MICROWAVE FILTERS DESIGN

1
MICROWAVE FILTERS DESIGN

• COURSE NOTES

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

3
LOWER FREQUENCY TECHNIQUES LIMITATIONS

• LOW FREQUENCIES ARE DEFINED TO BE BELOW _at_ 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

4
CLASIFICATION OF FILTERS BY PASS BAND TYPES
Attenuation
Attenuation
L. P. F
H. P. F.
0
0
Freq.
Freq.
fc
Attenuation
fc
Attenuation
b.w.
B. P. F.
B. S. F.
b. w.
0
0
Freq.
fo
Freq.
fo
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

6
CLASIFICATIONS BY RESPONSE TYPE (INSERTION LOSS
FUNCTION)

• BUTTERWORTH OR MAXIMALY FLATE T(w)
  1 (w/wo) n
• TCHEBYCHEFF OR EQUAL RIPPLE PASS BAND T(w)
  1 e2 Tn(w/wo)
• INVERSE TCHBYCHEFF MAXIMALLY FLATE PASS BAND
  EQUAL RIPPLE STOP BAND T(w) 11/ e2 Tn(w/wo)
• ELLIPTIC FUNCTION OR QUASIELLIPTIC FUNCTION
  (EQUAL RIPPLE IN BOTH PASS BAND AND STOP BAND)
• BESSEL THOMPSON (FLATE GROUP DELAY)

7
CLASSIFICATION BY FRACTIONAL BAND WIDTH

• NARROW BAND FILTERS RELATIVE (bw/fo) BANDWIDTHS
  LESS THAN _at_ 5
• MODERATE BAND WIDTH RELATIVE BANDWIDTHS
  BETWEEN _at_ 5 TO 25
• WIDE BAND FILTERS RELATIVE BANDWIDTHS GREATER
  THAN 25
• TECHNIQUES USED FOR DESIGN OF EACH TYPE DIFFER
  SIGNIFICANTLY

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

9
FILTERS TRANSMISSION MEDIA
PRINTED CIRCUITS AND SUSPENDED SUBSTRATES
100
LUMPED LC
10.
RELATIVE B.W.
COAXIAL
DIELECTRIC RESONATORS
1.0
WAVEGUIDES
.1
.01
P L S C X K Q V W
FREQUENCY BAND DESIGNATION
10
UNLOADED QS FOR BASE STATION FILTERS
(Technology Drivers)
Qu
100K
E
Dual Mode, materials, etc.)
D
(Multiple Modes)
10K
C
Technology Gap
(Materials Plating)
Increased Circuit Complexity
B
A
Cost
1K
ACoaxial Resonators, Ceramic Dielectric BCoaxial
Resonators, Air Dielectric C Single Mode Cavity
Resonators D Single Mode Cavity Resonators,
Delectrically Loaded E HTS Planar Resonators
Size
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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

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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 LNAS TRANSMIT REJECT FILTERS,
  HPAS HARMONIC REJECT FILTERS, UP DOWN
  CONVERTERS FILTERS

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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

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TYPICAL COMMUNICATIONS REPEATER
Power Amplifiers
Antenna
LNA
Tx Reject Filter
LO
Up Converter
Input Multiplexer
Output Multiplexer
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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

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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

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TYPICAL INSERTION LOSS SPECIFICATION MASK
INSERTION LOSS
0.6dB
e .05 dB
BW
36 MHz
40 dB
50dB
60 dB
70 dB
FREQUENCY
f0 (4000 MHz)
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TYPICAL GROUP DELAY SPECIFICATION MASK
GROUP DELAY
FREQUENCY
f0 (4000 MHz)
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METHODS OF FILTER DESIGN

