Wideband circularly polarized leaky‐wave antenna with flat gain using printed ridge gap waveguide

A wideband beam scanning circularly polarized (CP) leaky‐wave antenna (LWA) at Ku band is proposed based on the printed ridge gap waveguide (PRGW). In this design, the printed technology is used to realize the ridge gap waveguide (RGW) structure, and a substrate layer is introduced to replace the air gap layer in conventional RGWs. The proposed beam scanning CP LWA has been fabricated. Measured results of the fabricated antenna prototype are carried out to verify the simulation analysis. It provides a wide impedance bandwidth of 22% ranging from 12 to 15 GHz while performing continuous frequency beam scanning from ?2° to +47°. Furthermore, it maintains the excellent CP characteristic with axial ratio (AR) below 1.5 dB and a flat gain response with variation less than 2 dB in the entire operation frequency band.     

Novel wide‐beam cross‐dipole CP antenna for GNSS applications

A wide‐beam circularly polarized (CP) cross‐dipole antenna for GNSS applications is proposed in this article. This cross‐dipole antenna is fed by a coaxial cable, on which the slots is added to optimize the impedance matching. These two pairs of dipole arms are designed with different lengths to obtain the circularly polarized radiation. Enhanced wide‐beam CP radiation characteristics can be achieved by curving the dipole arms and adjusting the distance between the arms and the metallic ground plane. The study of proposed antenna performance with different geometric parameters has been conducted. The final antenna exhibits a good impedance bandwidth (IBW) of ～13.1% (1.50‐1.71 GHz), and the 3‐dB axial‐ratio bandwidth is over 7% (1.52‐1.64 GHz). Broad pattern coverage of more than 140°, pure CP radiation at all designed bands and a wide 3 dB axial‐ratio beamwidth (ARBW) of nearly 150° makes this antenna an excellent candidate for satellite communications and navigation systems.     

Broadband printed quadrifilar helix antenna using parasitic strip technique

A circularly polarized (CP) printed quadrifilar helix antenna (QHA) with enhanced bandwidth is proposed in this communication. This QHA is fed by a feeding structure with superior performance, which uses wide‐band 90° and 180° planar bulun. The feeding network can simply realize the 90° phase shift and four equal power divisions within a wide band range. Enhanced impedance matching and CP radiation characteristics can be achieved with the parasitic strips between helix arms. The study of proposed antenna performance with different geometric parameters has been conducted. The final antenna exhibits a good impedance bandwidth (IBW) of approximately 37.4% (1.65‐2.41 GHz), and the 3‐dB axial‐ratio bandwidth (ARBW) is over 43.9% (1.6‐2.5 GHz). Broad pattern coverage, pure CP radiation at all designed bands and a wide 3 dB axial‐ratio beam width of 150° makes this antenna an excellent candidate for satellite communications and navigation systems.     

Wide‐angle scanning circular polarization phased array based on polarization rotation technology

A wide‐beam circular polarization (CP) antenna and a wide‐angle scanning phased array based on novel polarization rotation reflective surface (PRRS) are proposed. The CP wide‐beam pattern is obtained by the combination of the radiation wave from the patch antenna and the orthogonal reflected wave from the PRRS with a 90° phase difference. The proposed CP wide‐beam antenna obtains the patterns with the 3‐dB beamwidth more than 136° and the axial ratio (AR) beamwidth more than 132° in the xoz‐plane. Furthermore, an eight‐element phased array based on the wide‐beam CP antenna element is also developed. The measured results show that the main beam of the array can scan from ?65° to 65° with a gain fluctuation less than 3 dB and the ARs at every scanning angle less than 3 dB.     

Epsilon‐shaped circularly polarized strip and slot‐loaded ultra‐wideband antenna for Ku‐band and K‐band

A compact epsilon‐shaped (ε) ultra‐wideband (UWB) antenna for dual‐wideband circularly polarized (CP) applications has been investigated in this article. It consists of a stepped stub loaded modified annular ring‐shaped radiator and modified CPW ground plane. The ground plane is loaded with two semicircular notches and a spiral‐shaped slot. The impedance bandwidth (IBW) is 97.02% (10.4‐30 GHz) along with an overall footprint of 20 × 20 mm². The fractional axial ratio bandwidth (3‐dB ARBW) for two wide bands is 38.50% (13.30‐19.64 GHz) and 6.45% (26.25‐28.00 GHz), respectively. The proposed antenna is left‐hand circularly polarized with a peak gain of about 5.09 and 5.14 dB in both 3‐dB ARBW bands. The proposed antenna is dominating other reported CP antenna structures in terms of number of CP bands, 3‐dB ARBW, IBW, peak gain, and dimensions.     

