A compact double‐layer wideband circularly polarized microstrip antenna with parasitic elements

In this article, a new broadband circularly polarized (CP) microstrip patch antenna (MPA) with a sequential phase (SP) square‐loop feeding structure is proposed. The presented antenna is composed of a square‐loop feeding structure, four L‐shaped parasitic patches with L‐shaped slots, four parasitic square patches, and a corner‐truncated square patch. At first, a SP square‐loop is designed as a feeding structure. Then, four L‐shaped parasitic patches with L‐shaped slots are utilized to generate one CP mode by a capacitive coupled way. At last, four parasitic square patches and a corner‐truncated square patch are together placed above the SP feeding structure to broaden the circularly polarized bandwidth (CPBW). The presented antenna has a wide 3‐dB axial ratio bandwidth (ARBW) of 16.7% (5.4 GHz, 4.95‐5.85 GHz), and a wide 10‐dB return loss bandwidth of 25.5% (5.5 GHz, 4.8‐6.2 GHz). The proposed antenna features compact structure and broad 3‐AR bandwidth which could completely cover the WLAN (5.725‐5.85GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band.     

A compact wideband circularly polarized antenna with two pairs of driven patch arrays

In this article, a new wideband circularly polarized (CP) antenna is presented. The antenna is composed of a circular‐loop feeding structure which provides sequential phase (SP), four primary‐parasitic crown patches and four secondary‐parasitic crown patches. The circular‐loop SP structure is used to feed the two pairs of crown patches by a capacitively coupled way. The presented antenna features a wide 10‐dB impedance bandwidth (IBW) of 23% (6 GHz, 5.31‐6.69 GHz), and a wide 3‐dB axial ratio bandwidth (ARBW) of 11.1% (5.875 GHz, 5.55‐6.2 GHz). The proposed antenna features compact structure and broad 3 dB‐ARBW, which could include the WLAN (5.725‐5.85 GHz), ITS (5.8 GHz), and WIFI (5.85‐5.925 GHz) band.     

A wideband circularly polarized antenna array with sequential rotation feed

A novel wideband circularly polarized (CP) antenna array is designed, which consists of a horizontally placed wideband phase shifting feed network and four vertically placed linearly polarized dipole antenna elements, and the circular polarization is realized based on sequential rotation feeding technology. By placing two parasitic strips and two grounding strips on the top and side of each T‐shaped dipole antenna element, the impedance bandwidth and circular polarization performance of the antenna can be further improved. The simulation results show that the 10‐dB impedance bandwidth of the antenna is 93% (1.56‐4.27 GHz) and the 3‐dB AR bandwidth is 80.7% (1.7‐4.0 GHz). The measured results are in good agreement with the simulation results. Due to the use of orthogonally placed wideband feed network and wideband array elements, the proposed antenna array has a wider circular polarization bandwidth than the similar antenna arrays reported.     

A wideband circularly polarized antenna using mutual coupling method

A novel wideband circularly polarized (CP) antenna is presented in this article. The proposed antenna consists of a four‐leaf clover patch, four L‐probes, and wideband networks. Based on the tightly coupled mechanism, the four L‐probes are formed as a ring with the adjacent ones kept close for strong mutual coupling. Consequently, the proposed antenna realizes a wideband impedance matching. Meanwhile, the four‐leaf clover patch is put closely inside of the ring for further improving the impedance bandwidth, which is proximity‐coupled fed by the four sequential‐rotation L‐probes with phase of 0°, 90°, 180°, and 270°. The four L‐probes are connected to the respective ports of a wideband feeding network by a two‐stage impedance transforming network. The measured results indicate that the proposed design has an impedance bandwidth of 66.7% from 1.0 to 2.0 GHz for VSWR ≤ 2 and a 3‐dB axial ratio bandwidth of 56.5% from 1.08 to 1.93 GHz. Furthermore, in the operating bandwidth, stable and symmetry radiation patterns and high gain are obtained. The design has a 3‐dB gain bandwidth of 38% from 1.3 to 1.9 GHz with a peak gain of 8.5 dBic.     

