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This paper proposes and analyzes a 2 × 2 multi‐input multioutput antenna based on an open‐loop resonator structure and an inverted L structure. The top layer of the antenna uses symmetric inverted hook‐shaped and inverted L branches and is connected to the bottom layer of the dual‐feed port and the ground plane using the VIAs, respectively. The open‐loop resonator structure at the bottom of the antenna and the top layer of the branched circuit are resonated to provide wide‐bandwidth and dual‐frequency characteristics. The substrate uses FR4 with an area of 40 × 30 × 0.8 mm3. Although the two antenna feed ports are very close to each other, using via to connect the defective bottom ground structure and the top inverted L‐shaped branch, the isolation still achieves an excellent performance of 15 dB. The antenna has multiband application characteristics, and the bands include 2.29–5.51, 6.14–10.26, 2.29–5.33, 5.19–6.64, and 6.78–10.16 GHz. In pattern and MIMO transmission efficiency measurement, the peak radiation efficiency is 89%, the peak gain is 8.5 dBi, and the ECC is less than 0.034. In the transmission efficiency measurement mode using 64‐QAM, watching the error vector magnitude at 2.56 and 5.11 GHz, the demodulation effect is very good, and the respective throughput results are 100% and 79.2%. The broadband characteristics of the antenna have a variety of applications, and it is simulated at the specific absorption rate, which meets the standards set by the Federal Communications Commission and is very suitable for use in wearable devices. The antenna can be applied to the X‐band, n77, n79, Sub‐6 GHz, WiMax, DSRC, WiFi 6, WiFi 6E, WiFi 7, C‐V2X, and C‐band. [ABSTRACT FROM AUTHOR]

In this paper, a novel method for detecting breast cancer utilizing an ultra-wideband (UWB) microstrip patch antenna operating in the UWB frequency range is presented. The promise of non-invasive, radiation-free breast cancer screening is provided by UWB technology. We give a brief overview of the difficulties in detecting breast cancer as well as the benefits of UWB technology in medical applications in this study. This study presents a compact printed microstrip patch antenna used for the bio-medical application at industrial, scientific, and medical (ISM) and UWB frequencies. The proposed antenna consists of a hexagonal-shaped microstrip patch antenna with a slotted ground antenna used for high bandwidth for a wider range of applications. The compact biomedical antenna is printed on Roger 5880 substrate with an overall dimension of 25*25 mm. Due to the high demand for results accuracy, Roger 5880 substrate material is used because it has good dielectric characteristics and loss factors that are appropriate for medical and radio frequency (RF) applications. A 50-ohm impedance line is used to feed the antenna. The proposed antenna has a higher bandwidth of almost 12.5 GHz at such a low frequency, starting from 3.53 to 16 GHz. The antenna has an acceptable gain of 3.38 Db, which is enough for the required application. The UWB microstrip patch antenna has the potential to improve breast cancer detection accuracy and reliability, which would aid in early diagnosis and better cancer patient treatment. This work represents a major advancement in the development of non-invasive, low-cost breast imaging methods for early cancer diagnosis. [ABSTRACT FROM AUTHOR]

In this paper, a MIMO antenna with broadband circular polarization is designed in a single‐layer substrate for the next‐generation Wi‐Fi 7 applications. The top of the substrate is designed with a periodic array of 5 × 5 circle patches and orthogonally placed four L‐shaped aperture CPW feeds on the bottom face of the substrate are used to feed the patches. The stubs are arranged across the apertures to achieve a broad bandwidth. The array of patches is used to achieve high gain over resonant frequency range and L‐shaped apertures are used to achieve circular polarization. The designed antenna with the above specifications has gained an impedance bandwidth of 20.4% (5.37–6.59 GHz), a 3 dB axial ratio bandwidth over the entire resonant frequency range of 25.61% (5.14–6.65 GHz) and a peak gain of 8.5dBi. [ABSTRACT FROM AUTHOR]

Summary: The proposed antenna is a small wideband monopole with wideband circular polarization using heterogeneous bidirectional recurrent neural network for both narrow and wide band applications (NWB‐MAD‐HBRNN). The electromagnetic structure is designed, fabricated, and simulated with 1 mm thickness on FR4 substrate material along dielectric constant 4.3. The proposed antenna includes 4.3–8.85 GHz for ultrawideband applications; it contains reconfigurable narrow band for L‐band 1.27 GHz, LTE, and ultrawideband applications. To enhance the antenna impedance bandwidth (BW) along axial ratio bandwidth (ARBW), a slit is etched at the antenna patch, a rectangular stub is inserted into the ground plane, and semicircular stub is added to the top of antenna feed line. The better agreement is observed in the measured and simulated gain performance of 4.8 dB for LTE band applications. The proposed NWB‐MAD‐HBRNN design provides 13.50%, 18.91%, and 22.58% higher bandwidth and 18.36%, 20.38%, and 27.58% lower return loss than the existing designs, such as bio‐inspired wideband antenna for wireless applications based on perturbation technique (BWA‐WA‐PA), a compact circularly polarized modified printed monopole antenna for wireless applications (CCP‐MPMA‐WA), and new multiband monopole antenna for certain broadband wireless applications along wireless personal communications (PA‐MMA‐BWA), respectively. [ABSTRACT FROM AUTHOR]

