Patent Application
20100060507
This invention relates to passive electronic warfare receivers and, more particularly, to methods and apparatus for detecting and measuring electromagnetic radiation using a digital antenna.
Current electronic warfare receivers use the same basic analog technology pioneered nearly 100 years ago. This analog technology detects radio and microwave band photons by using an antenna and shielded cabling. The received photons are focused by the antenna to maximize the induced voltage in the shielded cable. The varying induced voltage is then filtered and mixed to achieve an appropriate intermediate frequency and bandwidth for measurement.
Current antennas, connecting cables and analog receiver hardware are both expensive and heavy. Most antenna and receiver systems cost in excess of $500,000 per unit, are in excess of 100 pounds in weight and require over 500 watts of power. This limits the platforms on which electronic warfare receivers can be utilized and the customer base willing to pay for such systems. Additionally, the measurement techniques utilized can process only one narrow frequency range at a time. If a large detection frequency range is required, the receiver is sequentially tuned through each frequency bandwidth, with enough time allowed at each interval to detect the desired signals. This lengthens the amount of time required to scan a large frequency range and to measure the signals present. Modern military radar uses stealthy, low probability-of-intercept signals that are radiating for short periods of time and are difficult to detect with limited bandwidth receivers. Additionally, problems arise when a signal of varying frequency moves outside the bandwidth currently being scanned. Techniques must be employed to reconstruct a signal detected at different times in different frequency bands. These techniques are not feasible for stealthy signals that may not reappear at regular intervals.
Accordingly, there is a need for improved electronic warfare receiver systems.
According to a first aspect of the invention, receiver apparatus comprises a digital antenna comprising a semiconductor device including a plurality of pixels, each pixel configured to produce a voltage that represents received photons at a photon frequency of the pixel, a measurement unit configured to sample the voltage of each pixel at multiple sampling times to acquire a set of voltage samples for each pixel and to record the set of voltage samples and corresponding sampling times, and a receiver processor configured to process the sets of voltage samples and corresponding sampling times to provide information on one or more detected signals represented by the received photons.
According to a second aspect of the invention, a method for receiving electromagnetic radiation comprises (a) detecting radiation with a digital antenna comprising a semiconductor device including a plurality of pixels, each pixel configured to produce a voltage that represents received photons at a photon frequency of the pixel, (b) sampling the voltage of each pixel of the digital antenna, (c) recording the voltage sample and corresponding sampling time for each pixel, (d) resetting each pixel following sampling, (e) repeating acts (b)-(d) to acquire a set voltage samples for each of the pixels in the digital antenna, and (f) processing the sets of voltage samples and corresponding sampling times to provide information on one or more detected signals represented by the received photons.
According to a third aspect of the invention, receiver apparatus comprises a digital antenna comprising an array of pixels, each pixel configured to produce a voltage that represents received photons at a photon frequency of the pixel, and a processing unit configured to sample the voltage of each pixel at multiple sampling times to acquire a set of voltage samples and to process the sets of voltage samples and corresponding sampling times to provide information on one or more detected signals represented by the received photons.
For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:
The present invention provides novel methods and apparatus for detecting and measuring electromagnetic radiation. The apparatus includes a digital antenna to detect electromagnetic radiation and a processing unit to process outputs of the digital antenna. The detected electromagnetic radiation may represent one or more signals transmitted by one or more emitters. Rather than relying on the induced voltage caused by an electric field, individual photons are collected by the digital antenna and converted directly into a binary value. The binary photon count represents the electromagnetic wave measurement. The apparatus is particularly useful in passive electronic warfare applications but is not limited to such applications.
In some embodiments, the digital antenna includes a semiconductor device configured as an array of pixels. The semiconductor device includes a doped semiconductor surface followed by a series of voltage potential well pixels. The semiconductor device is doped to lower the energy gap of the valence band below the threshold of radio frequency photons. When a radio frequency photon strikes the semiconductor device, an electron is excited into the conduction band and is trapped by a potential well pixel. Each trapped electron lowers the voltage of the pixel. The number of electrons contained in a pixel at any given time can be determined by measuring the voltage of the pixel.
