<s>
A	O
microwave	B-Algorithm
cavity	I-Algorithm
or	O
radio	O
frequency	O
cavity	O
(	O
RF	B-Algorithm
cavity	I-Algorithm
)	O
is	O
a	O
special	O
type	O
of	O
resonator	O
,	O
consisting	O
of	O
a	O
closed	O
(	O
or	O
largely	O
closed	O
)	O
metal	O
structure	O
that	O
confines	O
electromagnetic	O
fields	O
in	O
the	O
microwave	O
or	O
RF	O
region	O
of	O
the	O
spectrum	O
.	O
</s>
<s>
Thus	O
it	O
can	O
act	O
as	O
a	O
bandpass	O
filter	B-Architecture
,	O
allowing	O
microwaves	O
of	O
a	O
particular	O
frequency	O
to	O
pass	O
while	O
blocking	O
microwaves	O
at	O
nearby	O
frequencies	O
.	O
</s>
<s>
A	O
microwave	B-Algorithm
cavity	I-Algorithm
acts	O
similarly	O
to	O
a	O
resonant	O
circuit	O
with	O
extremely	O
low	O
loss	O
at	O
its	O
frequency	O
of	O
operation	O
,	O
resulting	O
in	O
quality	O
factors	O
(	O
Q	O
factors	O
)	O
up	O
to	O
the	O
order	O
of	O
106	O
,	O
compared	O
to	O
102	O
for	O
circuits	O
made	O
with	O
separate	O
inductors	O
and	O
capacitors	O
at	O
the	O
same	O
frequency	O
.	O
</s>
<s>
They	O
are	O
used	O
in	O
oscillators	O
and	O
transmitters	O
to	O
create	O
microwave	O
signals	O
,	O
and	O
as	O
filters	O
to	O
separate	O
a	O
signal	O
at	O
a	O
given	O
frequency	O
from	O
other	O
signals	O
,	O
in	O
equipment	O
such	O
as	O
radar	B-Application
equipment	O
,	O
microwave	B-Application
relay	I-Application
stations	O
,	O
satellite	O
communications	O
,	O
and	O
microwave	O
ovens	O
.	O
</s>
<s>
RF	B-Algorithm
cavities	I-Algorithm
can	O
also	O
manipulate	O
charged	O
particles	O
passing	O
through	O
them	O
by	O
application	O
of	O
acceleration	O
voltage	O
and	O
are	O
thus	O
used	O
in	O
particle	O
accelerators	O
and	O
microwave	O
vacuum	O
tubes	O
such	O
as	O
klystrons	O
and	O
magnetrons	B-Device
.	O
</s>
<s>
An	O
external	O
power	O
source	O
is	O
usually	O
coupled	O
to	O
the	O
cavity	O
by	O
a	O
small	O
aperture	B-General_Concept
,	O
a	O
small	O
wire	O
probe	O
or	O
a	O
loop	O
.	O
</s>
<s>
Resonance	O
frequencies	O
of	O
a	O
rectangular	O
microwave	B-Algorithm
cavity	I-Algorithm
for	O
any	O
or	O
resonant	O
mode	O
can	O
be	O
found	O
by	O
imposing	O
boundary	O
conditions	O
on	O
electromagnetic	O
field	O
expressions	O
.	O
</s>
<s>
For	O
a	O
microwave	B-Algorithm
cavity	I-Algorithm
,	O
the	O
stored	O
electric	O
energy	O
is	O
equal	O
to	O
the	O
stored	O
magnetic	O
energy	O
at	O
resonance	O
as	O
is	O
the	O
case	O
for	O
a	O
resonant	O
LC	O
circuit	O
.	O
</s>
<s>
To	O
better	O
understand	O
the	O
utility	O
of	O
resonant	O
cavities	O
at	O
microwave	O
frequencies	O
,	O
it	O
is	O
useful	O
to	O
note	O
that	O
the	O
losses	O
of	O
conventional	O
inductors	O
and	O
capacitors	O
start	O
to	O
increase	O
with	O
frequency	O
in	O
the	O
VHF	B-Algorithm
range	O
.	O
</s>
<s>
Conventional	O
inductors	O
are	O
usually	O
wound	O
from	O
wire	O
in	O
the	O
shape	O
of	O
a	O
helix	B-Application
with	O
no	O
core	O
.	O
</s>
<s>
Even	O
if	O
the	O
Q	O
factor	O
of	O
VHF	B-Algorithm
inductors	O
and	O
capacitors	O
is	O
high	O
enough	O
to	O
be	O
useful	O
,	O
their	O
parasitic	O
properties	O
can	O
significantly	O
affect	O
their	O
performance	O
in	O
this	O
frequency	O
range	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
in	O
the	O
VHF	B-Algorithm
or	O
microwave	O
regions	O
,	O
a	O
capacitor	O
may	O
appear	O
to	O
be	O
an	O
inductor	O
and	O
an	O
inductor	O
may	O
appear	O
to	O
be	O
a	O
capacitor	O
.	O
</s>
<s>
Air-filled	O
microwave	B-Algorithm
cavities	I-Algorithm
confine	O
electric	O
and	O
magnetic	O
fields	O
to	O
the	O
air	O
spaces	O
between	O
their	O
walls	O
.	O
</s>