This paper proposes a broadband optical transparent antenna using a transparent conductor film on a transparent polyethylene terephthalate (PET) substrate. The planar wide‐slot antenna coupling fed by microstrip has a wide impedance bandwidth, so it is selected to design the transparent antenna. The upper surface of the PET substrate is a microstrip line with a fork‐shaped tuning branch, and the lower surface is a wide slot. They were made of transparent conductor film. Finally, a new capacitive coupling method is used to feed the transparent antenna. The transparent conductor film used in the antenna is metal mesh, which was developed by 3M company. The metal mesh with an open area greater than 80% to achieve high transmittance. The measured results show that the impedance bandwidth is 177% (0.30–5.0 GHz), and the gain of the antenna varies from 5.06 to 7.8 dBi over the entire frequency band. Therefore, it can be well applied to the current indoor mobile communication system. [ABSTRACT FROM AUTHOR]

Abstract A planar antenna with dual‐linearly polarised end‐fire radiation is proposed. A tapered double‐sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high‐order modes: the first high‐order even mode and the first high‐order odd mode. A two‐port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline‐to‐slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively.

In this report, a Ka‐band, broadband, omnidirectional, with a top metal disk antenna is proposed. The antenna is fed by an air waveguide. The TE10 mode of the waveguide can efficiently be converted into an air coaxial TEM mode by a compact waveguide air coaxial transition. After matching and adjusting, the dielectric substrate is loaded and then transited to the metal radiation structure loaded with a top metal disc to obtain omnidirectional electromagnetic waves efficiently converted to free space. By optimizing the sizes of waveguide to air‐coaxial transition structure and disk, and so on, a good broadband omnidirectional antenna performance is finally achieved. The measured fractional impedance bandwidth is larger than 30% with the reference of S11⩽−10 $\leqslant -10$ dB, which fully verifies the rationality of the design. In addition, measured patterns at the plane of different azimuth angles almost coincide with each other, which shows an excellent omnidirectional pattern. [ABSTRACT FROM AUTHOR]

A planar antenna with dual‐linearly polarised end‐fire radiation is proposed. A tapered double‐sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high‐order modes: the first high‐order even mode and the first high‐order odd mode. A two‐port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline‐to‐slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively. [ABSTRACT FROM AUTHOR]

ABSTRACT A novel circularly polarised (CP) antenna design, termed differential mode (DM) and common mode (CM) design, is presented with equal‐amplitude in‐phase feed (EAIPF) in this article. At first, the CM and DM of the antenna are excited separately using the dual ports. Then, the CP antenna is obtained with EAIPF by adjusting the radiation amplitude of CM and DM, due to the orthogonality with a 90° phase difference for CM and DM. Finally, the obtained operational bandwidth of the presented antenna is 1.75–2.30 GHz (27.1%), with a reflection coefficient

This paper provides a clear demonstration that a coplanar stripline (CPS) as a balanced line can act to re-establish the phase balance in the presence of phase deviation from a 180° distance between two input signal lines connected to the CPS. A half-wave delay line splitter connected to a CPS works as a balun to feed a balanced antenna, such as a quasi-Yagi antenna. This type of balun structure has been widely used to feed balanced antennas with a frequency bandwidth of up to 60%. Nevertheless, no clear explanation has been given regarding how the broadband antennas could be implemented with this type of balun structure. In this paper, through 3D EM simulations and measurements, it is shown that the half-wave delay line splitter indeed only results in the 180° phase balance at one frequency, but the subsequently connected CPS acts to recover the phase balance between the signal lines. The CPS can recover the phase balance within a phase imbalance of ~π/3, which determines the usable bandwidth of this structure. For a demonstration, with a center frequency of 10 GHz, samples of the half-wave delay line splitter connected to a CPS are fabricated and measured. [ABSTRACT FROM AUTHOR]

A novel circularly polarised (CP) antenna design, termed differential mode (DM) and common mode (CM) design, is presented with equal‐amplitude in‐phase feed (EAIPF) in this article. At first, the CM and DM of the antenna are excited separately using the dual ports. Then, the CP antenna is obtained with EAIPF by adjusting the radiation amplitude of CM and DM, due to the orthogonality with a 90° phase difference for CM and DM. Finally, the obtained operational bandwidth of the presented antenna is 1.75–2.30 GHz (27.1%), with a reflection coefficient < −10 dB and axial ratio <3 dB. This CP antenna design eliminates the need to design 90° phase shifter as well as reduces the complexity of the feed structure of CP antennas, providing a novel idea for the design of CP antennas. [ABSTRACT FROM AUTHOR]

A technique employing the use of directly coupled stacked patches to increase impedance bandwidth with reduced cross-polarization is proposed in this paper. The top stacked multi-resonator configurations are directly excited by employing metallic shorting posts (vias) between the metallic patches. In stacked directly coupled MSA, a bandwidth of 25.8% and a gain of 8.8 dBi with a gain variation of ±0.2 dB over the band are achieved. The cross-polar levels for this configuration are less than −15 dB and −5 dB at lower and upper frequencies, respectively. To suppress the cross-polar components, a symmetrically direct-coupled stacked MSA design is proposed. In this configuration, a bandwidth of 26.1% and a gain of 9.3 dBi with ±0.3 dB variation over the entire bandwidth are achieved. The cross-polar levels are significantly suppressed up to −25 dB and −16 dB at lower and upper frequencies, respectively. The proposed antenna configurations are designed and fabricated. The experimental results agree with the simulated results. [ABSTRACT FROM AUTHOR]

