Abstract:
A portable wideband harmonic signal generator includes circuitry for generating a signal having a selected fundamental frequency, for producing a signal having a harmonic series of the selected fundamental frequency, for transferring the signal having the harmonic series using a balanced impedance output, and for directionally transmitting transferred signal having the harmonic series using a directional antenna having a characteristic impedance that is matched to the balanced impedance output. There is thus provided a compact, efficient transmitter and antenna assembly for transmitting a wideband signal.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     This application is a divisional of prior U.S. patent application Ser. No. 13/167,935 filed on 24 Jun. 2011 and claims the benefit under 35 U.S.C. §121 of the prior application&#39;s filing date. 
     CROSS REFERENCE TO OTHER PATENT APPLICATIONS 
     This patent application is co-pending with the following related U.S. patent application Ser. No. 13/167,935 by the same inventors, Richard S. Frade and Kenneth White. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to high frequency communications and is directed more particularly to a design for a portable wideband antenna-radiated signal generator. 
     (2) Description of the Prior Art 
     Often, personnel such as EM (electromagnetic) and communication engineers/technicians require a test signal to be generated in order to perform continuity tests of an RF (radio frequency) transmission path through an antenna that is coupled to a receiver. To perform such tests, the personnel are often required to carry relatively expensive, sensitive, large, and heavy test equipment that inconveniently rely upon line power. The testing is especially even more problematic when operating on vessel platforms such as submarines where personnel are required to carry the test equipment through the submarine sail to conduct the test. Commonly encountered difficulties encountered while performing the tests include requirements that personnel must carry heavy and bulky test equipment, that expensive equipment be available, procedures that entail long test setup and breakdown times, and the need for ship power to power the test equipment. 
     In the prior art, wideband signal generation is addressed: 
     In Telewski (U.S. Pat. No. 3,777,271), a step recovery diode is driven by two or more frequencies to form a harmonic generator. 
     In McEwan (U.S. Pat. No. 5,274,271), an output pulse generator for wideband applications is disclosed. 
     In Nelson et al. (U.S. Pat. No. 5,369,373) the step recovery diode 14 is disclosed that is driven by a sine-wave oscillator 12. In response, a wideband series of harmonics of the fundamental frequency is produced by frequency oscillator 12. The output of the step recovery diode 14 is supplied to one or more bandpass filters or lowpass filters which provide selection windows so that only a specified number of harmonic lines are passed within a selection window. 
     In Nellson, (U.S. Pat. No. 5,793,309) a short-range electromagnetic transceiver is disclosed in which an oscillator 14 excites a step recovery diode 12. The output of step recovery diode 12 is provided to a filter 24 that acts as a harmonic filter and selects the particular frequency of transmission. The output of filter 24 is gated to produce a short RF pulse which is a harmonic of the input excitation signal and is in the GHz range. The short RF pulse is propagated normal to the circuit and through space until it is dissipated or reflected from a target back into the antenna  20 . 
     As indicated in the references above, a need still exists for an efficient portable wideband antenna-radiated signal generator system design. An additional need exists for an energy efficient method for producing a wideband antenna-radiated signal. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention is to provide a compact high efficiency transmitter and antenna. 
     It is a further object of the present invention to provide an energy efficient method for producing a non-gated continuous wave wideband antenna-radiated signal. Other objects and advantages of the present invention will be apparent from reading the disclosure herein. 
     In accordance with the present invention, a portable wideband harmonic signal generator includes circuitry for generating a signal having a selected fundamental frequency, for producing a signal having a harmonic series of the selected fundamental frequency, for transferring the signal having the harmonic series using a balanced impedance output, and for directionally transmitting transferred signal having the harmonic series using a directional antenna having a characteristic impedance that is matched to the balanced impedance output. There is thus provided a compact, efficient transmitter and antenna assembly for transmitting a wideband signal. 
