Temperature calibration system for a ferroelectric phase shifting array antenna

Telecommunication systems and methods for driving a phased-array antenna ing a plurality of spaced antenna elements that radiate and receive a beam of radio frequency signals. Each of a plurality of ferroelectric phase shifters connect to a different one of the antenna elements. A signal processor system, having a receiver and a frequency synthesizer communicates with the phase shifters under the control of a data processor system. A joystick connects to the data processor system for permitting manual input of beam steering information thereto. The data processor system responds to the joystick inputs by controlling the relative phase shifts of the signals propagating in the ferroelectric phase shifters. The system further includes a temperature sensor circuit for sensing the temperature of each of the ferroelectric phase shifters. This temperature sensor circuit connects to the data processor system for inputting temperature information that the data processor system uses to calculate calibration error factors. The data processor system uses the joystick inputs and the calibration error factors to apply concurrent calibrated analog control voltages to the ferroelectric phase shifters for controlling their relative phase shifts. The joystick permits an operator to manually control the position of the beam in real time, or to effect automatic beam scanning and control the scanning rate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to the field of telecommunication systems 
that employ electronically steerable antennas. More particularly, the 
invention relates to telecommunication systems having apparatus and 
methods for controlling, steering and automatically calibrating phase 
shifters for phased-array antennas. 
2. Description of the Prior Art 
Many telecommunication systems employ electronically steerable phased-array 
antennas for forming a narrow beam that can scan a particular field of 
view. In general, a phased array antenna is an antenna with two or more 
driven elements. The elements are fed with a certain relative phase, and 
they are spaced at a certain distance, resulting in a beam pattern that 
exhibits gain in some directions and little or no radiation in other 
directions. 
Phased-array antennas have found widespread use in military target 
acquisition radar systems. Such phased-array antennas permit the radar to 
be rapidly scanned electronically in three dimensions with no movement of 
the antenna elements. The outputs from the active antenna elements are 
formed into a steerable beam that can be used to detect and track multiple 
targets, such as satellites, missiles, aircraft and similar vehicles. 
Although usually complex and expensive, the phased-array radar has a 
gradual failure mode and can continue to function even if many individual 
elements fail. 
System designers have available several technologies for accomplishing 
phase-shifter control for operation of phased-array antennas. Some phase 
shifters use ferrite materials while others use semiconductor devices, 
such as PIN diodes, field effect transistors and varactors. The operating 
mechanism in semiconductor phase shifters is essentially based upon the 
control of conduction and/or capacitance properties arising out of device 
doping characteristics. The operating mechanism of ferrite phase shifters 
usually depends on controlling its magnetic and/or high-current inductance 
properties. Control of ferroelectric material typically depends on 
controlling a voltage, which usually requires less current draw than what 
is needed to control other types of phase shifters. Because 
ferroelectric-based phase shifters operate under a fundamentally different 
principal than do semiconductor-based phase shifters, they have a number 
of distinct advantages over such devices. 
Although semiconductor-based phase shifters, which usually employ 
transistors, are advantageously compact, they can be severely limited to 
only small signal applications. Attempts to employ high-power phase 
shifters of the semiconductor type often result in degrading the microwave 
characteristics of the antenna. Furthermore, small-signal phase shifters 
are usually subject to damage in the presence of strong signals, jamming 
signals, or electrical noise including electromagnetic pulses. 
Ferrite-based phased arrays normally handle high power much better than 
most semiconductor devices and are less susceptible to damage in the 
presence of high-power signals and electromagnetic pulses. However, other 
features prevent the widespread use of ferrite-based phase shifters. 
First, each ferrite phase shifter of an assembly must usually be a 
separately manufactured module that must be electrically matched with 
other modules. These requirement can add greatly to overall assembly cost. 
Second, ferrite-based phase shifters are normally unidirectional, which is 
acceptable for transmit-only or receive-only systems but is inferior for 
transmit-receive systems. A transmit-receive steerable array using 
nonreciprocal ferrite phase shifters would need double the number of 
phase-shifter elements that are needed for a system using reciprocal 
elements, thereby increasing system complexity and cost. 
