# A Dual-Polarized Dual-Band Patch Antenna Based on Orthogonal Modes Manipulation

Authors: Run Liu; Xiaoqing Tian; Boyu Sima; Zhiwei Sun; Yantao Yu; Hailin Cao
Journal: International Journal of Antennas and Propagation
 (2022)

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## Abstract

In this paper, a co-caliber structure for dual-polarized dual-band (DPDB) radiation is presented through cross-polarized modes manipulation. After introducing slots and a connection branch into a typical patch antenna, two orthogonal radiation modes with different electrical-length achieved a meandered current mode at the lower frequency and a patch radiation mode at the higher frequency. The radiation patterns at both frequencies are patch-like, benefitting from certain feeding designs. The dual frequencies can be manipulated independently since their working modes are independent. In addition, compared with the traditional patch, the proposed antenna performs a higher aperture efficiency with a miniaturized antenna dimension. The antenna is finally fabricated and measured. The measured results showed that the antenna is evidently cross-polarized working at 10.38 GHz and 14.2 GHz and the gains are 5.57 dB and 6.82 dB, respectively. With the advantages of being compact, easily fabricated, and integrated, the proposed antenna can be potentially utilized in antenna research, polarization manipulation, multichannel communication system, and so on.


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## Body

## 1. Introduction

Dual-polarized dual-band (DPDB) antenna, that can work at multi-band with different polarizations, is desirable owing to its wide applications, for instance, polarization reconfiguration, interference reduction between communication channels and antennas integration. It is a comprehensive subject of dual-band antenna and dual-polarized antenna designs. Dual-band antennas can provide two communication channels based on the orthogonality between frequencies, that have been widely studied [1–4]. Dual-polarized antenna is a type of radiation structure, in which the polarization can be manipulated. It is also widely applied in communication based orthogonality between cross-polarizations. The feasible approaches for designing dual-polarized antennas mainly include multi-feed or multi-caliber strategies [5–12]. An omnidirectional antenna with an artificial magnetic conductor reflector was proposed in [8], achieving dual-polarized radiation by a multi-caliber structure. In [10], the antenna realized dual-linear-polarized radiation by multi-feed design, in which one feed is a balanced-probe feed and the other one is a slot-coupled feed.Recently, DPDB antenna with multi-ports or multi-caliber is paid focus in such research area. One feasible approach for DPDB antenna design is a multi-layer antenna [13–15]. By constructing a multi-layer structure, a low-profile antenna, with an omnidirectional linear-polarized (LP) EM radiation at the lower band, meanwhile, a unidirectional circular-polarized (CP) radiation at the higher band, was achieved by introducing an artificial magnetic-conductor structure [13]. In [14], an omnidirectional CP and a unidirectional LP radiation were realized in two bands with different modes, where a TM01 model is generated by open slots at the lower frequency, and a TM02 model is generated by short pins at the higher frequency. However, these works mainly need multi-ports or multi-caliber. The DPDB antennas with co-caliber generally achieved polarization shift between linear- and circular polarization. It is still a challenge for a co-caliber DPDB antenna to generate cross-linear-polarized electromagnetic (EM) waves at different frequencies. This is because (i) the orthogonal current components at different frequencies are difficult to be generated by a single caliber, and (ii) the cross-polarized current should work independently for the purpose that the designed antenna has good cross-polarization isolation. In addition, following the desire for integration, the antenna should be miniaturized, which results into a significant reduction of the gain [16–19]. Therefore, a feasible mechanism for introducing cross-polarized radiation components is desired for DPDB antenna.In this report, a co-caliber DPDB antenna employing patch structure is represented based on cross-polarized modes manipulation. After loading a U-shape slot and a short branch on the patch antenna, the desired current distribution forTM10 mode at the higher frequency and the cross-polarized current for TM01 mode at the lower frequency isstructured. The TM10 mode is achieved by patch radiation, while the TM01mode is achieved by structuring an orthogonal meandered current. The radiation patterns of both modes are patch-like. Meanwhile, the proposed modes can be manipulated independently, which can perform an independent manipulation of the operating frequencies. Another noteworthy advantage of this co-caliber antenna is that the gain at lower frequency is well maintained. The gain was only reduced by 1 dB when the radiation aperture was cut to 60%, which indicates a high aperture efficiency. The proposed antenna is fabricated and measured at last. The measurement results coincided with the simulation ones and theoretical prediction well. The proposed antenna performed compact, easily fabricated, and integrated, which can be potentially utilized in antenna research, polarization reconfiguration, multi-channel communication system, etc.


