UWB Fractal Antennas with Low Group Delay Variation

Abstract

In this paper, two Sierpinski carpet UWB fractal antennas are designed and fabricated. The first fractal antenna is an antenna that has not any notch filter. The second one is an antenna with double notch filters. Antenna without notch filter has an operating band of (3.1–10.8) GHz with a gain of 5.3 dB at 10 GHz. This antenna has a low group delay variation. Antenna with double notch filters working at (3.36–12) GHz band shows a gain reduction and higher group delay at the filters operating band. Out of the notch filters operating band, the antenna has a low group delay variation and a gain near to the gain of the antenna without notch filters. The MIMO version of the antenna shows an operating band up to 10.8 GHz and isolation between ports higher than 15 dB.

Appendix

Figure 15 shows the Sierpinski carpet with rectangle recursion at different iterations.

Fig. 15

Sierpinski carpet with rectangle recursion at different iterations

Figure 16 shows the Sierpinski carpet with rectangle recursion at fourth iteration. This shape is used to construct the radiating element of the antenna.

Fig. 16

Sierpinski carpet with rectangle recursion at fourth iteration

Figure 17 shows the fabricated MIMO antenna without notch filters. The antenna consists of two radiating elements with a metallic barrier between them. This barrier is used to increase the isolation between the two radiating elements. The metallic barrier has a length of 20 mm and a width of 1.25 mm. Separation between the radiating elements is 10 mm.

Fig. 17

MIMO antenna

Figure 18 shows a comparison between the simulated and measured S₁₁ of the MIMO antenna. It can be noticed that the fabricated antenna works well within the band (2.9–10.8) GHz, i.e., it has S₁₁ lower than − 10 dB in the above mentioned band.

Fig. 18

comparison between the simulated and measured S₁₁ of the MIMO antenna

Figure 19 shows a comparison between the simulated and measured S₂₁ of the MIMO antenna. It can be noticed that the fabricated antenna works well (with an isolation higher than 15 dB) within the band (2.5–15.0) GHz.

Fig. 19

Comparison between the simulated and measured S₂₁ of the MIMO antenna

The Envelope Correlation Coefficient of the MIMO antenna is given by:

$${\mathbf{ECC}} = \frac{{\left| {{\mathbf{S}}_{11}^{*} {\mathbf{S}}_{12} + {\mathbf{S}}_{21}^{*} {\mathbf{S}}_{22} } \right|^{2} }}{{\left[ {1 - \left( {\left| {{\mathbf{S}}_{11} } \right|^{2} + \left| {{\mathbf{S}}_{21} } \right|^{2} } \right)} \right]\left[ {\left( {1 - \left| {{\mathbf{S}}_{12} } \right|^{2} \left| {{\mathbf{S}}_{22} } \right|^{2} } \right)} \right]}}$$

(4)

In the band (3.1–10.6) GHz, the Envelope Correlation Coefficient (ECC) is lower than 0.02 and the diversity gain is higher than 9.9 dB.