Third, control circuits for ferrite-based phase shifters typically include 
high-current magnetic coils that require high power. These coils can 
induce phase shifts even when the antenna is not scanning. Further, these 
high-impedance control circuits usually require individual impedance load 
matching to be executed after antenna production which can result in 
manufacturing delays. Also, there is normally a need for a large-gauge 
thickness in most ferrite phase-shifter substrates to handle the large 
power requirements without disintegrating or loosing signal fidelity. 
Fourth, ferrite phase shifters are far more susceptible to environmental 
changes, such as ambient temperature and/or pressure changes, due to their 
high-current operation. Some calibration techniques that employ trimming 
to compensate for errors due to changing ambient conditions often find 
trimming to be extremely difficult or impossible to perform properly 
without degrading phase-shifter performance. Therefore, antenna 
calibration becomes more time dependent, lossy, and near impossible to 
realize using a ferrite-based antenna control. 
Consequently, those concerned with the development of telecommunication 
systems that employ phased-array antennas have long recognized the need 
for improved phase-shifter controls that reduce their traditionally high 
costs and improve the poor performance of the manual, lossy calibration 
techniques associated with prior art systems. It is contemplated that an 
ideal phase-shifter control for a system that employs a phased-array 
antenna would be: capable of reciprocal signal propagation; operable at 
low-power levels; inexpensive to manufacture; light weight and compact; 
implemented with less complex circuitry and structure; less time dependent 
to calibration; capable of low-power trimming with unidirectional 
calibration; capable of high-speed calibration processing; and 
controllable with a low-power digital circuitry. The present invention 
fulfills this need. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide unique 
digital control and automatic calibration techniques for ferroelectric 
phase shifters that are used to steer phased-array antennas. 
To attain this, the present invention contemplates a unique 
telecommunication system comprising a phased-array antenna having a 
plurality of spaced antenna elements for radiating and receiving a beam of 
radio frequency signals. A plurality of phase shifters each have one of 
its ends connected to a different one of the antenna elements. A signal 
processor system connects to the other ends of the phase shifters for 
processing the radio frequency signals. A data processor system controls 
the signal processor system, and connects to the phase shifters for 
controlling the relative phase shifts of the radio frequency signals 
propagating in the phase shifters. 
The system further includes a manually operable beam steering control 
connected to the data processor system for inputting beam steering 
information. The data processor system is responsive to the beam steering 
control for controlling the relative phase shifts of the radio frequency 
signals propagating in the phase shifters. The system further includes a 
sensor circuit for sensing a parameter, such as temperature, of the phase 
shifters. The sensor circuit connects to the data processor system for 
inputting information that the data processor system responds to when 
controlling the relative phase shifts of the radio frequency signals 
propagating in the phase shifters. 
When the phase shifters are ferroelectric phase shifters, the data 
processor system applies analog control voltages to the phase shifters for 
controlling the relative phase shifts. The beam steering control permits 
an operator to manually control the position of the beam in real time, or 
to effect automatic scanning and control the beam scanning rate by 
controlling the input of the beam steering information. 
According to another aspect of the invention, there is provided a 
telecommunication method for radiating and receiving a beam of radio 
frequency signals with a phased-array antenna having a plurality of spaced 
antenna radiators. The method comprises the steps of generating a radio 
frequency signal, and propagating the radio frequency signal along a 
plurality of parallel phase-shifting paths with each of the phase-shifting 
paths having elements for regulating the amount of phase shift therein. 
The method includes feeding a different one the antenna radiators with the 
radio frequency signals propagating in a different one of the phase 
shifting paths. Further, the method contains the step of inputting beam 
steering information to a data processor system for controlling the 
elements for regulating the amount of phase shift in each of the paths.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, there is shown in FIG. 1 a telecommunication 
system in the form of a phased-array radar 20. It is to be understood that 
radar 20 is only exemplary and that the present invention is applicable to 
a variety of other types of telecommunication systems. Radar 20 includes 
frequency synthesizer 21 for generating radio-frequency (rf) energy for 
transmission by phased array antenna 22. The output of frequency 
synthesizer 21 connects to transmission switch 25, which has input/output 
lines 27 that connect to the system ends of a set of planar ferroelectric 
phase shifters 31-34. Ferroelectric phase shifters 31-34 also have antenna 
ends that connect to phased-array antenna 22 via lines 51-54. Phase 
shifters 31-34 are reciprocal devices in that energy may travel in either 
direction between their antenna ends and system ends. 
