Abstract
A new broadband planar dual-polarization base station antenna is proposed, the antenna consists of two broadband plane coplanar base station antenna units, and so it has features of plane antenna. Two broadband plane station antenna units can, respectively, form double polarization in the direction. We analyzed the relative positions between the two antenna units and their effects on the performances of the antenna, especially for the influence of isolation. Broadband antenna has the characteristics of the broadband station antenna, and bandwidth is also guaranteed. The measured results show that the antenna can obtain 45% relative bandwidth, and 30 dB isolation degree also can be got, and the radiation performance is also good. Measurement results confirmed that the antenna gain can be guaranteed among 48% relative bandwidth, 15 dB of gain is got among bandwidth of 1.69–2.78 GHz, the isolation degree of different polarization method can reach 30 dB, and the measurement gain of two polarization methods of antenna both can reach 8.5 dBi.
1. Introduction
With the rapid growth of wireless mobile services and increase of the users’ number, the high capacity requirements in mobile communication system are increased very rapidly. In the dual polarized antenna, the polarization diversity and frequency reuse technology can be adopted, which can contribute to the improvement of capacity in communication system, and they have got a wide application in the station antenna [1–3]. Now at current stage, the 2G (Second-Generation) and 3G (Third-Generation) communication systems coexist; LTE (Long Term Evolution) communication system has entered new stage of comprehensive promotion. So the broadband dual-polarization station antenna which can support all 2G, 3G, and 4G (LTE) systems will play the important function which cannot be ignored [4–6].
Dual-polarization station antenna has been widely used in mobile communication system; the isolation degree between different polarization ports is an important performance index. In order to obtain high isolation degree, dual polarized patch antenna adopts L-shaped probe coupling feed and aperture coupled feeding method. And it is inevitable that complex feed structure and multilayer structure will be adopted. In the dual-polarization antenna with the structure of cross or parallelogram, three-dimensional structure is usually adopted. The above two kinds of double polarization plane structure of station antenna have failed to realize the plane structure [7–10].
In the paper, a new broadband planar double polarization base station antenna is proposed, the antenna consists of two broadband plane coplanar base station antenna units, and it has plane features. Two broadband plane base station antenna units, respectively, formed double polarization in the two directions.
We analyzed the relative position between the two antenna units and its effect on the performance of the antenna, especially for the influence of isolation. Broadband antenna also has the same performance as broadband base station antenna, and bandwidth is also guaranteed. The measured results show that the antenna gets 45% relative bandwidth, and 30 dB isolation also can be guaranteed, and the radiation performance is also good [11].
2. Structure of Antenna
Broadband plane station antenna has the characteristics of broadband, high gain, simple structure, small volume, and so forth. Usually length of oscillator antenna and the patch antenna are about the one-half of wavelength, by contrast, the broadband surface of base station antenna structure, and small size (size of the antenna is only ), which make the antenna easy to facilitate −45° and 45° polarization integration. If we put two broadband plane orthogonal base station antenna units on one plane, the planar antenna structure can be realized: one of the antenna units is put in 45° polarization direction and the other antenna unit is put in 45° polarization direction, and thus the formation of 45° dual-polarization can be realized [12–15].
Broadband plane 45° dual-polarization base station antenna model diagram is as shown in Figure 1: 45° polarization antenna radiation body contains −45° polarization unit and 45° polarization unit, two polarization units are bent at the end of the parallel half wave, and 45° polarization unit and −45° polarization unit are both printed on the same piece of dielectric substrate and they are placed in reflex plate. We use the high frequency electromagnetic simulation software Ansoft HFSS v12 to make the parameter optimization of broadband plane 45° double polarization base station antenna; the optimal parameters are listed in Table 1.
3. Results of Simulation
We make the simulation of broadband plane 45° depolarization station antenna, and the optimal structure parameters are as shown in Table 1, and the results are as shown in Figure 2. Relative bandwidth of the antenna is about 48%, 15 dB impedance bandwidth ( or ) covers the frequency band of 1.69 GHz−2.78 GHz, isolation () is higher than 30 dB in the entire bandwidth, which identifies that the broadband antenna has the same performance of broadband planar station antenna, and high isolation double polarization is formed.
Figure 3 gives out the antenna gain simulation results: 45° and −45° polarization units are both kept above 8.5 dBi; Figure 4 gives out the simulation results of horizontal half power beam width of the antenna, within frequency of 1.7 GHz–2.7 GHz: antenna has a consistent level of half power beam width among −45° and 45° polarization units, beam width is within , 45° polarized vertical half power beam width is , and vertical half power beam width of polarization is . Figure 5 gives out the antenna pattern simulation results of −45° and 45° polarization direction pattern in the frequency of 1.7 GHz, 2.2 GHz, and 2.7 GHz; results show that the antenna has the stable radiation pattern and cross polarization is maintained under 15 dB.
(a) 1.7 GHz, −45° polarization
(b) 2.2 GHz, −45° polarization
(c) 2.7 GHz, +45° polarization
(d) 1.7 GHz, −45° polarization
(e) 2.2 GHz, −45° polarization
(f) 2.7 GHz, −45° polarization
The simulation results show that 45° dual-polarization broadband plane station antenna has good broadband performance, and it can realize the high degree of isolation in the whole frequency range, and its radiation pattern is also stable. It is confirmed that the antenna can overcome the problem of bandwidth and high isolation in the broadband, and it also can achieve the bandwidth of the two polarization and consistent radiation patterns.