2D circularly polarized antenna array fed by spoof surface plasmonic waveguide

A two‐dimensional high‐gain circularly polarized (CP) patch array antenna operating in Ku band is proposed in this article. To excite a novel spoof surface plasmonic transmission line (SSP‐TL), which is mounted vertically on the ground, a waveguide with a transition are used for the momentum and impedance matching. A SSP‐TL 4‐way power divider is then used to feed a 4 × 7 circular patch array by travelling waves. Therefore, the CP radiation is generated on the patches located between the parallel SSP‐TLs. Avoiding the deterioration in axial ratio, 90° phase difference between adjacent SSP‐TLs is designed by tuning the height of the SSP‐TLs, as the dispersion property is influenced by the height of the corrugations obviously. The simulated maximum gain of 20.6 dBi is achieved at 15.2 GHz, together with the axial ratio of 0.8 dB. A prototype is fabricated and measured to validate the proposed antenna array.     

A dual circular‐slot microstrip antenna for GPS application

A novel single probe‐fed circularly polarized (CP) microstrip antenna design for global positioning system application is proposed. To achieve good CP radiation at 1575 MHz, two circular slots of dissimilar sizes are embedded separately into the radiating element and the ground plane. This CP design possesses the advantages such as simple in structure, uncomplicated fine‐tuning technique, and ease in manufacturing tolerances. Parametric studies via simulation are carried out to comprehend the vital parameters that will affect the impedance matching and frequency of the CP radiation. Prototypes of the proposed antenna have been constructed and experimentally studied. The measured results show a 10‐dB bandwidth and 3‐dB axial ratio bandwidth of 2.28 and 0.89%, respectively. Furthermore, stable gain variation at around 3.6 dBic is also observed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

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.     

Substrate fields modulation with defected ground structure: A key to realize high gain,wideband microstrip antenna with improved polarization purity in principal and diagonal planes

Rectangular microstrip patch antenna with circular headed dumbbell shaped defect in ground plane has been studied experimentally for concurrent improvement in its gain, bandwidth and polarization purity in principal and 45° diagonal planes. Around 9–9.5 dBi peak co polarized (CP) gain, 22% impedance bandwidth along with minimum 19–20 dB of CP‐cross polarized (XP) isolation in both principal and 45° diagonal plane are achieved with the present structure. These observed improvements in results from present antenna are justified with physical insight. The present structure is simple and easy to manufacture. The geometry of the defect in ground plane has been shaped judiciously to modulate the fields beneath the patch efficiently for simultaneous improvement of the three parameters. Very close mutual agreement between simulation and measure results are revealed. The present investigation provides an insightful, visualization‐based understanding of concurrent improvement of all these parameters. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:174–181, 2016.     

Broadband circularly polarized antenna with moon‐shaped parasitic element

A broadband circularly polarized (CP) circular patch antenna with an L‐shaped ground plane and parasitic element is studied. The use of this L‐shaped ground is to achieve short probe feed connection to the circular patch, while maintaining a certain height between the circular patch and ground plane, so that good impedance matching and bandwidth enhancement can be attained. To achieve CP radiation, two notches are initially loaded diagonally into the circular patch, and to further enhance the CP bandwidth, a novel technique of loading a small size moon‐shaped parasitic element into the notched circular patch is proposed. By doing so, the CP bandwidth of proposed antenna can be tremendously increased by approximately 10%. The experimental results show that the proposed CP antenna can yield impedance bandwidth and CP bandwidth of 835–1150 MHz and 839–968 MHz, respectively, with good gain level of 7.6 dBic. Therefore, this proposed wideband CP antenna can be used for UHF (ultrahigh frequency) RFID (radio frequency identification) reader antenna that operates within the universal RFID bands (840 ? 960 MHz). © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:387–395, 2016     