Phased-array antenna 22 has sixteen antenna elements 40 arrayed in four 
columns 35-38 with four elements 40 in each column. The four antenna 
elements 40 in each of columns 35-38 are joined in common and connect to a 
different one of the antenna ends of ferroelectric phase shifters 31-34 
via lines 51-54, respectively. Although other variations are possible, it 
is assumed for this description that antenna elements 40 are conventional 
planar ferroelectric microwave radiators. 
Processor system 60, which includes a conventional processor and an 
associated memory (not shown), has switch control output line 61 which 
connects to a control terminal of transmission switch 25. Conventional 
display monitor 62 also connects to processor system 60, as do the X and Y 
outputs of conventional joystick 64 and the output of standard keyboard 
63. Lines 68 connect processor system 60 to digital-to-analog (D/A) 
converter 69, which has output lines 71 that connect to different ones of 
the phase-shift control terminals of phase shifters 31-34. 
Temperature sensor circuit 42 connects to temperature sensors 43 which are 
mounted on each of phase shifters 31-34. Temperature sensor circuit 42 
transmits temperature information to processor system 60 via line 45. The 
use of temperature sensors 43 in the preferred embodiment is only 
illustrative, and it is contemplated that other sensors that measure one 
or more additional ambient conditions that can effect the phase-shift 
accuracy of phase shifters 31-34, such as pressure, humidity, magnetic 
field, etc., may also be used. 
Switch 25 further includes output lines 47 which connect to an input of 
radar receiver 48, which processes conventional radar signals before 
passing them to processor system 60 via line 49. Radar receiver 48 
connects to frequency synthesizer 21 via line 56 to obtain a reference 
signal to be used for down-conversion of the received signals during 
signal processing. Processor system 60 transmits conventional control 
signals to radar receiver 48 and frequency synthesizer 21 via lines 55. 
In general, phased-array radar 20 operates to transmit or receive radar 
signals via phased-array antenna 22. During a transmit period, processor 
system 60 operates transmission switch 25 to cause it to transmit rf 
energy generated by frequency synthesizer 21 to phase shifters 31-34 via 
parallel input lines 27. Processor system 60 also outputs phase-shift data 
to D/A converter 69, which converts that data into analog control voltages 
that are applied to the phase-shift control terminals of phase shifters 
31-34. Phase shifters 31-34 respond by shifting the phase of the energy 
propagating therein as a function of the control voltages applied to their 
phase-shift control terminals. In general, each control voltage will be 
different and may vary at a predetermined rate, thereby causing phase 
shifters 31-34 to produce different and varying phase shifts that result 
in producing a narrow antenna beam pattern that scans a given field of 
view along the directions of double-headed arrow 39. 
More specifically, during a transmit period, rf energy from phase shifters 
31-34 drives antenna elements 40. Because columns 35-38 are appropriately 
spaced at a certain distance and are driven at different phases, a highly 
directional radiation pattern results that exhibits gain in some 
directions and little or no radiation in other directions. Consequently, 
the radiation pattern of phased-array antenna 22 will produce a focused 
beam that can be steered in the directions indicated by double-headed 
arrow 39 in a plane perpendicular to columns 35-38. 
During a radar receive period, a reciprocal process takes place. 
Specifically, phased-array antenna 22 feeds received signals to the 
antenna ends of phase shifters 31-34 where they are shifted in phase. 
Processor system 60 operates transmission switch 25 so that these 
phase-shifted signals are passed to radar receiver 48 via lines 27 and 47. 