     The above and other features of the invention, including various novel details of construction and combinations of parts, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular assembly embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will be apparent with reference to accompanying drawings in which is shown an illustrative embodiment of the invention, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
         FIG. 1  is a diagram of a system implementing one embodiment of the current invention; 
         FIG. 2  is a diagram of a system implementing another embodiment of the current invention; 
         FIG. 3  is a diagram of a impedance matching and drive network for a step recovery diode of an embodiment of the current invention; 
         FIG. 4  is a diagram that illustrates an ideal frequency input and idealized frequency response of an embodiment of the network of  FIG. 3  in accordance with the current invention; 
         FIG. 5  is a diagram of a tapered micro-stripline of an embodiment of the current invention; 
         FIG. 6  is a diagram that illustrates a frequency response of the an embodiment of the tapered micro-stripline of  FIG. 5  in accordance with the current invention; and 
         FIG. 7  is a diagram of a system implementing a further embodiment of the current invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , a cross-sectional, view of the proximal end and side of an exemplary portable wideband antenna-radiated signal generator is shown and referenced generally by numeral  10 . Signal generator  10  includes a housing  12  that is arranged to be easily held in a single hand of a user. Housing  12  encases (and/or otherwise captivates) power unit  14 , human interface (not shown), wideband generator  18 , balun  20 , antenna  22 , and optional laser designator  26 . Housing  12  thus provides a common assembly for mounting various components of the signal generator 
     Power unit  14  includes a power source (such as a battery) and is controllably actuated in response to mechanical actions and/or electrical commands generated human interface. For example, initial actuation of power unit  14  causes power to be supplied to wideband generator  18 . 
     The human interface  16  is arranged to allow a user to select operating parameters for controlling wideband generator  18 . For example, a user can select a fundamental frequency (from 0 Hz to over 1.5 GHz) for generating a wideband signal (based on the selected fundamental frequency), output power of the wideband generator, output signal harmonic spacing, and operating mode (such as “off,” “stand-by,” and “normal”). 
     The wideband generator includes (and as discussed further below with respect to  FIG. 2 ) a programmable signal generator for producing a variable fundamental frequency signal. The variable fundamental frequency signal is coupled (directly or indirectly) to a step-recovery diode to produce an output signal that includes series of harmonics. 
     The output signal is coupled to balun  20  for wideband impendence matching. Balun  20 , for example, is a tapered stripline having 50 ohms (unbalanced) input impedance and 20 ohms (balanced) output impedance. A tapered stripline exhibits the characteristic of passing frequencies having wavelengths greater than around twice the length of the tapered portion of the tapered stripline. An example balun is discussed below with reference to  FIG. 5  and  FIG. 6 . 
     The output of balun  20  is coupled to antenna  22 . Antenna  22  is arranged to maximize the efficiency of radiation and directionality of a wideband radiated signal  24  (thus contributing to the overall efficiency of signal generator  10 ). In an embodiment, antenna  20  is a traveling wave antenna arranged as a “vee” (V-shaped) dipole antenna. Thus, antenna  20  is a passive component that exhibits relatively flat impedance characteristics over a wide range of input frequencies and minimizes reflection of input frequencies. When the fundamental frequency being broadcast has a wavelength that is greater than five times the length “l” of the antenna  20 , termination is not typically required. Otherwise, proper termination of antenna  20  results in substantially no reflections. 
     Each of the radiators of antenna  20  are arranged in a vee-shaped pattern having an angle of 2θ (where the angle θ is the angle between one radiator and the central axis of propagation of wideband radiated signal  24 ). The radiators of antenna  20  arranged with the proximal portion of the antenna  20  having the radiators more closely spaced together and the distal portion of the antenna  20  having ends of the radiators spaced further apart. Angle 2θ can be selected to maximize constructive interference of sidelobes radiated by each radiator along the central axis of propagation of wideband radiated signal  24 . 
     The housing  12  of signal generator  10  includes an optional laser  26  for designating a point in an area (e.g., for targeting purposes) that is irradiated by the signal generator  10 . Laser  26  is controlled by the human interface and powered by power unit  14 . Laser  26  can be configured to produce laser beam  28  in response to the signal generator  10  being programmed to radiate power. Thus, laser  26  can also serve as a warning indicator that the signal generator is actively transmitting. 
     Referring now to  FIG. 2 , a diagram of another embodiment of portable wideband antenna-radiated signal generator is shown. Signal generator  30  includes a battery  32  for purposes of supplying power to electrical components of the signal generator  30 . The battery  32  (as well as the other components of signal generator  30 ) is sized to fit with in a hand-held housing of the signal generator  30 . The power output of battery  32  is coupled to power regulation circuit  34  for control and regulation. 
     Micro-controller  36  is arranged to provide and receive human commands to and from a human interface  38 . For example, a user can use the human interface  38  to provide commands for controlling the signal generator, such as providing a command to activate (e.g., “turn on”) or deactivate the signal generator  30 . 
