Comparing the obtained results with previous dual-band mi- crostrip antennas with circular polarization referenced in the intro- duction part, it can be verified that our measured reflection coefficient presents a wider bandwidth than , and is similar to [3, 4] where feed- ing networks were also used. On the other hand, the measured gain and axial ratio as a function of frequency is very similar to the gain and axial ratio presented in [3, 4]. However, the proposed antenna has a more compact size thanks to the use of the annular-rings and the reduction of the substrate size. Finally, it must be emphasized that the dual-band antenna shown in  presents a compact size because it is composed of only one layer. However, it only has a good axial ratio at boresight in the interesting bands, worse 4 dB axial ratio beamwidth and lower values of gain than our.
techniques have been proposed to solve this problem. In , the authors use microstrip line as impedance transformer to realize matching with the characteristic impedance of 50 Ω. In [4–8], the technique of coupling feeding is used to improve the impedance matching. Loading gaps, slits, or stubs on the ring is another method to be involved , but the patch mainly works at linear polarization, and polarization rotation can be caused by the loading. However, the above approaches hardly provide wide impedance bandwidth because of the single resonant frequency. Stacking parasitic patch above the annularring can greatly reduce the value of input impedance [10, 11], and the bandwidth can be broadened obviously due to exciting two adjacent resonant frequencies. But in , the authors did not provide the relative parametric studies on the antenna performance, especially, the CP performance when the antenna works in circular polarization.
In this paper, a novel dual-broadband circularlypolarizedantenna using two special slots and single microstrip-coupled feed is introduced and investigated. By optimizing the key geometrical parameters of the antenna, two wide impedance bandwidths of 35.0% (1.91–2.72 GHz) and 46.5% (4.36–7.00 GHz) are obtained, as well as two axial ratio bandwidths are 2.36–2.56 GHz and 5.68–6.04 GHz, respectively. Good agreement between the simulated and measured results is also achieved, which implies that the proposed antenna is a good candidate for dual- broadband circularlypolarized wireless systems.
In this communication, a practical method has been discussed for controlling the vertical HPBW of circularlypolarizedmicrostrip antennas. This method is based on a parasitic ring right above the microstripantenna. A prototype antenna based on the proposed method was designed, at 2.492 GHz for CNSS application, fabricated and tested. The measurements showed it could effectively widen the vertical HPBW and improve the gain for low elevation angle. The structural parameters of the parasitic ring are key factors for determining the vertical HPBW. Besides, it could maintain good omnidirectional characteristics for the horizontal radiation pattern. This structure is simple and easy to manufacture.
Abstract—A compact circularlypolarizedmicrostripringantenna is presented for Global Navigation Satellite systems (GNSS) application in this paper. The antenna consists of a ring-shaped slotted ground and a radiation patch which is fed by a T-like coupling feedline. The radiation patch is a square ring strip embedded within two inverted L-shaped strips and a rectangular strip. The overall size of the proposed antenna is 0.38 × 0.38 × 0.038λ 3 g (λ g is the guide wavelength at the frequency of 1575 MHz).
many attractive features, microstrip patch antennas have received considerable attention for wireless communication applications [2–12]. In  a patch antenna was developed for HIPERLAN to operate at higher order mode and at the frequency band of 5 GHz, 6.1% bandwidth and 4.2 dB gain were achieved. The design of dual frequency shorted stacked patch antenna  and shorted E-shaped patch antenna  are also developed for the application in wireless communication. Dual frequency antennas for wireless LAN also developed [6, 7]. Current research works also include miniaturized multiband short circuited microstrip antennas [9–11] and wideband proximity coupled microstrip antennas [12–18]. Single layer microstrip antennas have very narrow bandwidth, but using multi-layered conﬁgurations like proximity coupled microstrip antennas or aperture coupled microstrip antennas, higher bandwidth can be achieved [12–18]. Design and development of compact printed antennas for wireless communications are also reported [19–28]. A thin wideband microstrip patch using two parallel slots is designed for WLAN . In  a triple band omnidirectional antenna, consisting of three pairs of back-to-back printed dipoles, for the operation at 2.4 GHz, 5.2 GHz and 5.8 GHz bands, is described. Design of eﬃcient patch antennas for the applications in wireless communication are reported in [21, 22]. The loop structure and two-layered meander strips are used to design small size and broadband antenna for mobile terminals . Important related work also reported by various authors [24–28] where broadband miniaturized printed antennas are developed.