Wideband leaky‐wave antenna with consistent gain and wide beam scanning angle based on multilayered substrate integrated waveguide composite right/left‐handed transmission line

In this article, a wideband leaky‐wave antenna is designed for consistent gain and wide beam scanning angle by using the proposed multilayered substrate integrated waveguide (SIW) composite right/left‐handed transmission line (CRLH TL). The proposed SIW CRLH structure consists of two parts: an interdigital fingers slot of rotating 45° etched on the upper ground of the SIW, and a rotated parasitic patch beneath the slot. Due to the continuous phase constants change from negative to positive values of the proposed SIW‐CRLH under the balanced condition, the designed LWA can achieves a continuous beam‐scanning property from backward to forward over the operating frequency band. The designed antenna is fabricated and measured, the measured and simulated results are in good agreements with each other, indicating that the designed antenna obtains a measured continuous main beam scanning from backward ?78° to forward +76° over the frequency range from 7.7 to 12.8 GHz with a consistent gain of more than 9.5 dB. Besides, the designed antenna also exhibits a measured 3‐dB gain bandwidth of 45.1% with maximum gain of 15 dB. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:731–738, 2016.     

Wideband dual‐element leaky‐wave antenna with constant gain and enhanced broadside radiation bandwidth using multilayered composite right/left‐handed substrate integrated waveguide

In this study, a wideband dual‐element leaky‐wave antenna (DE‐LWA) is proposed to achieve constant gain and wideband broadside radiation by using multilayered composite right/left‐handed substrate integrated waveguide. The proposed DE‐LWA consists of two leaky‐wave radiator elements which are with slanted and vertical interdigital fingers slot arrays. To verify the simulated results, the proposed DE‐LWA is fabricated and measured. The measured results are in good agreement with the simulated ones, indicating that the fabricated antenna obtains broadside gain of 12.5 dB with variation of 1.0 dB over the frequency range of 8.725‐9.25 GHz (5.84%). Moreover, the proposed DE‐LWA also can provides a beam scanning property from backward ?80° to forward +80° over the frequency range from 7.4 to 12.7 GHz with a constant gain of more than 10 dB. Besides, the electromagnetic performances of this work are better than those of the recently reported similar work in the references.     

A novel low‐cost high‐gain antenna design from cuboids and differential strips

This article proposed a novel broadband high‐gain antenna designed by suspended cuboids and differential shorting strips on a circular ground plane. The design structure of the proposed antenna is simple and all its components such as cuboids, strips, and ground plane are fabricated by a copper sheet of thickness 0.5 mm. The proposed antenna has measured ?10 dB impedance bandwidth (IBW) 45% (2.35‐3.7 GHz) with broadside gain of 10.1 ± 0.4 dBi over IBW. The use of differential strips in inner cuboid improved the cross polarization and enhanced the broadside gain. The measured antenna has low cross polarization is below 25 dB in the broadside direction over IBW. The proposed antenna has 1 dB gain‐bandwidth 53% (2.2‐3.8 GHz) in the broadside. The antenna has been fabricated and measured; the results show a good agreement with simulated results.     

A 2 × 2 array antenna with circular polarization and conical beam radiation

A circular disk patch antenna loaded with a hemi‐circular slot is initially proposed for achieving circular polarization (CP). To exhibit broad CP bandwidth that can cover the WLAN 2.4 GHz operating band, the patch antenna is fed by an L‐shaped probe. To further attain conical beam radiation with peak gain of ～8 dBic at ±30 degrees theta angle (θ), a 2 × 2 array type is proposed in this study, in which four circular disk patch array elements are arranged in a sequentially rotated fashion via a corporate feed network. Here, desirable 3‐dB axial ratio (AR) bandwidth and 10‐dB impedance bandwidth of ～5% and 21% were measured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:223–228, 2014.     

