4/6/2022

Dual Polarized Slot Antenna

What is claimed is:

Design Of Wideband Dual Polarized Slot Antenna
A Dual-polarization Slot Antenna Using A Compact Cpw Feeding Structure

This paper presents a low-profile coplanar dual-polarized dual-band base station antenna array. A slotted patch antenna operating from 0.82 to 0.99 GHz with four shorting strips is proposed and analyzed. Dual antennas - (left) the slot antenna, (right) the dipole antenna. Note that a voltage source is applied across the short end of the slot antenna. This induces an E-field distribution within the slot, and currents that travel around the slot perimeter, both contributed to radiation. The dual antenna is similar to a dipole antenna.

1. A phased array comprising:

a first plurality of radiators having a first polarization and including a first coupling portion, a first radiating aperture, and a twist portion connecting said first coupling portion to said first radiating aperture;

a second plurality of radiators having a second polarization, different from said first polarization and including a second coupling portion, a second radiating aperture, and an offset portion connecting said second coupling portion to said second radiating aperture; and,

means for positioning said first and second plurality of radiators such that radiating patterns of said first and second plurality of radiators are congruent.

2. The phased array according to claim 1, wherein said first and second plurality of radiators are used alternately during transmission and simultaneously during reception.

3. The phased array according to claim 1, wherein said means for positioning includes means for mating said first and second plurality of radiators together.

4. The phased array according to claim 1, wherein an assembly of said first plurality of radiators includes a first azimuth manifold assembly, a second azimuth manifold assembly, each manifold assembly being connected through a respective phase shifter to a respective twist portion.

5. The phased array according to claim 4, further comprising means for connecting said first azimuth manifold assembly and said second azimuth manifold assembly to one another.

6. The phased array according to claim 1, wherein

said first coupling portion includes a manifold assembly;

said twist portion includes a twist plate; and

a phase shifter connecting the manifold assembly and the twist plate.

7. The phased array according to claim 6, wherein said twist plate includes a double ridged waveguide having section rotated with respect to incoming and outgoing waveguides, said section additionally having side walls which are split in two paths extending across the respective incoming and outgoing waveguides.

8. The phased array according to claim 6, wherein said phase shifter comprises a toroid phase shifter.

9. The phased array according to claim 8, further comprising phase matching transitions at an input and output of the phase shifter.

10. The phased array according to claim 9, wherein said phase matching transitions include at least one dielectric layer in a channel of a block, said at least one layer having a higher dielectric constant than said block.

11. The phased array according to claim 9, wherein said phase shifter comprises a toroid phase shifter which includes a housing and means for mounting said toroid phase shifter and said phase matching transitions in said housing.

12. The phased array according to claim 11, wherein said means for mounting includes a compliant member for accommodating height differences between said toroid phase shifter and said phase matching transitions.

13. The phased array according to claim 12, wherein said compliant member covers a portion of said toroid phase shifter and a portion of said phase matching transition and said means for mounting further includes a conductive member between said compliant member and portions of said toroid phase shifter and said phase matching transitions.

14. The phased array according to claim 1, means for delivering energy to and from said first and said second plurality of radiators.

15. The phased array according to claim 14, wherein said means for delivering energy includes a difference channel connected to a top of a first manifold of said first plurality of radiators and to a top of a second manifold of said first plurality of radiators.

16. The phased array according to claim 15, wherein said means for delivering energy further includes another difference channel connected to a side of the first manifold and to a side of said second manifold.

17. The phased array according to claim 15, wherein said means for delivering energy further includes a summation channel connected to a side of the first manifold and to a side of said second manifold.

18. The phased array according to claim 15, wherein said difference channel occupies a plane adjacent to a plane of a summation channel between said first and second manifold.

Design Of Wideband Dual Polarized Slot Antenna

19. The phased array according to claim 18, further comprising a common wall between said difference channel and said summation channel, said common wall having a slot therein, wherein a position of said difference channel relative to the slot impedance matches the difference channel.

20. The phased array according to claim 18, further comprising two collinear channels orthogonal to and in the plane of the summation channel and a corner feature which matches impedance of said two collinear channels and the summation channel.

