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