In this article, a dual-sense triband circularly polarized modified slot antenna loaded with metamaterial structures such as split-ring resonator and cross strips is proposed. The first resonant frequency is generated using the modified square slot which produces the two degenerative modes required to achieve circular polarization (CP). The corners of slot antenna are extended to obtain the orthogonal modes. The second resonant band is obtained using the single split-ring resonator. Two micro-splits in Split Ring Resonator (SRR) orthogonal to each other produces CP due to electric field generated by the micro-splits. The third resonance band is obtained due to loading of cross strips. The orthogonal phase is adjusted by varying the length of cross strips, so that the CP is achieved. All resonance bands are tuned independently. The measured impedance bandwidth of 31.68%, 4.55%, and 8.6% is obtained in first, second, and third bands respectively. The axial ratio bandwidth of 13.04%, 2.7%, 8.6% and peak gain of 3.8 dBic, 3.9 dBic, 3.7 dBic are obtained respectively. The simulated radiation efficiencies of above 80% is achieved in all bands. The left-hand CP is obtained in first two band as co-polarization and right-hand CP is obtained at the third band as co-polarization with respect to cross-polarization radiation. The cross-polarization of minimum −10 dB is obtained in all three bands. The proposed design is well suitable for the Bluetooth, n78 and n79 5G applications.

This paper presents a systematic design approach for developing a semiflexible multiple-input–multiple-output antenna system operating in the millimeter wave frequency spectrum, specifically designed for body-worn applications in biotechnologies. The designed antenna features dual flower-shaped antenna radiators placed in a spatial diversity configuration. Strategic modifications have been implemented by integrating dual crescent-shaped slots in the ground layer to attain the targeted frequency band of 25.7–30.6 GHz. Later, the upper edge of the ground plane is truncated in order to achieve circularly polarized radiation characteristics at 29.4 GHz with 3 dB ARBW of 0.6 GHz (29.1–29.7 GHz). The realization of circular polarization in the antenna geometry is validated through the analysis of characteristic mode theory. A maximum gain of 5.6 dBi is attained along with a port isolation of >30 dB. The proposed antenna undergoes analysis to assess its performance in the bending conditions and specific absorption rate, besides validation of diversity metrics encompassing envelope correlation coefficient, diversity gain, channel capacity loss, total active reflection coefficient, and mean effective gain has also been conducted. Finally, the proposed antenna structure is fabricated, and its performance is validated and subsequently compared with that of its simulated counterpart.

An 8 × 8 butler Vivaldi beam-steering antenna array is introduced for X-band application. Circularly polarized array is made of eight Vivaldi elements with 1×8 platform and an 8×8 beam feeding network. Vivaldi radiating element is used in array form to enhance impedance bandwidth and overall efficiency such as gain. Using microwave passive components, for instance, 3 dB branch line couplers and crossover help to have orthogonal modes for feeding each of the elements, hence circular polarization property is achieved. Extracted results show that the array has an impedance bandwidth over 7–12.7 GHz (~58%) for VSWR≤2 and an axial-ratio bandwidth of 3.15 GHz that is between 8.15 and 11.3 GHz (~33%). The peak gain of antenna array is 18 dBi at 10 GHz. The proposed beam-steering antenna with compact size and good operation is capable to cover an angle range from −42 to 55 degree in whole operation frequency.

A triple-frequency operated concentric annular ring microstrip antenna which is single fed is presented. The proposed antenna with three concentric annular rings and two symmetrical notches on its outer ring and having a cross slot in its ground surface shows triple band at resonance frequency 1.22760, 1.57542, and 2.18 GHz, respectively. At the first two bands (GPS L2 and GPS L1), circular polarization characteristic is observed and the third band observes linear polarization finding its application in Universal Mobile Telecommunication System (UMTS). The complete dimension of the antenna designed and fabricated is only 51.6 × 51.6 × 1.6 mm3. Experimental results depict the proposed antenna gain of 3.31, 3.55, and 3.50 dBi in three bands, respectively, and closely matches with the theoretical results.

This study investigates a low-profile circularly polarized (CP) antenna using coplanar waveguide feeding. Rectangular-shaped slots and an inverted L-shaped slit are entrenched into the ground plane to enhance the impedance bandwidth of the antenna. Furthermore, the antenna is implemented with six elliptical electromagnetic band gap structures on its substrate to enhance the −10 dB return loss bandwidth and also to generate CP waves. The experimental and theoretical results closely match each other and indicate that a simple and compact design antenna with dimensions of 0.317λ0 × 0.317λ0 × 0.023λ0(λ0 is the operating wavelength at 4.74 GHz in free space) achieves 36.9% (3.91–5.68 GHz) of the −10 dB return loss bandwidth and 9.98% (4.09–4.52 GHz) of the 3-dB axial ratio bandwidth, thus making it a favorable entrant for radio altimeter and wireless avionics infra-communication systems.

