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 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.     

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.     

Substrate integrated waveguide dual‐frequency dual‐sense circularly polarized cavity‐backed slot antenna

A novel design of dual‐frequency dual‐sense circularly polarized (CP) substrate integrated waveguide (SIW) cavity‐backed slot antenna is presented for dual‐band wireless communication systems. The proposed antenna consists of square SIW cavity, asymmetrical bow‐tie‐shaped cross slot and probe feed. Due to use of asymmetrical bow‐tie‐shaped cross slot, circularly polarized wave radiates at two different frequencies with opposite sense of polarizations. The RHCP radiation occurs at (10.45‐10.54) GHz (Lower band) and LHCP occurs at (11.26‐11.34) GHz (Upper band). Moreover, in each band, sense of polarization can be change by changing the feed position. The front to back radiation ratio (FTBRR) is more than 10.5 dB and cross polarization level is lower than ?20 dB in both the bands.     

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 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.     

Circularly polarized slot antenna array with sequentially rotated feed network for broadband application

This article presents a novel circularly polarized sequentially rotated slot antenna array (CPSSAA) designed to operate at a frequency of 5.5 GHz. This antenna is suitable for communication applications such as WLAN/WiMAX. Method of feeding is based on sequential rotation with seven quarter‐wavelength transformers. In this case, the elements with 200 Ω impedance could be replaced by other elements with different input impedance. Reducing the elements input impedance, maximum power can be transferred to the elements. Because the lower losses in transmission line occur in presence of lower impedance, the 3 dB axial‐ratio bandwidth of the CPSSAA extends to ～1.3 GHz. The CPSSAA was designed to operate over the frequency range between 4.5 and 6.4 GHz corresponding to an impedance bandwidth of 34.86% for VSWR < 2. Acceptable agreement between the simulation and measured results validates the proposed design. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:358–363, 2015.     

Low‐cost and wideband circularly polarized slot antenna array

A slot antenna with wideband circular polarization (CP) array, which operates on millimeter waves band, is proposed. A four‐direction sequential rotation technique is used in the feed network to feed the 2 × 2 slot element based on waveguide. The shot element resonates at both the fundamental mode and the high‐order mode. The slot element is studied in high order mode, and the radiation lobe can be redirected by changing the size of the slot element, thus improving the multi‐lobe problem. A strong single lobe is formed in the +z‐direction by using the ground edge diffraction characteristics of the slot element in the waveguide. The designed broadband characteristics are obtained through the appropriate combination of the feed network and CP antenna. The prototype of the antenna with an overall size of 137 mm × 137 mm × 0.6 mm³ is processed and verified by experiments. The prototype of the slot array is processed and examined. The test results display that the device has good performance of |S₁₁| < ?10 dB bandwidth of 3.72 to 6.56 GHz (2.84 GHZ, 55.25%), a 3 dB axial ratio bandwidth of approximately 4.39 to 5.43 GHz (21.18%).     

Novel dual‐band asymmetric U‐shaped slot antenna for dual‐circular polarization

A novel dual‐band, dual‐circularly polarized antenna is proposed and fabricated. The proposed antenna consists of an asymmetric U‐shaped slot and an inverted L‐shaped slot which are designed to excite two orthogonal E vectors with equal amplitude and 90° phase difference (PD), in addition, fed by a coplanar waveguide (CPW) Furthermore, a left‐hand circular polarization in the direction of z > 0 and a right‐hand circular polarization instead of the opposite direction both at the lower and upper bands are exhibited by the radiations of the antenna. Good agreement is achieved between the measurement and simulation, which indicates that a 10‐dB bandwidth of 38.75% from 2.56 to 3.8 GHz and 21.8% from 10.01 to 12.53 GHz, while a 3‐dB axial‐ratio bandwidth (ARBW) of 13.4% from 2.77 to 3.2 GHz and 9.23% from 10.25 to 11.25 GHz at two operation bands, respectively, are covered in the designed antenna. To explain the mechanism of dual‐band dual‐circular polarization, the analysis of magnetic fields distributions and a parametric study of the design are given. Meanwhile, compared to other recent works, a single layer structure, wider axial ratio and impedance bandwidths and a more compact size are the key features of the proposed antenna.     

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%.     