21. The phased array according to claim 14, wherein said means for delivering energy includes a difference channel connected to a bottom of a manifold of said second plurality of radiators and a summation channel on a side of said manifold.

Design

22. The phased array according to claim 14, wherein said means for delivering energy includes a calibration channel connected to a manifold of said first plurality of radiators and to a manifold of said second plurality of radiators.

A Dual-polarization Slot Antenna Using A Compact Cpw Feeding Structure

23. The phased array according to claim 1, further comprising manifolds which transfer energy to and from said first and second plurality of radiators, and said first and second coupling portions include dielectric waveguides which couple the manifolds to first and second radiating apertures.

24. The phased array according to claim 23, wherein said dielectric waveguide includes a coupling window and said manifold includes a coupling slot to be aligned with said coupling window.

25. The phased array according to claim 24, further comprising means for aligning said dielectric waveguide and said manifold.

26. The phased array according to claim 25, wherein said means for aligning includes staking posts in said dielectric waveguide and corresponding holes in said manifold.

27. The phased array according to claim 25, wherein said means for aligning includes bars on either side of said coupling slot.

28. The phased array according to claim 24, further comprising means for preventing leaking of radiation between said dielectric waveguide and said manifold.

29. The phased array according to claim 28, wherein said means for preventing leaking of radiation includes serrations on outer edges of said coupling window.

30. The phased array according to claim 28, wherein said means for preventing leaking of radiation includes appropriately spacing bars on either side of said coupling slot.

31. The phased array according to claim 24, further comprising a raised pad in said coupling window, said raised pad insuring that said dielectric waveguide contacts a region of air waveguide immediately surrounding said coupling slot.

32. The phased array according to claim 24, further comprising a plurality of coupling slots arranged in series, a last coupling slot in said series being grounded with a short circuit.

33. The phased array according to claim 32, wherein said short circuit includes a shorted transmission line one quarter of a wavelength from a center of said last coupling slot and capacitive stub one-eighth of a wavelength from said center of said last coupling slot.

34. The phased array according to claim 1, further comprising ground plane stubs integrated into said second plurality of radiators and conductive material providing connections between adjacent radiators.

35. The phased array according to claim 1, further comprising means for impedance matching radiators to free space.

36. The phased array according to claim 35, wherein said means for impedance matching includes providing an inductive iris in radiators of said first plurality and a ridge in radiators of said second plurality.

37. The phased array according to claim 35, wherein said means for impedance matching includes an electrically thin, high dielectric sheet closely spaced from both said first and second plurality of radiators.

38. A method of forming RF manifolds comprising steps of:

providing a clad plate from which a manifold wall is to be formed;

machining the clad plate to form the manifold wall;

positioning a manifold cover on top of the manifold wall via upper and lower portions of a crate assembly;

applying brazing material to the top of the manifold wall; and,

applying pressure evenly across a joint formed between the manifold cover and the manifold wall via a pair of U-shaped channels and a compression spring located between the upper portion of the crate assembly and a clamping plate contacting the manifold cover.

39. The method according to claim 38, wherein said step of applying pressure includes providing bars running perpendicular to the joint below the manifold wall, the bars being much heavier than the manifold wall and cover.

40. The method according to claim 39, wherein said step of machining additionally includes machining a chamfer in a top portion of the manifold wall.

Introduction

Recently, circularly polarized (CP) omnidirectional antennas are of great interest since they can effectively reduce multipath effects, enhance the stability of wireless communication systems and provide a wide signal coverage. Therefore, a large number of efforts have been put into developing CP omnidirectional antennas [1–8]. In Ref. 1, by introducing shorting vias and vortex slots into a monopolar patch antenna, omnidirectional radiation patterns and wide axial ratio (AR) bandwidth were achieved. Based on dielectric resonator antennas, the designs presented in Refs. 2 and 3 could achieve AR bandwidths of 25.4 and 54.9%, respectively. However, the aforementioned designs all had profiles of more than 0.1λ₀, which are not appropriate for space-limited applications. Patch antennas have advantages of low profile and simple structures, and are therefore suitable for designing CP omnidirectional antennas [4–8]. For instance, in Refs. 4–6, the antennas loaded with curved branches owned profiles of lower than 0.07λ₀ and AR bandwidths of more than 14%. In Refs. 7 and 8, by cutting slits on radiating patches and ground planes, CP omnidirectional radiation performances were obtained and the antenna heights were only 0.028 and 0.026λ₀, respectively.