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 microstrip antenna with defected patch surface for low cross polarization applications

A simple and single element wide slot dipole loaded shorted rectangular microstrip antenna has been proposed and investigated experimentally for broad impedance bandwidth and improved cross polarized (XP) radiation compared to maximum co‐polarized (CP) gain without changing the co‐polarized (CP) radiation pattern. Around 23‐35 dB isolation between CP and XP radiation along with 25% impedance bandwidth is achieved with the proposed structure. The measured gain of the antenna is around 6.2 dBi over the entire band. The present antenna is very simple and easy to manufacture. Unlike the other structures, the present one is free from back radiation in terms of XP fields. The design of the antenna structure is theoretically justified and rigorously analyzed. The present investigation provides an insightful, clear visualization‐based understanding of the concurrent improvement in both the impedance bandwidth and XP performance with the present structure.     

Wideband high aperture efficiency antennas with beam switching for mmWave 5G base stations

A compact metamaterial inspired sub‐wavelength unit cells are integrated into wideband Vivaldi antenna. A high gain Vivaldi antenna with 50% impedance bandwidth is proposed. The dimensions of the antenna are 1.55 λ₀ × 3.2 λ₀ at 28 GHz. Gain enhancement of 3‐dB achieved by placing metamaterial unit cells in the aperture of the antenna. These unit cells aid in phase correction of the antenna. The 1‐dB gain bandwidth of antenna is 42% with a peak gain of 12.5 dBi indicating high pattern integrity. Corrugations of varying length are introduced in the ground plane to improve front‐to‐back ratio without altering the input impedance bandwidth. The aperture efficiency of the metamaterial loaded Vivaldi antenna is 78% at 28 GHz. The proposed element is used in a stacked module to achieve wide angular coverage of 120°.     

A compact broadband coplanar waveguide fed circularly polarized printed monopole antenna with asymmetric modified ground plane

In this communication, a broadband circularly polarized (CP) monopole antenna with coplanar waveguide (CPW) feeding is proposed. It consists of a modified rectangular monopole, an asymmetric ground plane, a two‐linked inverted L‐shaped strips on the left CPW ground, and two rectangular horizontal slots in asymmetric CPW ground plane. The overall dimension is only 0.47λ _o × 0.47λ _o. The antenna prototype has been fabricated. The measured results indicate that a broad ?10 dB impedance bandwidth (IBW) of 107.5% (4.3 GHz, 1.85‐6.15 GHz) and a broad 3 dB axial ratio ARBW of 104.3% (4 GHz, 1.855‐5.9 GHz) can be achieved; the average realized gain is 2.3 dBi for the entire CP band. The proposed antenna is an attractive candidate for several wireless communication systems.     

Eccentric annular slot patch antenna with frequency agility for UHF RFID reader applications

The design of a simple ultrahigh frequency RFID (radio frequency identification) reader antenna that can operate within the North America RFID band (902–928 MHz) is studied. To generate circular polarization (CP) radiation in this band, a novel method of loading two narrow open‐ended slots (slits) into an eccentric annular slot patch is proposed. To allow optimum impedance matching with enhanced CP bandwidth, the radiating patch is loaded to an L‐shaped ground plane. From the experimental results, the proposed antenna can yield an impedance bandwidth (10‐dB return loss) between 650 MHz to 1125 MHz, while good CP bandwidth (3‐dB axial ratio, AR) from 901 MHz to 930 MHz is also attained. Furthermore, gain level and efficiency of more than 7.8 dBic and 90%, respectively, were also measured. By simply removing one of the slits, this proposed antenna can also be modified to operate within the China (840–846 MHz) and European (865–868 MHz) RFID band.     

A circular patch antenna with parasitic element for UHF RFID applications

This article initially proposes a directly‐fed circular patch antenna with L‐shaped ground plane for Radio Frequency Identification (RFID) applications in the 900 MHz (902?928 MHz) ultrahigh frequency (UHF) band. To achieve circularly polarized (CP) radiation, two arc‐shaped notches are loaded into the main patch. To enhance the CP bandwidth so that the proposed antenna can also cover the UHF RFID band for Europe (866?869 MHz), a parasitic element is printed besides the main patch. Experimental measurements show that the 10‐dB return loss bandwidth of the proposed antenna was 30.95% (833?1138 MHz) and its corresponding 3‐dB axial ratio bandwidth was 8.95% (865?946 MHz). Good gain and radiation efficiency of more than 7 dBic and 90%, respectively, were also exhibited across the two desired UHF RFID bands. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:681–687, 2015.