2012 IEEE Asia-Pacific Conference on Antennas and Propagation, August 27-29, 2012, Singapore
Study on Design Parameters of Waveguide Polarizer for Satellite Communication Soon-mi Hwang Korea Electronics Technology Institute Seongnam-si, Republic of Korea
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Je-min Kim Korea Electronics Technology Institute Seongnam-si, Republic of Korea
[email protected] [email protected]
Kwan-hun Lee Kwang Woon University Seoul, Republic of Korea
[email protected]
TE10 x (3dB)
Abstract— In thesis, we analyze operation theory of iris polarizer for satellite-communication and suggest design parameters. We compare theoretical values and simulated values(commercial software), and propose the phase difference according to each design parameters changes.
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TE10 x (3dB)
Keywords : Design parameters of polarizer, Waveguide polarizer, Iris polarizer, Waveguide Iris polarizer
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Figure 1. Modes in waveguide iris polarizer I. INTRODUCTION
Radio waves used in the satellite communication are usually circularly polarized to avoid the Faraday rotation caused by the ionosphere. To generate a linearly polarized wave in reflector antenna feeds, a waveguide-type polarization transformer, commonly called polarizer, is generally employed. In the kind of waveguide polarizer is dielectric insertion type, septum insertion type, iris(= corrugation) type. Among these, iris polarizer have broadband and the manufacture is easy[1-2].
II. OPERATION THEORY The iris polarizer is consisted of a number of thin metallic fins arranged on two opposite walls of a square waveguide. Pair of fins placed on two opposite walls is called an iris. The iris acts as a shunt capacitor in the transmission line for the mode with its electric field normal to the iris. When the electric field is parallel to the iris, the iris can be represented as a series inductor. In the former case, the capacitive loading increases the phase propagation constant, while in the latter case the phase propagation constant is decreased. When a linearly polarized wave with its electric field at 45 degrees to the iris is incident on the input plane of the iris polarizer, it is converted to a circularly polarized wave after propagating through the polarizer. If we make 90 o phase difference of these two modes of waveguide, we can make the circularly polarized wave. If Df = 90 o is satisfied, Db | A band = Db | B band is formed in A and B bands. Figure 1 illustrates modes in waveguide iris polarizer.
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When the iris of the same interval is arranged inside the waveguides, the iris is represented by Figure 2.
b
l
l
(a) +
+ V1 -
B Yo
B Yo
I2
I1
Yo, b
Yo¢ , b ¢
l
V2 -
l
(b)
Figure 2. Periodically loaded transmission lines and its equivalent circuit (a) Inside iris, (b) equivalent circuit (β, β’: Phase propagation constant, l : Length, B/Y0 : Normalized iris susceptance, Y0, Y0’: Admittance) [3]
b ¢l = cos -1 [cos b l - B / Y0 sin b l ]
(1)
1/ 2
ù Y0¢ é B 2 B = ê1 +2 cot b l ú Y0 ë Y02 Y0 û
(2)
Between the empty waveguide and the waveguide with iris, the phase difference is expressed as follows: ΔVq = b ¢l - b l
(3)
If B/ Y0>0, the phase difference is positive and the iris acts as a capacitor. If B/ Y0