## 2. Antenna Design

The proposed DPDB antenna is represented in Figure1, which is based on printed circuit board (PCB) technology. It was printed on Taconic TLY-5 substrate, of which its permittivity is equal to 2.2, loss tangent is 0.009, and thickness h equals 0.762 mm. The patch structure was printed on the top layer, while a metallic background was on the bottom. The antenna was feedback-fed with a typical SMA, of which the characteristic impedance equals 50 Ω. An unbalanced U-shape slot is introduced into a patch structure, while the slot is partitioned by a short branch along the y-direction, as shown in Figure 1. The antenna was simulated utilizing the High-Frequency Structural Simulator (HFSS) in this research.Figure 1
Geometry of the proposed antenna (p=12mm, Lx=5.5mm, Ly=5.4mm, x1=1.2mm, x2=1mm, x3=1mm, wf=1mm, l1=0.2mm, and l2=1mm).The antenna radiates by two areas based on the radiation current distribution, as shown in Figure1. The two modes were induced by independent surface currents in certain radiation areas. At the higher frequency at 13.9 GHz, the antenna works in patch radiation mode to generate TM10 mode, which further achieves x-polarized radiation. Because the radiation current is straight, its electrical length is relatively short which determines the antenna works at a higher frequency. At the lower frequency at 10.38 GHz, the antenna works in meandered radiation mode to generate TM01 mode, which further achieves y-polarized radiation. The current of this mode is meandered which means its electrical length is relatively long so this mode works at a lower frequency. The radiation of both modes is directional as what to patch radiation [20]. In this case, the DPDB antenna with orthogonal modes manipulation is achieved by a single radiator while a single feed.The antenna is developed from a typical patch, to a patch with a slot cut, to the proposed antenna, correspondingly shown in Figures2(a)–2(c). Firstly, a typical rectangular patch antenna was designed, of which the working frequency was around 15 GHz, as shown in Figure 2(d) by the black line. Then, an unbalanced U-shape slot is introduced into the designed patch. There exists a single working frequency of the patch, as shown in Figure 2(d) by the red line. The frequency shown with the red line shifts slightly to 14.4 GHz. At last, a short branch along the y-direction is introduced to divide the U-shape slot. A lower working frequency is performed, while the higher frequency is kept, as shown in Figure 2(d) by the green line. The working frequency and the −10 dB bandwidth are equal to 10.38 GHz and 1.1% for the lower frequency, and 13.9 GHz and 3.8% for the higher frequency respectively. Three concerns were considered when we introduced the branch: (i) for dual-polarization working, its direction should be perpendicular to the polarization of the original patch; (ii) for dual-band working, the radiation current is constructed meandered; (iii) for shaping the radiation as patch-like (Gaussian beam), the equivalent current-length in the +y-half patch should be shorter than that in the −y-half patch. Herein, we discuss our method of designing the feeding structure. At the higher frequency, the antenna works in the typical patch-radiation mode, so that the feeding point is slightly off-center along the x-direction for the impedance matching and the Gaussian-beam radiation. At the lower frequency, the antenna works in meandered-current mode, and the feeding structure is designed by manipulating the radiation current. By certainmanipulations of the current paths, the equivalent electrical length in the −y-half patch is greater than that in the +y-half patch, which can be regarded as a substitute scheme of “off-center feeding.” In this case, the radiation pattern is shaped in Gaussian-beam as well.Figure 2
(a) A typical rectangular patch antenna. (b) Patch with slot cut. (c) Patch with the short branch loaded. (d) Simulated of different antennas.
(a)(b)(c)(d)The evolution of the antenna clearly showed that the additional lower frequency was introduced by the short branch. The operating mechanism of the antenna is shown in Figure3 by its current distribution in vector. In the case without the short branch loaded, the surface current performed as that in a typical patch antenna, mainly in both x edges with x-polarization, forming the TM10 mode according to the cavity model theory [21]. After introducing the branch, at the lower frequency, there exist two current components along x and y, respectively. For the y-polarized component, the currents along with two paths are within the same direction, however, the x-polarized currents are along three paths, of which their directions are reversed. Hence, a y-polarized EM wave is radiated by TM01 working mode. On the other hand, a typical current distribution for TM10 mode generation was kept as what it was before loading the branch at a higher frequency, resulting in an x-polarized EM wave radiation, as shown in Figure 3(c). In this case, a DPDB is achieved, of which polarization at the dual-frequencies are orthogonal, by orthogonal modes of design.Figure 3
(a) Simulated surface current distribution with U-shape slot loaded. Simulated surface current distribution with the short branch loaded at (b) 10.38 GHz and (c) 13.9 GHz.