• 1. IMAGE PARAMETER METHOD (EARLY 1920S)
• BASED ON A WAVE VIEWPOINT OF CIRCUITS

1
2
2
1
1
1
2
2
ZI2
ZI2
ZI1
ZI1
ZI2
ZI2
Etc. to Infinity
Etc. to Infinity

• IMAGE IMPEDANCES ZI1, ZI2 AND IMAGE PROPAGATION
  FUNCTION
• g ARE DEFINED BY

I1
I2
ZI1


ZI2
E2
E1
Eg
eg (E1/E2) (ZI2 / ZI1)1/2
-
-
ZI1
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CONSTANT K-HALF SECTIONS
ZI1,
ZI2
L1 1
RI2
ZI2
ZI1
j XI1
C2 1
1
RI1
a , b
1
a
j XI2
b
p/2
w
1
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M-DERIVED HALF SECTIONS
ZI1,
ZI2
L1 m
RI2
L(1-m2 )/m
ZI1
j XI1
ZI2
1
C2 m
RI1
a , b
1
a
j XI2
b
p/2
1/(1-m2)1/2
w
1
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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

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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.

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EXAMPLE OF CASCADE SYNTHESIS CYCLE
FILTER TO BE SYNTHESIZED (UNKNOWN)
2
T(jw) lt 1 - lt w lt Q(s) Strictly Hurwitz
8
8
T(s) P(s)/Q(s)
REMAINING UNKNOWN SECTION
2
T1(s) P1(s)/Q1(s)
Extracted Section of Known Elements and Values
T1(jw) lt 1 - lt w lt Q1(s) Strictly Hurwitz
8
8
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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 ITS 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

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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

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LOW PASS COAXIAL FILTERS
DIELECTRIC SLEEVE
HIGH IMPEDANCE LINES (SERIES LS)
COAXIAL CONNECTOR
LOW IMPEDANCE LINES (SHUNT CS)
SEMI-LUMPED ELEMENTS EQUIVALENT CIRCUIT
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HIGH PASS COAXIAL FILTERS
SHUNT L
SERIES C
COAXIAL CONNECTOR
SEMI-LUMPED ELEMENTS EQUIVALENT CIRCUIT
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MICROSTRIP LOW PASS FILTERS
METALIZED CIRCUIT PATTERN
DIELECTRIC SUBSTRATE OVER GROUND PLANE
30
BAND PASS COAXIAL FILTERS
DUMBELL BANDPASS COAXIAL FILTER
DIELECTRIC SLEEVE
l/4 RESONATORS
SERIES CAPACITORS
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PARALLEL COUPLED LINES
l/4
CENTER CONDUCTOR PATTERN
OUTER CONDUCTOR HOUSING
DIELECTRIC SHEET
OVERLAY COUPLED LINES
SUSPENDED SUBSTRATE LINE

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

32
BANDPASS END COUPLED MICROSTRIP FILTERS
METALIZED CIRCUIT PATTERN l/2 RESONATORS
DIELECTRIC SUBSTRATE OVER GROUND PLANE
33
INTERDIGITAL COMBLINE BAND PASS FILTERS
OPEN CIRCUIT END
COUPLING IRIS
SHORT CIRCUIT END
INNER CONDUCTORS OF COAXIAL RESONATORS
TOP VIEW
SIDE VIEW
34
WAVEGUIDE FILTERS
INDUCTIVE WINDOWS (MODERATE BANDWIDTHS)
DIRECT COUPLED USING IRIS (NARROW BANDWIDTHS)
35
RIDGE WAVEGUIDE FILTERS
36
DUAL MODE CIRCULAR WAVEGUIDE FILTERS
TUNING SCREWS
INPUT IRIS
OUTPUT IRIS
2
3
6
1
4
5
37
Dual Mode Dielectric or Conductor Loaded
Resonator Filter
Dielectric or Conductor Loading
Input Coax Probe
Output Coax Probe
2
6
3
1
4
5
38
Dual Mode Dielectric or Conductor Loaded
Resonator Filter in Rectangular Enclosure
M67
M23
M36
M12
M56
M14
M45
M78
M34
M58
8-Pole Dual Mode Longitudinal Dielectric or
Conductor Loaded Resonator Filter in Rectangular
Enclosure