Abstract—A single-feed dual-band dual-sense circularlypolarized (CP) microstripantenna is proposed. The antenna consists of a circular radiating patch with a ring slot, two substrates with an air layer sandwiched between them and a capacitive coupling feed. The two resonant frequencies are controlled by the size of the circular radiating patch and the ring slot. By introducing the perturbation, the fundamental resonant mode splits into two orthogonal degenerate modes, and the CP radiation pattern is obtained. Capacitive disk coupling feed is also used in the design to enhance the bandwidth. The key parameters of the design are investigated to show how to obtain dual-band and dual-sense CP. The proposed antenna prototype is fabricated and measured, and experimental results show that good CP radiation performances are obtained at both resonant frequencies.
Abstract: A circularlypolarizedmicrostrip short backfire antenna (CPMSBA) with two ring corrugated rim using aperture coupling feed method is proposed in this paper. The antenna is designed to operate in KU-band. The simulation results verify the circular polarization. The CP antenna provides good and stable radiation pattern over the whole frequency range. The axial ratio bandwidth bw AR is 3.74%, gain is
plane. First, to gain equal magnitude of two orthogonal resonant modes, a Wilkinson divider  is introduced with two output ports along x- and y-axes, respectively. However, in Fig. 1(c), the length diﬀerence of section f g and de is set up to be 46 mm, which is equal to the guided quarter-wavelength at the operating frequency of 900 MHz band to generate 90 degrees phase diﬀerence. Next, a vertical strip with the size of 8 × 17 mm 2 is used to connect the right-angle corners of dual L-shaped strip at point e and g, respectively. For a wider CP operating bandwidth at UHF band, the above annular-ring patch antenna with an air substrate is coupled-feed by dual L-shaped strips to excite TM 11 mode. The
Multifarious microstrip antennas have been presented for GPS applications [4–7]. The proposed antenna in  is a dual-band circularlypolarized cavity-backed annular slot antenna for GPS receiver with single-feed. Its 10 dB impedance bandwidths are 45 MHz in L 2 and 20 MHz in L 1 , while the 3 dB AR bandwidths are 11 MHz in L 2 and 9 MHz in L 1 . The bandwidth is quite too narrow. An antenna
Circularlypolarized (CP) microstrip antennas are widely used in radar, navigation, and satellite communication realms owing to their small size, low proﬁle, great ﬂexibility, and many other advantages . Circular polarization is produced by using the feeding structure to excite two orthogonal linearly polarized modes with a 90 ◦ phase diﬀerence [2–13]. A single-fed circularlypolarized patch antenna can be designed by slotting or chamfering on a square patch [2–4]. For these single-fed patch antennas, the measured − 10 dB return loss bandwidth and 3 dB axial ratio bandwidth are less than 5% and 2%, respectively. Circular polarization can also be obtained by a ringantenna with an asymmetrical structure [5–8]. When operated in the fundamental mode, the size of the annularring patch antenna is smaller than that of the circular or rectangular patch for a given frequency. Reference  presents a circularlypolarizedannular-ring patch antenna achieved by a simple microstrip feed line through the coupling of a fan-shaped patch on the same plane of the antenna. The impendence bandwidth (IBW) is 2.3% (2 . 68 ∼ 2 . 74 GHz), and axial-ratio bandwidth (ARBW) is 0.6% (2 . 69 ∼ 2 . 71 GHz). In , a circularlypolarized cut ringmicrostripantenna is proposed, and the measured ARBW is 4.2%. A novel miniaturized CP implantable annular-ringantenna is proposed in , which has 2.49% ARBW. Reference  proposes a polarization-reconﬁgurable antenna based on ringcircularlypolarizedmicrostripantenna. The IBW is 16.7%, and the ARBW is 3.2%. Some structures, which enhance the bandwidth of single-fed circularlypolarized patch microstrip antennas, are studied [9–11]. Reference  designs a circularlypolarizedantenna composed of a U-slot square patch with truncated corners supported by a substrate with dielectric constant of 10.02. A measured IBW of 15.2% (1 . 53 ∼ 1 . 78 GHz) and ARBW of 3.2% (1 . 56 ∼ 1 . 61 GHz) is achieved. A circularlypolarized single-layer asymmetrical U-slot microstrip patch antenna is proposed in . The asymmetrical structure of the U-slot provides two diﬀerent current paths for the two orthogonal modes required for circular polarization. The measured
