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A new leaky-wave antenna is presented here that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. Part I presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations. Part II describes and derives the modifications required in the theory to account for flanges and/or finite stub length, and Part III is devoted to measurements at X-band and from 40 to 60 GHz on both the propagation properties and the radiation patterns; excellent agreement with the theory is demonstrated. Index Terms-Leaky-wave antennas. I. INTRODUCTION A leaky-wave line-source antenna is basically an open waveguide possessing a mechanism that permits a slow leakage of power along the length of the waveguide. This length then constitutes the radiating aperture of the line source and the radiation occurs in the form of a conical fan beam that is narrow in the plane of scan. When the aperture is horizontal and faces upward, the radiated beam is customarily scanned in elevation by varying the frequency. Most of the early leaky-wave antennas were based on closed rectangular waveguide where leakage was produced by introducing a physical cut in the waveguide top or side wall in the Manuscript

Several leaky-wave antennas have been described in recent years that possess excellent properties, and they all have in common a parallel-plate stub guide of finite height as part of the cross section. For taller stubs and for larger leakage rates (wider radiated beams), some interesting new exotic interactions occur due to coupling between the desired leaky mode and another leaky mode, which is a modification of the “channel-guide” mode. Although we have described such coupling behavior briefly previously, this basic new feature (the coupling between two leaky (complex) modes) is not generally known, and is discussed here in more detail and in a more general context. In addition to a broad qualitative discussion, numerical results are presented for structures based on NRD guide and on stub-loaded rectangular guide. We believe that these effects are universal to all leaky-wave structures that possess a finite stub height in the cross section, so that the discussion here serves as a model for what to expect for other structures

This study is concerned with a new type of dominant mode power leakage from uniform lengths of printed‐circuit waveguides, such as microstrip line, slot line, and coplanar waveguide. These leakage effects, which are presently not recognized and can therefore be unexpected as well as undesired, occur at higher frequencies, and are therefore important for millimeter‐wave integrated circuits and high‐speed circuits. The cross talk and coupling that result can ruin the performance of a complex, high‐density circuit unless the leakage effects are understood and controlled. The leakage effects reported here occur on uniform lengths of printed‐circuit waveguide on which the dominant mode is purely bound at ordinary microwave frequencies but becomes leaky at higher frequencies; they appear in addition to the leakage produced by conversion into surface waves at various discontinuities. The nature of the leakage is described, and numerical results are presented for several structures as illustrations of the variety of ways this type of leakage can arise.