Design

Designing a UWB high-power-microwave travelling-wave antenna

22nd April 2014
Nat Bowers
0

This application note from Computer Simulation Technology discusses the design and implementation of high-power-microwave (HPM) travelling-wave antenna. The antenna is designed to be driven by a high-power, single-shot signal generator with 1ns pulse-width at the -3dB power points, and peak voltage of up to 100kV.

Since the signal generator is equipped with an air-filled coaxial-waveguide output, a coaxial-waveguide to parallel-plates transition was also designed and fabricated. Initial theoretical electrical parameters and characteristics along with physical dimensions of the system were solved and derived using MATLAB. Then, the components comprising the antenna were modeled, solved and optimised using CST STUDIO SUITE. Using the CAD export capabilities in CST STUDIO SUITE, fabrication models and schematics were produced from the simulation model. The antenna was fabricated and measured results agree with simulation results to a great extent.

Lately, there has been a considerable increase of interest among both academic institutes and industrial companies around the world in transient HPM sources and HPM radiating elements for numerous military and civilian applications.

In HPM systems, the radiating elements play a crucial role in the design of the system. The impact of the radiating energy on the system itself is a major limitation, as equipment in close proximity to the antenna might suffer damage if the radiated energy is not directed properly. Furthermore, in order to radiate the high-power pulse (HPP) effectively and efficiently, several aspects must be carefully adhered to:

  1. Ultra-wideband (UWB): The HPP signal is UWB by nature due to its very short duration. Therefore, the antenna must meet a very demanding criterion of ultra-wideband operation bandwidth.
  2. Directivity: The antenna should be directional so that energy is not directed to any personnel or other equipment in close proximity.
  3. High efficiency: The radiating element and feed must be tightly matched in order to avoid standing-waves which might cause voltage breakdown.
  4. Power dissipation: In order to dissipate and withstand nonradiating energy while avoiding voltage breakdown, the antennas for HPM applications are fairly massive.
  5. Dispersion: In several applications, such as UWB radar, the dispersion of the antenna may also be needed to be taken into consideration as these systems rely upon correlations between the transmitted and received signal. The dispersion of the antenna is the spreading effect of the pulse resulting from variations in the antenna’s phase-centre over the wide frequency band.

Download and read the full CST application note below.

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