A Simple Patch Antenna with Enhanced Isolation Without Extra Structure

A simple patch antenna with enhanced isolation and without extra structure is devised. The isolation is enhanced by 5 dB by loading two shorting pins, and the working frequency is not changed at 3.45 GHz. Radiation pattern is little changed after loading two shorting pins. There is no additional structure between the two antennas. Isolation is strengthened through the structure of the antenna itself.


Introduction
The isolation between two antennas is receiving increasing attention with the development of antenna integration.
The structure is utilized to enhance isolation, but the extra structure will make the radiation pattern slightly asymmetrical [1].A decoupling surface is applied to enhance isolation, but the profile is higher [2].The fractal decoupling structure enhanced isolation, but the extra structure will enhance the complexity of the entire structure [3].Parasitic resonators are an effective structure to strengthen isolation in [4].The metasurface is taken to strengthen the decoupling, but the size is slightly larger in [5].A stepped impedance resonator decoupling structure is applied to enhance decoupling, but the size becomes bigger [6].The isolation structure located in the middle of two antennas is designed [7]- [10].In my work, isolation is strengthened through the structure of the antenna itself.

Antenna I and Antenna II
To confirm the mechanization of the isolation enhancement, a traditional path antenna is first devised.The overall structure is depicted in Figure 1.The material F4B whose permittivity is 2.65, height is 2 mm.Detailed dimensions are displayed in Table I.The antenna is devised and analysed through commercial software HFSS.Radiation patch of antenna I and antenna II are tightly attached to the top of the dielectric slab, and the copper cladding layer is tightly attached to the surface of the dielectric slab.The radiation patch of the two antennas is in the same plane.The dielectric slab of the two antennas is connected each other in the same plane.The ground of the two antennas is connected each other in the same plane.The gap of the antennas is about 0.14 wavelength at the resonant frequency.The signal is loaded in the two antennas through the feeding line.
The result of the simulated S-parameters is obtained by using HFSS.The result is listed in Figure 2. The antenna work from 3.4GHz to 3.5GHz.The central frequency is about 3.45 GHz.The S12 of the traditional antenna at central frequency is about -17 dB.The radiation pattern of the traditional is simulated, and the symmetry characteristic is obtained from the result displayed in Figure 3.The antenna radiates energy along the Z-axis from the simulated radiation pattern.The current distributed on the top patch is simulated whose results are depicted in Figure 4, and the direction of the current is along -X axis, the size of the patch is about one-quarter wavelength at the resonant frequency.

Antenna III and antenna IV
To confirm the mechanization of the isolation enhancement, another patch antenna loading a shorting pin is devised on the basis of a traditional path antenna.The overall structure is depicted in Figure 5.
The material F4B's permittivity is 2.65, height is 2 mm.The detailed dimensions are displayed in Table II.The antenna is devised and analysed through commercial software HFSS.The radiation patch of antenna III and antenna IV is tightly attached to the top of the dielectric slab, and the copper cladding layer is tightly attached to the surface of the dielectric slab.The radiation patch of the two antennas is in the same plane.The dielectric slab of the two antennas is connected each other in the same plane.The ground of the two antennas is connected each other in the same plane.The gap of the antennas is about 0.14 wavelength at the resonant frequency.The signal is loaded in the two antennas through the feeding line.
The result of the simulated S-parameters is obtained by using HFSS.The result is listed in Figure 6.The antenna work from 3.33GHz to 3.43GHz.The central frequency is about 3.38 GHz.The S12 of the traditional antenna at central frequency is about -18 dB.The radiation pattern of the traditional is simulated, and the symmetry characteristic is obtained from the result displayed in Figure 7.The antenna radiates energy along the Z-axis from the simulated radiation pattern.The current distributed on the top patch is simulated whose results are depicted in Figure 8, and the direction of the current is along -X axis, the distance between shorting pin 1 and the end of the radiation patch is about one-quarter wavelength at the resonant frequency.

Proposed antenna
The proposed antenna loading two shorting pins is devised on the basis of a traditional path antenna.The overall structure is depicted in Figure 9.The material F4B's permittivity is 2.65, height is 2 mm.The detailed dimensions are displayed in Table II.The antenna is devised and analysed through commercial software HFSS.The radiation patch of antenna V and antenna VI is tightly attached to the top of the dielectric slab, and the copper cladding layer is tightly attached to the surface of the dielectric slab.The radiation patch of the two antennas is in the same plane.The dielectric slab of the two antennas is connected each other in the same plane.The ground of the two antennas is connected each other in the same plane.The gap of the antennas is about 0.14 wavelength at the resonant frequency.The signal is loaded in the two antennas through the feeding line.
The result of the simulated S-parameters is obtained by using HFSS.The result is listed in Figure 10.The antenna work from 3.4GHz to 3.5GHz.The central frequency is about 3.45 GHz.The S12 of the traditional antenna at central frequency is about -22 dB.Radiation pattern of the traditional is simulated, and the symmetry characteristic is obtained from the result displayed in Figure 11.The antenna radiates energy along the Z-axis from the simulated radiation pattern.The current distributed on the top patch is simulated whose results are depicted in Figure 12, and the direction of the current is along -X axis, the distance between shorting pin 1 and the end of the radiation patch is about one-quarter wavelength at the resonant frequency.

Conclusion
In this paper, a simple patch antenna with enhanced isolation and without extra structure is devised.The isolation is enhanced by 5dB by loading two shorting pins, and the central frequency is not changed at 3.45 GHz.The radiation pattern is little changed after loading two shorting pins.There is no additional structure between the two antennas.Isolation is strengthened through the structure of the antenna itself.

Figure 1 .
The structure of the antenna I and II: (a) vertical view, (b) side view.

Figure 2 .
Figure 2. Simulated S11 and S12 of the antenna I and II.

Figure 3 .
Figure 3. Simulated radiation pattern of the antenna I and II.

Figure 4 .
Figure 4. Current direction of the antenna I and II.

Figure 5 .
The structure of the antenna III and IV: (a) vertical view, (b) side view.

Figure 6 .
Figure 6.Simulated S11 and S12 of the antenna III and IV.

Figure 7 .
Figure 7. Simulated radiation pattern of the antenna III and IV.

Figure 8 .
Figure 8.Current direction of the antenna III and IV.

Figure 9 .Figure 10 .
Figure 10.Simulated S11 and S12 of the antenna V and VI.

Figure 11 .
Figure 11.Simulated radiation pattern of the antenna V and VI.

Figure 12 .
Figure 12.Current direction of the antenna V and VI.

Table I :
Detail size of the antenna I and II

Table II :
Detail size of the antenna III, IV, V and VI.