(10)

For proving the validity of the above equivalent circuit model, the simulated reflection coefficient of the proposed PIUWA for TE polarization under HFSS and ADS (Advanced Design System) are depicted simultaneously in Fig.3(b). As shown in the picture, the circuit model agrees well with the calculated results of HFSS. The value of R_L andR_H is optimized in HFSS for achieving desire absorbing performance. And the final value of the equivalent circuit parameters is obtained by tuning and optimizing in circuit simulation, here we use C₁ =0.073pF,L₁ =5.9nH, C₂ =0.036pF,L₂ =2.5nH, Z₁ =94Ω,β₁h₁ =90@17.5GHz,Z₂ =285Ω,β₂h₂ =110@14.1GHz. Different from the three resonances in most wideband absorbers, the proposed PIUWA generates four resonances in the absorption band which across 4.0 to 23.4GHz with a fractional bandwidth of 142%. The four resonance peaks are represented by f_(i) (i =1,2,3,4). To prove that the added resonance is owing to the presence of the cascaded transmission line between the two dipoles, here we simulated the model without the vertical substrate in the middle of the two dipoles for comparison, as shown in Fig.3(b). We can see that the comparative model only creates three resonance points within the absorption band from 4.5 to 21GHz with FBW of 129.4%. From the results above, we know that the existence of the cascaded transmission line between the two dipoles generates another resonant peak, at the same time the absorption bandwidth increased.

To get insight understand of the four resonant peaks, we give the susceptance curves for the different constituent parts of the proposed PIUWA, as depicted in Fig.3(c). From (2) we know that the admittance of the PIUWA can be calculated as follows: