K5TRA
CAVITY and COMBLINE FILTERS, COMBINERS and DUPLEXERS
2K5TRA
COUPLED QUARTER WAVE RESONATORS
l/4 RESONATOR LOOP COUPLED l/4 CAVITY
INTERDIGITAL FILTER COMBLINE FILTER with
INTERDIGITAL PORT COUPLING
3K5TRA
PARALLEL RESONATORS
THIS IS A GOOD LUMPED REPRESENTATION OF A l/4 RESONATOR
4K5TRA
CAVITY RESONATOR with LOOP COUPLING
STOPBAND
PA
SS
BA
ND
• 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
5K5TRA
LADDER FILTER BASIC BUILDING BLOCK
• Passband: Z1 short and Z2 open
• Stopband: Z1 open and Z2 short
6K5TRA
IMPEDANCE INVERTERS PROVIDE REUSE OF RESONATOR TYPE
• 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
Z INVERTER Y INVERTER
7K5TRA
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).
4,0
l Z
Transmission Line
J (or K) Inverter
CZ
0
0
1
- C
C
- C C
- C - C
LZ 00
L
- L - L
- L
L
- L
LCC
LZ
1, 00
L
C C
L L
C
8K5TRA
NARROW FILTERS WITH CAPACITIVE Z INVERTER
Z INVERTER
Z INVERTER
COMBLINE REPRESENTATION
9K5TRA
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.
10K5TRA
900 MHz COMBLINE DUPLEXER
ADJACENT STOPBAND
REJECTION SET BY
REFLECTIVE END
RESONATOR
11K5TRA
900 MHz DUPLEXER with 3l/4 CAVITIES
12K5TRA
SIX l/4 CAVITY FILTER
13K5TRA
l/4 CAVITIES
with added
REJECTION ENHANCEMENT NOTCH
LOOP COUPLED PASS CAVITY
14K5TRA
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
15K5TRA
Z INVERTER ‘FLIPS’ TERMINAL CHARACTERISTIC
l/4 CAVITY l/4 CAVITYl/4 Z INVERTER
ST
OP
BA
ND
PA
SS
BA
ND
ST
OP
BA
ND
PA
SS
BA
ND
16K5TRA
TWO CAVITY CASCADE FILTER with l/4 Z-INVERTER
17K5TRA
CAVITY TRANSMITTER COMBINER
l/4 CAVITY TUNED F1
l/4 CAVITY TUNED F2
l/4 Z INVERTER
l/4 Z INVERTER
F1 M
AT
CH
,
F2 O
PE
N
F2 M
AT
CH
,
F1 O
PE
N
CAN BE EXTENDED TO MORE
PORTS AS A ‘STAR’ COMBINER
18K5TRA
FOUR CAVITY DUPLEXER
l/4 CAVITY TUNED F1
l/4 CAVITY TUNED F2
l/4 Z INVERTER
l/4 Z INVERTER
l/4 CAVITY TUNED F1
l/4 CAVITY TUNED F2
l/4 Z INVERTER
l/4 Z INVERTER
F1 MATCH,
F2 OPEN
F2 MATCH,
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.
19K5TRA
DUPLEX NARROW AND WIDE BAND PORTS
C2 L 2 LC2 L 2 L
C L C L
CAVITY TUNED F1
3l/4
CAVITY TUNED F1
l/4
l/4l/4
CAVITY
TUNED F1
CAVITY
TUNED F1
l/4l/4
• Notch filter formed by BP cavities offset by l/4
• Narrow and wide band duplexer formed by combined pass and notch filters