<s>
The	O
two	O
F	B-Protocol
connectors	I-Protocol
at	O
the	O
bottom	O
of	O
the	O
device	O
are	O
for	O
connection	O
to	O
downleads	O
.	O
</s>
<s>
A	O
distributed-element	B-Algorithm
filter	I-Algorithm
is	O
an	O
electronic	B-Architecture
filter	I-Architecture
in	O
which	O
capacitance	O
,	O
inductance	O
,	O
and	O
resistance	O
(	O
the	O
elements	O
of	O
the	O
circuit	O
)	O
are	O
not	O
localised	O
in	O
discrete	O
capacitors	O
,	O
inductors	O
,	O
and	O
resistors	O
as	O
they	O
are	O
in	O
conventional	O
filters	O
.	O
</s>
<s>
There	O
is	O
no	O
precise	O
frequency	O
above	O
which	O
distributed	B-Algorithm
element	I-Algorithm
filters	I-Algorithm
must	O
be	O
used	O
but	O
they	O
are	O
especially	O
associated	O
with	O
the	O
microwave	O
band	O
(	O
wavelength	O
less	O
than	O
one	O
metre	O
)	O
.	O
</s>
<s>
Distributed-element	B-Algorithm
filters	I-Algorithm
are	O
used	O
in	O
many	O
of	O
the	O
same	O
applications	O
as	O
lumped	O
element	O
filters	O
,	O
such	O
as	O
selectivity	O
of	O
radio	O
channel	O
,	O
bandlimiting	O
of	O
noise	O
and	O
multiplexing	B-Protocol
of	O
many	O
signals	O
into	O
one	O
channel	O
.	O
</s>
<s>
Distributed-element	B-Algorithm
filters	I-Algorithm
may	O
be	O
constructed	O
to	O
have	O
any	O
of	O
the	O
bandforms	O
possible	O
with	O
lumped	O
elements	O
(	O
low-pass	B-Algorithm
,	O
band-pass	O
,	O
etc	O
.	O
)	O
</s>
<s>
There	O
are	O
many	O
component	O
forms	O
used	O
to	O
construct	O
distributed-element	B-Algorithm
filters	I-Algorithm
,	O
but	O
all	O
have	O
the	O
common	O
property	O
of	O
causing	O
a	O
discontinuity	O
on	O
the	O
transmission	O
line	O
.	O
</s>
<s>
The	O
development	O
of	O
distributed-element	B-Algorithm
filters	I-Algorithm
was	O
spurred	O
on	O
by	O
the	O
military	O
need	O
for	O
radar	B-Application
and	O
electronic	O
counter	O
measures	O
during	O
World	O
WarII	O
.	O
</s>
<s>
When	O
the	O
war	O
ended	O
,	O
the	O
technology	O
found	O
applications	O
in	O
the	O
microwave	B-Application
links	I-Application
used	O
by	O
telephone	O
companies	O
and	O
other	O
organisations	O
with	O
large	O
fixed-communication	O
networks	O
,	O
such	O
as	O
television	O
broadcasters	O
.	O
</s>
<s>
Distributed-element	B-Algorithm
filters	I-Algorithm
are	O
mostly	O
used	O
at	O
frequencies	O
above	O
the	O
VHF	B-Algorithm
(	O
Very	B-Algorithm
High	I-Algorithm
Frequency	I-Algorithm
)	O
band	O
(	O
30	O
to	O
300	O
MHz	O
)	O
.	O
</s>
<s>
The	O
most	O
noticeable	O
difference	O
in	O
behaviour	O
between	O
a	O
distributed-element	B-Algorithm
filter	I-Algorithm
and	O
its	O
lumped-element	O
approximation	O
is	O
that	O
the	O
former	O
will	O
have	O
multiple	O
passband	B-Algorithm
replicas	O
of	O
the	O
lumped-element	O
prototype	O
passband	B-Algorithm
,	O
because	O
transmission-line	O
transfer	O
characteristics	O
repeat	O
at	O
harmonic	O
intervals	O
.	O
</s>
<s>
These	O
spurious	O
passbands	B-Algorithm
are	O
undesirable	O
in	O
most	O
cases	O
.	O
</s>
<s>
Development	O
of	O
distributed-element	B-Algorithm
filters	I-Algorithm
began	O
in	O
the	O
years	O
before	O
World	O
WarII	O
.	O
</s>
<s>
Much	O
development	O
was	O
carried	O
out	O
during	O
the	O
war	O
years	O
driven	O
by	O
the	O
filtering	O
needs	O
of	O
radar	B-Application
and	O
electronic	O
counter-measures	O
.	O
</s>
<s>
The	O
initial	O
non-military	O
application	O
of	O
distributed-element	B-Algorithm
filters	I-Algorithm
was	O
in	O
the	O
microwave	B-Application
links	I-Application
used	O
by	O
telecommunications	O
companies	O
to	O
provide	O
the	O
backbone	B-General_Concept
of	O
their	O
networks	O
.	O
</s>
<s>
The	O
discontinuity	O
can	O
be	O
represented	O
approximately	O
as	O
a	O
series	O
inductor	O
,	O
or	O
more	O
exactly	O
,	O
as	O
a	O
low-pass	B-Algorithm
T	O
circuit	O
as	O
shown	O
in	O
figure	O
4(a )	O
.	O
</s>
<s>
Impedance	O
transformers	O