     Such commands are received by the micro-controller  36 , which in turn (for example) sends control signals to the power regulation circuit  34  for switchably coupling power from the battery  32 . The micro-controller  36  is arranged to control other components of the signal generator  30  as further described below. In various modes of operation the micro-controller  36  may offer differing test scenarios to a user (from which the user can select a particular test scenario). Each test scenario includes a list of values of various operating parameters, so that the user is not required to individually enter each of the operating parameters of a particular test scenario. 
     The micro-controller  36  is arranged to control DDS (direct digital synthesizer)  40  to provide a selectable fundamental frequency, which is selected from a range including for example, from DC (direct current) to a frequency above 1.5 GHz. DDS  40  typically includes a crystal oscillator reference and is programmable in real time to produce a selected frequency. The frequency of the fundamental frequency is selected, for example, in response to a command received by the user interface  38 . The DDS  40  is controllably powered by power regulation circuit  34 . 
     RF amplifier  42  is coupled to the output of DDS  40  such that the RF amplifier  42  receives a fundamental frequency signal having a frequency as programmed by the micro-controller  36 . The RF amplifier is arranged to receive a command from the micro-controller  36  to specify an amount by which to amplify the received fundamental frequency signal. The RF amplifier  42  is controllably powered by power regulation circuit  34 . 
     RF switch  44  is coupled to the output of the RF amplifier  42  to receive the amplified fundamental frequency signal. The RF switch  44  is arranged to receive a command from the micro-controller  36  to specify whether the amplified fundamental frequency signal is to be coupled to a lower frequency bypass path or a harmonic generator frequency path (which tends to act as a high-pass filter). The lower frequency bypass path is typically used when broadcast signals of the signal generator  30  have lower frequencies (e.g., from direct current to around 1.5 GHZ). Using the lower frequency bypass path when testing lower frequency responses can be used to avoid high-pass filtering (by impedance matching components such as wideband matching network  64 , discussed below) of lower frequency components of the signal to be broadcast by signal generator  30 . 
     Accordingly, low-frequency matching network  46  is arranged to receive the amplified fundamental frequency signal when the RF switch  44  is configured to couple the amplified fundamental frequency signal to the low-frequency matching network  46 . The low-frequency matching network  46  is arranged to receive the amplified fundamental frequency signal in an unbalanced medium and to provide the amplified fundamental frequency signal using a medium that is balanced with respect to transmitting wide-band antennas  54 . 
     The harmonic generator frequency path is selected when the RF switch  44  is arranged to couple the amplified fundamental frequency signal (e.g., received from the RF amplifier  42 ) to the drive and bias network  48 . When the harmonic generator frequency path is selected, the drive and bias network is arranged to stabilize, match impedances, and drive the SRD (step recovery diode)  50 . The SRD  50  is a microwave diode having steep doping profiles and relatively narrow junctions for optimizing diode charge storage. The fast recovery of injected charge for the SRD  50  provides a rapid transition period and efficiently produces a wide range of harmonics of the frequency of the amplified fundamental frequency signal. The operation of drive and bias network  48  and SRD  50  are described more fully below with respect to  FIG. 3  and  FIG. 4 . 
     The wideband harmonic output of SRD  50  is coupled to wideband matching network  52 . A wideband matching network  52  matches the impedance of the output of SRD  50  with the wideband antennas  54 . An example of a wideband matching network  52  is described below with respect to  FIG. 5  and  FIG. 6 . An example of wideband antennas  54  is antenna  22  that is described above with respect to  FIG. 1 . 
     Referring now to  FIG. 3 , the operation of drive and bias network  48  and SRD  50  is now described. A network  56  is formed by (passive) components choke  58 , capacitor  60 , and resistor  62 , capacitor  64 , choke  66 , capacitor  68 , and choke  70  coupled to SRD  50 . The network  56  receives an input signal that includes a fundamental frequency at node Vin and provides an output signal at node Vout that includes harmonics of the received fundamental frequency of the input signal. 
     The amplified fundamental frequency signal (from the RF amplifier  42 , for example) is received at input node Vin. Choke  58 , capacitor  60 , and resistor  62  are arranged as a high-pass filter for increasing the stability of the output of the SRD  50 . Resistor  62  is selected to bias the input voltage of the SRD  50 . A low-pass filter is formed by capacitor  64  and choke  66  and is arranged to match the impedance of the network  56  with the source impedance of the incoming amplified frequency signal. A second low-pass filter is formed by capacitor  68  and choke  70  and is arranged to drive and enhance harmonic frequencies output by SRD  50 . 
