Broadband circularly polarized Z‐shaped dipole antenna with parasitic strips

A Z‐shaped dipole antenna with parasitic strips is proposed for wideband and unidirectional circular polarization operation in this article. The dipole arms are bent into L‐shape for circular polarization, and printed balun is used to achieve good impedance matching. To further extend the axial ratio bandwidth, two parasitic strips are employed to introduce an additional band of circularly polarized operation at the high frequency. Measured results demonstrate that the proposed antenna has a 10‐dB impedance bandwidth of 63.3% (1.64‐3.16 GHz) and a 3‐dB axial ratio bandwidth of 51.1% (1.72‐2.9 GHz). Stable radiation patterns with gain around 9 dBic along +z‐axis are also observed.     

Broadband gap‐coupled half‐hexagonal microstrip antenna fed by microstrip‐line resonator

Half‐hexagonal microstrip antenna (H‐HMSA) is a compact version of HMSA, as it resonates at the same fundamental mode frequency. In this article, a compact configuration of a single layer, broadband gap‐coupled H‐HMSA has been proposed. Gap‐coupled H‐HMSA is fed indirectly by a λ/2 microstrip‐line resonator. Broad bandwidth (BW) is achieved with an effective use of resonance introduced by λ/2 resonator and gap‐coupled half‐hexagonal radiating patches. A peak gain of 7.07 dBi and measured BW (S₁₁ ≤ ?10 dB) of 11.5% at the center frequency of 5.2 GHz have been achieved, which occupies a small volume of 0.023 λ₀³ including the ground plane. The radiation patterns remain in the broadside direction throughout the return loss BW. Simulated results of the proposed antenna configuration are experimentally validated with good agreement.     

Novel single‐fed broadband circularly polarized antenna for GNSS applications

This letter presents the design of a broadband microstrip CP antenna using single‐fed technique. The feeding network is integrated within the coupling feed patch to simplify the structure. The proposed antenna is designed for Global Navigation satellite System (GNSS) operating at 1575.42 ± 10.23 MHz (GPS: L1 band), 1559～1592 MHz (Galileo: E2‐L1‐E1 band), 1602 ± 5.625 MHz (GLONASS: L1 band) and 1559.052～1591.788 MHz & 1610～1626.5 MHz (BeiDou Navigation Satellite System B1 and L band). Another advantage of this antenna is the much wider bandwidth in both VSWR and 3 dB axial‐ratio compared with traditional single‐fed CP antennas. Details of design, simulated and experimental results of this CP antenna are presented and discussed. The measured results confirm the validity of this design which meet the requirement of GNSS applications.     

New broadband circularly polarized antenna with an inverted F‐shaped feedline

In this article, we present a new broadband CP square‐slot antenna with an inverted F‐shaped feed‐line. The antenna is composed of an inverted F‐shaped feed‐line, pairs of isosceles triangular chamfers, I‐shaped slots, rectangular slots and triangular patches, and a Z‐shaped strip. By introducing these strips and slots into the square‐slot, multiple CP modes can be stimulated simultaneously, which eventually enhances 3‐dB ARBW and 10‐dB impedance bandwidth (IBW) of the presented antenna. The measured results show that its IBW (|S₁₁| < ?10 dB) is about 7.2 GHz (87.8% from 4.6 to 11.8 GHz) and its ARBW (AR < 3 dB) is 8.3 GHz (96% from 4.5 to 12.8 GHz).     

A WiMAX circularly polarized antenna array using slot‐coupling feeding technique

In this letter, we present a circular polarization antenna array using the novel slot‐coupling feeding technique. This antenna includes eight elements which are installed in line, each array element is fed by means of two microstrip lines with equal amplitude and phase rotation of 90°. The feeding microstrip lines are coupled to a square patch through a square‐ring slot realized in the feeding network ground plane. With the presence of the slots, this antenna array is able to cover the range of frequency of 3 GHz to 4 GHz. The size of the proposed antenna array is 7λ × 1.8λ × 0.4λ. The measured gain is 15.2 dBi and the bandwidth of S11< ?10 dB is 1 GHz (3–4 GHz, 28%). The antenna array is suited for the WiMAX applications. With the use of slot‐coupling feeding technique, the measured bandwidth for axial ratio < 3 dB is about 24% in the WiMAX frequency band (3.3–3.8GHz). The measured HPBW of the y–z planes is larger than 62°. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:567–574, 2016.     

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 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.     

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 low‐profile circularly polarized dielectric patch antenna and array

A square dielectric patch (DP) resonator fusing with the bottom substrate is studied for designing low‐profile circularly polarized (CP) antenna. Based on the theoretical investigation using the constructed analysis model, it can be found that the proposed DP resonator possesses a pair of degenerate dominate modes (TM₁₀₁ and TM₀₁₁), which can be split by introducing perturbations on the DP resonator and then used to design CP antenna fed by a microstrip line directly. To verify the proposed idea, a 2 × 2 array fed by a dual Marchand balun network is designed and implemented. Reasonable agreement between the measured and simulated results is observed. Experimental results show that a measured impedance bandwidth is 380 MHz (5.18‐5.56 GHz) for |S₁₁| < ?10 dB and the 3‐dB axial ratio bandwidth is 90 MHz (5.32‐5.41 GHz). The measured gain is up to 11.77 dBic with a cross polarization of about ?20 dB in the boresight direction.     

