Cavity and Combline Filters, Combiners, and Duplexers

Cavity and Combline Filters, Combiners, and Duplexers

CAVITY and COMBLINE FILTERS, COMBINERS and DUPLEXERS
K5TRA
COUPLED QUARTER WAVE RESONATORS
l/4 RESONATOR
INTERDIGITAL FILTER
K5TRA
2
LOOP COUPLED l/4 CAVITY
COMBLINE FILTER with
INTERDIGITAL PORT COUPLING
PARALLEL RESONATORS
THIS IS A GOOD LUMPED REPRESENTATION OF A l/4 RESONATOR
K5TRA
3
STOPBAND
K5TRA
4
PASSBAND
CAVITY RESONATOR with LOOP COUPLING
•
•
•
Parallel LC model
High Z at resonance
Low Z (slightly inductive) in stopband
•
Resonance at l/4 and 3l/4
•
70% more Qu typical at 3l/4
LADDER FILTER BASIC BUILDING BLOCK
• Passband: Z1  short and Z2  open
• Stopband: Z1  open and Z2  short
K5TRA
5
IMPEDANCE INVERTERS PROVIDE REUSE OF RESONATOR TYPE
Z INVERTER
Y INVERTER
• Impedance inverter interface between similar resonators
provides maximum stopband attenuation
• Most common impedance inverter is transmission line that is an
odd multiples of l/4
K5TRA
6
IMPEDANCE INVERTERS
• Impedance (or admitance) inverters
can be used to convert parallel
resonance to a series resonance
characteristic.
• The canonic impedance inverter is
the l/4 line.
• LC forms provide moderate
bandwidth Z inversion.
• Capacitive T and p sections are for
narrow band applications. Negative
C is absorbed into resonator
(cancels some positive C).
Transmission Line
J (or K) Inverter
Z0 ,
L
 
L
C
Z0 
L
,
C
1
LC
-C
-C
Z0 
1
 0C
-L
L
-L
Z 0  0 L
7
C
C
L
K5TRA
0 
-C
C
-L
4
L
C
-C
l
-L
NARROW FILTERS WITH CAPACITIVE Z INVERTER
Z INVERTER
Z INVERTER
COMBLINE REPRESENTATION
K5TRA
8
COMBLINE FILTERS in UHF DUPLEXER
• Combline filter formed by capacitive coupled (E field) l/4 resonators.
• Resonator tuning with capacitive probe into open end.
• Inverter coupling capacitance tuned with grounded screw between
resonators.
• Port coupling resonators are interdigital inductive coupled (H field).
• Outer port reflective resonator sets near stopband rejection.
K5TRA
9
900 MHz COMBLINE DUPLEXER
ADJACENT STOPBAND
REJECTION SET BY
REFLECTIVE END
RESONATOR
K5TRA
10
900 MHz DUPLEXER with 3l/4 CAVITIES
K5TRA
11
SIX l/4 CAVITY FILTER
K5TRA
12
l/4 CAVITIES
with added
REJECTION ENHANCEMENT NOTCH
LOOP COUPLED PASS CAVITY
K5TRA
13
REJECTION ENHANCEMENT ADDED TO PASS CAVITY
•
•
•
X can be an inductor for a notch
above the pass frequency
X can be a capacitor for a notch
below the pass frequency
X can be an LC network to provide
adjustable rejection above or below
the pass frequency
REFLECTION CAVITY
WITH SHUNT NOTCH
K5TRA
14
Z INVERTER ‘FLIPS’ TERMINAL CHARACTERISTIC
K5TRA
15
STOPBAND
l/4 CAVITY
l/4 Z INVERTER
PASSBAND
PASSBAND
STOPBAND
l/4 CAVITY
TWO CAVITY CASCADE FILTER with l/4 Z-INVERTER
K5TRA
16
l/4 Z INVERTER
CAN BE EXTENDED TO MORE
PORTS AS A ‘STAR’ COMBINER
K5TRA
17
F2 OPEN
l/4 CAVITY TUNED F2
F1 OPEN
l/4 Z INVERTER
F1 MATCH,
l/4 CAVITY TUNED F1
F2 MATCH,
CAVITY TRANSMITTER COMBINER
FOUR CAVITY DUPLEXER
F1 MATCH,
l/4 CAVITY TUNED F1
l/4 CAVITY TUNED F1
F2 OPEN
l/4 Z INVERTER
l/4 Z INVERTER
l/4 Z INVERTER
l/4 Z INVERTER
F2 MATCH,
l/4 CAVITY TUNED F2
l/4 CAVITY TUNED F2
F1 OPEN
• Duplexer operation is the same as with cavity transmitter combiner
• Duplexer performance requires better rejection of other cavity
channel frequency. (Isolation of transmitter from receiver in repeater)
• Additional rejection of alternate channel can be added to cavity
response.
K5TRA
18
DUPLEX NARROW AND WIDE BAND PORTS
CAVITY TUNED F1
2L
C
CAVITY TUNED F1
2L
2L
C
2L
3l/4
l/4
l/4
l/4
l/4
CAVITY
TUNED F1
C
K5TRA
L
l/4
CAVITY
TUNED F1
C
L
• Notch filter formed by BP cavities
offset by l/4
• Narrow and wide band duplexer
formed by combined pass and notch
filters
19