Dual‐band dual‐polarized compact planar monopole antenna for wide axial ratio bandwidth application

In this article, a geometrically simple, microstrip line‐fed planar monopole structure with slanting edge ground plane is designed to realize the dual‐band dual‐polarized operation. The proposed antenna consists of a rotated U‐shaped patch and an electromagnetically coupled L‐shaped parasitic radiating element. Owing to the combination of microstrip line‐fed radiating patch and a slanting‐edge rectangular ground plane on the opposite side of the substrate, the proposed dual‐band antenna can generate broad axial ratio bandwidth (ARBW) in the upper frequency band. The overall dimension of the prototype is only 32 × 32 × 1.6 mm³. The measured results validate that the proposed antenna has two operational frequency bands, 29.84% (1.54‐2.08 GHz) for linearly polarized radiation and 71.85% (3.96‐8.4 GHz) for circularly polarized radiation. Measured result shows that 3‐dB ARBW of the proposed antenna is 73.54% (3.80‐8.22 GHz) in the higher frequency band. It shows that the higher frequency band exhibits a left‐hand circularly polarized radiation in the boresight direction.     

A novel wideband circularly polarized modified square‐slot antenna with loaded strips

In this article, a novel inverted L‐shaped microstrip‐fed wideband circularly polarized (CP) modified square‐slot antenna is designed. By cutting a pair of triangle chamfers and introducing a pair of triangle patches at the square‐slot, the antenna achieves a wideband CP radiation. Moreover, CP performance of the antenna can also be remarkably enhanced by protruding an L‐shaped strip and embedding a tuning rectangle slot into the slot ground. The measured results demonstrate that the axial‐ratio bandwidth for AR < 3 is 75.1% (from 4.45 to 9.8 GHz) and the impedance bandwidth (|S₁₁| < ?10 dB) reaches 65.8% (from 4.95 to 9.8 GHz). In addition, surface current studies are performed to illustrate the operating mechanism of CP operation, and the antenna has bidirectional radiation characteristics with an average gain of ~4 dBic within the CP band.     

A small single fed broadband circularly polarized slot antenna

In this research, we present a simple single fed small broadband circularly polarized (CP) antenna. The proposed structure has the advantage of simultaneously obtaining broadband ARBW and IMBW in a small size (0.64λ × 0.62λ × 0.01λ), where λ is the free‐space wavelength at the center frequency. The measured S₁₁ BW is 100% (2.15‐6.44 GHz), which is completely overlapped by the measured ARBW of 108.7% (2.09‐7.07 GHz), which are wider than most published papers. The antenna consists of an off‐center microstrip feed line, an inverted rectangular bracket‐shape (IRBS) parasitic strip, and a modified ground plane. The modified ground plane has three linked slots and a protruded L‐shaped stub (LSS). The IRBS parasitic strip and the feed line are on one side of the substrate, whereas the ground plane is on the other side. The IRBS and LSS are overlaid up and down. The novelties of the structure are that the design mechanics is simple and clear as follows: (a) The three linked slots make the ground asymmetrical, and the asymmetrical ground makes the broadband IMBW in a small size preliminarily formed. Though the AR is around 8 dB, the fluctuation of AR inside the operation frequency band is little. (b) The off‐center feeding line, IRBS parasitic strip, and the LSS chain together through capacitance coupling, and the current path is formed, then the AR below 3 dB in the whole frequency band is generated. The peak gain and radiation efficiency are of 5.5 dBi and 95%, respectively. The proposed antenna is a good candidate for the application of various wireless communication systems, such as WLAN, WiMAX, and RFID.     

A miniaturized circularly polarized multi‐dipole antenna with wide axial‐ratio beamwidth via loading loop resonators

A miniaturized, loop resonators (LRs)‐loaded, circularly polarized (CP) multi‐dipole antenna with wide axial‐ratio (AR) beamwidth is proposed and demonstrated in this article. The radiator of this CP antenna consists of two pairs of parallel dipoles loaded with four LRs at their corners. By increasing the length of the LR, or decreasing the coupling space between the dipole and the LR, the effective length of the dipole can be lengthened significantly and thus the working frequency can be reduced without increasing the whole aperture size. As a result, a miniaturized radiator structure is completed. A feeding network consisting of a T‐shaped coupling feeding structure and four coplanar striplines having different lengths are specially designed to feed these dipoles with approximately the same magnitude and 90° phase quadrature. What is more, a cavity reflector is employed to achieve a unidirectional radiation with wide axial‐ratio beamwidth. The radiator of the proposed CP antenna has a small aperture size of only 0.34λ₀ × 0.34λ₀, where λ₀ is the free space wavelength at the working frequency. Measured results are in a good agreement with the corresponding simulated counterparts. Especially, the experimental results show that the antenna has achieved a wide AR beamwidth of 182° and 174° at the center frequency in the xoz and yoz planes, respectively.     