Only signals arriving at antenna elements 40 from a predetermined 
direction, determined by the relative phase shift imparted by phase 
shifters 31-34 and the spacing of antenna elements 40, will add 
constructively in receiver 48. Since, in general, processor system 60 
varies the phase-shifter control voltages at a given rate, phase shifters 
31-34 will produce corresponding relative phase shifts of the received 
signals. Consequently, antenna 22 will generally scan along the path 
indicated by the double-headed arrow 39. After radar receiver 48 detects 
the received signals in a conventional manner, it passes the detected 
information to processor system 60 for storage and display on display 
monitor 62, or for other processing. 
Keyboard 63 and joystick 64 permit operator control of radar 20. An 
operator uses keyboard 63, in a conventional manner, to request processor 
system 60 to perform conventional radar functions, such as determining and 
displaying target locations, velocity, identification, etc. An operator 
initiates manual or automatic beam steering with joystick 64. The operator 
manually sets an antenna beam into a specific angular position by rotating 
the handle of joystick 64 into a corresponding angular position along its 
X direction, there being no signal on the Y output at this time. Processor 
system 60 responds to reception of the corresponding X output signal from 
joystick 64 by calculating an appropriate set of phase-shift data which is 
sent to D/A converter 69. D/A converter 69 converts the phase-shift data 
into analog control voltages that control the phase shifts of phase 
shifters 31-34. As described above, the resulting antenna beam pattern of 
antenna 22 will now be directed in accordance with the joystick X setting. 
To point the antenna beam in a particular direction, the operator simply 
holds joystick 64 in a corresponding position. Also, the operator may 
continuously move the handle of joystick 64, in which case the antenna 
beam will follow along and perform a corresponding real-time scanning of 
the antenna beam. 
To perform automatic beam scanning, the operator moves the handle of 
joystick 64 in the Y direction. The degree of rotation in the Y direction 
of joystick 64 will determine the beam scanning rate. Processor system 60 
responds to the Y output from joystick 64, regardless of the X output, by 
generating appropriate sets of phase-shift data at a rate determined by 
the Y output. The sets of phase-shift data are transmitted to D/A 
converter 69 which then generates sets of control voltages for application 
to phase shifters 31-34. This action causes the antenna beam pattern to 
continuously scan at a rate determined by the joystick Y setting. For 
example, a maximum antenna beam scanning rate would ensue when joystick 64 
is fully deflected in the Y direction. Additionally, beam scanning at some 
minimum rate would ensue when the operator deflects joystick 64 to some 
predetermined minimum value in the Y direction. When the operator deflects 
joystick 64 below the minimum value in the Y direction, there would be no 
Y output and manual beam steering would be possible with appropriate 
deflections in the X direction. 
In response to receiving data from temperature sensor circuit 42, processor 
system 60 performs automatic temperature calibration of phase shifters 
31-34 before outputting phase-shift data on lines 68. As described above, 
conventional ferroelectric phase shifters can be sensitive to many ambient 
conditions, such as temperature, pressure, humidity, etc. It is 
contemplated in the present invention that appropriate sensors measure 
these ambient conditions and input appropriate data to processor system 60 
for use in calibration of phase shifters 31-34. Specifically, processor 
system 60 is preloaded with a calibration function that represents the 
relationship between the ambient conditions, such as temperature, and 
calibration error factors that may be multiplied with basic phase-shift 
data to produce calibrated phase-shift data. FIG. 2 depicts a calibration 
curve that illustrates a relationship between temperature and calibration 
error factors for a set of typical planar ferroelectric phase shifters 
31-34. Although the calibration function may be stored in processor system 
60 in various forms, it is preferred that calibration polynomials be 
constructed and stored for more rapid real-time generation of the 
calibration error factors. The following equation represents an 
illustrative example of a polynomial that corresponds to the calibration 
curve of FIG. 2: 
EQU EF=(a+bT+cT.sup.2 +dT.sup.3 +eT.sup.4) 
where the coefficients have the following values: a equals 0.797116794; b 
equals 0.004336266; c equals 0.000114612; d equals 1.8994*10.sup.-6 ; and 
e equals -1.958*10.sup.8 ; and EF and T are the calibration error factors 
and temperatures, respectively. 