Terahertz band gap is the range of frequency lying between the microwave band and the optical band, its range spectrum starts from 0.1 THz to 10 THz. This band provides unallocated wide bandwidth as well as very high-speed communication in the futuristic applications. This article presents a broadband microstrip 1 x 2 array antenna powered by hybrid coupler in terahertz band (around 2.45 THz). To reach this Broadband antenna, at first, a wideband 3 dB hybrid coupler is designed and optimized. After that, two basic elements of square shaped with slots are fed by the two output ports of the coupler. The results obtained reports that the suggested antenna offers – 10 dB wide bandwidth equals to 846 GHz (from 1.91 to 2.77 THz) with good impedance matching, maximum directivity equals to 8.86 dBi at the operating frequency 2.45 THz. Additionally, it offers the capability of beam steering which can be obtained by switching of the input ports of the coupler. Thus, the antenna can produce two beams at ±30°. The structure and simulation results of the proposed antenna have been done on Rogers RT/duroid 5880 substrate. The total size of the proposed microstrip array antenna is 110 x 112 x 1.56 μm³. Due to its capability of beam steering and broadband characteristic, the proposed antenna is a potential candidate for Terahertz band applications such as materials characterization in the THz band, medical imaging and future high-speed wireless communication. [ABSTRACT FROM AUTHOR]

This article deals with the design and analysis of a microstrip 1 x 8 magic-T power divider (MTPD) for ISM band (industrial and medical band) array antenna application. First, a basic 1 x 2 magic-T power divider is designed and optimized. It can divide the power supply in two equal parts (3 dB) in-phase agreement. Then a 1 x 4 power divider has been designed using two identical 1 x 2 magic-T basic power dividers; it divides the power supply into four equal parts (6 dB) in-phase agreement. Finally, the proposed broadband 1 x 8 magic-T power divider is constituted by the assembly of two identical 1 x 4 magic-T power dividers; it can divide the power supply into 8 equal parts (9 dB) in phase agreement. As results obtained, the proposed 1 x 8 power divider has a  10 dB wide bandwidth equals about 506 MHz (2.022 GHz to 2.528 GHz) with a minimum reflection coefficient S11 equals about – 19.12 dB at the operating frequency 2.4 GHz. Moreover, the module of the transmission coefficients (S12, S13, S14, S16, S16, S17, S18 and S19) equal about – 9 dB with a negligible phase shift equals to 2.8° between the output signals. The design and simulation results of the proposed 1 x 8 power divider is carried out by HFSS EM simulator using the substrate Rogers RT/duroid 5880 with the total size 424 x 49 x 1.56 mm³. The proposed power divider is a potential candidate to feed an array antenna, amplifiers and modulators of eight elements in the ISM band around 2.4 GHz (2.022 GHz-2.528 GHz). [ABSTRACT FROM AUTHOR]

This paper presents a broadband miniaturized Fabry–Perot cavity resonator antenna (CRA) made of novel electromagnetic bandgap (EBG) superstrate as partially reflecting surface (PRS) and reactive impedance surface (RIS) backed rectangular patch antenna. To the best of the authors' knowledge, the proposed EBG exhibits the highest stopband bandwidth (BW) with a bandgap existing between 7.37 and 12.4 GHz (50.9%). Frequency-selective property of the EBG is utilized under plane wave incidence to demonstrate it as PRS superstrate in CRA antenna. The cavity is excited with a rectangular microstrip antenna which is made of two dielectric substrates with an additional RIS layer sandwiched between them. The RIS provides wideband impedance matching of the primary feed antenna. A 7 × 7 array of the EBG superstrate is loaded over the patch antenna having an overall lateral dimension of only 45 × 45 mm2 or 1.62 λ 0 × 1.62 λ 0 where λ 0 is the free space wavelength at the center frequency of 10.8 GHz. The proposed Fabry–Perot CRA (FP-CRA) achieves gain enhancement of 6.59 dB as compared with the reference antenna and has a 10 dB return loss BW of 23.79% from 10.07 to 12.79 GHz. A prototype of the FP-CRA is fabricated and experimentally tested with single and dual layers of EBG superstrate. Measured results show BWs of 21.5 and 24.8% for the two cases with peak realized gain of 12.05 and 14.3 dBi, respectively. Later a four-element antenna array with corporate feeding is designed as the primary feed of the CRA. The simulation result shows a flat gain of >13 dBi with gain variation <1.2 dB over the impedance BW of 13.2%. [ABSTRACT FROM AUTHOR]

A W-band H-plane horn array antenna with tilted radiation beam based on waveguide structure is proposed in this paper. The designed antenna array consists of four H-plane antenna elements and a broadband feed network. The distribution of excitations is determined by the theory of maximum power transmission efficiency (MMPTE). A multiple branch coupler, two T-junctions and three fixed phase shifters are employed to construct the feed network, which can generate the required amplitude and phase in broadband frequency range from 80 GHz to 100 GHz. The computer numerical control (CNC) milling machines technology is employed to machine the feed network and antenna. All measured and simulated results are in good agreement, which verify the feasibility of the theory of MMPTE to generate a radiation beam directed to any angle from −35° to 35° with suitable excitation provided by the proposed feed network in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a broadband circularly polarized array antenna is presented, which consists of four loop slot antennas based on metasurfaces. The antenna element is a loop slot antenna fed by a microstrip line. Cross slots are added to the loop slot to improve the antenna bandwidth, and four corner-cut square metasurfaces are loaded above it, thus generating circularly polarized radiation. The antenna adopts a sequential phase (SP) feed network to realize broadband characteristics. The antenna has been fabricated and experimented. The overall size of the antenna is 78 × 78 × 10.1 mm3 (approximately 1.22 λ0 × 1.22 λ0 × 0.15 λ0), the antenna array has a measured |S11| < −10 dB bandwidth of 3.6–6.2 GHz (53.1%) and a 3-dB axial ratio bandwidth of 3.7–4.8 GHz (28.32%). Furthermore, the antenna also has radiation with a peak gain of 5.5 dBi. [ABSTRACT FROM AUTHOR]