     Referring now to  FIG. 4 , the input and output frequency characteristics of network  56  are discussed. Plot  72  represents an idealized fundamental frequency (generated by DDS  40 , for example) that is provided as an input to network  56 . Plot  74  represents an idealized frequency response of network  58  to the input fundamental frequency. Plot  74  illustrates a series of harmonics of the fundamental frequency wherein the amplitude of each harmonic generally decreases with increasing distance (in frequency) of each harmonic from the input fundamental frequency. Thus, when the fundamental frequency is adjusted (by changing a controllable input of DDS  40 , for example), the spacing and location of the illustrated harmonics vary in response to the change of the fundamental frequency. The output of network  56  is typically coupled to a wideband matching network, such as balun  20 . 
     Referring now to  FIG. 5 , a wideband matching network for matching the output impedance of a harmonic generator to an input impedance of a wideband antenna is discussed. Wideband matching network  56  is illustrated as a (passive) tapered micro-stripline  78 . Tapered micro-stripline  78  includes an input section  80 , the tapered/middle section  82 , and an output section  84 . Input (proximal) section  80  has a characteristic impedance of around 25 ohms and is about 30 mils wide. Tapered/middle section  82  has a length  76  that extends about 300 mils lengthwise and has a width that gradually tapers over the 300 mil distance of about 30 mils wide to about five mils wide. Output (distal) section  84  has a characteristic impedance of around 50 ohms and is about five mils wide. Thus, the characteristic impedance of tapered micro-stripline  78  gradually varies from input impedance of 25 ohms to an output impedance of 50 ohms across the length  76  of the middle section  82 . The frequency response of the tapered micro-stripline  78  is now discussed with reference to  FIG. 6 . 
       FIG. 6  illustrates the frequency response of the tapered micro-stripline as illustrated in  FIG. 5 . Plot  86  generally illustrates a frequency response of the tapered micro-stripline  78  over a range input frequencies extending from direct current (DC) to 50 GHz. For example, a response such as “return loss” in dB is illustrated using curve  88  and a “reflection coefficient” (as a linear function) is illustrated using curve  90 . The response to frequencies higher than the illustrated 50 GHz are similar to the responses illustrated in the 10-50 GHz portion of plot  86 . In particular, the maximum amplitudes for input frequencies greater than around 10 GHz (theoretically) maintains a value of around −40 dB as the input frequencies extended towards infinity. Thus, the tapered micro-stripline is arranged to efficiently transmit higher frequencies without appreciable “roll-off” (e.g., progressively higher attenuation of higher frequencies) of the higher-end harmonics produced by an SRD such as SRD  50 . 
       FIG. 7  illustrates testing of a communication system using a portable wideband antenna-radiated signal generator. Vessel  92  includes a relatively inaccessible area such as a sail area  94 , wherein the sail area  94  includes components of a communication system that are to be tested. The components include visible components (such as an antenna  96 ) and hidden components (such as cabling and transceivers, not shown). A portable wideband antenna-radiated signal generator (such as signal generator  10 ) is used to externally irradiate antenna  96  for testing (for example) continuity from the antenna  96  to a transceiver within the vessel  92 . The signal generator  10  is typically used at location that is proximate to the sail and is around 3 meters distance from a target antenna. The signal generated by signal generator  10  can be measured using equipment coupled to components of the communication system within vessel  92 . Thus, the signal generator  10  can be used to easily and efficiently test components of a communication system, even when components of the communication system are included in a relatively inaccessible area. Likewise, the signal generator  10  can be used to easily and efficiently test components of the communication system even when relatively expensive assets (such as non-hand-portable test equipment and/or satellite communications) are not available or relatively costly to use. 
     Additionally, the signal generator  10  can be used to perform signal-to-ratio (SNR) tests in conjunction with available communication system assets. For example, a satellite  98  can establish a communication session with a transceiver aboard vessel  92  via antenna  96 . A user can, for example, select a fundamental frequency or frequency spacing (such as the “comb” spacing of harmonics) and power level for a signal to be transmitted from the signal generator  10 . (As discussed above, a user can select a test scenario, which then selects test parameters appropriate for programming operational parameters of the signal generator  10  to act as a signal generator for a particular test scenario.) The level of the power output of the signal generator  10 , the distance of the signal generator  10  to the antenna  96 , the frequency and/or frequency spacing of the output power of the signal generator  10 , and the measured strength of a signal from the satellite  98  can be used to determine the SNR response of the communication system. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description only. It is not intended to be exhaustive nor to limit the invention to the precise form disclosed; and obviously many modifications and variations are possible in light of the above teaching. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.