Broadband planar antenna is the flat structure, and it is formed by two coplanar orthogonal base station antennas, and it can be put with coaxial antenna phalanx in the vertical direction; it will be a new kind of broadband dual-polarization base station antenna.
4. Results of Measurements
According to the antenna structure parameters shown in Table 1, we adopt the optimal structural parameters of antenna to make 45° dual-polarization base station antenna, and broadband plane antenna is measured; the results confirmed that the antenna can realize the broadband and high isolation, and the dual-polarization radiation pattern is stable and it can also cover different bandwidth of frequencies.
4.1. Manufacturing of Antenna
Broadband plane 45° dual-polarization base station antenna involves radiator, baffle, coaxial feeder, insulation support structure, and fixed structure. Antenna radiator is fixed support structure in the baffle plate. Radiator includes one +45° polarization unit and one −45° polarization unit; they are printed in the same piece of dielectric substrate. Each unit is a broadband polarization plane base station antenna unit, for example, +45° polarization unit; its structure includes a pair of half wave oscillators bended at the end, parallel dipole coplanar microstrip lines, and L-shaped coupled microstrip lines.
Half wave oscillator is used to connect the half wave oscillator coplanar microstrip lines printed on the back of the dielectric substrate, L-shaped microstrip lines are printed in the front of the dielectric substrate, the dielectric substrate has nonmetal hole, the inner conductor of coaxial feeder of nonmetallic hole is described by welding on L-shaped microstrip line, and the outer cores are welded to the coplanar microstrip line. By the same token, the −45° polarization unit is the same. Dielectric substrate uses high frequency dielectric substrate Rogers, 4350B: the relative dielectric constant is , thickness of dielectric is 0.76 mm, and loss angle is ; coaxial cables are soft coaxial RG-316 with impedance of 50 Ω. Manufactured antenna is as shown in Figure 6.
4.2. Measurement Results and Analysis
In the parameter measurement of parameter of 45° dual-polarization station antenna, we adopt Agilent N5230A-420 two-port network analyzer. In the measurement of radiation pattern, gain, and half power beam width, we use the far field test system of the Seventh Research Institute of China Electronics Technology Group, namely, the microwave anechoic chamber.
According to the principle of reciprocity, we take broadband plane 45° dual-polarization base station antenna as a receiving antenna in the radiation pattern test and adopt the gain comparison method to measure antenna gain. Half power beam width and other radiation characteristic parameters are calculated through test data.
Figure 7 presents the simulation and measured results of return loss of broadband plane 45° dual-polarization base station antenna. The simulation and experimental results are in good agreement. The return loss bandwidth of antenna measured is 15 dB in the frequency of 1.6 GHz–2.78 GHz. The dual-polarization port isolation obtained by simulation and measured is below −30 dB on the whole work frequency.
Figure 8 is about the antenna gain. The measurement gain of dual-polarization is maintained at 8.5 dBi. The measured gain is about 1 dB lower than simulation gain. This is because, in the simulation, the loss brought by the coaxial feeder and the head of SMA are not put into consideration.
Figure 9 presents the half power beam width diagram of antenna, respectively, in dual polarization. The horizontal plane half power beam width of the antenna is maintained at the range of and vertical half power beam width is maintained at the range of .
(a) +45° polarization
(b) −45° polarization
The antenna patterns of antenna simulation, measured simulation, and measurement are as shown in Figure 10, which, respectively, is about the horizontal and vertical radiation pattern of 45° polarization antenna and measured gain of 45° polarization at frequencies 1.7 GHz, 2.2 GHz, and 2.7 GHz, the radiation pattern is stable, and the two polarization radiation patterns are similar.
(a) 1.7 GHz, +45° polarization
(b) 2.2 GHz, +45° polarization
(c) 2.7 GHz, +45° polarization
(d) 1.7 GHz, −45° polarization
(e) 2.2 GHz, −45° polarization
(f) 2.7 GHz, −45° polarization
Thus, we can conclude that the simulation design of broadband plane 45° dual-polarization station antenna is verified. The characteristics of the designed antenna are adopting broadband base station antenna unit and flat structure; through polarization units of two directions of , it can achieve the dual polarization, through adjusting the distance of the center of the two units and it gets relative minimal mutual coupling impedance, and thus the high isolation is obtained.
The measured results show that the antenna can obtain 48.8% relative bandwidth and 30 dB high isolation, and the bandwidth and radiation pattern are consistent. Broadband plane 45° dual-polarization station antenna can be used as a base station antenna in 2G/3G/LTE (4G) communication system.
5. Conclusion
In the paper, a broadband plane 45° dual-polarization base station antenna is presented, which adopts broadband base station antenna unit, and it has the flat structure. Through putting two polarization units in two directions of 45°, it achieved the dual polarization. Through adjusting the center distance between two polarization units and their relative placement, it can meet the conditions of the minimum mutual coupling impedance and also can obtain high degree of isolation. Measurement results confirmed that the antenna gain can be guaranteed among 48% of whole bandwidth, 15 dB gain can cover the bandwidth of 1.69 GHz−2.78 GHz, the isolation degree between different polarization units can reach 30 dB, and the measurement gain of two polarization units both can reach 8.5 dBi. The designed broadband plane 45° dual-polarization base station antenna is suitable for the station antenna in the 2G/3G/4G communication system.
Conflict of Interests
The author declares that there is no conflict of interests regarding the publication of this paper.