In practice, the broadband feeding network on the back side of an antenna can have a nonnegligible effect on the antenna's back radiation due to the feeding network's radiation contribution. Thus, a back-radiation cancellation scheme is proposed by co-designing the antenna and its feeding network to solve this problem. The antenna and its feeding network can be viewed as a two-element array. Their radiation toward the antenna's backward direction can cancel each other when both have equal amplitude and opposite phases along the back direction. A differential fed dielectric resonator antenna (DRA) through a rat-race coupler (${180}^\circ $ hybrid coupler) and a T-shaped broadband differential feeding network are compared and analyzed to verify the proposed scheme. In addition, a $1\!\times\!4$ DRA array with a T-shaped broadband differential feeding network in a previous work (where the feeding network's radiation effect on the back side was overlooked) is used for experimental validation of the proposed scheme. Simulations and measurements demonstrate significant back-radiation suppression than the ideal differential feeding network. [ABSTRACT FROM AUTHOR]

In this letter, a method named double phase-compensation is first proposed to drastically reduce the profile of traditional transmitarray antenna (TA) based on ray tracing principle. Previously, the folded transmitarray antenna (FTA) has realized the profile reduction to 1/3. It is known that there is an urgent need for more compact antenna nowadays. If the FTA's profile is further reduced, the focus-to-diameter (F/D) ratio should be decreased which will result in obvious aperture efficiency reduction. To further reduce the FTA's profile with unchanged F/D for keeping high efficiency, the extra phase compensation is innovatively added on the FTA's reflector. Hence the TA's profile can be reduced to lower than 1/3 and be flexibly adjusted as needed. Three FTA models are designed for comparison and demonstration. The simulation and experimental results indicate that the extra phase compensation successfully alleviates the efficiency drop caused by directly reducing the profile of FTA. Significantly, the method provides an efficient approach to further improve the compactness of antenna system and is very meaningful for TA miniaturization. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized metasurface antenna with low radar cross section (RCS) is proposed. Four metasurface elements are arranged orthogonally in a 2×2 array and fed with a 90° phase difference to achieve circular polarization radiation. Each metasurface element is a nonuniform subarray of 4×4 metallic patches. Attributed to the nonuniform property of the metasurface element, two characteristic modes with different resonant frequencies but with similar surface current distributions are formed. By optimizing the geometric parameters of the nonuniform element, the two modes are merged with each other, resulting in bandwidth (BW) broadening of the proposed antenna. Simulated and measured results show that the designed antenna has a −10 dB impedance BW of 49.60%, 3 dB axial ratio BW of 33.13%, and peak gain of 13.17 dBic. Moreover, the RCS reduction is higher than 6 dB in the entire operation frequency band. Additionally, the antenna has a low profile of 0.08λ (λ is the free-space wavelength at an operation frequency of 8.25 GHz). [ABSTRACT FROM AUTHOR]

This letter proposes a wideband high-gain left-/right-handed circularly polarized (L/RHCP) patch antenna using a mirror flip approach. The antenna consists of a ring-shaped metal square patch with truncated corners and a two-port feed network in a simple construction. The dual-port feed and truncated corners realize a wide axial ratio bandwidth (ARBW). Moreover, the L/RHCP is easily changed by mirroring the flipped feed network without redesigning the overall topology. The impedance bandwidth (IBW) (S11 < −10 dB) of 58.6% (2.97–5.43 GHz)/47.6% (2.8–4.55 GHz) and 3 dB ARBW of 44.3% (3.09–4.85 GHz)/34.6% (2.96–4.2 GHz) are achieved for L/RHCP antenna. Finally, two prototypes were fabricated and measured for validation. The proposed L/RHCP patch antenna was found to be insensitive to feed position. The IBWs of the proposed LHCP and RHCP antennas showed a wide degree of overlap. The low profile, high gain, small size, and higher robustness of our antenna than traditional patch antennas demonstrate the advantageous of our design for communication, power transmission, and medical fields. [ABSTRACT FROM AUTHOR]

Abstract A novel antenna design technique is proposed, which offers bandwidth enhancement up to the limits defined by element radiation efficiency. The employed technique is referred as frequency pulling (FP) as it mimics the ‘insertion loss design methodology of band‐pass filters’. This is essentially a wideband matching approach pushing the antenna efficiency to the limits set up by radiation efficiency. There are three options towards this trend: (i) first to enhance a single element bandwidth (compact element) exploiting its possibly multiple symmetrical feeding points as distinct resonator ports, (ii) frequency pulled array as to design a small antenna array (less than about 10 elements) where each element acts as a resonator and (iii) second order frequency‐pulled array as to build a small array using compact elements of category (i). Similar to the band‐pass filter design, all antennas or distinct‐port circuits resonate at the same resonant frequency when isolated, cascading two or more of them; FP yields to multiple‐overlapping successive resonances in their overall response. Although the proposed technique is general within this first effort, it is applied to simple patch antenna elements exhibiting multiple symmetrical feeding points, namely two—for rectangular, four—for square and five—for pentagonal. The third option is applied to an array of three compact 4‐feeding point square elements offering triple bandwidth with respect to the already wideband single element. However, this is achieved at the expense of a significant beam squint. Thus, in general, these wideband compact elements should be used within a classical array design. Further bandwidth enhancement using FP to antenna elements with inherent multiple resonances as patches with slots or truncated edges constitutes our next task. Their inherent wider bandwidth in radiation efficiency is expected to allow multiply higher bandwidths when exploited with our FP technique.