A tunable wideband omnidirectional circularly polarized antenna regulated by the gravity field

In this article, a tunable wideband omnidirectional circularly polarized (CP) antenna regulated by the gravity field based on the liquid metal Hg is investigated. Under the action of the gravity field, Hg flows in the upper and lower parts by rotating such an antenna, which can constitute dissimilar resonant units to achieve the dynamic regulation of the operating bandwidths. The proposed antenna consists of four tilted glass containers that are filled with Hg in the upper or lower parts, and a feeding structure for power distribution and impedance matching. To verify concept of the design, equivalent prototypes have been fabricated and measured. The measured results are roughly consistent with simulated results within a reasonable error range. The antenna has a 10‐dB impedance bandwidth of 44.3% (2.37‐3.72 GHz), and a 3‐dB axial ratio (AR) bandwidth of 18.9% (2.83‐3.42 GHz) when the proposed antenna is not rotated (state I). When such an antenna is rotated (state II), it has a bandwidth of 40.7% (2.35‐3.55 GHz) with S₁₁ below ?10 dB, and a bandwidth of 22.9% (2.40‐3.02 GHz) with AR below 3 dB. Therefore, the operating band of the antenna can be altered between two wide bands. The proposed antenna has the advantages of tunable bandwidth, novel efficient regulation mechanism, and simple structure.     

Novel square slot circularly polarized antenna with broadband characteristics

In this article, a novel wideband circularly polarized (CP) square-slot antenna with perturbation elements is proposed. The antenna comprises of an inverted L-shaped feeding line, pairs of corner cuts, a rectangular slot, and a semi-elliptical patch. The numerous CP resonant modes were excited simultaneously using these slots and patches as perturbation elements. To verify this concept, an antenna prototype was built and tested. The measured results indicate the ?10-dB impedance bandwidth (IBW) is 69.2% (2.42–4.98, 3.7 GHz) and 3-dB axial ratio bandwidth (ARBW) is 59% (2.58–4.74, 3.66 GHz). Furthermore, the measured peak gain is 4.3 dBi, and the gain variation within the certain bandwidth is less than 1 dB. Therefore, the presented antenna features wide CPBW and stable gain characteristics.     

A broadband circularly polarized monopole antenna

A compact modified C‐shaped monopole antenna with broadband circular polarization is proposed, fabricated and measured. The antenna structure is simple and only consists of combined modified C‐shaped radiation patch and an improved ground plane with the overall size of 25 × 25 × 1 mm³. By cutting the corner on the modified C‐shaped patch and adding triangular stubs on the ground plane, the wide impedance bandwidth and axial ratio bandwidth are achieved. The design process of the antenna is given, and the circular polarization mechanism of the circularly polarized antenna is analyzed from the surface current distributions. The measured impedance bandwidth is 95.2% (4.4‐12.4 GHz) with return loss better than 10 dB, and the measured 3 dB axial ratio bandwidth is 96.8% (4.42‐12.72 GHz). The peak gain is above 3.0 dBi within the working band, which indicates that it is suitable for application of ultra‐wideband (UWB) wireless communication systems and satellite communication systems.     

Wide‐bandwidth multifrequency circularly polarized monopole antenna for wireless communication applications

In this article, wideband circularly polarized monopole antennas with multiresonating frequencies are presented for Bluetooth, WLAN, WiMAX, and X‐band applications. The designed antennas have dimensions of 50 × 35 × 1.6 mm³. Two different substrates (FR4‐epoxy and PTFE) are used for fabricating the antennas. The antennas consist of corner truncated I‐shaped and C‐shaped strips excited by a 50 Ω microstrip feed line. The parametric analyses are performed with the help of Ansoft HFSS V.11 EM simulator. Both antennas have been fabricated and measured. The measured percentage bandwidth of the antenna made by FR4 substrate is 31.32% (centered at 1.66 GHz), and 64.85% (centered at 5.69 GHz). The percentage bandwidth of antenna made by PTFE substrate is 20.57% (centered 2.43 GHz) and 68.74% (centered at 7.39 GHz). In addition to that, there exists 3 dB AR bandwidth for LHCP of about 1050 MHz for 5.2 GHz WLAN‐band. The reflection coefficient, radiation patterns, and the gains of both the antennas are studied in detail. It is found that the measured and simulated results are in good agreement.     

