Variable power divider

Details Variable power divider Variable power divider

2002-11-08

2004-09-07

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Plural channel systems

Having branched circuits

C333S111000

Reexamination Certificate

active

06788165

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to wireless communication systems using passive networks, and more particularly, to a planar variable power divider with low passive intermodulation for use on printed circuit boards to convert a single input RF signal into two output RF signals of constant phase throughout the adjustment range but with variable amplitudes as a function of movement of a single phase shifter that is part of the variable power divider.
BACKGROUND OF THE INVENTION
A large class of microwave components can be formed by combining two phase shifters and two fixed power dividers (combiners). The fact that both of these components may be made to operate over broad frequency bands at relatively high RF power levels has made this general structure useful in constructing variable power dividers, switches, and fixed circulators for active electronic warfare and beamforming in antenna applications for communication satellites and radar.
General Discussion of Conventional Technology
FIGS. 1 through 5
illustrates five conventional configurations incorporating two phase shifters and two fixed power dividers to function as variable power dividers and switches.
FIGS. 1 through 4
illustrates networks having four ports and
FIG. 5
illustrates a network having three ports. Other networks exist having three or four ports, and networks having greater numbers of ports can be realized with fixed power dividers having greater numbers of ports and additional phase shifters. Networks having greater numbers of ports can be realized using networks having three or four ports as building blocks. The three or four port configurations presented in
FIGS. 1 through 5
can be realized as either switches (having two states) or variable power dividers (having a continuum of states).
In the case of a switch, only two values of phase shift (and therefore two states) are available: those phase settings corresponding to state
0
and state
1
. For the variable power divider, the setting of phase shifters &phgr;
1
and &phgr;
2
may vary continuously over a predetermined range of values. The use of phase shifter pairs having unlike insertion phases will result in different phase values for state
0
and state
1
than the ones shown. The use of phase shifters with nonreciprocal phase properties will result in different phase values corresponding to the forward (transmit) or reverse (receive) signal propagation through the device. Four port circulators can be made using the configurations in
FIGS. 1 through 4
comprised of four external ports with fixed phase states when the phase shifters have nonreciprocal phase properties.
The configuration illustrated in
FIG. 1
uses a zero degree/one-hundred-eighty degrees hybrid power divider and a quadrature (zero degree
inety degrees) hybrid power divider. The output voltage signals, b
3
and b
4
, at Ports
3
and
4
described by the equations in
FIG. 1
correspond to an input signal at Port
1
. The input signal at Port
1
provides in-phase signals of equal amplitude to the variable phase shifters &phgr;
1
and &phgr;
2
. Ideally no signal appears at Port
2
when a signal is applied to Port
1
, and Port
2
can be described as the “isolated port” for signals applied to Port
1
. Similarly, a signal applied to Port
2
does not appear at Port
1
. The phase difference, &Dgr;&phgr;=&phgr;
1
−&phgr;
2
, is the controlling parameter for the output signal amplitudes at Ports
3
and
4
and the sum of the two phase values can vary the output signals phase. The sum of the two phase values must be equal to a constant phase value throughout the range of adjustment for the output signals to have a constant phase value.
Simultaneously altering the phase values in a complementary fashion can accomplish variable power divider output signal amplitude variation while maintaining a relatively constant output signal phase values throughout the range of adjustment. The variable power divider function of varying the output signal amplitudes can be accomplished by varying the phase value of one phase shifter while the phase of the other phase shifter remains at a fixed value. The output signals phase values are substantially a constant quantity only when the phase quantity (&phgr;
1
+&phgr;
2
) is substantially equal to a constant value throughout the range of adjustment.
The range of phase values to control the signal amplitudes between the switch states for the configuration illustrated in
FIG. 1
is ninety degrees. The table in
FIG. 1
identifies the phase values for &phgr;
1
and &phgr;
2
where &Dgr;&phgr;=−90 degrees for switch State
0
and &Dgr;&phgr;=+90 degrees for switch State
1
. State
0
corresponds to the condition where ideally all of the available signal input to Port
1
appears at Port
4
. State
1
corresponds to the condition where ideally all of the available signal input to Port
1
appears at Port
3
. Values of the &phgr;
1
and &phgr;
2
phase values in the table greater than zero represents a greater phase delay relative to the zero degree value for signals input to phase shifters &phgr;
1
and &phgr;
2
having identical phase values.
In other words, &phgr;
1
=0 degrees and &phgr;
2
=90 degrees is a condition where the signal output from &phgr;
2
is delayed 90 degrees relative to the signal output from &phgr;
1
. In other words, &phgr;
1
=0 degrees and &phgr;
2
=90 degrees is a condition where the signal output from &phgr;
2
lags
90
the signal output from &phgr;
1
by 90 degrees. The insertion loss of the phase control devices can be minimized when the phase control devices have the minimum range of phase adjustment corresponding to the desired range of amplitude adjustment.
The configuration of
FIG. 5
having three external ports is the same as
FIG. 1
except the input divider does not have the isolated Port
2
and the input divider consequently is a reactive type power divider and not a hybrid power divider. The operation of the configuration in
FIG. 5
is identical to that of FIG.
1
.
The configuration illustrated in
FIG. 2
uses two quadrature hybrid power dividers as compared to the mixed hybrid configuration illustrated in FIG.
1
. The range of phase values to control the signal amplitudes between the switch states in
FIG. 2
is one-hundred-eighty degrees and the insertion loss of the phase shifters can be greater than the configuration in FIG.
1
.
The configuration illustrated in
FIG. 3
uses zero degree/one-hundred-eighty degrees hybrid power dividers rather than mixed hybrids (
FIG. 1
) or quadrature hybrids (FIG.
2
). In this configuration, one-hundred-eighty degrees of phase shift is required of each phase shifter. The output signals at Ports
3
and
4
have phase values that are different by ninety degrees.
The configuration of
FIG. 4
is the same as
FIG. 2
with an additional fixed phase delay, &phgr;
0
, and a length of transmission line, L, so the two signal phases coincide at the input to the respective variable phase shifters &phgr;
1
and &phgr;
2
. This configuration has the same overall functionality as the configuration in FIG.
1
.
Specific Discussion of Conventional Technology
U.S. Pat. No. 4,485,362 to Campi et al. teaches a three-port, variable microwave stripline power divider that has a variable output over a wide range at one output without appreciably changing the power output at the other output, but which requires electronic patch devices and circuitry to vary the power split.
U.S. Pat. No. 5,473,294 to Mizzoni et al. teaches a planar variable power divider but which requires use of two quadrature hybrids and two variable phase shifters, and uses waveguide, not microstrip technology, and requires use of two sliding mechanisms to close the four hybrid output circuits. The block diagram for Mizzoni et al. conforms to
FIG. 4
knowing that the quadrature hybrids with sliding shorts as described by Mizzoni et al. are well known in the art as being two port phase shifters.
A variable power divider op

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