An equivalent network for square and rectangular shaped microstrip radiating elements is derived. In order to simplify the problem the radiating element is considered as two slots separated by a transmission line of low characteristic impedance. The slots are characterized by their radiation pattern, directivity, and equivalent admittance. A design procedure for open circuit halfwave resonators and for arrays of such resonators is given. Finally, some antennas in the X band are designed and measured.

Linearly polarized microstrip antennas

An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations. >

Planar near-field to far-field transformation using an equivalent magnetic current approach

Presented here is a method for computing near- and far-field patterns of an antenna from its near-field measurements taken over an arbitrarily shaped geometry. This method utilizes near-field data to determine an equivalent electric current source over a fictitious surface which encompasses the antenna. This electric current, once determined, can be used to ascertain the near and the far field. This method demonstrates the concept of analytic continuity, i.e., once the value of the electric field is known for one region in space, from a theoretical perspective, its value for any other region can be extrapolated. It is shown that the equivalent electric current produces the correct fields in the regions in front of the antenna regardless of the geometry over which the near-field measurements are made. In this approach, the measured data need not satisfy the Nyquist sampling criteria. An electric field integral equation is developed to relate the near field to the equivalent electric current. A moment method procedure is employed to solve the integral equation by transforming it into a matrix equation. A least-squares solution via singular value decomposition is used to solve the matrix equation. Computations with both synthetic and experimental data, where the near field of several antenna configurations are measured over various geometrical surfaces, illustrate the accuracy of this method.

Near-field to near/far-field transformation for arbitrary near-field geometry utilizing an equivalent electric current and MoM

Approximate boundary conditions are a means for simulating material and surface effects in scattering and propagation. A number of conditions are discussed, and criteria are given for their validity.

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Approximate boundary conditions

A millimeter-wave dual frequency circularly polarized feed for an offset reflector antenna is being developed for a portable satellite ground terminal. The two frequency bands are Q - and K -bands for transmit and receive, respectively. A compact feed design consisting of a single corrugated horn with two circular waveguide concentric openings at the horn throat is described. Good aperture efficiency and low sidelobes in both of the frequency bands are achieved.

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A compact Q-K-band dual frequency feed horn

An analytically simple and sufficiently accurate asymptotic solution for the eigenvalues of spherical surface waves in corrugated conical horns is described. An iterative procedure for numerical evaluation of the exact eigenvalues associated with the surface waves of the lowest order is presented here.

Eigenvalues of spherical surface-wave modes in corrugated conical horns

Radiation from axially asymmetric aperture fed paraboloids employing source multipole expansions

Correction to "On Expansion of Cylindrical Bessel Function"

In this paper a criterion is established for the minimum distance of separation between the probe antenna and the test antenna that would result in accurate spherical near-field antenna measurements possible without probe correction. This criterion is arrived at by considering two different types of test antennas and calculating their near-fields with and without directivity of the scanning probe.

M. Narasimhan

Papers

Eigenvalues of spherical surface-wave modes in corrugated conical horns

Radiation from axially asymmetric aperture fed paraboloids employing source multipole expansions

Correction to "On Expansion of Cylindrical Bessel Function"

The effect of probe directivity in spherical near-field antenna measurements

Radiation from prime-focus paraboloids fed by rectangular waveguide horns employing source multipole expansions