ITS (Intelligent Transport System) has received much attention as a system for traffic safety and environmental protection. ITS applications such as ETC (electric toll collection system), GPS (global positioning system), SDRAS (satellite digital audio radio service) and VICS (vehicle information and communications system) have been proposed and are widely used presently. In order to use all these applications, multi band antennas represent an effective solution as car antennas for the ITS. In the ITS, a circularlypolarized wave is used in the ETC, SDRAS and GPS, while a linearly polarized wave in the VICS. Therefore, car antennas have to radiate both circularlypolarized waves and linearly polarized waves. In [1, 2], dual band microstrip antennas (MSAs) with two feed ports for ITS have been proposed. However, in the design for antennas with the multi feed ports, the isolations between the feed ports have to be reduced, which makes the design of the antenna difficult.
Now days, Compact circularlypolarizedmicrostripantennaantenna plays an important role in satellite communication and airborne communication due to its small size, light weight, ease of fabrication and installation . Microstripantenna has serious limitation like small bandwidth, low gain, low efficiency and small power handling capacity. Bandwidth can be enhanced by increasing the height of substrate, decreasing the dielectric constant of substrate, non contact feeding techniques, cutting different shaped slots like H Shape , Bowtie, C shape, L Shape etc., Corporate feeding , stacked arrangement of patches  and defected ground structure [7-8]. The polarization is an important parameter to limit the wireless communication distance due to the resulting wave having an angular variation. The circular polarization provides solution of this problem. It allows the receiver to maintain constant received power at any wave angles . Linearly polarization requires polarization matching between transmitting and receiving antenna but circularlypolarizedantenna solves this problem. Many researchers have worked on designing of the circular polarizedantenna. For generating circular polarization, two equal amplitude orthogonal feed configurations are used. The
band using PIN diode as a switch. A PIN diode is incorporated in the slot etched on rectangular patch antenna. The frequency band selectivity is achieved by controlling the state of the switch inserted in the antenna. In  authors have designed a dual frequency dual polarizedmicrostripantenna fed along the diagonal, embedded with a square slot having three extended stubs for frequency tuning. Two additional stubs of the same dimensions are also incorporated at right angles to the base arm. By changing the dimensions of the base arm and stubs in a uniform manner the ratio of the operating frequencies can be lowered. In  a broadband high gain microstrip patch antenna using slot is proposed. The slot use on the patch’s surface affects the radiation characteristics of the proposed antenna. By using slot on rectangular patch with coaxial probe feed a wide bandwidth is achieved.
A Compact and Robust circularlypolarizedmicrostrip patch antenna was designed and simulated using High Frequency Simulation Structure tool . The simulated results of antenna consists return loss, VSWR and radiation patterns achieved their optimum values. The Return loss valueachieved for less than-10dB and the voltage standing wave ratio less than two. A circularlypolarized patch antenna with different shapes of parasitic shorting strips for a new size reduction technique has been investigated analytically. The radiation pattern can be obtained for different shapes of shorting strip. Size reduction of ring shaped patch antenna can be achieved most efficiently by using high permittivity substrate.Simulation results good enough to satisfy our requirement to fabricate it on hardware. The proposed antenna is suitable for GPS satellite communications applications.