Compact microstrip antennas with very wide ARBW and triple circularly polarized bands

This article presents two compact circularly polarized microstrip antennas with a very wide 3 dB axial ratio bandwidth and triple circularly polarized bands. A hexagonal stub (circular polarization element) along with tuning element in the ground plane is used for achieving wide 3 dB ARBW in antenna‐1, while a novel approach of using a parasitic strip around the circular polarization element is used in antenna‐2 for introducing band elimination notches in the circularly polarized band of antenna‐1. The antenna‐1 has a ?10 dB impedance bandwidth of 12.34% (3.8‐4.3 GHz), 84.02% (4.9‐12 GHz), and 3 dB ARBW of 79.94% (4.9‐10.9 GHz). The antenna‐2 displays circularly polarized band elimination notch characteristics with ?10 dB impedance bandwidth of 24.80% (3.85‐4.94 GHz), 31.72% (6.1‐8.4 GHz), 25.35% (9.3‐12 GHz), and 3 dB ARBW of 4.84% (4.63‐4.86 GHz), 19.08% (6.02‐7.29 GHz), and 5.7% (9.54‐10.1 GHz). Both the antennas are designed and fabricated on FR4 substrate of dimension (0.52 × 0.52 × 0.04)λ₀ at a frequency of 7.9 GHz.     

A new broadband circularly polarized square‐slot antenna with low axial ratios

A new broadband circularly polarized (CP) square‐slot antenna with low axial ratios is proposed in this article. The antenna is comprised of an L‐shaped microstrip line with tapered section and a square‐slot ground plane with some stubs and slots, which are utilized as perturbations for the desirable antenna performance. By loading stubs and slots in the square‐slot ground plane, the 2‐dB axial ratio bandwidth (ARBW) and 10‐dB return loss bandwidth for the presented antenna can be markedly improved. The measured results show that its 2‐dB ARBW is 4.2 GHz (54.2% from 5.65 GHz to 9.85 GHz) and its 10‐dB return loss bandwidth is about 8.9 GHz (92.7% from 5.15 GHz to 14.05 GHz). The proposed antenna features compact structure and broad 2‐AR bandwidth which could completely cover the WLAN (5.725‐5.85 GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band.     

A new dual C‐shaped rectangular dielectric resonator based antenna for wideband circularly polarized radiation

This article presents a new dual C‐shaped rectangular dielectric resonator (DR) based antenna for generation of wideband circularly polarized (CP) radiation. The proposed antenna comprises of a pair of C‐shaped rectangular dielectric DR and a metal strip with a coaxial probe. By utilization of a metal strip at the side surface of C‐shaped rectangular DR, the wideband CP radiation is achieved from the proposed dielectric resonator antenna (DRA). Fundamental orthogonal modes (TE^x_δ11 and TE^y_1δ1) are excited using the rectangular DRA with a metal strip for the generation of CP fields. The proposed antenna with dual C‐shaped rectangular CP DRA provides the measured ?10 dB reflection coefficient bandwidth of 30.07% (3.22 GHz‐4.36 GHz) with measured 3‐dB axial ratio bandwidth of 14.81% (3.25 GHz‐3.77 GHz) at the boresight. The proposed antenna covers the useful Wi‐MAX band.     

