###### Abstract  
A modified Wilkinson Power Divider is proposed in this paper that utilizes defected ground structure (DGS) in parallel with an isolation resistor. The proposed DCS section is incorporated between the output ports, and the isolation resistor is soldered in parallel with the DGS in the ground plane, instead of on the top plane as in a conventional Wilkinson power divider, to achieve improved or preferable isolation. The proposed design is comprised of two pairs of microstrip transmission lines with equal impedances and varied electrical lengths. The parameters of the main circuit and the DGS section are acquired separately. The parameters of the proposed main circuit are derived by applying conjugate matching theory. Dumbbell-shaped DGS is introduced in the ground plane between the output ports, which acts as a parallel resonator, yielding an attenuation pole at the resonant frequency that contributes to improved isolation. By applying the previous well-known circuit theory, the lumped elements of the equivalent circuit of the DGS were achieved. The physical dimensions of the equivalent circuit for the DGS section were obtained by three-dimensional EM simulation. The measured results show improved isolation, return loss and better bandwidth as compared with other similar works. Furthermore, the proposed circuits designed at resonating frequencies of 3 and 2 GHz presented comparatively good return losses, \(S_{11}\) of about \(-25.54\) and \(-31.24\) dB, respectively, and achieved improved isolations, \(S_{32}\) between the output ports, in an order of about \(-40.83\) and \(-36.05\) dB, respectively, which is rather exceptional and desirable. Wikinson power divider; isolation; defected ground structure +
Footnote †: journal: selected
the reduction of the overall circuit size and complexity [8]. In [9], DGS is introduced in the ground plane to reduce the size of the power divider as well as to improve the performance of the power divider. As the DGS can also delay the group velocity, with the help of a single cell DGS or single dumbbell-shaped DGS, it is possible to obtain a single attenuation pole or a frequency response characteristic of a low-pass filter [10]. In [11], DGS is proposed to utilize as a resonator by illustrating its applications in various bandpass filter designs. Two dumbbell-shaped DGSs are used to achieve a two-pole bandpass filter, hence proving the equivalent potential of DGS to design dividers, couplers and filters and enhance the performance of respective microwave components. As the dumbbell-shaped DGS can act as a parallel resonator, it thus produces an attenuation pole at a certain frequency [12]. Therefore, this characteristic of DGS can be used to achieve preferable isolation by utilizing it in parallel with the isolation resistor. In contrast to conventional WPD, which comprises two \(\lambda/4\) transmission lines and an isolation resistor soldered on a top plane between these two quarter-wavelength transmission lines, this paper proposes a modified Wilkinson power divider that introduces dumbbell-shaped DGS in the ground plane and the isolation chip resistor is soldered on the DGS to yield desired or better isolation. Each quarter-wave branch of a conventional Wilkinson power divider is substituted by two sections of transmission line with the characteristic impedance of \(Z_{1}\) and \(Z_{2}\) and the length of \(l_{1}\) and \(l_{2}\), respectively. The characteristic impedances of both sections \(Z_{1}\) and \(Z_{2}\) are fixed at 60 \(\Omega\). To design the proposed DGS-powered WPD circuit, the physical dimensions and equivalent lumped circuit parameters of the DGS section and the proposed WPD were extracted by applying the field analysis method and circuit analysis theory. The physical dimensions of the DGS section were obtained separately by performing EM simulation. These methods were successfully applied to extract the required values and dimensions of the proposed equal power divider.