are	O
also	O
used	O
in	O
hybrid	O
mixtures	O
of	O
lumped	O
and	O
distributed-element	B-Algorithm
filters	I-Algorithm
(	O
the	O
so-called	O
semi-lumped	O
structures	O
)	O
.	O
</s>
<s>
Another	O
very	O
common	O
component	O
of	O
distributed-element	B-Algorithm
filters	I-Algorithm
is	O
the	O
stub	O
.	O
</s>
<s>
They	O
are	O
most	O
useful	O
in	O
the	O
upper	O
VHF	B-Algorithm
and	O
lower	O
UHF	O
bands	O
whereas	O
stubs	O
are	O
more	O
often	O
applied	O
in	O
the	O
higher	O
UHF	O
and	O
SHF	B-Algorithm
bands	O
.	O
</s>
<s>
This	O
also	O
behaves	O
as	O
a	O
resonator	O
,	O
but	O
is	O
commonly	O
used	O
in	O
low-pass	B-Algorithm
filter	I-Algorithm
applications	O
with	O
the	O
resonant	O
frequency	O
well	O
outside	O
the	O
band	O
of	O
interest	O
.	O
</s>
<s>
A	O
low-pass	B-Algorithm
filter	I-Algorithm
can	O
be	O
implemented	O
quite	O
directly	O
from	O
a	O
ladder	O
topology	O
lumped-element	O
prototype	O
with	O
the	O
stepped	O
impedance	O
filter	O
shown	O
in	O
figure	O
5	O
.	O
</s>
<s>
Low-pass	B-Algorithm
filters	I-Algorithm
are	O
commonly	O
used	O
to	O
feed	O
direct	O
current	O
(	O
DC	O
)	O
bias	O
to	O
active	O
components	O
.	O
</s>
<s>
The	O
purpose	O
of	O
incorporating	O
resonators	O
is	O
to	O
improve	O
the	O
stopband	B-Algorithm
rejection	I-Algorithm
.	O
</s>
<s>
However	O
,	O
beyond	O
the	O
resonant	O
frequency	O
of	O
the	O
highest	O
frequency	O
resonator	O
,	O
the	O
stopband	B-Algorithm
rejection	I-Algorithm
starts	O
to	O
deteriorate	O
as	O
the	O
resonators	O
are	O
moving	O
towards	O
open-circuit	O
.	O
</s>
<s>
Another	O
common	O
low-pass	B-Algorithm
design	O
technique	O
is	O
to	O
implement	O
the	O
shunt	O
capacitors	O
as	O
stubs	O
with	O
the	O
resonant	O
frequency	O
set	O
above	O
the	O
operating	O
frequency	O
so	O
that	O
the	O
stub	O
impedance	O
is	O
capacitive	O
in	O
the	O
passband	B-Algorithm
.	O
</s>
<s>
If	O
ω1	O
and	O
ω2	O
are	O
the	O
frequencies	O
of	O
the	O
passband	B-Algorithm
edges	O
,	O
then	O
:	O
</s>
<s>
Both	O
types	O
of	O
parallel-coupled	O
filters	O
,	O
in	O
theory	O
,	O
do	O
not	O
have	O
spurious	O
passbands	B-Algorithm
at	O
twice	O
the	O
centre	O
frequency	O
as	O
seen	O
in	O
many	O
other	O
filter	O
topologies	O
(	O
e.g.	O
,	O
stubs	O
)	O
.	O
</s>
<s>
However	O
,	O
suppression	O
of	O
this	O
spurious	O
passband	B-Algorithm
requires	O
perfect	O
tuning	O
of	O
the	O
coupled	O
lines	O
which	O
is	O
not	O
realized	O
in	O
practice	O
,	O
so	O
there	O
is	O
inevitably	O
some	O
residual	O
spurious	O
passband	B-Algorithm
at	O
this	O
frequency	O
.	O
</s>
<s>
The	O
chief	O
advantage	O
of	O
this	O
design	O
is	O
that	O
the	O
upper	O
stopband	O
can	O
be	O
made	O
very	O
wide	O
,	O
that	O
is	O
,	O
free	O
of	O
spurious	O
passbands	B-Algorithm
at	O
all	O
frequencies	O
of	O
interest	O
.	O
</s>
<s>
General	O
forms	O
of	O
these	O
are	O
similar	O
to	O
stub	O
low-pass	B-Algorithm
filters	I-Algorithm
except	O
that	O
the	O
main	O
line	O
is	O
no	O
longer	O
a	O
narrow	O
high	O
impedance	O
line	O
.	O
</s>
<s>
This	O
topology	O
has	O
both	O
low-pass	B-Algorithm
and	O
band-pass	O
characteristics	O
.	O
</s>
<s>
(	O
ii	O
)	O
the	O
first	O
spurious	O
passband	B-Algorithm
is	O
at	O
2ω0	O
,	O
as	O
opposed	O
to	O
3ω0	O
for	O
the	O
λ/4	O
stub	O
filter	O
.	O
</s>
<s>
Konishi	O
describes	O
a	O
wideband	O
12GHz	O
band-pass	O
filter	O
,	O
which	O
uses	O
60°	O
butterfly	O
stubs	O
and	O
also	O
has	O
a	O
low-pass	B-Algorithm
response	O
(	O
short-circuit	O
stubs	O
are	O
required	O
to	O
prevent	O
such	O
a	O
response	O
)	O
.	O
</s>
<s>
As	O
is	O
often	O
the	O
case	O
with	O
distributed-element	B-Algorithm
filters	I-Algorithm
,	O
the	O
bandform	O
into	O
which	O
the	O
filter	O
is	O
classified	O
largely	O
depends	O
on	O
which	O
bands	O
are	O
desired	O
and	O
which	O
are	O
considered	O
to	O
be	O
spurious	O
.	O
</s>
