Periodic and regular metal posts, a photonic bandgap (PBG) structure for guiding surface waves in a parallel-plate waveguide is proposed. The isotropic PBG structure is applied to the design of an asymmetric parallel-plate waveguide Luneburg lens (APWLL). The relation between the dimensions of the metal posts and the required refraction index in the lens is derived with transmission-line theory and the transverse resonance method. Different lattices for the entire lens are also investigated. For verification, an antenna for a 76.5 GHz adaptive-cruise control radar is fabricated, consisting of an APWLL, a primary feed, and symmetric corrugated flares to improve the property of the antenna in elevation. Measured results verify the PBG structure design in the APWLL.

A photonic bandgap (PBG) structure for guiding and suppressing surface waves in millimeter-wave antennas

Major advances in millimeter-wave antennas have been made in recent years, in particular in two areas. A new class of leaky-wave antennas based on open millimeter waveguides has been proposed and investigated, and substantial progress has been achieved in integrated antennas where active and passive circuits, possibly in monolithic form, are combined with the radiating elements in one compact unit. Interesting developments have taken place also in a third group of millimeter-wave antennas, that of microstrip antennas and printed circuit antennas in general. An attempt is made to summarize these developments. >

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Millimeter wave antennas

The high-frequency asymptotic solution of diffraction by a conducting subreflector is studied. By using Keller's geometrical theory of diffraction and the newly developed uniform asymptotic theory of diffraction, the scattered field is determined up to an including terms of order k^{-1/2} relative to the incident field. The key feature of the present work is that the surface of the subreflector is completely arbitrary. In fact, it is only necessary to specify the surface at a set of discrete points over a random net. Our computer program will fit those points by cubic spline functions and calculate the necessary geometrical parameters of the subreflector. In a companion paper by Y. Rahmat-Samii, R. Mittra, and V. Galindo-Israel, the scattered field from the submflector is used to calculate the secondary pattern of an arbitrarily shaped reflector by a series expansion method. Thus, in these two papers, it is hoped that we have developed a "universal" computer program that can analyze most dual-reflector antennas currently conceivable. It should also be added that our method of calculation is extremely numerically efficient. In many cases, it is one order of magnitude faster than the conventional integration method based on physical optics.

Diffraction by an arbitrary subreflector: GTD solution

Due to the low atmospheric absorption over W-band, numerous applications are expected, which should be developed at low cost. Short wavelength makes the dimension of antennas in this frequency range small, which usually requires sophisticated and expensive fabrication process. This communication presents a class of integrated wideband pyramidal horn antennas which can be made of low-cost multilayered printed circuit board (PCB) process. The proposed horn antenna radiates along the broadside to the substrate and uses substrate integrated waveguide (SIW) as its feeder. Transverse slot on the top metallic surface at the end of SIW is deployed to drive the horn antenna. Metalized via holes are used to synthesize the horn walls. The opening of the horn antenna is discretely flared from the bottom to the top layer. Measured bandwidth of the antenna is 35 GHz (70-105 GHz) while a relatively constant gain of 10 ± 1 dB is obtained over most of the bandwidth.

Millimeter-Wave Integrated Pyramidal Horn Antenna Made of Multilayer Printed Circuit Board (PCB) Process

Dual mode horns employed commonly as feeds for parabolic reflector antennas generate a radiation pattern that can be well-approximated by a Gaussian beam. To determine the far field of the antenna, it has been customary to perform integrations either of the physical optics currents on the reflector surfaces or of the ray optically determined field in the antenna aperture. These time-consuming integrations may be avoided if the Gaussian beam is tracked directly from the feed horn via subreflectors, if any, to the main reflector and then to the far zone. The tracking of such fields may be accomplished either by the complex-source point method or, in principle, by evanescent wave tracking. The former utilizes a complex coordinate space while the latter tracks fields entirely in the physical (real) coordinate space. For a parabolic antenna with an offset beam feed centered at the focus, both methods are examined here and an assessment is made of how the one can best complement the other. Numerical comparisons with results deduced elsewhere by a semi-heuristic procedure, and with experimental data, reveal the accuracy and versatility of the complex ray procedure.

Asymptotic analysis of parabolic reflector antennas

The corrugated horn has been established as an antenna with low sidelobes and backlobes, rotationally symmetric patterns (for square pyramidal and conical horn shapes), and broad-band performance [1]-[9]. These properties make this horn useful for many applications. Previous studies have used conventional aperture integration techniques to evaluate the patterns of the corrugated horn. In general, the near axis E -plane radiation pattern of a pyramidal corrugated horn may be adequately predicted from standard analysis established for the H -plane patterns of conventional horn geometries [3]. This method, however, fails to predict the far-out sidelobe and backlobe radiation levels. The work presented here uses a knowledge of the aperture fields to predict the pattern using aperture integration and diffraction theory. The assumptions made concerning the aperture fields were verified by probing the internal fields and aperture fields of an X band corrugated horn. The results of this field probing are contained in the Appendix. The method of solution used in this paper parallels that used in previous publications [10]-[12]. Specifically, the pattern in the main beam region is computed using conventional aperture integration procedures, the contribution of the H -plane edges is found using a slope diffraction analysis, and the contribution of the E -plane edges is found by use of duality.

Pattern analysis of corrugated horn antennas

Using recent developments of the geometrical theory of diffraction (GTD), the complete E - and H -plane patterns of Cassegrain antennas are computed. The pattern in the main beam region is computed by conventional aperture integration methods and the GTD analysis is used to evaluate the far-out lobes caused by spillover and by various edge diffraction processes. The effects of the edge curvature and surface curvature are included in the computations.

C. Mentzer

Papers

Pattern analysis of corrugated horn antennas

A GTD analysis of the far-out sidelobes of cassegrain antennas