This paper presents design and analysis of a beam switchable 1 × 2 array patch antenna fed by a 2 × 2 Butler matrix based hybrid coupler for 2.45 GHz radio frequency identification (RFID) reader applications in the ISM band. The proposed beam switchable array antenna arrangement consists of two identical patch elements, a pleated quarter-wavelength impedance transformer (PQWIT), and a hybrid coupler. The concept of PQWIT has been utilized to reduce the overall implementation area of the patch elements. The overall area of the patch element is miniaturized by 50% due to the implementation of PQWIT. This miniaturized antenna is used as a radiating element for designing a beam switchable 1 × 2 array antenna fed by a hybrid coupler. The proposed antenna prototype has been fabricated on a 1.56 mm thick Rogers RT/duroid 5880 substrate with a physical area of 1 1 2 × 1 0 0 mm2. The simulation and measured results exhibit good agreements. The designed antenna offers a broad bandwidth of 844 MHz (1.956–2.80 GHz), peak gain of 8.86 dB, peak radiation efficiency of 99.52% and has two switchable beams in the directions − 3 0 ∘ and + 3 0 ∘ . The suggested switched beam array antenna is suitable for RFID reader applications at 2.45 GHz for tracking of moving objects. [ABSTRACT FROM AUTHOR]

In this article, a novel design of broadband circularly polarized (CP) folded reflectarray (FRA) antenna is proposed. The CP FRA consists of two kinds of metasurfaces (MSs) and a linearly polarized (LP) open waveguide antenna as the feeding source. The bottom MS functions as the main reflector, which is capable of realizing cross-polarization conversion and beam focusing simultaneously. The upper MS is utilized as a subreflector, which could reflect LP wave coming from the feeding source and transmit its orthogonal counterpart into CP wave. For demonstration, the MS-assisted CP FRA antenna is fabricated and measured. Numerical results are consistent with experimental ones, illustrating a peak gain of 24.1 dBi and a peak aperture efficiency of 51% at 9.9 GHz. The 3 dB gain bandwidth and 3 dB axial ratio (AR) bandwidth are achieved as 27.5% (8.8–11.6 GHz) and 43.9% (8–12.5 GHz), respectively. The proposed CP FRA provides a new avenue to realize broadband high-efficiency CP antenna, which may find great potentials in modern wireless communication systems. [ABSTRACT FROM AUTHOR]

In this communication, a circularly polarized (CP) double-folded transmitarray antenna (DFTA) is proposed and experimentally verified for the first time in the open literature. It is designed based on a receiver–transmitter metasurface (RTMS) and a polarization rotating (PR) metasurface (MS). A linearly polarized (LP) patch antenna is integrated on the RTMS instead of a horn antenna to feed the DFTA. Through double-folded reflecting, twice PR, LP wave receiving, CP wave transmitting, and transmission phase manipulating, the LP spherical wave from the feed is transformed into the high-gain pencil-shaped CP beam. The strategies innovatively break the restriction that the previous folded reflectarray (FRA) and folded transmitarray (FTA) antennas are only LP. Moreover, the double-folded design further reduces the antenna profile to about 1/4 of the focal length. The simulation and experiment results are in good agreement, which exhibits a peak gain of 21.8 dBic at 9.8 GHz and a maximum aperture efficiency of 40%. Meanwhile, the DFTA obtains a −1 dB gain bandwidth of 6% (9.6–10.2 GHz), in which the axial ratio is lower than 1.5 dB. [ABSTRACT FROM AUTHOR]

A design methodology of the dual-band Fabry–Perot-cavity (FPC) antenna is proposed, realizing dual-broadband high gain and keeping the simplicity of one low-profile resonant cavity. A ray optics model is applied to obtain the phase resonance condition for dual-band FPC antennas. The proposed antenna employs a tightly stratified partial-reflective-surface (PRS), an artificial-magnetic-conductor (AMC) ground, and a dual-band microstrip feed. The PRS modulates independently the dual-band reflection coefficient to maintain a large amplitude and a positive phase gradient. Meanwhile, an AMC ground is distinctively employed to compensate for the transmission phase difference of the lower band when the cavity height meets half the wavelength of the upper one, enabling eventually a low-profile uni-cavity. Furthermore, a dual-band microstrip feed with two asymmetric slots is customized as the primary radiator. Detailed electromagnetic studies are carried out to illustrate the operating mechanisms of these components. Finally, a proof-of-concept prototype is fabricated covering the entire global 2.4 and 5 GHz WiFi bands. The measurement results agree well with the simulation, and the 3 dB gain bandwidths of 7.2% and 16.2% with peak gains of 13.6 and 15.0 dBi over two wide bands of 2.42–2.60 and 5.1–6 GHz are achieved, respectively, with a single cavity height of 26.8 mm. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) magnetoelectric (ME) dipole antenna loaded with parasitic loop is presented in this communication. The proposed ME dipole antenna is fed through the slot-coupled feeding method, in which a microstrip line is used to couple the energy to the antenna by the slot etched on the ground plane. By introducing a parasitic loop coplanar with the horizontal patch, extra CP modes are generated due to the coupling with the radiation patch. Combining with the original CP mode, the simulated 3 dB axial-ratio (AR) bandwidth is enhanced from 12.2% to 45.8% with an increment of 33.6%. The measured results show that the 10 dB impedance bandwidth is 55.3% (3.4–6.0 GHz) and the 3 dB AR bandwidth is 42.1% (3.62–5.55 GHz). Moreover, the proposed antenna owns flat gain and stable unidirectional radiation patterns within the designated frequency band. [ABSTRACT FROM AUTHOR]

