Millimeter-Wave Antenna of a Travelling-Wave Long Sinusoidal Slot in the Narrow Face of a Rectangular Waveguide
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Millimeter-Wave Antenna of a Travelling-Wave Long Sinusoidal Slot in the Narrow Face of a Rectangular Waveguide A. Oral Salman
Received: 28 May 2010 / Accepted: 13 October 2010 / Published online: 27 October 2010 # Springer Science+Business Media, LLC 2010
Abstract A travelling-wave long sinusoidal slot in the narrow face of a millimeter-wave (Ka-Band) rectangular waveguide is investigated. To the best of our knowledge, a slot of this shape is applied to the narrow face of a rectangular waveguide for the first time at this frequency range. The analytical study is based on the magnetic current model. Experimentally, far-field and S-parameters are measured and a good match is obtained between analytical and measured patterns. Frequency scan rates and velocity ratios of the structure are calculated. The effect of the sinusoidal slot’s geometrical parameters (amplitude, period and number of periods) on the radiation patterns is also investigated. The drawback of the sinusoidal radiator is its cross-polarized beam that is not convenient for antenna applications. These co and cross-polarized beams scan in two different angle regions. To filter/suppress the cross-polarized beam, a grid polarizer is mounted to the sinusoidal slot and a 15 dB suppression level is reached. S-parameters measurement shows that the antenna efficiency increases remarkably after the application of the grid polarizer to the slot. Keywords Millimeter-waves . Slotted-waveguide antenna . Leaky waves . Travelling-wave antenna . Cross-polarization suppression . Grid polarizer/filter
1 Introduction The slotting of a waveguide surface is a well-known and efficient way to obtain a radiator. One of the first theoretical studies of a narrow slot in a rectangular waveguide was given in 1948 [1]. The circuit parameters and attenuation constant of a continuous longitudinal slot and a narrow radiating slot in rectangular waveguide were analyzed by the microwave network approach or transverse resonance method in [2] and [3], respectively.
A. O. Salman (*) TUBITAK UEKAE (The National Research Institute of Electronics and Cryptology), Information Technologies Institute, Sensor Technologies Group, P. O. Box: 74, 41470 Gebze, Kocaeli, Turkey e-mail: [email protected]
J Infrared Milli Terahz Waves (2010) 31:1438–1451
1439
The shape and the dimensions of a slot is a critical issue in creating slottedwaveguide radiators. A long slot is a travelling-wave structure, which has a length more than three wavelengths and it is terminated properly. The radiated fields of this slot can be calculated by introducing a magnetic current along the slot [4, 5]. The slottedwaveguide antennas (SWA) are well-known structures [4–7]. They are widely used in radar and communication applications. They have simple structure, light weight and low level side lobes. Their efficiency is also high. The disadvantage of the SWAs is their low bandwidth due to their waveguide type excitation. Generally, rectangular-profiled waveguides are used in creating SWAs due to the need of si
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