CPW‐fed C‐shaped slot antenna for broadband circularly polarized radiation

A novel broadband circularly polarized (CP) C‐shaped slot antenna fed by a coplanar waveguide is presented. The broadband CP operation can be achieved simply using a C‐shaped slot in the ground to produce orthogonal surface currents for left‐hand circular polarization. Using the semicircle‐shaped radiator patch, wide impedance bandwidth and broad axial‐ratio (AR) bandwidth can be obtained simultaneously. The measured results show that the proposed antenna can provide a 10‐dB impedance bandwidth of 105% from 2.78 to 8.92 GHz, and a 3‐dB AR bandwidth of 70.4% from 2.9 to 6.05 GHz. Finally, an antenna prototype with a reflector for unidirectional pattern applications is also developed. The proposed antenna has broader impedance and CP bandwidths but with a more compact size compared with the previous designs. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:739–746, 2015.     

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.     

Compact broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

Balanced circularly polarized square loop antenna under even‐mode resonance

Design approach to a novel balanced, circularly polarized (CP) square loop antenna under even‐mode resonance is proposed in this paper. The loop antenna is diagonally fed by a fork‐like dipole launcher. By matching the respective natural boundary condition of the loop radiator and the dipole launcher, the resonant even‐mode with inherent CP radiation characteristic can be sufficiently excited. Both the bi‐ and uni‐directional cases are designed and investigated. A bi‐directional CP loop antenna with a 3‐dB ratio axial ratio (AR) bandwidth of 6.6% is designed at first. A uni‐directional antenna having a planar metallic reflector is further designed. The uni‐directional loop antenna exhibits excellent uni‐directional CP performance with a high front‐to‐back ratio of 40dB and a 3‐dB AR bandwidth of 7.6% in both theory and experiment.     

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 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.     

Broadband circularly polarized printed falcate‐shaped monopole antenna

In this study, a simple broadband circularly polarized (CP) printed monopole antenna for S/C‐band applications is proposed. The CP antenna is composed of a falcate‐shaped monopole with a right‐angle trapezoid stub, then wide impedance and axial ratio (AR) bandwidths are achieved. By placing one rectangular split‐ring resonator above the stub for generating upper CP mode, both of impedance and CP performances are further improved. The proposed antenna is fabricated on a FR4 substrate and measured. The measured ?10‐dB impedance bandwidth is 107%, ranging from 2.4‐7.9 GHz, and the measured 3‐dB AR bandwidth is 94% (2.4‐6.6 GHz), covering the entire wireless local area network (WLAN) and WiMAX bands.     

Gain enhancement of circularly polarized antenna with dual‐polarization conversion transmitarray

A dual‐polarization conversion transmitarray is proposed for a circularly polarized (CP) transmitarray antenna. The designed transmitarray realizes the polarization conversion and gain enhancement for the circular polarization incident wave. The transmitarray can transform the left‐hand circularly polarization (LHCP) wave and the right hand circularly polarization (RHCP) wave into RHCP and LHCP waves, respectively. Two CP patch antennas are designed as source antennas to illuminate the transmitarray and form the transmitarray antenna. The experimental and simulation results show that the designed transmitarray realizes the polarization conversation and the gain enhancement for two CP antennas indeed.     

High inter‐port isolation dual circularly polarized slot antenna with interdigital capacitor

A planar dual circularly polarized slot antenna is presented. The designed antenna has two tilted “8” shaped slots fed by microstrip lines, one each for transmission (T_X) and reception (R_X) operations. The isolation between the two ports (T_X and R_X) is augmented by means of an interdigital capacitor based bandstop filter. The proposed antenna has an impedance bandwidth of 361 MHz centered at 2.293 GHz (2.113‐2.474 GHz) with the isolation between the ports being >17.6 dB which goes up to a value as high as 46 dB within the band of operation. The 3 dB axial ratio (AR) bandwidth is 11.52% centered at 2.1275 GHz (2.005‐2.25 GHz). Because of its high inter‐port isolation within the AR bandwidth, the design is suitable as a full‐duplex antenna for applications in S‐band.     

Ultrawideband circularly polarized antenna with dual band‐notched characteristics

This article presents an ultrawideband (UWB) crossed dipole antenna with circularly polarized (CP) and dual band‐notched characteristics. The proposed design is based on two orthogonal tapered dipoles for UWB CP operation and a square‐shaped cavity for high broadside gain over the entire operating bandwidth (BW). To generate dual band‐notched characteristics, two separated slots are inserted into each dipole's arm. This antenna yields measured impedance BW of 100% (3.2‐9.6 GHz) with dual‐band rejection centered at 5.2 and 5.8 GHz. Correspondingly, dual rejected bands are also observed in the original UWB CP band, which ranges from 3.2 to 8.2 GHz. Additionally, the proposed antenna exhibits high broadside gains better than 6.2 dBic and radiation efficiency greater than 82%.     

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.