Abstract—In this paper, a novel quad-band combination of circularly-polarizedmicrostripantenna is proposed. This antenna has multi-frequency and quad-polarization with multiple coaxial probes, which cover four bands of the BeiDou navigation system (BDS), meeting diﬀerent application requirements. By using a stacked structure to achieve feed and using symmetrical slotted method to place the coaxial probes, the multi-frequency antenna is connected together through the middle co-aperture. Meanwhile, the feed position and size are constantly optimized until get the most suitable one, and the necessary perturbation is obtained. We also introduce a broadband stripline 90 ◦ bridge. Ultimately, the circularly-polarized and multi-frequency operation is achieved. Furthermore, the novel design enables easy implementation, miniaturization, wide band, which can meet the application requirements and promote the development of the BDS, which can be combined with the Internet of Things technology, applied to life and production.
In the literature, CSSSRR has been widely used [6, 7]. The CSSSRR unit contains two coupled open loops; therefore, it has two gaps. A similar unit denoted by gapped ring pair element was studied in . In , we have studied that gap in an open loop may block current flow in a specified direction. This property was employed to reduce cross polarization gain of a linearly polarized reflect array. In this paper, effect of gaps of the CSSRR on gain enhancement for a circularlypolarizedantenna is investigated.
receiver orientation  than for linearly polarized antennas. Although Microstrip antennas in their basic form normally provide linear polarization, circular polarization can be obtained by certain modification to the basic antenna geometry and /or feed. These modifications includes adjusting the dimensions of basic patch with one or more feed, trimming the corners of the square patch, feeding the patch at adjacent sides, cutting the slots inside the patch, and feeding the patch(rectangular) from its corners along the diagonals.Several CP antennas available in this literature. In conventional single feed circularlypolarizedMicrostripantenna design, a substrate with high permittivity s often used to make the antenna compact but it has an inherent drawback of low axial ratio bandwidth. The antenna reported in  has axial ratio (<3dB) of just 0.65%.To enhance the axial ratio bandwidth, a thicker substrate is normally used. But the axial ratio band and impedance matching band does not overlap when the substrate thickness is increased . The antenna reported by  has axial ratio bandwidth of 6.3% with straight feed and increases up to 14.1% with L-strip feed which is a corner trimmed CP antenna with U-shaped slot cut on the patch to insure wide impedance bandwidth. The antenna reported in  and  are having axial ratio bandwidth of 14% and 23% respectively.Since these antennas consist of stacked configurations and hence they are very difficult to fabricate. The probe feed H –shape Microstripantenna fed along with its diagonal to get circular polarization have axial ratio bandwidth of just 1.3%.
This paper consists of different types of techniques and geometries which are designed and used by different authors to increase bandwidth, achieve good quality circularlypolarized radiations. One of the techniques is single feed, stacked, slotted circularlypolarizedmicrostripantenna in which circular polarization is achieved with using two circular slots , A wideband circularlypolarizedantenna using three stacked patches and fed by a hybrid coupler  was designed for UHF RFID applications. Recently, asymmetric-slotted microstrip square patches were also designed for size reduction of circularlypolarizedmicrostrip antennas. But, demerits of these antennas have a narrow circularlypolarized radiation bandwidth and low gain, and are designed for hand held or portable RFID readers . A wideband circularlypolarized RFID antenna with high gain for a fixed reader has a longer reading range compared to a narrowband small circularlypolarizedantenna (low gain) used in a handheld or portable reader. A stackedring over the radiating patch  is also used to improve the circularlypolarizedantenna‟s performance. A wideband circularlypolarizedstackedantenna is also designed using the main patch fed by four probes, which are sequentially connected to the suspended microstrip feed line .
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