Therefore, using the temperature data input by temperature sensor circuit 
42 on lines 45 and the internally stored calibration function, such as 
shown in the calibration curve of FIG.2 or the above corresponding 
polynomial, processor system 60 determines corresponding calibration error 
factors that are factor multiplied with basic phase-shift values that are 
calculated based only on the X and Y outputs of joystick 64 to obtain the 
phase-shift data which is output to D/A converter 69. 
FIG. 3 is a processor flow diagram primarily illustrating the phase-shifter 
control functions of processor system 60. In response to an operator input 
from keyboard 63 as determined in read STEP 80, processor system 60, in 
control STEP 81, performs conventional control of frequency synthesizer 21 
and radar receiver 48. Processor system 60 performs these control 
functions via lines 55. Additionally, radar receiver 48 uses the output of 
frequency synthesizer 21 to help process its input signals in a manner 
well known to those skilled in these arts. 
Processor system 60 next reads the output of radar receiver 48, in read 
STEP 83, updates stored data, in update STEP 84, and displays appropriate 
data, e.g., radar information, on display monitor 62 in display STEP 85. 
Next, processor system 60 reads the X and Y outputs from joystick 64 and 
the temperature information from temperature sensor circuit 42 in read 
STEP 86. Processor system 60 then performs new-data decision STEP 90 to 
determine if the most recently read data in read STEP 86 is different from 
the previously stored data stored in update data STEP 84, or from default 
data at system startup. If the data read in read STEP 86 is not new, 
processor system 60 looks at its input data to determine, in decision STEP 
91, if a new operator request has been made via keyboard 63. If the 
operator enters an exit command at keyboard 63, as determined in decision 
STEP 92, the process follows the yes path and exits at exit STEP 93. On 
the other hand, if the operator enters another command, such as a new 
transmit/receive request, processor system 60 returns to control STEP 81 
to perform appropriate control of frequency synthesizer 21 and/or radar 
receiver 48. If in decision STEP 91 processor system 60 finds that no 
operator command was entered, it returns to read STEP 83 to read and 
update the received signals. 
If in decision STEP 90 processor system 60 finds that the data read in read 
STEP 86 is new data, as compared to the most recently stored corresponding 
data (or default data at system startup), processor system 60 then 
proceeds along the yes path of decision STEP 90. Processor system 60 now 
performs polynomial calculations (or table lookup), in calculate STEP 94, 
to determine the calibration error factors based on the inputs from 
temperature sensor circuit 42 and the stored temperature calibration 
function (e.g., see the calibration curve in FIG. 2). 
Based on the X and Y positions of joystick 64, processor system 60 next 
calculates, in calculate STEP 95, the basic phase-shift values for phase 
shifters 31-34. This calculation assumes that temperature has no effect on 
phase-shifter performance. In generate STEP 96, processor system 60 factor 
multiplies the basic phase-shift values and the calibration error factors 
to generate the phase-shift data and control voltages for use, in control 
STEP 97, in controlling phase shifters 31-34. Switch control signals are 
also applied to switch 25 in control STEP 97. Processor system 60 then 
proceeds to decision STEP 91 and the process continues as described above. 
The set of the most recent data read in read STEP 86 is stored in update 
STEP 84 for use in new-data decision STEP 90. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. As mentioned above, the 
inventive technique may be readily applied to different types of 
telecommunication systems that employ a variety of other types of phased 
array antennas. The number of antenna elements and, therefore, 
ferroelectric phase shifters could be increased considerably. The number 
of antennas could also be increased so that a two- or three-dimensional 
field of view could be scanned. However, those skilled in these arts will 
recognize from the above teachings that telecommunication systems having 
control, beam-forming, and automatic calibration capabilities for a 
ferroelectric phase shifting array can have the following desirable 
features: low-power voltage-controlled phase shifters for driving antenna 
elements; automatic, real-time calibration of ferroelectric phase-shift 
errors; and digital circuitry for beam construction and steering using 
ferroelectric phase shifters. Consequently, the telecommunications system 
of the present invention will be: relatively inexpensive to manufacture; 
capable of reciprocal signal propagation; operable at low-power levels; 
light weight, compact and less complex; and highly stable under adverse 
operating conditions such as rapidly changing temperatures, pressures and 
the like.