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FractalComs Exploring the limits of Fractal Electrodynamics for the future telecommunication technologies INFORMATION SOCIETY TECHNOLOGIES (IST) PROGRAMME. Quality Factor and Radiation Efficiency Measurement of Genetically Designed Planar Monopoles WP4 Fractal devices development
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FractalComs Exploring the limits of Fractal Electrodynamics for the future telecommunication technologies INFORMATION SOCIETY TECHNOLOGIES (IST) PROGRAMME Quality Factor and Radiation Efficiency Measurement of Genetically Designed Planar Monopoles WP4 Fractal devices development Task 4.3: Prototype construction and measurement J.M. González and J. Romeu May 2003
University of Granada Request (1) • University of Granada applied GA for the design of Koch-like small antennas, developing a Pareto tool to optimize several characteristics of pre-fractal wire antennas simultaneously. • The code was also used to generate Euclidean structures to investigate wether fractal shapes might be the best alternative for the design of efficient antennas with minimum resonant frequency. • NEC was used to carry out the simulations. • The space to be filled by the antennas was a rectangle of dimensions h x w.
Pre-fractal Meander Line Zigzag Resonant Freq. 825 MHz 868 MHz 827 MHz Matching Freq. 878 MHz 836 MHz 836 MHz Matching -7.3 dB -8.3 dB -7.6 dB Quality Factor 12.8 14.1 13.6 Efficiency 96.7 % 96.7 % 97.1 % University of Granada Request (2) w=1.73 cm h=6.22 cm a=6.45 cm a=6.24 cm Copper wire = 0.2 mm
Fabricated Monopoles (1) • Standard electronics printed circuits board photo-etching technology was used to manufacture the monopoles. • FR4 fiberglass substrate: thickness 0.25 mm. Copper strips: 0.29 mm width and 0.25 m thick to have the same electrical section than the wire models. • Monopoles were mounted on a 80 x 80 cm ground plane. • Connection to the RF source through an SMA connector.
Pre-fractal Meander Line Zigzag /4 Fabricated Monopoles (2)
@ at resonance f0: Zcap=R+jXcap Zin=Rr+R+jXin @ RLC model: Measurement Procedure (1) • and Q measured using the Wheeler cap method. • The input impedance of the AUT is measured at the resonant frequency of the antenna with and without a cap. The cap is a metallic surface that completely encloses the AUT. /2
Rotated free-space input impedance Rotation Angle Matching Freq. Matching Freq.= Resonant Freq. Resonant Freq. Free-space input impedance Rotated Wheeler cap input impedance Wheeler cap input impedance Measurement Procedure (2) • To accurately model the input impedance of the antenna as an RLC circuit (series or parallel) a rotation on the measured data is applied to the Smith chart plot.
2 TM 01,1 TM 01,5 TM 01,9 TE 11,i TE 21,i 0 -2 -4 Return Losses (dB) radianlength limit -6 -8 -10 -12 0.1 1 2 3 4 5 6 f (GHz) Measurement Procedure (3) • The cap used to carry out the measurements was an aluminium cylinder (height: 12.5 cm; diameter: 6 cm). Modes inside a cylindrical cap excited by a /4 monopole resonant at 694 MHz and skewed 10º.
Measurement Results (1) • Radiation Efficiency t: strip thickness; w: measured strip wideness; w': desired strip wideness; : measured radiation efficiency; ': corrected radiation efficiency; simulated: computed radiation efficiency;
Measurement Results (2) • Quality Factor Q: measured quality factor; Qsimulated: computed quality factor;
Conclusions • The expected behavior of GA designs was assessed by comparison with a /4 monopole. • Differences between simulated and measured designs: • wires / strips ( same electrical section) • no connector / SMA connector soldering losses • conductivity of copper additional losses • Not corrected effects: • contact between cap and ground plane • sistematical errors: do not influence measured but Q
