Wave transmission lines and networks – Coupling networks – Delay lines including long line elements
Reexamination Certificate
1998-02-27
2001-08-14
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Delay lines including long line elements
C333S139000, C333S262000
Reexamination Certificate
active
06275121
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a microwave circuit and, more particularly, to a process for transforming the waveform of a gate bias signal. The gate bias signal controls a field effect transistor (FET) switch in a phase shifter, which shifts the phase of a microwave input signal by on-off action of the FET switch.
BACKGROUND OF THE INVENTION
In the prior art, a phase shifter is employed as one of the component circuits of a phased array antenna and the like.
FIG. 13
is a block diagram schematically showing the configuration of a prior art phased array antenna. In the figure, a phased array antenna
200
includes a plurality of antenna elements
211
,
212
,
213
, and
214
. The antenna
200
changes the direction D of an incoming or outgoing electromagnetic wave by controlling the phase of the electromagnetic waves in the antenna elements
211
,
212
,
213
, and
214
.
The antenna
200
includes amplifiers
221
,
222
,
223
, and
224
, all of which amplify microwaves going out from or coming into the corresponding antenna elements
211
,
212
,
213
, and
214
, and phase circuits
231
,
232
,
233
, and
234
, all of which shift the phases of microwaves going out from or coming into the corresponding antenna elements
211
,
212
,
213
, and
214
. The phase circuits
231
,
232
,
233
, and
234
are connected to a signal source
260
and a signal receiver
270
via corresponding directional couplers
251
,
252
,
253
, and
254
.
The antenna
200
also includes a control circuit
240
which controls the phase circuits and the directional couplers. More specifically, the control circuit
240
controls the phase shift of the phase circuits
231
,
232
,
233
, and
234
with 5-bit control signals Pc
1
, Pc
2
, Pc
3
, and Pc
4
, respectively, and switches the connection of each phase circuit to the signal source
260
or to the signal receiver
270
with a control signal Kc.
FIG. 13
shows a phased array antenna which has four antenna elements for simplicity of description. There are more than four antenna elements in an actual phased array antenna.
FIG. 14
shows the specific configuration of the phase circuit having input and output terminals
23
a
and
23
b,
respectively. As shown in
FIG. 14
, each of the phase circuits
231
,
232
,
233
, and
234
of
FIG. 13
comprises five switched-line phase shifters
230
a,
230
b,
230
c,
230
d,
and
230
e,
all of which provide different phase shifts. The phase shift is defined as the difference in phase between signals at the phase shifter output and input.
The first shifter
230
a
comprises first and second transmission lines
13
and
14
which have electrical lengths that differ by &lgr;/32 (&lgr; is the wavelength of a propagating microwave), an input switch
311
which selects between input terminals of the transmission lines
13
and
14
, and an output switch
312
which selects between the output terminals of the transmission lines. The second to fifth shifters
230
b,
230
c,
230
d,
and
230
e
have almost the same configuration as that of the first shifter
230
a.
However, in the second shifter
230
b,
the difference in electrical length between the first and second transmission lines is &lgr;/16; in the third shifter
230
c
the difference in electrical length between the first and second transmission lines is &lgr;/8; in the fourth shifter
230
d
the difference in electrical length between the first and second transmission lines is &lgr;/4; and in the fifth shifter
230
e
the difference in electrical length between the first and second transmission lines is &lgr;/2.
Further, the switching actions of each pair of the input and output switches
311
and
312
of each phase shifter are respectively controlled by switch control signals Pca, Pcb, Pcc, Pcd, and Pce as a control signal of each phase circuit. In the phase circuit so constructed, the phase of microwave input can be varied in steps of 11.25° in the range of from 11.25° to 348.75° using a 5-bit control signal.
FIG.
11
(
a
) shows a detailed configuration of the above-mentioned switched-line shifter. Note that for the simplicity of description a phase shifter
230
represents the shifters
230
a,
230
b,
230
c,
230
d,
and
230
e
without distinction in FIG.
11
(
a
) because the distinction among these shifters is only the phase shift as described with respect to FIG.
14
.
The phase shifter
230
includes an input switch
311
(shown in
FIG. 14
) comprising a first input-side FET element
50
a
connected between a high-frequency frequency input terminal (RF input terminal)
2
and the input terminal of a transmission line
13
and a second input-side FET element
50
c
connected between the RF input terminal
2
and the input terminal of a second transmission line
14
. The phase shifter
230
also includes an output switch
312
(shown in
FIG. 14
) comprising a first output-side FET element
50
b
connected between a high-frequency output terminal(RF output terminal)
3
and the output terminal of the transmission line
13
and a second output-side FET element
50
d
connected between the RF input terminal
3
and the output terminal of the second transmission line
14
.
Since all elements constituting the phase shifter
230
are fabricated on a monolithic microwave IC (MMIC) substrate, GaAs MESFETs are employed as the FET switches
50
a,
50
b,
50
c,
and
50
d.
The bias voltage applied to the sources and drains of the FET switches
50
a,
50
b,
50
c,
and
50
d
is provided by the power-source voltage (5V) because of restrictions on the power-source from the external system (a phased array antenna control circuit). In each of the FET elements fabricated on the substrate there is an effective inductance L between the source and the drain. Therefore, as shown in FIG.
11
(
a
), the power-source voltage (5V) is applied via a bias resistance
1
to the source of one of the four FET switches constituting the phase shifter (here the one is the FET switch
50
d
), thereby setting the potential between the source and drain of each FET switch at 5V.
In the prior art phase shifter
230
, 5V is applied to the gate terminals
5
a,
5
b,
5
c,
and
5
d
of the respective FET switches as the on-potential which places each FET in the on-state, and 0V is applied to the gate terminals
5
a,
5
b,
5
c,
and
5
d
of the respective FET switches as the off-potential which places each FET element in the off-state.
In the phased array antenna
200
shown in
FIG. 13
, a microwave signal generated by the signal source
260
is supplied to the phase circuits
231
,
232
,
233
, and
234
via the directional couplers
251
,
252
,
253
, and
254
, respectively. The microwave signal is then subjected to a process that shifts its phase forward or backward by a given amount in each of the phase circuits before being applied to the amplifiers
221
,
222
,
223
, and
224
, respectively. Finally, the microwave signals amplified in the amplifiers are radiated from the antenna elements
211
,
212
,
213
, and
214
into the air.
The traveling direction of the microwaves radiated by the antenna
200
is a direction D that is perpendicular to a wavefront W. The wavefront W consists of parts having the same phase in the microwave signals radiated from the antenna elements. In other words, microwaves are radiated from the antenna
200
in the direction D. The radiation direction D depends on the phase shift set by the control signals Pc
1
, Pc
2
, Pc
3
, and Pc
4
in the phase circuits
231
,
232
,
233
, and
234
.
The only electromagnetic waves coming into the phased array antenna
200
are electromagnetic waves reflected from a target, i.e., from the direction D. The incoming electromagnetic waves are supplied to the amplifiers
221
,
222
,
223
, and
224
via the antennas
211
,
212
,
213
, and
214
. The incoming electromagnetic waves are amplified in the amplifiers and then supplied to the receiver
270
via the directional couplers
251
,
252
,
253
, and
254
.
As described with respect to
FIG. 14
, the phase shifters
230
a,
Maruyama Takaya
Nakajima Yasuharu
Sasaki Yoshinobu
Lee Benny
Leydig & Voit & Mayer
Mitsubishi Denki & Kabushiki Kaisha
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