Leaky-Wave Antennas with Low Sidelobes Based on Stub-Loaded Ridge-Rectangular Waveguides

1. Introduction Leaky-wave antennas based on an open-waveguide structure can become a candidate of millimeter-wave antennas. Since such a structure is already open, leakage is produced by introducing not a physical cut, but asymmetry of the structure. As a result, it supports a leaky mode (instead of a bound mode) and therefore radiates all along its length, possess flexibility in beamwidth and scans the angle of maximum radiation by changing the frequency. One of these open-waveguide structures for antenna purposes is the stub-loaded ridge rectangular waveguide[1][2], which consists of a ridge rectangular waveguide with an asymmetrically located stub guide. This guide radiates in a single polarization (with negligible cross polarization at all scan angles) and its width can be reduced to less than a half wavelength by the ridging effect, so that for use of a scanning array antenna, extra main beam due to a grating lobe can be avoided. Furthermore, since this guide has many structural parameters, it can be expected to develop an antenna with high performance, for example, with low sidelobes. The design of such an antenna has been tried by using the equivalent circuits[1], but it can not use practically because the guide includes many conductor edges at which the fields diverge, and then the equivalent circuits do not give the accurate design data. Therefore we have first developed the accurate analytical method incorporating the singular field behavior into the aperture-field expressions[2]. This method is possible to design a leaky wave antenna with high performance. So in this paper, we have proposed a design procedure of a leaky wave antenna with low sidelobes and developed the antenna with the Taylor distribution of –30dB sidelobes based on the stub-loaded ridge rectangular waveguide. The validity of the designed antenna has been verified numerically and experimentally.