CSRR Loaded Multi Substrate Antenna for 4G LTE and Wi-MAX Applications

It is recommended to use low profile, low cost, easy to integrate with microwave circuits and miniaturized antenna in general and particular for wireless LAN applications such as Wi-MAX and 4G Long-Term Evolution (LTE)1-3. Microstrip Patch Antenna (MPA) with Complementary Split Ring Resonator (CSRR) can provide all above features with limitation of narrow bandwidth. Various techniques have been reported to enhance the bandwidth such as using air as substrate4 increase in substrate thickness, adding parasitic elements and making slots in patch5. Using different shapes of patches such as E-shape6-8 and U-shape9 300-400 MHz band width has been achieved. However these structures are resonant at only single frequency. There is need of a compact antenna with multiband capability with miniaturization. In this paper a multi band antenna is proposed to design numerically for applications in Land Sbands with high gain. The antenna is designed with dual layer substrate. A layer of substrate is constituted with two superimposing substrates with different relative dielectric constant. The substrates used herein are FR-4 and Foam whose permittivities (εr) are 4.4 and 1.06 respectively. The proposed antenna is designed using Computer Simulation Technology (CST) package software10. Here, three antennas are designed and results are compared for suitable applications.


Introduction
It is recommended to use low profile, low cost, easy to integrate with microwave circuits and miniaturized antenna in general and particular for wireless LAN applications such as Wi-MAX and 4G Long-Term Evolution (LTE) [1][2][3] . Microstrip Patch Antenna (MPA) with Complementary Split Ring Resonator (CSRR) can provide all above features with limitation of narrow bandwidth. Various techniques have been reported to enhance the bandwidth such as using air as substrate 4 increase in substrate thickness, adding parasitic elements and making slots in patch 5 . Using different shapes of patches such as E-shape 6-8 and U-shape 9 300-400 MHz band width has been achieved. However these structures are resonant at only single frequency. There is need of a compact antenna with multiband capability with miniaturization.
In this paper a multi band antenna is proposed to design numerically for applications in L-and S-bands with high gain. The antenna is designed with dual layer substrate. A layer of substrate is constituted with two superimposing substrates with different relative dielectric constant. The substrates used herein are FR-4 and Foam whose permittivities (ε r ) are 4.4 and 1.06 respectively. The proposed antenna is designed using Computer Simulation Technology (CST) package software 10 . Here, three antennas are designed and results are compared for suitable applications.

Details of Antenna Geometry
The E-shape MPA with only one substrate has been used for wide band applications 3 . It is proposed to design three antennas with single and dual layer substrates with E-shape patch as a feed point in each design. Geometry of proposed design-1 antenna is 'Ls' ×'Ws'× (h1+h2) mm 3 and design parameters of design -2 and -3 are 'Ls' ×'Ws'× 2(h1+h2) mm 3 Table.-1 shows the antenna dimensions for all three designs. Figure 1 shows the E-shape patch Micro-strip Patch Antenna (MPA) with foam and FR-4 as substrate.

Results and Discussions
The simulation results are presented in this section. The results includes returnloss, Surface Current Distribution (SCD), radiation pattern and 3D gain. Figure 3 shows the return loss versus frequency for the three designs 1, 2 and 3. It is observed that design-1 has wide band at center frequency 2.25GHz with range of bandwidth from 2.06-2.38GHz. Design-2 has shown wide bandwidth at center frequency 2.15GHz with range from 1.93-2.35GHz respectively. While the design-3 showed resonance at three frequencies 1.13, 1.77 and 2.4GHz. ~250 MHz bandwidth is observed at central frequency 2.4 GHz. However, this design showed poor BW at frequenciews in L-band region.   The SCD of design-1 antenna at resonant frequency 2.25GHz is shown in Figure 4. Maximum current distribution is observed in the patch especially between the slots in the design-1 which corresponds to the radiation from this section of the patch. The 3D gain of design-1 is shown in Figure 5. The simulated gain of design-1 is given 8.97dBi at frequency 2.25GHz. The radiation pattern in E & H planes for a design-1 at resonance frequency 2.25GHz is shown in Figure 6.

Analysis of Design-2
The SCD of design-2 at 2.15 GHz is shown in Figure 7. It is observed that active E-shape patch is coupling with the passive patch.  The 3D gain of design-2 is shown in Figure 8. The simulted gain for design-2 is as much as 8.95dBi at frequency 2.15GHz. The radiation properties of design-2 at frequency 2.15GHz is shown in Figure 9.

Analysis of Design-3
Design-3 has three CSRR structures on the passive patch. The SCD of design-3 is shown in Figure 10 at three frequencies. It is observed that SCD is maximum at the CSRR structure at respective three frequencies. The gain of all three frequencies 1.13, 1.77 and 2.4GHz are 4.2, 7.28 & 9.01dBi. This is high gain that can be observed from a low profile MPA. Figure 11a, b and c shows the normalized fields patterns in E-and H-planes at 1.13, 1.77 and 2.4GHz respectively.

Conclusion
A multiband multi-layer substrate antenna with E-shape active patch CSRR antenna has been designed for 4G LTE and WiMAX wireless LAN applications. By incorporating CSRR in design-3 it was observed design-3 resonanted at three frequencies 1.13, 1.77 and 2.4GHz with gains as much as 4.2, 7.28 and 9.01dBi. ~250 MHz bandwidth was observed at central frequency 2.4 GHz. It has covered frequencies in L and S-bands.

Acknowledgment
The simulation work has been carried out at the Microwave lab, School of Electronics Engineering (SENSE), VIT University, Vellore, Tamil Nadu, and India.