CIICT 2009 Proceedings

4 mm -10 0 , -8 0 , -3 mm -8 0 , -6 0 , -4 0 ,-2 0 , 0 0 , 2 0 ,4 0 , 6 0 , 8 0 6 0 , -4 0 , -2 0 ,0 0 , 2 0 , 4 0 ,6 0 , 8 0 , 10 05 mm -12 0 , -10 0 ,-8 0 , -6 0 , -4 0 ,-2 0 , 0, 2 0 , 4 0 ,6 0 , 8 0 , 10 0 ,20mm12 0 10 mm -20 0 , -16 0 ,-12 0 , -8 0 ,-4 0 , 0 0 , 4 0 ,8 0 , 12 0 ,16 0 , 20 0-30 0 , -25 0 ,-20 0 , -15 0 ,-10 0 , -5 0 , 0 0 ,5 0 , 10 0 , 15 0 ,20 0 , 25 0 , 30 0 L—39.78 mmRe(z)1201001mm3mm2mm804mm10mm605mm4020mm200-30 -20 -10 0 10 20 30Angle(degree)1mm 2mm 3mm 4mm 5mm 10mm20mm ref8060(a)40WW2LW3HL1W1W—9.17 mmH—7.75 mmL1—22.65 mmW1—5.6 mmW2—2mmW3—2mmFigure 1: The PIFA antenna in free spaceFigure 2: The PIFA rotating along the y axis(Clockwise rotation represents a negative angle andcounterclockwise rotation represents a positiveangle)Im(z)200-30 -20 -10 0 10 20 30-20-40-60Angle(degree)1mm 2mm 3mm 4mm 5mm 10mm20mmref(b)Figure 3: (a) The real part and (b) imaginary partof port impedance variations with separation androtation angles at 2.44 GHz. The curves of refrepresent the PIFA port impedance in free space,where the ripple is caused by simulation numericalerrorsPort impedance is a parameter to demonstrateantenna detuning effects in a complex userenvironment, which impacts the resonant frequency andavailable power to antenna. To list the detail effects toantenna, the impedance is divided into real andimaginary parts instead of the usual S 11 . As exhibited inFigure 3 (a), the real part of the port impedancedecreases with rising separation and the deviationdecreases as well. Figure 3 (b) shows the imaginarypart of the port impedance, the slopes of the curves aregradually reduced with the growing separation whichcould be explained by weaker coupling between thePIFA and the human phantom. Approximate equationsare introduced to described these variations.Equation 1: The real part of the port impedanceRe( z ) = f d + n , d [1]( ) ( θ )8