. Kawthar Zaki 25

3. COMPUTER-AIDED DESIGN AND OPTIMIZATION

• START BY SPECIFICATIONS OF DESIRED RESPONSE OVER A BAND OF FREQUENCIES AND A GIVEN NETWORK OF ELEMENTS OF KNOWN (ASSUMED) STARTING VALUES

• ANALYZE THE NETWORK TO FIND IT’S RESPONSE OVER THE SPECIFIED FREQUENCY BAND

• COMPARE THE CALCULATED RESPONSE TO THE DESIRED RESPONSE BY FORMING AN ERROR FUNCTION

• CHANGE THE ELEMENT VALUES OF THE NETWORK (WITHIN CERTAIN BOUNDS) ACCORDING TO CERTAIN PRESCRIBED RULES TO MINIMIZE THE ERROR FUNCTION

• ITERATE THE PROCESS UNTILL THE ERROR FUNCTION IS REDUCED TO ZERO, DOES NOT DECREASE IN SUCCESSIVE ITERATIONS OR A PRESPECIFIED NUMBER OF ITERATIONS IS EXCEEDED

Dr. Kawthar Zaki 26

FILTER REALIZATIONS

• LOW PASS AND HIGH PASS SEMI-LUMPED ELEMENTS– COAXIAL

– MICROSTRIP & STRIPLINE

• BAND PASS NARROW AND MODERATE BANDWIDTHS– COAXIAL “DUMBELL”

– MICROSTRIP PARALLEL COUPLED AND END COUPLED

– SUSPENDED SUBSTRATE

– INTERDIGITAL, COMBLINE (COAXIAL)

– WAVEGUIDES: RECTANGULAR, CIRCULAR SINGLE & DUAL MODE AND RIDGE WAVEGUIDE

– DIELECTRIC OR METALLIC LOADED RESONATORS

• BAND STOP FILTERS

Dr. Kawthar Zaki 27

LOW PASS COAXIAL FILTERS

COAXIAL CONNECTORHIGH IMPEDANCE LINES

(SERIES L’S)

LOW IMPEDANCE LINES(SHUNT C’S)

SEMI-LUMPED ELEMENTS EQUIVALENT CIRCUIT

DIELECTRICSLEEVE

Dr. Kawthar Zaki 28

HIGH PASS COAXIAL FILTERSSHUNT L

SERIES C

COAXIAL CONNECTOR

SEMI-LUMPED ELEMENTS EQUIVALENT CIRCUIT

Dr. Kawthar Zaki 29

MICROSTRIP LOW PASS FILTERS

METALIZED CIRCUIT PATTERN

DIELECTRIC SUBSTRATE OVER GROUND PLANE

Dr. Kawthar Zaki 30

BAND PASS COAXIAL FILTERS

DIELECTRICSLEEVERESONATORS

SERIES CAPACITORS

‘DUMBELL’ BANDPASS COAXIAL FILTER

Dr. Kawthar Zaki 31

PARALLEL COUPLED LINES

DIELECTRIC SHEET

OUTER CONDUCTOR & HOUSING

CENTER CONDUCTOR PATTERN

SUSPENDED SUBSTRATE LINE

• MICROSTRIP PRINTED CIRCUIT REALIZATION• RECTANGULAR COUPLED BARS FOR WIDER BANDWIDTHE & HIGHER Q’S• POSSIBLE SUSPENDED SUBSTRATE REALIZATION (HIGHER Q)

OVERLAY COUPLED LINES

Dr. Kawthar Zaki 32

BANDPASS END COUPLED MICROSTRIP FILTERS

METALIZED CIRCUIT PATTERN RESONATORS

DIELECTRIC SUBSTRATE OVER GROUND PLANE

Dr. Kawthar Zaki 33

INTERDIGITAL & COMBLINE BAND PASS FILTERS

INNER CONDUCTORS OFCOAXIAL RESONATORS

SHORT CIRCUIT END

COUPLING IRIS

TOP VIEW SIDE VIEW

OPEN CIRCUIT END

Dr. Kawthar Zaki 34

WAVEGUIDE FILTERS

INDUCTIVE WINDOWS (MODERATE BANDWIDTHS)

DIRECT COUPLED USING IRIS (NARROW BANDWIDTHS)

Dr. Kawthar Zaki 35

RIDGE WAVEGUIDE FILTERS

Dr. Kawthar Zaki 36

DUAL MODE CIRCULAR WAVEGUIDE FILTERS

1

23

456

INPUTIRISOUTPUT

IRIS

TUNING SCREWS

Dr. Kawthar Zaki 37

Dual Mode Dielectric or Conductor Loaded Resonator Filter

1

23

45

6

Dielectric or Conductor Loading

Input Coax Probe

Output Coax Probe

Dr. Kawthar Zaki 38

Dual Mode Dielectric or Conductor Loaded Resonator Filter in Rectangular Enclosure

8-Pole Dual Mode Longitudinal Dielectric or Conductor LoadedResonator Filter in Rectangular Enclosure

M12M23

M14 M34M45

M56M36

M78

M67

M58