Communications: directive radio wave systems and devices (e.g. – With particular circuit – With polarization
Reexamination Certificate
2001-07-24
2003-08-19
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
With polarization
C342S013000, C342S082000, C342S083000, C342S175000, C342S195000, C342S361000
Reexamination Certificate
active
06608587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital polarimetric system and, more particularly, to a digital polarimeter for controlling the generation of polarization agile signals in a signal transmission system.
2. Description of the Related Art
Ground-based and airborne radar systems have long been used to detect and track hostile targets, such as aircraft and missiles. Typically, a radar system transmits RF signals, such as a sequence of pulses, toward the target. The surface of the target reflects at least some portion of the incident signal energy back toward the radar antenna where the pulse echo is detected, allowing the radar system to determine the target's range, angle or velocity.
To counter the effectiveness of such radar systems, electronic warfare (EW) systems attempt to interfere with radar signals by generating electronic counter measure (ECM) signals designed to confuse, mislead or overwhelm the radar system. By accurately determining the polarization of an arriving radar signal, an EW system can transmit a signal with the same polarization back to the radar system to interfere with the echo signal, or transmit a signal with an orthogonal polarization to deceive or jam the radar system. EW systems have relied on polarimeters to accurately measure the polarization of received radar signals and to control the polarization of the ECM signals transmitted back to the radar system.
Modern EW systems typically include a dual polarized antenna capable of receiving and transmitting RF signals with identifiable horizontal and vertical signal components. Such systems employ two polarimeters: a receive polarimeter, involving a four terminal network inserted into the receiver line; and a transmit polarimeter embedded in the input lines to a pair of power amplifiers which supply the components of signals to be transmitted to input terminals of the dual polarized antenna. The receive polarimeter measures the polarization of intercepted signals and generates two phase signals which represent the determined polarization. The transmit polarimeter receives the phase signals from the receive polarimeter and controls the polarization of a transmitted signal in accordance therewith, thereby producing a polarization agile signal that correspond to the determined polarization of the intercepted signal. Essentially, the transmit polarimeter is an analog network device that accepts one input RF signal and produces two signal components with a specific amplitude and phase relationship determined by the parameters supplied by the receive polarimeter.
EW system technology development was in its infancy at the time polarimeters in currently operational systems were developed; consequently, present polarimeter designs are based on analog components. These analog-based designs result in polarimeters that are bulky, heavy, costly, and that dissipate significant RF signal power. Although polarimeters based on digital technology could potentially avoid these problems, the extraordinarily high digital sampling rates that would be required to accurately measure and apply polarization are not feasible with current technology.
A receive digital polarimeter that overcomes this barrier to use of digital polarimeters is described in U.S. patent application Ser. No. 09/711,168, entitled “Digital Polarimetric System,” filed Nov. 13, 2000, hereby incorporated herein by reference in its entirety. The system described therein includes a digital polarimeter that employs a signal time stretching technique and digital signal processing of the time-stretched signal to accurately measure the polarization of a received RF signal with commercially available digital hardware. A superheterodyne receiver down converts received RF signal components to an intermediate frequency (IF), and analog-to-digital converters sample the signal components at much lower sampling rates than would otherwise be required to accurately measure the signal polarization. Each signal sample is “time stretched” by storing each sample in M locations in a memory, such that N samples occupy M×N memory locations. A digital signal processor applies incremental phase shifts to the digital samples until a phase-shifted combination of the digital samples yields a minimum null output. The phase shifts producing the minimum null identify the polarization of the received signal. The stretching and digital processing yield the required number of samples per cycle of the received signal for accurate polarization measurement, thus effectively increasing the digital sampling frequency.
The aforementioned system produces highly accurate polarization measurements with currently available analog-to-digital converters. By using commercially available digital hardware, the digital implementation makes polarimetric systems affordable to more EW systems than the more expensive conventional analog polarimeters. Furthermore, the use of digital polarimeter techniques avoids potential performance degradation caused by cross leakage signals typically present in conventional analog polarimeters, is more compact, lower in weight, more power efficient, and offers a greater mean time between failures than conventional high-power analog polarimeters.
While this digital receive polarimeter provides many advantages, it would be beneficial if similar advantages could be realized in a transmit polarimeter. Without improvements with respect to the transmit polarimeter, designs that include conventional analog transmit polarimeters may remain unaffordable in many small or low-cost EW systems. Furthermore, operational EW systems will remain burdened with the disadvantages of the more expensive, less reliable, bulky, heavy, high power consumption, analog transmit polarimeters. Accordingly, there remains a need for a reliable, inexpensive and compact transmit polarimetric system that uses currently available digital technology to overcome the performance limitations of analog transmit polarimeters.
SUMMARY OF THE INVENTION
Therefore, in light of the above, and for other reasons that become apparent when the invention is fully described, an object of the present invention is to employ digital polarimetric techniques to control the generation of polarization agile transmission signals using commercially available digital hardware.
A further object of the present invention is to reduce manufacturing and maintenance costs of polarimetric systems.
Yet a further object of the present invention is to eliminate performance degradation caused by electromagnetic signal leakage in transmission systems that employ polarimetric devices.
A still further object of the present invention is to reduce power requirements associated with transmission systems that employ polarimetric devices.
Another object of the present invention is to reduce the size and weight of polarimetric systems.
Yet another object of the present invention is to increase the reliability of transmission systems that employ transmit polarimetric devices, for example, increased mean time between failures (MTBF).
It is a further object of the present invention to make practical the delivery of polarization signal data to a remotely located transmitter.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
In accordance with the present invention, a digital polarimeter employs a signal time stretching technique to apply polarization phase shift characteristics to digitally generated polarization agile signal components using commercially available digital hardware. An RF signal to be transmitted is down-converted to an intermediate frequency (IF) and digitally sampled at a rate feasible with currently-available analog-to-digital converters. Horizontal and vertical signal components of the sampled IF signal are generated, and the digital samples of the two signal components are stored in
Cikalo Joseph
Sparrow Mitchell S.
Edell, Shapiro & Finnan,LLC
Gregory Bernarr E.
ITT Manufacturing Enterprises Inc.
LandOfFree
Digital polarimetric system for generating polarization... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital polarimetric system for generating polarization..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital polarimetric system for generating polarization... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092511