Abstract:
A spectrum analyzer includes a resonator board that in turn has a substrate and a plurality of resonators. Each resonator may include a first segment that includes a first segment discontinuity and that may also define a boundary and a second segment that has a second segment discontinuity. The second segment may be spaced from the first segment and wherein the second segment is disposed within the boundary defined by the first segment. The resonator board may also include a plurality of wires each of which may be generally parallel to each other and each having a resonator interposed therebetween.

Description:
This application is a divisional application of U.S. Patent Office application Ser. No. 10/886,273, entitled “Passive Radio Frequency Power Spectrum Analyzer,” which was filed on Jun. 24, 2004 now U.S. Pat. No. 7,061,220. A patent based on that Parent application is about to be granted. That Parent application was filed by the same inventors herein, is currently pending before the U.S. Patent Office and, under 35 USC § 120, is “an application similarly entitled to the benefit of the filing date of the first application.” This divisional application is being filed under 35 USC § 120, 35 USC § 121 and 37 CFR § 1.53 (b), and priority from the Jun. 24, 2004 effective date of the Parent application (Ser. No. 10/886,273) is hereby claimed. 

   GOVERNMENT INTEREST 
   The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of the United States of America without the payment of any royalty thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to devices and methods for analyzing an electromagnetic signal and, more particularly, to devices and methods of analyzing an electromagnetic signal power spectrum. 
   2. Related Art 
   Spectrum analyzers for use in analyzing signals at radio frequencies are available. For example, U.S. Pat. No. 6,392,397 to Thomas describes a spectrum analyzer that includes a frequency converter for converting, at each of a series of frequency settings, a received radio frequency signal into an intermediate frequency signal, each intermediate frequency signal being derivable from more than one nominal received radio frequency signals. The converter includes a frequency synthesizer for synthesizing the frequencies of the frequency settings and a mixer for mixing each synthesized frequency with the received radio frequency signal in a complex manner such that the candidate frequency intervals corresponding to an arbitrary frequency interval F if  are given by N.F ref ±F if , where N is any positive integer and F ref  is the synthesized frequency. 
   In operation, the spectrum analyzer carries out a frequency analysis of each intermediate frequency signal to produce a power spectrum thereof and constructs a composite received radio frequency signal power spectrum corresponding to each intermediate frequency signal power spectrum. The composite radio frequency signal power spectrums are then operated on by the spectrum analyzer to provide the actual power spectrum of the received radio frequency signal. 
   Such a power spectrum analyzer suffers from the drawback of high cost and complexity resulting from extensive circuitry including filters, dividers, clocks, etc. 
   SUMMARY OF THE INVENTION 
   In accordance with an embodiment of the present invention, a spectrum analyzer comprises a resonator board that in turn comprises a substrate and a plurality of resonators. Each resonator may comprise a first segment that comprises a first segment discontinuity and that may also define a boundary and a second segment that comprises a second segment discontinuity. The second segment may be spaced from the first segment and wherein the second segment is disposed within the boundary defined by the first segment. The resonator board may also comprise a plurality of wires each of which may be generally parallel to each other and having a resonator interposed therebetween. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following detailed description is made with reference to the accompanying drawings, in which: 
       FIG. 1  is a diagram showing a power spectrum analyzer comprising a matrix of resonators, generally parallel wires and an array of detectors in accordance with one embodiment of the present invention; 
       FIG. 2  is a diagram showing further details of a resonator of  FIG. 1 ; and 
       FIG. 3  is a diagram showing a power spectrum analyzer in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   One embodiment of the present invention concerns a device and a method for analyzing an electromagnetic power spectrum preferably in the radio frequency (RF) range. The device is lightweight and simple as compared with prior devices and methods and may comprise a matrix of resonators and wires configured to focus a particular wavelength of a signal at a particular angle. An array of detectors may be spaced from the resonators, e.g., split ring resonators, to indicate a particular wavelength based on the angle at which the signal is focused. 
   Referring now to  FIG. 1 , a power spectrum analyzer in accordance with one embodiment of the present invention is illustrated generally at  10 . In this embodiment, the power spectrum analyzer  10  comprises a resonator assembly or board  12  and an array of detectors  14 . 
   The resonator board  12  may comprise a substrate  16 , wires  18  and resonators  20 . The substrate  16  comprises a dielectric material such as PTFE or FR-4 and is more preferably a ceramic material manufactured by the Rogers Corporation of Rogers, Conn. 
   The wires  18  may comprise a metallic substance such as copper (Cu), Tin (Sn), aluminum (Al), Silver (Ag) or Gold (Au) and may be deposited on the substrate via, e.g., chemical vapor deposition (CVD) or formed via photolithography. The wires  18  are preferably deposited in such a manner that they are generally parallel to one another and in combination with the resonators  20  comprise a periodic matrix of resonators and parallel wires. The wires  18  are preferably located midway between the between the resonators  20  and such that the spacing between each of the wires and each of the resonators is generally equivalent. The wires  18  may comprise a thickness that is approximately five to ten times the skin depth. For example, at about 10 GHz, the skin depth of a copper wire may be approximately 670 nanometers and, accordingly, the thickness may be approximately 6700 nanometers or about 0.275 mils. 