(a)(b)(c)Based on the analysis above, the two frequencies can be manipulated independently to obtain a flexible frequency design, since the current paths of lower and higher frequency cases are separated from each other. As shown in Figures3(b) and 3(c), the radiation current paths at 10.38 GHz are mainly along the minimum-x and the middle-y lines, while the one at 13.9 GHz is along both sides in the direction-direction. Rooting the principle that the frequency is dependent on the length of radiation current, and x3 and x2 are employed to manipulate the lower and higher frequencies independently. As observed, the lower frequency runs from 10.8 GHz to 9.8 GHz when x3 shifts from 0.7 mm to 1.5 mm with step 0.2 mm, while the higher frequency that remained is as depicted in Figure 4(a). For manipulating the higher frequency, it shifted from 14.9 GHz to 13.5 GHz in the cases that x2 shift from 0.5 mm to 1.3 mm, while the lower frequency is fixed, as shown in Figure 4(b). Therefore, the independent manipulation verified the proposed method. Such a property can be applied in tuning the working frequencies independently by introducing tuneable devices, such a as tuneable inductor or diode, into the current path.Figure 4
SimulatedS11 of the proposed antenna with different (a) lengths of x3, (b) lengths of x2, (c) lengths of l1 and (d) lengths of l2.
(a)(b)(c)(d)Two more parameters are also analyzed herein for a better illustration of the proposed method. The performance with differentl1, the width of the short branch, is firstly presented in Figure 4(c), which l1 is shifted from 0.2 mm to 0.6 mm with the step of 0.1 mm. Based on the mechanism of this antenna, l1 affects the radiation impedance of the meandered-current mode at the lower frequency, and the magnitude of S11 at the lower frequency is shifted evidently. Figure 4(d) shows the S11 with difference l2 which is shifted from 0.6 mm to 1.4 mm with the step of 0.2 mm. l2 is a parameter to determine the position of the feed, which will affect the working modes at both the dual-frequencies. When l2 is decreased, the resonance wavelength of the meandered-current mode and the typical patch mode will increase, therefore, both the working frequencies are red-shifted. The parameters analysis in the above coincides are our well verified design method.Beside the S-parameters, the following radiation performance is investigated. For the lower frequency at 10.38 GHz, its performance in 3D and 2D views is provided in Figures5(a) and 5(c). The pattern showed a typical patch radiation, where its gain is equal to 5.67 dB. From the 2-D view, the antenna at 10.38 GHz is y-polarized, where its cross-polarized gain peaked around −8.5 dB, i.e., the polarization isolation equals to −14.17 dB. This is a litter higher compared with typical patch, because there exists a radiation current along x direction. For the higher frequency at 13.9 GHz, the radiation performances are shown in Figures 5(b) and 5(d) for 3-D and 2-D views respectively. The antenna is x-polarized with gain around 7.27 dB, while its gain of cross-polarized component is −13.7 dB. The radiation is still patch-like, of which the polarization isolation equals to 20.97 dB. This is very coincident with patch radiation. In addition, the radiation efficiency is simulated and depicted in Figure 5(e), that the antenna efficiency is approximately 84% and 93% at the working bands 10.38 GHz and 13.9 GHz, respectively. This demonstrates the antenna has high efficiency at both the working bands. In this case, a DPDB antenna with orthogonal polarization in dual working frequencies is designed in a common radiation caliber, through the cross currents, i.e., cross modes TM01,TM10 manipulation. Note that, the radiations at both the dual frequencies are typically patch-like because: first at the lower frequency, the current path is meandered, therefore, the current in x-axis has the same direction; second at the higher frequency, the feeding via is off-centered as the typical patch design.Figure 5
Simulated radiation performance of the proposed antenna. (a) 3D view at 10.38 GHz. (b) 3D view at 13.9 GHz. (c) Radiation pattern onxoz and yoz plane at 10.38 GHz. (d) Radiation pattern on xoz and yoz plane at 13.9 GHz. (e) Simulated antenna efficiency of the proposed antenna.
(a)(b)(c)(d)(e)Furthermore, an advanced feature should be noticed here is that the antenna performs a higher aperture efficiency in the lower frequency. Comparing with typical patch as shown in the top-right corner in Figure6 which worked at 10.38 GHz as well, the antenna aperture is reduced by 60% in this work. This indicates that the proposed antenna performs a miniaturization property. As a consensus that the gain will lower about 3 dB when the aperture decreases 50%. However, as shown in Figure 6, the gain only reduced around 1 dB, from 6.7 dB in typical patch to 5.75 dB in this work. Meanwhile, the −3 dB beamwidth is little changed, that 64°(yoz), 97°(xoz) for antenna at this work compared with 63°(xoz), 92°(yoz) for typical patch. This advanced property benefits from the meandered current distribution.Figure 6
Simulated gain of the designed antenna and the typical patch.


