Electrical Electronics

By E.V. Jull

Substitute equipment of aperture antenna research are defined during this book.

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Additional resources for Aperture antennas and diffraction theory

Sample text

The power radiated from an aperture in the z = 0 plane can be calculated from eqn. 2. With aperture fields E, H given by eqns. t For a resonant circuit a quality factor Q is defined as the ratio of the capacitive or inductive reactance of the circuit to its resistance and is a useful indicator of the frequency bandwidth of the circuit, the reciprocal of Q. A difficulty arises in applying this concept to antennas however, in that the stored electric and magnetic energies are individually singular.

F(k1)/(F[0); blocked the pattern is broad so that over the central portion of the antenna radiation pattern F'ik^^Fik^-S. The patterns F(kx)IF(Q) and F'tf^/FiO) are shown in Fig. , where it is apparent that aperture blockage narrows the main beamwidth. It also raises the level of the first sidelobe. If F(0) = 1 andp is the normalised level of the first sidelobe in the unblocked pattern, then F'(0)/F(0)= 1 - 5 / F ( 0 ) and F'/F(0) =p + S/F(0) at the first sidelobe in the blocked pattern. 16) which always exceeds p .

Soejima, 1963;Hansen, 1964). 1 Approximations and limitations A few examples of the application of Fourier transform theory to the calculation of the radiation properties of some practical antennas are given here. These examples are chosen to illustrate the method and nature of the approximations necessary in its application. The major approximation of the Kirchhoff or Fourier transform method is the assumed form of the field in the aperture plane both inside and outside the aperture. Usually the tangential electric field is assumed zero outside the aperture and the incident field in the aperture.