This communication presents a millimeter-wave wideband dual-polarized low-temperature cofired ceramics (LTCC) antenna array based on metasurfaces (MSs) for beam-scanning applications. Benefiting from the wideband and large-freedom property of MS-based structures, a novel ±45° dual-polarized wideband MS-based antenna (MSA) element with high isolation is designed. The antenna element is fed by two orthogonal striplines on different layers, through a crosslike dog-bone slot and a narrow slot, respectively, to realize the two polarizations. The feeding structure consists of slot–stripline–slot–stripline from top to bottom and is specially designed to improve the polarization isolation of the antenna element. The proposed MSA element is compactly arranged with a small distance ($ < 0.5\lambda$) to construct a 4 $\times $ 4 array integrated in an LTCC package, where via walls with metal ring strips are loaded between adjacent elements to reduce the gain fluctuation. Consequently, the array can achieve a good beam-scanning capability over a wide band of 19.5% with a maximum scanning angle up to ±55° and a small gain variation of less than 3 dB. Meanwhile, the active $S$ parameters almost always remain below −10 dB, enabling good impedance matching when scanning at all angles. With these features, the proposed design has potential for application in 5G base-station systems. [ABSTRACT FROM AUTHOR]

Transmitarray (TA) antenna has great research value based on its unique advantages of low profile, high gain, and flexible performance, especially in the field of spaceborne, airborne, and unmanned aerial vehicles. Unfortunately, traditional TA antennas are usually of flat structures, which lack conformal flexibility and installation simplicity in certain complex application scenarios. In this letter, a broadband bifocal conformal TA antenna is proposed based on a designed concave‐cylindrical‐shaped triple‐layer TA surface with phase modulation capability. The broadband bifocal conformal TA antenna is simulated, fabricated, and measured by assembling the TA surface with a dual‐mode conical horn as a feed antenna. To better demonstrate the beam scanning stability of the bifocal TA antenna, a monofocal TA antenna is designed and simulated as a comparison. Simulation and experimental results confirm that the proposed bifocal conformal TA antenna can achieve a high gain of 24.4 dBi at 30 GHz and a 3‐dB gain bandwidth of 13.3% (27.4–31.3 GHz) under normal incidence. Antenna peak gain fluctuation is less than 1 dB with a maximum beam scanning range of ±30∘ $\pm 3{0}^{\circ }$, which is much more stable than that of the monofocal TA antenna (3.6 dB). The proposed design can be a promising candidate in many military and civilian application scenarios. [ABSTRACT FROM AUTHOR]

In this paper, a differentially fed broadband dual‐polarised dipole antenna with parasitic elements is proposed. The presented antenna comprises a pair of strip dipoles as driven elements, four square patches as internal parasitic elements, four rectangular patches with cut corners as external parasitic elements, and two pairs of coaxial cables as feeding structures placed orthogonally to excite the driven strip dipoles to achieve ±45° dual polarisation. Furthermore, two additional dual‐polarisation modes can be simulated and a broadband dual‐polarised antenna can be obtained by positioning the external and internal parasitic elements to the end and at the edge of driven elements, respectively. The presented antenna provides wide bandwidth using these dual‐polarisation modes. The measurement results indicate that the presented antenna has excellent characteristics with a wide impedance bandwidth (IBW) of 68.4% (|Sdd11| < −18 dB and 1.30–2.65 GHz) and high isolation (|Sdd21| < −30 dB) within the IBW. Additionally, the four‐element array of the broadband dual‐polarised antenna with differential feeding characteristics was designed. The results show that the measured IBW is 59.7% (|Sdd11| < −15dB and 1.35–2.50 GHz). By contrast, the isolation between the two ports exceeds 30 dB across the impedance passband and has potential applications in multiple wireless communication systems owing to the wide bandwidth coverage (frequency division duplexing (FDD), digital communication system (DCS), personal communication system (PCS), Universal Mobile Telecommunications System (UMTS), and Long Term Evolution (LTE) frequency bands). [ABSTRACT FROM AUTHOR]

In this letter, we present a simple-feed dual-polarized Fabry–Perot antenna with broadband and high-isolation for in-band full-duplex applications. Its feeding element consists of a two-port patch antenna with one aperture coupled port and one microstrip-line-fed port for a high isolation without adding any out-of-phase power divider. For broadband and high-gain radiation, the two-port patch is incorporated with a stacked-patch and partially reflecting surface while maintaining the structure symmetry. The final design with an overall size of $\sim\! 1.9\lambda _{\text{min}}$  × 1.9 $\lambda _{\text{min}}$  × 0.48 $\lambda _{\text{min}}$ ($\lambda _{\text{min}}$ is the free-space wavelength at the lowest operational frequency) has been fabricated and tested. The measurements result in a 10 dB return loss bandwidth of 19.1% (4.84–5.86 GHz), an isolation of $\ge$ 43 dB, a realized broadside gain of 12.4–14.2 dBi, cross-polarization level of $\le$ −30 dB, and side-lobe level of $\le$ −18 dB across 5.00–5.95 GHz. [ABSTRACT FROM AUTHOR]

