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A peculiar feature of the antennas developed by IEMR, Ltd. is their operability at high levels of radiated power with a relatively high gain, the antenna size being minimum achievable.

Those antennas are designed, above all, to operate in pulsed generators producing high-power output both over broad- and narrow frequency bands.

To meet the above purposes, IEMR, Ltd. has developed and manufactured a number of antennas designed to radiate high-power pulsed signals. These antennas are as follows:

  • Horn antennas;
  • Coaxial-sector antenna;
  • Helical antennas;
  • Fractal antennas;
  • Plasma antennas.

Out of this entire set of the antennas we shall provide a brief description of only two types of the antennas that are of intense interest for applications in high-power pulsed generators and operable both over narrow- and broad frequency bands.

Coaxial-sector antennas

A coaxial-sector antenna was first developed and tested as part of the MILO (Magnetic Insulation Linear Oscillator) generator in 1986. The general view of this antenna is presented in Fig. 1.

   
 Fig. 1. Photograph of coaxial-sector antenna on measurement-taking test bed.  

The experimental research conducted to date and results of the appropriate computer simulations indicate that this kind of antenna has pretty good emission characteristics, a rugged structure and a relatively small size and weight.

Results of the experimental studies on the directivity pattern of the antenna are given in Fig. 2.

     
 Fig. 2. Experimentally obtainable directivity patterns of coaxial-sector antenna in E- and H-planes.  

Our proprietary antenna has the following performances:

  • Emission frequency, 2 GHz;
  • Mode of emission, recurring pulses;
  • Pulse width, 80-100 ns;
  • Power output, 0.9-0.95 GW;
  • Maximum antenna diameter, ≤ 35 cm.

This antenna forms the maximum radiation field along the axis of the generator. However, there may be certain assignments for which the axis of the directivity pattern must be shifted in relation to the axis of the generator at a certain angle.

Fig. 3 gives a modified version of coaxial-sector antenna the angle between the axis of which and that of the directivity pattern is several tens of degrees.

   
 Fig. 3. Photograph of coaxial-sector antenna the axis of directivity pattern of which is turned relative to that of antenna.  

This antenna has the following performances:

  • Operating frequency, 1.6 GHz;
  • Mode of operation, recurring pulses;
  • Pulse width, 80-100 ns;
  • Power output, 0.9 to 0.95 GW;
  • Maximum antenna diameter, ≤ 27 cm;
  • Maximum gain, ≥ 10 dB.

  • Antennas of this type are very efficient as part of various kinds of high-power pulsed microwave generators.

    Explosion-driven plasma antennas

    R&D and construction of plasma antennas (PA) is at present one of the most promising directions in the area of antenna theory and practice. Those antennas have, as their radiating element, plasma formations with various plasma parameters, different techniques of its production and variable geometry depending on the antenna applied purpose and emission characteristics assigned.

    A peculiar feature of the ongoing work at IEMR, Ltd. is development, production and proof-of-the-principle studies made on such PA the plasma of which is produced using explosives.

    Such approach enables to create conductive plasma jets with a high temperature and density over a relatively great length. However, to form them requires development of custom-made cartridges that provide for jet parameters assigned.

    The construction of PA may involve the use of either single jets as radiating elements or a set of plasma jets in order to create antennas of more complex configurations, such as, for example, multi-beam antennas. Also feasible is the employment of more sophisticated plasma formations in order to configure PA of dedicated shape.

    We shall now provide a description, as an example, of four-beam antenna the beams of which are created by plasma jets as formed by explosives. A photograph of this antenna complete with the driver and four cartridges in place is given in Fig. 4.

       
     Fig. 4. Explosion-driven four-beam plasma antenna 1 – Antenna driver system; 2 – Explosive-containing cartridges inserted in place to form two plasma jet-driven beams each; 3 – Plasma jet outlets; 4 – Detonator; 5 – Generator-radiated power feeder cable.  

    The experimental studies indicate that the four-jet explosion-driven plasma antenna has the following performances:

  • Central frequency, 700 MHz;
  • Breadth of spectral line of emission frequencies, 600-800 MHz;
  • Antenna gain in the operating frequency band, ≥ 7 dB.

    • More R&D in this direction shall allow to improve drastically the performances of these antennas despite the difficulties encountered during creation of the high-conduction plasma jets that are formed using explosives.

    Plasma explosion-driven antennas, the difficulties during their development notwithstanding, are extremely promising for applications in very diverse areas and, in particular, for their use in compact microwave generators that are operable in the low-frequency range at high levels of power radiation.

    Broadband log-periodic antenna array for high-power level operation

    The log-periodic antennas and arrays on their base belong to a widely used and well-studied antenna type. Nonetheless, the use of such antennas for radiated emission of broadband waveforms, both single and in bursts, presents a very complicated, although important, problem the resolution of which may result in its possible diverse applications in many scientific areas.

    IEMR, Ltd. has developed such a log-periodic antenna array that can emit single broadband impulses and bursts of several such impulses for operation at the levels of radiated power emission of 0.5-1 GW.

    The general view of one of the configurations of such a dedicated antenna array is given in Fig.1.

    Fig.1. General view of log-periodic antenna array used to emit broadband impulses with high level of peak radiated power emission, as shown with driver unit in test bed.

    The main characteristics of the array are as follows:

    Fig. 2 (а,b) shows the oscillogram of single broadband impulse as received by a broadband detector at a distance of 20 m from the antenna (a) and its wavelet spectrum (b).

    а)

    b)

    Fig.2 (a,b).Oscillogram of single broadband impulse (a) with peak power level 600 MW and its wavelet spectrum (b)

    Fig.3 (а,b) gives the oscillogram of a burst containing three broadband impulses picked up by the broadband detector at a distance of 20 m and its wavelet spectrum. The peak power level is 600 MW.

    а)

    b)

    Fig.3 (а,b). Oscillogram of burst of impulses (a) and its wavelet spectrum (b)

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