Application of dual-polarized microstrip antenna for transmitting and receiving

This paper designs a dual-linear polarization square microstrip patch antenna with a stacked structure. This method uses a probe to feed the lower patch and excites the upper parasitic patch through coupling, so that the microstrip antenna resonates at two resonant points, so that the antenna can achieve a total impedance bandwidth of 12.2% in two frequency bands. At the same time, by orthogonally feeding the two ports in perpendicular directions to each other, dual-linear polarization can also be successfully achieved.

1 Antenna model and parameter design

The antenna model given in this paper is shown in Figure 1. The model uses a square microstrip patch because the square microstrip patch has good polarization radiation symmetry and is easy to process and manufacture. The antenna realizes horizontal/vertical dual-polarization radiation through orthogonal feeding of two ports. As can be seen from Figure 1, the antenna is mainly composed of a metal base plate, a square radiation patch and a square parasitic radiation element. The two layers of radiation elements are printed on a square Rogers RT/duroid 5880 (dielectric constant 2.2, loss tangent 0.0009) dielectric board with a side length of 60mm. The lower dielectric board is 2mm high and the upper dielectric board is 3mm high. The two dielectric boards are separated by an air layer with a thickness of 1mm. The positions of the two feeding points are both located on the center line of the lower patch, where port1 is located on the center line of the x direction, and the distance from the center of the patch is d1, and port2 is located on the center line of the y direction, and the distance from the center of the patch is d2.

Assuming that the initial resonant frequencies of the upper and lower patches are 2.07 GHz and 2.25 GHz respectively, the initial size L1 of the lower patch can be calculated to be 48.9 mm by equation (1).

Where: c is the speed of light; f is the resonant frequency; εr is the dielectric constant of the medium.

The calculation of the side length of the upper patch involves an air layer with a thickness of 1 mm. The equivalent dielectric constant (εe=1.83) between the upper patch and the ground plane, including the air layer and the two layers of dielectric, can be calculated according to formula (2). Then, εe is used to replace εr in formula (1), so that the side length L2 of the upper patch is calculated to be 49.4 mm.

Where: i represents the number of dielectric layers; hi is the thickness of the i-th dielectric layer; εri is the dielectric constant of the i-th dielectric layer.

After calculation, the initial dimensions of each parameter in Figure 1 can be obtained, see Table 1.

2 Simulation Results Analysis

The calculated values ​​of the parameters given in Table 1 can be further optimized using the simulation software HF-SS to obtain the best reflection loss S11 parameter curve within the required design frequency band (transmitting frequency band: 2.025GHz~2.120GHz, receiving frequency band: 2.2GHz~2.3GHz). Figure 2 shows the simulation curves of the reflection loss S11 and port isolation S12 parameters.

As shown in Figure 2, within the designed frequency band, the maximum value of the reflection loss is also around -6dB, and most of them are below -10dB, that is, the impedance bandwidth with S11 less than -6dB is 1.96 GHz to 2.13GHz in the transmitting frequency band and 2.22GHz to 2.31GHz in the receiving frequency band. The relative values ​​are calculated to reach 8.2% and 4% in the transmitting frequency band and the receiving frequency band respectively. At this time, the isolation parameter curves of the two ports are also below -20dB, which shows that the port isolation is good. In addition, since the two ports are vertically polarized ports and horizontally polarized ports, it also shows that the polarization isolation is good.

The gain pattern of the antenna at the center frequency is shown in FIG3 . It can be seen that the half-power beamwidth of the pattern is approximately 2θ0.572°, which can meet the design requirement of 2θ0.5 ≥ 60°.

In addition, the author also conducted simulation tests on the gain at several key frequency points of the antenna, and their gain conformality is good. It can be estimated that the half-power beamwidth is greater than 60 degrees in both the transmitting and receiving frequency bands. In addition, the gain values ​​at the frequency points of 2.02, 2.07, 2.12, 2.20, 2.25, and 2.30 GHz are all greater than 8dBi, and the gain basically increases with the increase of frequency.

3 Conclusion

The transceiver frequency-dividing stacked microstrip antenna proposed in this paper can form a double-peak resonance characteristic after loading the parasitic patch unit, thereby achieving a wider impedance bandwidth, and the simulated gain within the impedance bandwidth is greater than 8dBi. In addition, this antenna also has a dual-polarization characteristic, and its communication information capacity can be doubled compared to the traditional single-polarization antenna, so it can be widely used in various communication systems.