A new method for the design of multilayer printed partially reflective surface (PRS) is proposed to achieve broadband, high efficiency, and miniaturization of Fabry–Pérot resonant antenna (FPRA). In this letter, every two-layer structure is regarded as a resonator to obtain a narrowband positive reflection phase gradient and then cascaded to obtain a broadband. Finally, a three-layer PRS is designed and integrated to form a C-band compact FPRA with overall dimensions of 0.65 λ0×0.65 λ0×0.52 λ0 (λ0 is the free-space wavelength at the center frequency). The antenna was simulated, fabricated, and validated. The results show it has a high aperture efficiency due to the small aperture and a wide impedance bandwidth well covering 4.0–9.57 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a low-RCS broadband high-gain antenna based on metasurface transmission array is proposed, consisting of two parts: a metasurface transmission array and a feed antenna. When designing the metasurface transmission array, the phase compensation method is used to achieve the beam convergence effect of metasurface in the broadband. By designing the elements and using the checkerboard arrangement, the RCS of the incident wave with fixed polarization can be reduced more than 10 dB at X band or Ku band. The feed antenna is designed as a microstrip magnetic and electric dipole antenna, which has the characteristics of small structure and wide impedance bandwidth. An antenna that can reduce RCS by more than 10 dB in Ku band is simulated and measured. The measurement and simulation results show that the −10 dB operating bandwidth of the high-gain antenna designed in this paper is 6.7~13.5 GHz, and the relative bandwidth is 67%. The designed metasurface can effectively improve the gain of the antenna in the operating frequency band. In this way, the design of high-gain antenna is realized, and the antenna has an obvious RCS reduction effect on the vertically incident y-polarized wave in the whole Ku band. The method to design an antenna in this paper realizes the regulation of radiation and scattering at the same time, which has important reference significance for expanding the function of transmission array antennae and has great application value. [ABSTRACT FROM AUTHOR]

We propose a dual circularly polarized (CP) substrate integrated waveguide (SIW) cavity-backed antenna with wide axial ratio (AR) beamwidth, which can generate the right-hand CP (RHCP) or left-hand CP (LHCP) radiation through exciting different ports. Dual CP radiations are accomplished by an SIW directional coupler (DC) in the bottom layer, which provides the desired amplitude and phase conditions for two orthogonal slots. By superposing phase centers of linearly polarized (LP) electric field elements, the proposed antenna achieves a good performance of 3 dB AR beamwidth of 165° in the desired azimuth cut plane. Furthermore, an eight-element dual CP linear phased array with a wide-angle beam scanning ability is comprised by this antenna prototype. Numerical and measured results show that the array antenna can scan its main lobe from – 59° to 58°. In general, the proposed antenna array fed by the SIW structure satisfies the requirement of a multipolarization wireless communication system for low profile, simple structure, and easy integration with planar circuits. [ABSTRACT FROM AUTHOR]

A dual-polarized wideband omnidirectional ceiling antenna with low gain variations (GVs) for 2G/3G/LTE/5G sub-6 GHz indoor applications is presented. The vertical-polarized (VP) antenna element that is arranged in the center is composed of a pair of orthogonal semicircular plates and a top-loaded circular brass disk, whereas the horizontal-polarized (HP) antenna element is comprised of four printed dipoles with truncated corners, four arc-shaped parasitic patches around the dipoles, and a 1-to-4 power divider feeding network on the bottom. The feeding network with the “hook”-shaped stubs cooperates with the slot between the adjacent printed dipoles to improve the isolation between the VP and HP antenna elements. Furthermore, the top-loaded circular brass disk, the four arc-shaped parasitic patches, and two pairs of extended strips printed along the ±45° direction are used to reduce the GVs but broaden the operating bandwidths. Experimental results demonstrate that a wide overlapped frequency bandwidth of 74.9% (1.66–3.65 GHz) with an excellent port isolation (≥40 dB) is achieved for the aforesaid application scenarios. [ABSTRACT FROM AUTHOR]

A wideband low radar cross-section (RCS) circularly polarized (CP) reconfigurable patch antenna array based on liquid metal (LM) has been proposed in this article. The array was formed by $4\,{\times }\,4$ CP C-shaped antenna elements fed with a sequential feeding network. The antenna element was designed with a pair of narrow slots, and a microchannel adhered to the top metal layer. The CP reconfiguration depends on the tuning of the slots by moving the LM in the channel. The patch antenna array can obtain good CP radiation and low RCS features without any extra RCS reduction structures other than the array elements. RCS reduction (RCSR) can be realized by $180^{\circ }\,{\pm }\,37^{\circ }$ reflection phase variations between two different antenna elements under normal incidence for both $x$ - and $y$ -polarizations. The antenna prototype has been fabricated and measured. The measured results show good agreement with simulated results. [ABSTRACT FROM AUTHOR]

A metasurface (MS)-inspired low-profile circularly polarized (CP) slot array with a wide CP band and broadband low radar cross section (RCS) is proposed in this communication. The slot array consists of four element antennas, four grounded substrates, and a sequential-rotated feeding network. In terms of radiation performance, the array yields a wide CP band resulting from the CP element antenna and the sequential-rotated feeding network. The CP element antenna is achieved due to the polarization conversion property of the MS-based superstrate. The feeding network with multiple related design parameters is optimized by an artificial intelligence (AI)-driven antenna design method to find the widest bandwidth. In terms of scattering performance, broadband RCS reduction is achieved by using a hybrid RCS reduction technique that combines two destructive interference principles. The $\vert \text{S}_{11}\vert < -10$ dB bandwidth reaches 53.2%, the AR < 3 dB bandwidth reaches 50%, and the RCS reduction bandwidth reaches 147.8% for a low-profile structure with a relatively low number of MS unit cells. A prototype was fabricated and measured. The measured and simulated results are in good agreement. [ABSTRACT FROM AUTHOR]