The potential well pixels in the digital antenna are precisely set to trap only electrons of a given energy. Each pixel is responsible for capturing the excited electrons from a specific photon frequency. The frequency bandwidth and resolution of the digital antenna depend on both the total number of pixels in the array and the energy tolerance of each pixel.
A block diagram of receiver apparatus in accordance with an embodiment of the invention is shown in
Digital antenna 10 may include an array of pixels 20, 22, 24, etc. on a semiconductor device as described below. Each pixel 20, 22, 24, etc. in digital antenna 10 is configured to detect photons at a specific photon frequency. In practice, each pixel detects photons over a limited frequency range. The photon frequencies of the pixels in the pixel array are selected to cover a desired frequency range. The digital antenna 10 may be configured to detect received photons over one or more frequency ranges or at specified photon frequencies. The number of pixels in digital antenna 10 depends on the number of photon frequencies of interest. The array of pixels may be configured as an array of rows and columns of pixels, but is not limited to this configuration. The digital antenna 10 may include any number of pixels.
In the embodiment of
Each pixel is capable of trapping only those electrons with a specific energy range above the bandgap. This limits the pixels to known frequency ranges. By staggering the pixel bandgaps at fixed intervals, a frequency range for the digital antenna is established.
The digital antenna pixels are preset to an arbitrary voltage. Each trapped electron changes the voltage of the pixel by a fixed amount. A high speed voltage sensor 50 and an accumulator 52, attached to each pixel, continuously read out and reset the voltage. The accumulator 52 “counts” the number of electrons in its pixel by subtracting the reading of voltage sensor 50 from the preset pixel voltage and dividing by the electron potential. The resulting count of the number of electrons in each pixel directly yields the number of photons received at the corresponding photon frequency of the pixel. Following each sample, the pixel voltage is reset. After a specified interval, the pixel is sampled again and the pixel voltage is again reset. This cycle continues indefinitely during the operation of the digital antenna. The accumulator 52 outputs the amplitude of each pixel by dividing the number of detected photons by the sample period, as shown in
The sampling frequency is based on the minimum pulse width measurement desired. For example, a digital antenna designed to detect a radar with a 500 nanosecond pulse width accuracy must read out each pixel at a rate of at least 2 MHz.
The amplitude outputs of each accumulator 52 are supplied to receiver processor 32 which performs the remainder of the signal measurement functions. The receiver processor 32 takes the set of all pixel amplitudes at a given time and subtracts a calibrated noise value from each pixel to determine which pixels contain amplitudes from photons of meaningful signals. The frequencies of the detected signals correspond to the photon frequencies of the detecting pixels. The number of consecutive data sets that contain the same signal are tracked to determine the pulse width of the signal. New pulse measurements are correlated to previous pulse measurements to determine the pulse repetition rate.
The angle of arrival of a detected signal can be any value within the field of view of the digital antenna. The digital antenna detects electromagnetic radiation directly incident on the semiconductor surface. Thus, the field of view can be tightly controlled by limiting the exposure of the semiconductor device. The receiver processor can measure the angle of arrival of a given signal by acquiring multiple channels of input from multiple digital antennas positioned in non-overlapping directions and noting the orientation of the antenna that detects a signal.
A timing diagram that illustrates an example of the outputs of pixels 20, 22 and 24 is shown in
Referring again to
Once signal measurements have been produced by the receiver processor, known electronic warfare software algorithms can be applied to determine the identification and location of the detected emitters.
An example of a digital antenna design in accordance with an embodiment of the invention is shown in
The measurement unit 30 acquires 1600 samples, one for each pixel, at each sampling time by measuring the voltages of the potential wells. The potential well voltage is reset after each sample is taken. The parameters of the detected signals are determined by receiver processor 32 as described above.
An example of receiver apparatus in accordance with a further embodiment of the invention is shown in
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