## 3. Experimental Results and Analysis

The proposed antenna is fabricated utilizing PCB process, of which the fabrication sample is shown in Figure7(a). The S-parameter of the antenna is measured, as shown in Figure 7(b), where the lower and higher resonant frequency are located at 10.6 GHz and 14.2 GHz, respectively. The measured 10-dB return-loss bandwidth is 200 MHz (10.5–10.7 GHz) in the lower band and 600 MHz (13.9–14.5 GHz) in the higher band, while the relative bandwidth is about 1.89% and 4.23%, respectively. The simulated result is also depicted in Figure 7(b) as a comparison, which coincides with the measurement one well.Figure 7
(a) Fabrication of the proposed antenna. (b) Simulated and measuredS11 of the proposed antenna.
(a)(b)The far-field patterns of the antenna were measured in an anechoic chamber. The radiation performance is shown in Figure8, of which Figure 8(a) shows the x- and y-polarized radiation results at the lower frequency on xoz and yoz plane, while Figure 8(b) shows what is at the higher frequency. For their own working polarization, the gain at lower frequency is 5.57 dB, with beamwidth (−3 dB) about 80°(yoz), 88°(xoz), while gain at higher frequency is 6.82 dB, with beamwidth (−3 dB) about 85°(yoz), 94°(xoz). The polarization isolation equals to 13.1 dB and 19.4 dB at lower and higher frequencies, respectively. All the radiation results coincide with the simulation ones, experimentally verifying the proposed method. Note that, the radiation pattern in Figure 8(b) is distorted, which is mainly caused by firstly the measurement error and secondly the shorter wavelength.Figure 8
Measured radiation performance of the proposed antenna. (a) Radiation pattern onxoz and yoz plane at 10.6 GHz. (b) Radiation pattern on xoz and yoz plane at 14.2 GHz.
(a)(b)We herein compare between some previous works and this work, as depicted in Table1. This antenna only has two metallic layers including one radiation patch and the metallic background, i.e., the radiation feature is achieved by a single coplanar structure. In addition, the antenna is generated by one feed, hence, the communication channels at the separated frequencies can work with one incident port. In Ref. [12, 16, 18, 22], the higher frequency multiplies the lower frequency, which is mainly achieved by manipulation of the higher mode. Thus, the flexible resonant frequency design cannot be obtained. Because the frequencies of our antenna work at two distinct modes, the two frequencies can be controlled independently in the design process. The key advanced performance is that the polarizations at different frequencies are cross-linear-polarized, resulting in a cross-mode generation through a coplanar structure. Since there only exist two metallic layers printed on a thin substrate, the structure is low profile and easily fabricated. Compared with the works in Table 1, our antenna has miniaturization feature in the lower frequency while the gain is well kept. For instance, the antenna dimension of [12] and our work is roughly the same at the lower frequency, however, the gain is 4 dB higher in this work, which means the coplanar structure has higher aperture efficiency.Table 1
Comparison with other dual-polarized dual-band antennas.
Ref.NPort numberFreq. (GHz)Ind-manPol.Pol-relGain (dBi)Dim. (λmin)[12]322.4/5.8NoLP/LPCo-1.5/5.20.48 × 0.48π × 0.005[13]311.38/1.57YesLP/CP—2/70.56 × 0.56 × 0.03[14]311.57/2.4NoCP/LP—0.7/10.24 × 0.24π × 0.02[16]322.45/5.8YesLP/LPCo-2/110.31 × 0.31 × 0.019[18]212.45/5.8NoLP/LPCo-4.16/4.340.16 × 0.16π × 0.025[22]232.45/5.8NoLP/LP—3.4/8.50.73 × 0.73 × 0.03[23]211.575/2.45NoCP/LP—5.1/5.030.37 × 0.4 × 0.016[24]423.5/4.9NoLP/LPCross7.1/8.20.93 × 0.93 × 0.13[25]7426.875/38.5NoLP/LPCross5/60.17 × 0.17 × 0.12This work2110.38/13.9YesLP/LPCross5.57/6.820.19 × 0.19 × 0.025λmin means the working wavelength at the lower working frequency. N means metallic layer number of antenna. Ind-man means independent manipulation of dual-frequency. Pol-rel means polarizations relationship of dual-polarization.


## 4. Conclusions

In this communication, we reported a method for linear-polarized DPDB design through modes manipulation. The proposed DPDB antenna radiates by a co-caliber structure, with characteristics including: (i) the polarizations at the dual frequencies are orthogonal, since two orthogonal current-paths with different equivalent electrical-length are generated in a co-caliber structure; (ii) the radiations at both the dual frequencies are patch-like. Such a radiation pattern at the higher frequency is achieved by off-centering the feeding, while what at the lower frequency is achieved through meandering the current path; (iii) the dual frequencies are achieved by two independent modes, therefore, they can be controlled independently with little interference. Besides, the antenna has a higher aperture efficiency with a miniaturized antenna aperture. The proposed method, as well as the antenna, are verified by simulation and measurement, which meet coincident results with the theoretical predictions. This research synthesizes the manipulations of frequency and polarization, which can be applied in polarization reconfiguration, digital communication, multi-band communication and antenna integration, etc.



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*Source: 2879735-2022-07-18.xml*