A wideband compact antenna with quad‐circular polarized bands in its operating regions

This article presents the design of an offset CPW‐fed slot antenna which exhibits a narrow impedance bandwidth (IBW; |S₁₁| ≤ ?10 dB) extending from 1.20 GHz to 1.45 GHz and another wide impedance bandwidth from 1.86 GHz to 8.4 GHz thus covering almost all the conventional operating frequencies. The antenna is loaded with semicircular and rectangular stubs and meandered microstrip lines to realize circular polarization at 1.35 GHz, 3.3 GHz, 4.9 GHz, and 7.5 GHz with axial ratio bandwidth (axial ratio ≤ 3 dB) of 19.25% (1.2‐1.46 GHz), 4.24% (3.24‐3.38 GHz), 4.1%(4.8‐5 GHz), and 5.2% (7.3‐7.69 GHz) respectively thus covering the GPS, WiMAX, WLAN, and X‐band downlink satellite communication application bands. The mechanism of generation of CP is discussed using vector analysis of surface current density distribution. The gain is fairly constant in the wide IBW region with maximum fluctuation of 1.2 dB. The structure is compact with an overall layout area of 0.27λ × 0.27λ, where λ is the free‐space wavelength corresponding to the lowest circular polarized (CP) frequency. A comparison of the proposed antenna with previously reported structures is performed with respect to impedance bandwidth, compactness, number of CP bands, LHCP to RHCP isolation and gain to comprehend the novelty of the proposed design. A prototype of the proposed antenna is fabricated and the measured results are in accord with the simulated results.     

一种双频段圆极化移动导航终端天线的设计

给出了一款应用于北斗导航卫星系统(CNSS)B1频段/S频段的双频圆极化缝隙天线的设计方法。该天线采用微带线进行馈电,在地板上开有两个方形螺旋槽,其总槽长度大约均为一个自由空间操作波长。通过调节螺旋槽的终点处的长度即可获得最适宜的轴比,从而实现圆极化。另外,还可以通过调节螺旋槽的宽度来获得较大的轴比带宽。在地板中央切去一个圆环形槽可增大感应电流的路径,从而降低圆极化的中心频率。通过仿真软件HFSS对天线结构参数进行优化设计,并制作实物。其仿真及实测结果表明:回波损耗小于-10 dB的阻抗带宽为38.5%,且在阻抗带宽内天线的相对轴比带宽也达到了大约5%。     

A new broadband circularly polarized antenna with a single‐layer metasurface

In this article, a new low‐profile broadband circularly polarized antenna with a single‐layer metasurface is designed. The metasurface is composed of 4 × 4 rotated rectangle‐loops. Compared to single rotated rectangle, introducing inner‐cut rectangle slot can increase the design flexibilities by changing this slot size for wider circularly polarized operating bandwidth and reduce the size of the antenna in same frequency. The proposed antenna has the advantages of a wide 3‐dB axial ratio bandwidth from 5.4 to 6.05 GHz and an excellent 10‐dB impedance bandwidth from 5 to 6.05 GHz.     

Bandwidth enhancement of a circularly polarized tapered crossed slot antenna with corner parasitic directors

This paper presents a single‐feed wideband circularly polarized (CP) antenna with tapered crossed slots and corner directors. According to the multi‐mode resonance concept, the antenna uses two identical cross placed Vivaldi‐like tapered slots as the wideband radiating elements, and four rectangular parasitic patch directors are connected on each corner of the ground for further enhancing the bandwidth. A simple second‐order stepped microstrip line with a via on the other side of the substrate is used to feed the antenna. Two pairs of capacitors and inductors are placed on each slot to realize a 90° phase difference for CP operation. The proposed antenna is designed, fabricated and measured. Simulation results are in good agreement with the measured results that demonstrate a 10 dB impedance bandwidth (IMBW) from 1.98 to 5.71 GHz (3.73 GHz, 97.01%) and a 3 dB axial ratio bandwidth (ARBW) from 2.13 to 3.91 GHz (1.78 GHz, 58.94%). The antenna outperforms most of the reported cross slot antennas for its wide IMBW and ARBW.     

A broadband circularly polarized slot antenna with a compact microstrip to CPW transition

A simple structure of broadband circularly polarized slot antenna based on coplanar waveguide (CPW) feeding is proposed in this article. To obtain circular polarization with a single feed, a transition from microstrip to CPW is designed to excite the even and odd modes of the CPW simultaneously. By adjusting the relative position and dimensions of the two circular patches introduced at the end of microstrip line and CPW, a 90° phase difference between two modes can be produced. When the two modes are coupled into the wide slot antenna, broadband circular polarization operation can be realized. The 10‐dB reflection coefficient bandwidth of the proposed antenna is 88.2% (2.49‐6.42 GHz) and 3‐dB AR bandwidth attains 50% (2.72‐4.49 GHz).