   The resonators  20  may form rows and/or columns and in combination with the generally parallel wires  18  are believed to form a “left-handed” material at microwave frequencies. A left-handed material may be generally defined as possessing a negative index of refraction, n, where, both the electrical permittivity (ε) and the magnetic permeability (μ) are simultaneously negative. The wires  18  may provide a negative permittivity aspect by acting on an electrical component of an electromagnetic field. The resonators  20  may provide a negative permeability effect by acting on a magnetic component of an electromagnetic wave. Also, the resonator board  12  is shown for illustrational purposes as comprising a two by four matrix of resonators  20 , although, it will be understood that merely a plurality of resonators may be employed in the practice of the invention. 
   Referring now to  FIG. 2 , each resonator  20  may comprise a pair of segments  22 ,  24  comprising a metallic substance such as copper (Cu), Tin (Sn), aluminum (Al), Silver (Ag) or Gold (Au). Similar to wires  18 , the segments  22 ,  24  may be deposited or formed on the substrate  16 . The segments  22 ,  24  preferably comprise rings as shown, although, it will be understood that other geometrical shapes such as squares, rectangles and combinations thereof may be employed. The segments  22 ,  24  comprise splits or discontinuities  26  that may function to decrease the resonant frequency of the segment and thereby substantially reduce the dimension of the segments for a given wavelength. The segments  22 ,  24 , as shown on the substrate  16  ( FIG. 1 ), together generally define a single plane, although, it will be appreciated that other configurations such as that defining multiple planes may be utilized. 
   For analyzing a power spectrum of radio frequency signals, the segments  22 ,  24  may be separated as shown by the dimension (d) that may be within the range of between approximately 0.1 mm and 1.0 mm. Each segment  22 ,  24  may have a thickness (c) that is within the range of between approximately 0.1 mm and 1.0 mm. Segment  22  may have an inner radius (r 1 ) that may be within the range of between approximately 15 mm and 1.5 mm and segment  24  may have an inner radius (r 2 ) that may be within the range of between approximately 12 mm and 1.2 mm. The foregoing dimensions are provided for illustrational purposes only and, it will be recognized that, each of the dimensions depend on the center frequency or wavelength that is to be analyzed. For example, for the separation dimension (d) of segments  22  and  24 , 1 mm would be suitable for a few GHz whereas 0.1 mm would be more appropriate for 10 GHz. 
   Referring again to  FIG. 1 , the array of detectors  14  may be mounted on a support (not shown) that extends in a linear direction that may be generally perpendicular to a plane defined by the resonator assembly  12 . Each detector may comprise an active device with gain such as a microwave transistor for increased sensitivity or a passive device such as a bolometer. 
   During operation of the power spectrum analyzer  10 , an electromagnetic signal, represented by arrows  30  is passed through a collimator that provides for parallel rays and restricts a portion of the electromagnetic signal as shown at  32 . The electromagnetic signal then passes through the resonator board  12  whereby, because of the matrix of wires  18  and resonators  20  the signal is focused to a particular location depending upon its wavelength (see solid, dashed and dotted lines  32 ,  34  and  36 ). More specifically, it is believed that when an electromagnetic signal enters the resonator board  12 , the signal encounters negative values of permeability (μ) and permittivity (ξ), as described above, whereby the signal may suffer from chromatic aberrations. That is, different wavelengths come to a focus at different distances from the resonator board  12 . Accordingly, the detectors  14  may be spaced linearly away from the resonator board  12  to thereby measure an amplitude for each wavelength whereby a frequency spectrum of the signal may be found. The detectors  14  may be located at a particular distance via calibration depending upon a desired wavelength or frequency. 
   Although not shown, it will be understood that several resonator boards  12  with wires  18  and resonators  20  of different dimensions (c, r 1  and r 2 ) and separations (d) may be combined to cover a broad frequency in accordance with the present invention. In such an arrangement, the electromagnetic signal would pass through the boards with the larger dimensions first, then progressively smaller dimensions. That way, in the initial resonator board  12 , the longer wavelengths would be focused while the shorter wavelengths may pass through, relatively unaffected, to the next resonator board which would focus increasingly shorter wavelengths, and so on. 
   Another embodiment of a power spectrum analyzer in accordance with the present invention is shown generally at  100  in  FIG. 3 . The power spectrum analyzer  100  may be generally similar to that described above in  FIGS. 1 and 2 , and corresponding components are labeled correspondingly, although, preceded by the numeral one ( 1 ) so that wires  18  in  FIG. 1  are identified as wires  118  in  FIG. 3 . Thus, this embodiment further comprises a set of wires  118  and resonators  120  disposed on a resonator board  112  and the electromagnetic signal being focused to a particular location depending upon its wavelength, as represented by solid lines  132  and dotted lines  136 . Reference for the particular aspects and functions of each component may be had by referring to the detailed descriptions of  FIGS. 1 and 2  above. 
   A difference in the power spectrum analyzer  100  from that of the power spectrum analyzer  10  is that the resonator board  112  is operated, as shown, in a reflective mode rather than a transmissive mode. In this way, it will be appreciated that electromagnetic signals will be reflected and focused for receipt by a particular detector in the array of detectors  114  in accordance with wavelength. Thereafter, the amplitude of each wavelength may be measured to provide a power spectrum analysis for the electromagnetic signal  130 . it will be recognized that at higher frequencies, the reflective mode may be preferable to the transmissive mode because it should suffer much lower losses. 
   While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments; it is to be understood that the present invention is not limited to these herein disclosed embodiments. Rather, the present invention is intended to cover all of the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.