With the blooming of wireless technologies, antennas with more than one operating band are becoming more and more necessary to satisfy various wireless standards. In Ref. 9, a dual-band CP omnidirectional antenna was proposed. By combining a dielectric resonator antenna and a patch antenna together, the design was able to realize AR bandwidths of 3.16 and 5.06% at two bands, separately. In Ref. 10, by utilizing a stacked-patch configuration, a dual-band frequency reconfigurable antenna was presented. In addition, based on artificial μ-negative transmission lines, a dual-band CP antenna was investigated in Ref. 11. As it is known, CP antennas are required for global positioning systems, satellite communications and linearly polarized antennas are needed for lots of other commercial applications. But few published designs are able to offer dual-band omnidirectional antennas with different polarization states in the two frequency bands. In Ref. 12, a dual-band dual-polarized antenna was proposed. Omnidirectional circular polarization is achieved in the low band and omnidirectional linear polarization is obtained in the high band. In Ref. 13, a dual-band antenna with different polarization and radiation properties over two bands for vehicular communications is presented. However, the AR bandwidth of the designs [12, 13] is too narrow to satisfy the modern wireless systems.

In this paper, a dual-band dual-polarized omnidirectional antenna is presented. The two bands are generated by two circular patches, separately. By adding a set of conductive vias and a coupled ring, the antenna bandwidths are enhanced significantly [14, 15]. Owing to the introduction of curved branches, a current loop can be formed to provide horizontally polarized field. Together with the vertically polarized field created by the lower circular patch, a CP omnidirectional radiation can be generated in the low band. To verify the design idea, a prototype was designed, fabricated and measured. Both simulated and measured results reveal that wide bandwidths, omnidirectional circular polarization and omnidirectional linear polarization can be achieved.

Antenna Geometry and Operating Principle

Antenna Geometry

Figure 1 shows the geometry of the proposed dual-band dual-polarized omnidirectional antenna and the detailed dimensions are listed in Table 1. As shown in Figure 1, the proposed antenna is mainly composed of an upper circular patch, an annular ring, a lower circular patch, a set of conductive vias, a ground plane, six curved branches and a coaxial probe. The upper circular patch is printed on the top of Substrate 1 (Taconic RF-30, thickness = 1 mm, ε_r = 3.0) and the annular ring is concentrically placed around the upper circular patch. The lower circular patch and the ground plane are printed on the top and bottom surfaces of Substrate 2 (Rogers 5,870, thickness = 3.175 mm, ε_r = 2.33). In order to excite two circular patches simultaneously to achieve a dual-band property, a clearance hole with a radius of 2.5 mm is etched in the center of the lower circular patch. In this way, the upper circular patch is directly fed by the inner conductor of the coaxial probe and the lower circular patch is fed by the coupling with the clearance hole. As a result, the design is able to operate at two bands. In addition, a set of N conductive vias (N = 15) are used to short the lower circular patch to the ground plane and six curved branches are loaded around the ground plane to contribute CP radiation in the low band.

FIGURE 1

FIGURE 1. Geometry of the proposed dual-band dual-polarized omnidirectional antenna: (A) Top view of Substrate 1; (B) Top view of Substrate 2; (C) Bottom view of Substrate 2; (D) Side view.

TABLE 1

Operating Principle

As previously stated, by adding the annular ring and a set of conductive vias into the antenna structure, antenna bandwidths can be enhanced dramatically. The curved branches are used to contribute CP radiation. Therefore, in this part, principles of the annular ring, the conductive vias and the curved branches will be further discussed.

In this design, the annular ring is concentrically placed around the upper circular patch. In consequence, when the upper circular patch is fed, the annular ring can be excited simultaneously by energy coupling. By tuning the radius of the upper circular patch, the size of the annular ring and the distance between them, their resonant frequencies can be moved in proximity to each other. Hence, a wide impedance bandwidth can be obtained in the high band.

