Wave transmission lines and networks – Coupling networks – Delay lines including long line elements
Reexamination Certificate
2002-04-30
2004-10-19
Callahan, Timothy P. (Department: 2816)
Wave transmission lines and networks
Coupling networks
Delay lines including long line elements
C333S139000, C342S361000
Reexamination Certificate
active
06806792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to monolithic microwave integrated circuit (MMIC) design, and in particular, to a broadband, 4-bit MMIC phase shifter for use in a phased array antenna employed in radar or communication systems to point or steer an RF (Radio Frequency) beam.
2. Description of the Related Art
In the prior art, a phase shifter is employed as one of the component circuits of a phased array antenna and the like.
FIG. 1
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
.
FIG. 1
shows a phased array antenna which has four antenna elements for simplicity of description. Typically, there are more than four antenna elements in an actual phased array antenna.
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. 2
shows the specific configuration of the phase circuit having input and output terminals
23
a
and
23
b
, respectively. As shown in
FIG. 2
, each of the phase circuits
231
,
232
,
233
, and
234
of
FIG. 1
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. 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.
Referring back to
FIG. 1
, 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
.
Increasing carrier frequencies in communications systems offer greater data transmission rates. Changing from X-band (8 GHz) to Ka-band (32 GHz) has the potential for a sixteen fold improvement in data rates for a given antenna size and transmitter power. In deep space missions, where the available DC power is limited, improving the amount of data returned in a given mission is of great interest.
The phase shifter is a key component in a phased array system. However, designing at Ka-band frequencies, especially regarding phase, is much harder than at lower frequencies. An error in line length amounting to 5° at X-band (8 GHz) becomes a 20° error at Ka-band (32 GHz). Modeling errors in switch devices, microstrip or MMIC components accumulate quickly. Conventional switching devices are far from ideal at Ka-band.
Additional factors must be considered when designing high frequency phase shifters. For example, design trade-offs for insertion loss, insertion balance between phase states and phase accuracy must be made. Further, each bit of the phase shifter uses a topology or circuit architecture appropriate for that particular phase shift, however, a topology that works well for large phase shifts may be inappropriate or inefficient for small phase shifts. Additionally, parasitic capacitances in the switches must be compensated for, or incorporated into, the phase shifter topology.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a broadband (Ka-band) MMIC phase shifter.
It is another object of the present invention to provide a broadband phase shifter which reduces the effect of parasitic capacitances in the switching elements.
The foregoing and other objects of the present invention are achieved by providing a broadband, 4-bit MMIC phase shifter. Rather than use exotic GaAs processing techniques to reduce the effects of parasitic capacitances in the switch elements, a standard pseudomorphic high electron mobility transistor (PHEMT) process is used, with phase shift architectures chosen to absorb the parasitic effects for broadband operation. Careful analysis of linear and EM simulations in combination with measured results has resulted in an improved four-bit design that is compact, broadband and has good insertion loss and balance, yet uses a standard 0.25 mm PHEMT process with standard bias voltages.
The four-bit selectable phase shifter for use in a phased array antenna of the present invention, which selectably causes an input signal to be shifted in phase, includes a first bit for selectively providing a 180° phase shift, wherein the first bit is a line/reflected bit; a second bit for selectively providing a 90° phase shift, wherein the second bit is a reflected bit; a third bit for selectively providing a 45° phase shift, wherein the third bit is a reflected bit; and a fourth bit for selectively providing a 22.5° phase shift, wherein the fourth bit is a high pass/low pass bit.
REFERENCES:
patent: 4458219 (1984-07-01), Vorhaus
patent: 6020848 (2000-02-01), Wallace et al.
patent: 6078223 (2000-06-01), Romanofsky et al.
patent: 6137377 (2000-10-01), Wallace et al.
patent: 6242990 (2001-06-01), Sokolov
patent: 6317075 (2001-11-01), Heide et al.
Callahan Timothy P.
Cooch Francis A.
Luu An T.
The Johns Hopkins University
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