A circularly polarized stub-matched inverted L-shaped antenna for C-band applications is presented in this communication. Antenna parameters of inverted L-shape on the radiating patch and slits, notch, square strips and stub on the ground plane and the effect of these are analyzed. The proposed optimized antenna (A5: 0.54λ0 × 0.54λ0 × 0.02λ0 mm3) is selected among antennas (A1 – A5) with 5.1 GHz design frequency after simulation through high-frequency structure simulator (HFSS). Circular polarization is obtained by introducing stub/perturbation on the ground plane. By introducing stub, the highest measured (S11 < − 10 dB) impedance bandwidth of 50.9% (3.48 – 5.86 GHz) is observed amongst the reported and compared bandwidths. Peak gain of 5.32 dBi and 3 dB axial ratio bandwidth of 16.2% (4.71 – 5.54 GHz) is reported in the present work. An antenna is useful in the entire downlink frequency (3.7 – 4.2 GHz) of the C band.

This literature presents a comprehensive, technical review of circularly polarized (CP) antennas for different applications in wireless communication, emphasizing on the recent developments in the concerned research. The article also presents a comparative study of various works reported in the open literature, with an aim to highlight the contribution of CP antenna systems in the chronological development of the wireless communication technology. The primary motive of this review is to (a) highlight the methodologies used by different researchers to portray and analyze the different aspects in which CP antennas find their applications in modern-day wireless communication, (b) provide a practical viewpoint of the future scope of the study, based upon the past and present state-of-art research trends and (c) provide a conceptual and technical support to present-day antenna designers to help the process of furtherance of innovation and multiple system integration. In conclusion, the article also throws some light upon the future scope of research in the vast domain of CP antenna applications.

This paper presents a novel design of a low profile circularly polarized (CP) metasurface (MTS) antenna with in-band radar cross-section (RCS) reduction property. The MTS is loaded as a superstrate on slot antenna and it can be viewed as a polarization-dependent MTS (PDMTS). The rectangular patch-based PDMTS is analyzed using characteristic mode analysis to find two orthogonal degenerate modes, which produces CP waves. Linearly polarized slot antenna is used to excite the PDMTS. The performance of PDMTS loaded slot antenna is analyzed numerically using full-wave analysis method. The PDMTS CP antenna is fabricated and its performance is tested experimentally. The proposed antenna has a compact structure and it has an overall size of $0.52{\lambda _0}\times 0.52{\lambda _0} \times 0.078{\lambda _0}$ (where ${\lambda _0}$ is the free space wavelength). The measured results show that the PDMTS antenna achieves $-10\,{\rm dB}$ impedance bandwidth of 29.41$\%$, 3-dB axial ratio bandwidth of 9.05$\%$, broadside gain of 6.34 dB, and monostatic RCS reduction of $-30.2\,{\rm dBsm}$ at the resonant frequency of 5.86 GHz. The simulated results are in well agreement with the measured results and it is well suited for C-band Radar and Satellite communication.

This paper presents a new technique for the enhancement of axial ratio (AR) bandwidth of a circularly polarized dielectric resonator antenna with a single feeding. To enhance the AR bandwidth, adjacent 3-dB AR passbands are merged by inserting the notches and conductive coating in the dielectric resonator. The dimensions of the notches and conductive coating are selected in such manner that impedance bandwidth remains approximately unchanged. The antenna provides the measured AR and impedance bandwidths of 55.22% and 66.45%, respectively.

Triple band circularly polarized fractal boundary microstrip antenna is proposed and experimentally studied. The two orthogonal sides of the square patch are replaced with asymmetrical fractal curves for circular polarization (CP) radiation. A 45° rotated asymmetrical fractal slot is embedded at the center of the fractal patch for triband CP operation. The indentation factors of the fractal curves are optimized for better CP emission. The inserted fractal slot redistributes the current elements on the patch for triband CP radiation. The proposed antenna is implemented over a single layer with a single probe feed, so it is simple to fabricate and is cost effective when compared with the existing stacked layered multiband antennas in the open literature. The measured 3 dB axial ratio bandwidths of the proposed antenna at 2.4, 3.4, and 5.8 GHz are 2, 1, and 1.8%, respectively, so it is well suited for WLAN and Wi-MAX wireless applications.

A circularly polarized (CP) broadband antenna is proposed for wireless applications in the range of 2–3 GHz frequency. It consists of asymmetrical Koch fractal boundary patch over a reactive impedance surface (RIS) substrate. The simulations of single-layer Koch fractal antenna, dual layer with square and fractal RIS elements are carried out in a systematic way for broadband CP radiation and corresponding results are presented. For better CP characteristics, properties of fractal curves and dimensions of RIS elements are optimized. The antenna with fractal RIS iteration order one (iteration1) is experimentally studied. The 10-dB return loss bandwidth is 50.35%, whereas 3-dB axial ratio bandwidth is 7.45%, which indicate that by applying fractals concept to RIS technique, with a single probe feed, broadband CP radiation can be obtained.