In a series of previous issued and pending U.S. Patent documents inventors named in connection with the present document and various groupings of their colleagues have disclosed a family of electronic warfare radio receivers that are usable in obtaining military and otherwise useful information from an incoming microwave frequency radio signal and have also disclosed significant components of such receivers. Early in this sequence of patent documents the name “monobit receiver” was used in referring to both one embodiment of such a receiver and subsequently as a generic or family name for such receivers. Each of these receivers as preferably embodied is of a wide band nature and employs the Fourier transformation as a tool for identifying characteristics of the incoming radio frequency signal. Additionally each of these receivers has the attribute of employing a simplified multiplication arrangement in making use of the Fourier transformation results in order that a simple and low cost realization of the receiver can be achieved.
In each of these simplified multiplications the Kernel function portion of the Fourier transformation is represented by a unit value, a magnitude of one or near one, in order to avoid the mechanization complexity of full fledged multiplication algorithm during the receiver step when complex numbers representing an input signal are multiplied by a second set of complex numbers representing the Fourier transformation Kernel function. Generally these simplified multiplications have in the past been accomplished by insuring the second set of complex numbers, i.e., the Fourier transformation results, involve real and imaginary values of unity or near unity. As implied by the name “monobit receiver” the earliest of these simplified Kernel function receivers employs a Kernel function approximation representable by a single binary bit of information while the later versions of the receiver and indeed the present invention involve Kernel function arrangements requiring a greater number of bits, i.e., three or four bits. In view of these greater numbers of bits it is of course necessary to accomplish an actual multiplication operation involving the Fourier transformation results however for feasibility purposes some form of simplified and readily accomplished multiplication is needed.
In order to better appreciate the present invention it may be helpful to regress briefly and consider the evolution of simplified Kernel function realizations in our work. Such evolution commences with the realization of a Fourier transformation using only multiplication by unity or in essence no multiplication in the Fourier transformation computation algorithm. Kernel function realization in this manner is first disclosed in a U.S. patent of Tsui et al., a patent numbered U.S. Pat. No. 5,917,737, a patent wherein Kernel function values are located on a circle of unit radius at angular locations of 5/4, 3 5/4, 5 5/4 and 7 5/4 radians i.e., at locations displaced by forty five degrees from the real and imaginary axes of a coordinate axis plot. Actual coordinate axis locations of 1+j, 1−j, −1+j and −1+j are used for the Kernel functions disclosed in the U.S. Pat. No. 5,917,737 patent. For reference simplification purposes this and the several other patents issued to various combinations of persons from our laboratory are herein referred-to as “our patent” notwithstanding the differing group of inventors, with perhaps one common inventor, associated with each patent.
Our U.S. Pat. No. 5,793,323 therefore relates to the U.S. Pat. No. 5,917,737 patent in that it discloses a single integrated circuit chip arrangement for a monobit receiver employing the approximated Kernel function of the U.S. Pat. No. 5,917,737 patent. This patent also discloses several implementation compromises possible in applying the simplified Kernel function to receiver apparatus and provides a receiver that can cover a one gigahertz spectrum with a frequency resolution of 9.77 megahertz.
Our U.S. patent application Ser. No. 09/917,589 filed on Jul. 30, 2001 also relates to the U.S. Pat. No. 5,917,737 patent in that it discloses the use of a monobit receiver in combination with several bandpass filters in order to increase the number of simultaneously processable signals and enhance the dynamic range capability of the overall system.
The invention of our U.S. patent application Ser. No. 09/944,616, filed on Sep. 4, 2001, provides a straightforward approach to the enhancement of dynamic range in a monobit family receiver by increasing the number of Kernel function locations used in the Kernel function approximation from the four locations of the U.S. Pat. No. 5,917,737 patent and the U.S. Pat. No. 5,963,164 patent to eight locations. In the application of Ser. No. 09/944,616 Kernel function values located at the 5/4, 3 5/4, 5 5/4 and 7 5/4 radian locations are added to the Kernel function values at 0, 5/2, 5, and 3 5/2 radians with the added four values being slightly increased in magnitude from true unit circle values and in fact having a magnitude of (2)1/2 or 1.414. Some of these eight location Kernel function values depart slightly from unity magnitude however the overall results of the eight-location Kernel function appear favorable.
Additional of our U.S. Patent and Trademark Office documents involving Kernel function realizations include the application of Ser. No. 10/115,819, filed on Apr. 3, 2002, and now issued as Statutory Invention Registration H2109. This document is titled “PASSIVE MICROWAVE DIRECTION FINDING WITH MONOBIT FOURIER TRANSFORMATION RECEIVER AND MATRIX COUPLED ANTENNA”
In addition to these previous patent documents wherein use of a Kernel function realization of unity or near unity value is employed in order to achieve a simplified multiplication operation the U.S. patent application Ser. No. 10/354,267, filed on Jan. 31, 2003, discloses an electronic warfare receiver wherein a Kernel function realization of other than unity magnitude is used in combination with a simplified multiplication arrangement accomplished with a bit shifting multiplication algorithm. In the of Ser. No. 10/354,267, document the simplified bit shifting algorithm multiplication can be implemented with such minimal complexity and cost as to make the non-unity magnitude of the Kernel function of little consequence. The present invention may be considered as an extension of this simplification multiplication through shifting concept.
The present invention may also start with the initial realization that a significant difficulty with the monobit electronic warfare receiver results form the fact that the two signal instantaneous dynamic range achieved in such a receiver is undesirably low. The instantaneous dynamic range relates to the receiver's capability to detect two simultaneous signals of different amplitude and can be an important consideration in a receiver use situation especially when a hostile adversary is involved. Because of the non-linear property of the approximated Kernel function in the Tsui et al. U.S. Pat. No. 5,917,737 patent receiver, the two signal instantaneous dynamic range of this receiver is limited to about 2 dB. Using a different Kernel function in the later tribit receiver of the Ser. No. 09/944,616 application can improve this instantaneous dynamic range to about 10 dB. A receiver arrangement according to the present invention can further improve this dynamic range characteristic. Each of the patent documents, issued or pending, identified in this BACKGROUND OF THE INVENTION DISCUSSION is hereby incorporated by reference herein.
The present patent document continues in this line of Kernel function and Kernel function receiver patents and thus provides additional insight into the simplified Kernel function utilization art. In the present invention additional improvement of the dynamic range achieved in the monobit family of receivers is pursued while relaxing the previously perceived need to limit multiplications to unity magnitude values.