As illustrated in Ref. 15, a non-zero resonant frequency of TM₀₁ mode can be created due to the loading of conductive vias. Together with the well-known TM₀₂ mode generated by the lower circular patch, a wide impedance bandwidth can be realized then. The number, radius, and location of the conductive vias have effect on impedance matching of the antenna, and these parameters can be determined based on the design guideline given in Ref. 15.

As it is known, CP radiation requires two orthogonal electric fields with an equal amplitude and 90° phase difference. In this design, TM_mn mode (m = 0, n = 1, 2) is generated by the vias-loaded lower circular patch, leading to vertically polarized electric field E_θ. And the introduction of curved branches can form a current loop around the ground plane, leading to horizontally polarized electric field E_φ. When these two orthogonal fields have an equal amplitude and a quadrature phase difference, CP radiation is achieved in the far field. Figure 2 gives the simulated current distribution on the lower circular patch and the ground plane at 2.4 GHz. It is seen that an equivalent vertical current formed by the circular patch and a current loop formed by the curved branch on the ground plane are excited simultaneously. Hence, circular polarization is achieved.

FIGURE 2. Simulated current distribution on the lower circular patch and ground plane.

Results

To verify the proposed design, a fully functional prototype shown in Figure 3 was fabricated and measured. Ansys HFSS, a vector network analyzer and a near-field measurement system were used to obtain the simulated and measured results.

FIGURE 3

Simulated and measured S-parameters and axial ratios (ARs) of the proposed antenna are given in Figure 4. From the figure, it can be seen that the measured impedance bandwidths for S₁₁ ≤ −10 dB are from 2.2 to 2.62 GHz in the low band and from 5.63 to 6.29 GHz in the high band, which agree well with the simulated results. The measured AR bandwidth for AR ≤ 3 dB is from 2.22 to 2.58 GHz. Therefore, the effective bandwidths of the proposed design are from 2.22 to 2.58 GHz and 5.63–6.29 GHz at two bands, respectively. Figure 5 shows the simulated and measured peak gains of the proposed antenna. The measured peak gains are approximately 4.3 dBic in the low band and 5.4 dBi in the high band. The discrepancies between the simulated and measured gains are mainly due to the fabrication tolerances and imperfect measurement system.

FIGURE 4. Simulated and measured S-parameters and ARs: (A) low band; (B) high band.

FIGURE 5

FIGURE 5. Simulated and measured antenna gains: (A) low band; (B) high band.

The simulated and measured radiation patterns in the azimuth plane (θ = 30°) and elevation plane (φ = 0°) at 2.35, 2.55 and 5.9 GHz are depicted in Figure 6. The measured radiation patterns are in well agreement with simulations. In the low band, omnidirectional radiation patterns can be observed and the left-hand (LH) CP fields are almost 15 dB stronger than the right-hand (RH) CP fields at θ = 30° and the whole azimuth plane, demonstrating LHCP radiation is achieved in the far field of the proposed design. In the high band, omnidirectional radiation patterns are also obtained and the cross-polarization levels are lower than −15 dB compared with the co-polarization counterpart in both planes. In consequence, a dual-band and dual-polarized antenna with well-controlled omnidirectional radiation patterns is realized in this design.

FIGURE 6

FIGURE 6. Simulated and measured radiation patterns: (A) 2.35 GHz; (B) 2.55 GHz; (C) 5.9 GHz.

Conclusion

In this paper, a low-profile dual-band dual-polarized omnidirectional antenna has been proposed. A prototype was constructed and measured to demonstrate the antenna performance. The proposed antenna can achieve bandwidths of 15 and 11.1%, gains of approximately 4.3 dBic and 5.4 dBi at two bands, respectively. Besides, omnidirectional radiations with low cross-polarization levels can also be obtained. With these properties, the proposed antenna shows superiorities over the reported designs and is attractive for indoor communication systems.

Data Availability Statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

Author Contributions

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

Funding

This work was supported by the Key Research and Development Project of Guangdong Province (2020B0101080001) and the National Natural Science Foundation of China (62071308). (Corresponding author: LG).

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

1. Yu D, Gong SX, Wan YT, Yao YL, Xu YX, Wang FW. Wideband omnidirectional circularly polarized patch antenna based on vortex slots and shorting vias. IEEE Trans Antennas Propag (2014) 62(8):3970–7. doi:10.1109/tap.2014.2325961