Wenlong Zhou

This paper presents applications for the suppression of the open stopband (OSB) in various periodic leaky-wave antennas using a tapered half-wavelength line. With the adoption of a slightly tapered half-wavelength line for each unit cell, the open stopband can be completely suppressed. The technique is very convenient for engineering application, without the calculation of the characteristic impedance of the line. It can be applied to various structures, including planar and non-planar structures. The design rule is generalized. Three examples are illuminated to demonstrate the applications. The first example is a series-fed microstrip patch antenna. The second one is a coaxial cable leaky-wave antenna. The third demonstrated antenna is a new substrate integrated waveguide (SIW) periodic leaky-wave antenna with trapezium slots. The SIW antenna owns the advantages of wide-angle scanning and high efficiency. A prototype of the SIW antenna is fabricated and measured, to validate the effectiveness of the technique.

Shorting vias loading in a substrate integrated waveguide (SIW) periodic leaky-wave structure is investigated for suppressing the open stopband. The SIW periodic leaky-wave structure with transverse slots can have the beam scanned in the backward and in the forward directions, but suffers from a large open stopband in which the reflection coefficient is increased and the gain drops drastically. A set of shorting vias are adopted to load the structure in each unit cell for suppressing the open stopband. The working principle of the technique is explained, with approximate equivalent circuits. When the slot and the shorting vias are spaced by a quarter guided wavelength, the series inductance in the slot can be canceled out by the shunt inductance in the shorting vias, and therefore, the open stopband can be suppressed. An antenna based on the via-loaded periodic structure is designed for validation. Simulation and measured results validate that the open stopband is successfully suppressed with the loading of shorting vias.

A simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but nonidentical elements per unit cell. With the technique, one needs only to optimize the distance between the two elements and the dimension of the second element, starting with a quarter of the period and the dimension of the first element. With the simple design procedure, the technique is practical and effective for the open-stopband suppression for various periodic leaky-wave antennas. Two periodic leaky-wave antennas with the technique are demonstrated. The first one is a new developed substrate-integrated waveguide antenna with two nonidentical transverse slots per unit cell. The antenna has a wide scanning range from the backward endfire to the forward direction and does not suffer from blind scanning points at endfires (if it is placed on an infinite ground plane). The antenna is theoretically investigated. The simulation and measured results are consistent with the theoretical results. The second one is a microstrip combline leaky-wave antenna, in which each unit cell contains two nonidentical open-ended stubs. The two examples validate that the technique proposed in this paper can completely eliminate the open stopband in periodic leaky-wave antennas.