Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-10-29
2001-09-11
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S372000
Reexamination Certificate
active
06288673
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an active antenna with an array of radiating elements with a redundant architecture.
Various types of antennas are used to transmit or receive electromagnetic radiation, especially in the microwave frequency region, depending on requirements. The active antenna with an array of radiating elements is of special interest since it provides a transmit or receive pattern which can be configured at will; it can also generate several transmit or receive patterns.
The elements of the array of the same antenna are, generally, of the same type, that is to say they are all planar, horn-shaped, dipoles, helices, etc. The amplitude and the phase of the feed signal to each element determine the characteristics of the radiation pattern.
A beam-forming network is provided in order to feed the elements. This network includes phase shifters and possibly attenuators. The number of outputs of this array is equal to the number of elements. Each output is connected to an element by a power amplifier and, possibly, a filter. In the case of a receive antenna, a low-noise amplifier is provided instead of a power amplifier. The channel associated with a radiating element is termed an active subsystem.
The beam-forming network supplies each element with a signal whose amplitude and phase are matched to the desired radiation pattern.
In certain antennas, the programming of the beam-forming network can be modified. In this case, the network is said to be active. In the converse case (i.e. if the programming cannot be modified), the network is said to be passive.
Such antennas are used in particular on board vehicles, especially satellites or spacecraft. For on-board applications, such as space applications, it is necessary to limit the effects of any equipment failures on the performance of the antenna, i.e. to enable the antenna to meet specifications over a determined lifetime despite an anticipated occurrence of equipment failures.
The deterioration which may arise on account of equipment failures include, for a transmit antenna, a reduction in the Equivalent Isotropic Radiated Power (EIRP), for reception, the G/T ratio (where G is the gain and T the noise temperature of the antenna) and, in both cases, an upturn in the sidelobes, that is to say a deterioration in the specified transmit or receive pattern.
In general, equipment failures occur in the active subsystems.
Various solutions have been used hitherto to maintain the EIRP or the G/T coefficient of the antenna and its pattern within acceptable limits.
For transmit antennas, a first solution consists in uprating the power amplifiers and having them deliver a power greater than the specifications. However, excessive energy consumption is never desirable, especially in a space application. Moreover, with this solution it is not possible to correct the upturns in the sidelobes caused by equipment failures.
A second solution, which is applicable to transmission and to reception, consists in providing a number of radiating elements which is greater than what is strictly required. For example if, to meet the specifications, a number N of radiating sources is necessary, then a number Q is added to make provision for equipment failures. This solution also has the drawback of excess energy consumption at the beginning of the life of the antenna.
Moreover, if the beam-forming network is passive, that is to say if the amplitude and the phase of the feed signal to each element are not controllable, the initial performance must be better than what is strictly required so that the antenna can withstand equipment failures. This constraint necessitates uprating and usually cannot compensate for the effects of equipment failures; in particular, sensitive performance factors such as the level of the sidelobes are degraded with no possibility of compensation. If the beam-forming network is active, the antenna can be reconfigured after equipment failures; however, in this case, the abovementioned drawback of excess energy consumption at the beginning of the life of the antenna still remains.
In a third solution, the amplifiers and, optionally, the beam-forming network employ redundancy. For example, a number of reserve amplifiers are provided to replace defective amplifiers. In order for the wiring to remain within reasonable limits, in terms of simplicity and of bulk, each reserve amplifier can replace only a very limited number of active amplifiers. This constraint makes it impossible to minimize the number of reserve amplifiers. Moreover, replacement requires additional equipment such as switching elements, thus rendering the embodiment more complex and increasing the mass and the cost as well as the bulk. Although this solution theoretically makes it possible to maintain performance, it is not always satisfactory since the increase in mass and bulk are not optimal, especially for space applications.
SUMMARY OF THE INVENTION
The invention remedies these drawbacks.
It makes it possible to preserve optimal transmission and/or reception performance with a minimum increase in mass and bulk.
The antenna according to the invention is characterized in that the transmitter (or receiver) array includes a number of elements and of associated active subsystems which is greater than the requirements for transmission (or reception), and in that, whilst operating, the number of elements, and hence of active subsystems, used is equal to the requirements.
Thus, in the case of transmission, both at the beginning of the life of the antenna (before equipment failures), and also subsequently, there is no need to provide for excess energy consumption.
When an active subsystem fails, the active subsystem of one (or more) previously unused element(s) is(are) activated. The location of this activated element is chosen so that transmission (and/or reception) continues to meet the requirements. In other words, the possibility of maintaining performance is facilitated by the additional degree of freedom constituted by the choice of the location of the replacement element. This property is especially important when the feed amplitude and phase of the elements cannot be modified (that is to say when the beam-forming network is passive) since, if this choice were not available, there would be a risk of the performance of the antenna being degraded despite the activation of an element after the failure of another element.
The increases in mass and in complexity associated with the invention are less than the corresponding increases for prior art antennas which offer good resistance to equipment failures. This is because the number of reserve active subsystems is minimized.
Thus, according to one feature of the invention, the number of reserve elements and their feeds is equal to the minimum number necessary to meet the requirements, provision being made for equipment failures which may occur during the lifetime of the antenna.
An antenna according to the invention meets all the specified requirements. Starting from a full array which is slightly oversized with respect to requirements, Q sources are eliminated to guarantee the specified radiation performance, after elimination, by optimizing the radiation pattern using for example the method described in one of the following articles:
Y. T. LO and S. W. LEE: “A study of space-tapered arrays”, IEEE Trans. Antennas Propagat., vol AP-14, No. 1, January 1966, pages 22-30;
B. D. STEINBERG: “The peak sidelobe of the phased array having randomly located elements”, IEEE Trans. Antennas Propagat., vol AP-20, No. 2, March 1972, pages 129-136;
M. I. SKOLNIK, J. W. SHERMAN III and F. C. OGG Jr.: “Statistically designed density-tapered arrays”, IEEE Trans. Antennas Propagat., vol AP-12, March 1964, pages 408-417;
Y. TSUNODA and N. GOTO: “Sidelobe suppression of planar arrays antennas by the multistage decision method”, IEEE Trans. Antennas Propagat., vol AP-35, No. 9 September 1987, pages 1017-1021;
T. NUMAZAKI, S. MANO, T. KATAGI and M. MIZUSAWA: “An improved thinning method for density tapering of plan
Dolmeta Florence
Voisin Philippe
Alcatel
Phan Dao
Sughrue Mion Zinn Macpeak & Seas, PLLC
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