Circularly polarized D‐shaped slot antenna for wireless applications

A multiband circularly polarized slot antenna for wireless local area networks (WLAN) and worldwide interoperability for microwave access (WiMAX) applications is designed, studied, and fabricated. Using modified ground plane structure, circular polarized characteristics are realized. An open rectangular loop is introduced on the ground plane to generate orthogonal modes at middle resonance frequency. At higher resonance frequency to improve axial ratio bandwidth, a D‐shaped radiator is used. Thus, the cooperation of modified ground plane, open loop resonator, and D‐shaped radiator improves performance of the antenna at all the required bands. The proposed microstrip antenna generates separate impedance bandwidths to cover frequency bands of WLAN and WiMAX applications. The realized antenna is relatively small in size 40 × 54 mm² or 0.26_ × 0.36_ where _ is the free‐space wavelength at the desired first resonant frequency 2.0 GHz and operates over frequency ranges 26% (2.0‐2.6 GHz), 8.9% (3.21‐3.51 GHz), and 50.6% (3.8‐6.38 GHz). In addition, the antenna exhibits 5% (2.32‐2.44 GHz), 5.8% (3.3‐3.5 GHz), and 5.2% (5.61‐5.91 GHz) Circular Polarization bandwidth, making it suitable for WLAN and WiMAX applications.     

Wideband and low profile polarization conversion meatasurface‐based circularly polarized slot antenna

The purpose of this study is to investigate the application of a polarization conversion meatasurface for constructing a low profile, wideband circularly polarized slot antenna, which consists of a new Polarization conversion metasurface (PCM)‐based square‐corner‐cut artificial magnetic conductor cell structure and a feeding slot antenna. PCM possesses two frequency points of polarization rotation (PR), produced by appropriately adjusting width between the two triangular metallic patches. A 39.3% (4.7‐7 GHz) of big PR band was realized through the combination of two neighboring PR frequency points. The impedance bandwidth of PCM based patch antenna was measured to be 43.5% (4.5‐7 GHz), with 17.2% (5.3‐6.3 GHz) of 3 dB axial ratio (AR) bandwidth and 0.045λ₀ of profile. It also generated 7.3 dBic of high broadside gain in operational bandwidth.     

Planar integrated substrate integrated waveguide circularly polarized filtering antenna

A new design of substrate integrated waveguide (SIW) circularly‐polarized (CP) filtering antenna is presented, which is based on dual‐mode (TE₁₀₂ and TE₂₀₁) cavities. The satisfying filtering performance of the antenna is realized by a coupled‐resonator circuit of two dual‐mode SIW cavities. And the radiating element of the antenna is a cavity‐backed CP slot antenna which is formed by a nonuniform ring slot integrated with the back cavity. To demonstrate the idea, a prototype antenna operating at X band is designed, fabricated, and measured. Measured results show that the 10‐dB impedance bandwidth is 4.2% (from 11.6 to 12.1 GHz), the 3‐dB axial‐ratio (AR) bandwidth is 4%, and the gain is 5.6 dBi at the center frequency of 11.8 GHz.     

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).     

Dual circularly polarized loop antenna using a pair of resonant even‐modes

Conceptual design of dual circularly polarized (CP) square loop antennas using a pair of resonant even‐modes for wireless sensor application is presented. A pair of even‐modes is simultaneously excited within a single, nonuniform square loop element and employed to realize a dual circular polarization characteristic. When the natural boundary conditions of the even‐modes and the feed lines are matched, respectively, a bidirectional dual CP loop antenna can be attained at first. Then, a unidirectional dual CP loop antenna is designed by introducing a simple metallic reflector. Both bidirectional and unidirectional designs exhibit dual CP performance with available operation bandwidth of 10.0% and 8.5%. The design approach is expected to get applications in dual CP antenna designs for wireless sensor systems.     

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.     

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.     

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.     

Planar endfire circularly polarized antenna using concentric annular sector complementary dipoles

A novel planar endfire circularly polarized (CP) antenna is presented and explored by using concentric annular sector complementary dipoles. The antenna is composed of a semicircular disk radiator operating at TM₁₁ mode and a concentric annular sector dipole operating at one‐half wavelength mode. A set of closed‐form formulas is derived to reveal the operation principle and employed to determine the geometrical parameters of the proposed CP antenna. The design approach is both numerically and experimentally validated. Good agreement between the theoretical, numerical and experimental results has demonstrated its endfire radiation beam in parallel with its plane. The fractional impedance bandwidth for |S₁₁| < ?10 dB is up to 6.45%, and axial ratio (AR) bandwidth of less than 3 dB is up to 14.43% in fraction, in addition to its simple geometry with only seven design parameters.