Asymmetric Surface Plasmon Polariton Defected Ground Structure with Triple-Band Rejection and its Application in a Gysel Power Divider with Harmonic Suppression

Figure 10 compares the HFSS simulated S-parameters of the SSP-DGS and ASSP-DGS. Three transmission zeros at f_z1a, f_z2a and f_z3a appear on the |S₂₁| plot of the ASSP-DGS.

Figure 10 Simulated |S₂₁| of SSP-DGS and ASSP-DGS compared (w₁ = 1.5, g₁ = 0.5, l₁ = 5.5, a₁ = 12, b₁ = 13.8, sspl_a1 = 13.4, a₂ = 11, b₂ = 8.7, sspl_a2 = 8.3, sspw_a = 0.25 and sspg_a = 0.4 mm).

Figure 11 Simulated |S₂₁| of ASSP-DGSs with different periodic number n_a (w₁ = 1.5, g₁ = 0.5, l₁ = 5.5, a₁ = 12, b₁ = 13.8, sspl_a1 = 13.4, a₂ = 11, b₂ = 8.7, sspl_a2 = 8.3, sspw_a = 0.25 and sspg_a = 0.4 mm).

Figures 11 and 12 compare simulated transmission responses of the ASPP-DGS with different periodic numbers n_a and groove depths sspl_a. The location of the transmission zero f_z1a is insensitive to the change of the smaller defect structure. The zeros at f_z2a and f_z3a, however, are both drawn lower in frequency when either n_a or sspl_a is increased.

An ASSP-DGS with triple-band rejection is constructed by first defining the transmission zero frequencies f_z1, f_z2 and f_z3 as well as the required rejection. A DB-DGS is designed with a transmission zero at around f_z2. Then, an SSP-DGS with two transmission zeros f_z1s and f_z2s is designed with its loading parameters adjusted to make f_z1s ≈ f_z1 and f_z2s > f_z3. Finally, the ASSP-DGS is designed, based on the SSP-DGS, with three transmission zeros f_z1a, f_z2a and f_z3a by adjusting the asymmetric defect structure to make f_z1a ≈ f_z1, f_z2a ≈ f_z2 and f_z3a ≈ f_z3.

Figure 12 Simulated |S₂₁| of ASSP-DGSs with different groove depth asspls (w₁ = 1.5, g₁ = 0.5, l₁ = 5.5, a₁ = 12, b₁ = 13.8, sspl_a1 = 13.4, a₂ = 11, b₂ = 8.7, sspl_a2 = 8.3, sspw_a = 0.25 and sspg_a = 0.4 mm). n_a = 8.

Figure 13 Gysel power divider layout with harmonic suppression: top view (a), bottom view (b).

POWER DIVIDER DESIGN

The power divider (PD) is a device that can divide an RF input signal into two or more output signals. Because it satisfies the reciprocity theorem, it can be used as a combiner as well. PDs are widely used as components in many microwave devices such as mixers, power amplifiers and antenna arrays. In these applications, unwanted harmonics caused by nonlinear circuit properties must be suppressed. A DGS can be incorporated as a harmonic rejection filter. The ASSP-DGSs are used to suppress the second, third and fourth harmonics.

The Gysel PD design with ASSP-DGSs is shown in Figure 13. The fabricated divider is shown in Figure 14. It is constructed on a 0.8 mm thick FR4 substrate with a relative dielectric constant ε_r of 4.4. The dimensions are:

w_gs1 = 1.9, w_gs2 = 1.7, l_gs1 = 10, l_gs2 = 22, l_gs3 = 18.5, l_gs4 = 43.5, l_gs5 = 15, l_gs6 = 16, g₁ = 0.5,

l₁ = 5.5, a₁ = 12, b₁ = 13.8, sspl_a1 = 13.4, a₂ = 11, b₂ = 8.7, sspl_a2 = 8.3, sspw_a = 0.25 and sspg_a = 0.4 mm.

Figure 14 Fabricated Gysel power divider with harmonic suppression: top view (a), bottom view (b).

Figure 15 Simulated and measured S-parameters of Gysel power divider with harmonic suppression: |S₁₁|, |S₂₂|, |S₃₃| (a) and |S₂₁|, |S₃₁|, |S₂₃| (b).

MEASUREMENTS

Figure 16 Simulated and measured |S₂₁| and |S₃₁| wideband performance of Gysel power divider with harmonic suppression.

Figure 15 shows simulated and measured S-parameters of the fabricated harmonic suppression Gysel PD. The matching bandwidth (|S₁₁|, |S₂₂| and |S₃₃| < -15 dB) around the center frequency of 0.7 GHz is 24.3, 35.7 and 37.1 percent, respectively. The port isolation bandwidth (|S₂₃| <-15 dB) is 30.1 percent. Measured |S₂₁| is -3.6 dB and |S₃₁| is -3.4 dB at 0.7 GHz.

Simulated and measured wideband |S₂₁| and |S₃₁| are shown in Figure 16. The suppression bandwidth (|S₁₁| and |S₂₂| < -15 dB) at the second, third and fourth harmonics is 26.4, 23.8 and 12.5 percent, respectively.

CONCLUSION

The ASPP-DGS described exhibits a response with three transmission zeros. Three harmonics can be suppressed simultaneously by adjusting the sizes of the DB grounds and the sizes of the internally loaded SSP structures. Performance is verified with the integration of four ASSP-DGSs into a Gysel PD providing second, third and fourth harmonic suppression. Both simulations and the measurements show suppression of the second, third and fourth harmonics with little loss at the operating frequency.

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