In this communication, a broadband endfire circularly polarized (CP) antenna with a low-profile feeding structure is proposed for millimeter-wave (mmW) applications. The array element consists of a horizontally oriented printed electric dipole and a vertically aligned tapered slot radiator, exciting two orthogonal radiated electric-field components simultaneously. The amplitude and phase relationships between these two field components can be adjusted by balancing the response of the tapered slot and dipole radiators, thereby producing a CP radiated wave. Importantly, a parasitic director is introduced near the printed dipole to compensate for the gain degradation of the dipole element at higher frequencies, thus significantly expanding the axial ratio (AR) bandwidth of the CP element. Compared with other reported endfire CP antennas, the proposed antenna owns a lower profile of feeding substrate (0.508 mm $\sim 0.056~\lambda _{0}$), making it amenable for convenient integration with planar front-end circuits. As a demonstration, a $1\times8$ array prototype is designed and measured, exhibiting an impedance bandwidth of 42.1% (27.45–42.1 GHz) and a 3 dB AR bandwidth of 35.8% (27.5–39.5 GHz). The demonstrated CP array is a promising candidate for wideband mmW applications due to its advantages of wideband, ease of integration with planar circuits, and low fabrication cost. [ABSTRACT FROM AUTHOR]

This communication introduces a new structure of wideband slot antenna with high gain and stable radiation patterns for millimeter-wave (mmW) applications. It is the first attempt to apply an air-filled I-shape slot excited by a substrate-integrated-waveguide (SIW) feed. The slot can achieve lower $Q$ -factor contributing to a wider bandwidth. In addition, the feature of even electric field distributions across the operating bandwidth produces very stable gain performance for the proposed antenna. The proposed antenna is realized using a single-layered PCB substrate with plated-through-hole technology, which is cost effective and easy to fabricate. In addition, a $1\times8$ antenna array based on the proposed antenna element is developed with a planar 1–8 SIW feeding network. The measurement results show that the proposed array can achieve an impedance bandwidth of 36.6% from 58 to 84 GHz with a peak gain of 16 dBi. These performances ensure that the proposed antenna array is a promising candidate for mmW communications. [ABSTRACT FROM AUTHOR]

This letter presents a novel design method of a compact wideband loop antenna for circularly polarized (CP) radiation based on two sets of common modes (CMs) and differential modes (DMs). Different CMs and DMs are excited in the loop antenna with the same amplitude of radiated electric fields by using equal-amplitude and in-phase excitation. A wideband CP radiation performance is achieved through the combination of two sets of CMs and DMs with an innate 90° phase delay. Moreover, the shared-aperture configuration of CMs and DMs achieves a size reduction. An experimental prototype was fabricated and measured to verify the design concept for CP operation. The experimental results indicate that an overlapped bandwidth of 2.30–3.40 GHz (38.6%) with |S11|<–10 dB, axial ratio <3 dB, and gain variation <1 dB is obtained within compact size of 0.4 λ0 × 0.4 λ0 × 0.009 λ0 (λ0 is the wavelength in free space at the center operating frequency). Such a compact, wideband, and stable-gain CP antenna with a simple feed strategy is a promising candidate for wireless communication. [ABSTRACT FROM AUTHOR]

In this article, the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an $LC$ series resonator modeling the feed plus two capacitively coupled $LC$ parallel resonators accounting for the radiating patches. Then, a deembedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modeling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) magnetoelectric dipole (ME-dipole) antenna with a wide impedance bandwidth and 3 dB axial ratio (AR) bandwidth is proposed. The antenna is fed by a microstrip line and coupled through a modified cross-slot on the ground plane. Based on the conventional linearly polarized (LP) ME-dipole, the proposed electric dipoles and the coupling slots are modified to generate the CP radiation. Simulated results of the antenna element show an impedance bandwidth of 72.8% from 16.35 to 35.08 GHz and a 3 dB AR bandwidth of 39.2% from 21.53 to 30.07 GHz. To enhance the gain of the antenna for practical application, a 4 $\times $ 4 antenna array with full-corporate feeding network is designed, fabricated, and measured. The measured results show that an impedance bandwidth of 66.95% from 17.26 to 34.63 GHz and a 3 dB AR bandwidth of 41.1% from 19.25 to 29.25 GHz are achieved. The proposed antenna can be applied to K-band, Ka-band satellite communications or fifth-generation (5G) millimeter wave (mmWave) communications at n257 (26.5–29.5 GHz) and n258 (24.25–27.5 GHz) bands. [ABSTRACT FROM AUTHOR]

We proposed a broadband e‐shaped circularly polarized (CP) patch antenna with single‐point feed, and the feed point is located at the center of the antenna. The structure of this new antenna includes a ground plate and an e‐shaped patch placed on a substrate. The measured impedance bandwidth of the proposed antenna is approximately 17.89% (3.47–4.15 GHz), and the measured 3‐dB axial ratio bandwidth (ARBW) is about 9.47% (3.63–3.99 GHz). The antenna can achieve the gain of 8.4 to 8.7 dBi within the ARBW. And at the center frequency (3.8 GHz), right‐hand CP to left‐hand CP isolation of the antenna can reach −33 dB. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) slot antenna unit that is composed of a sector‐shaped radiator and an irregular pentagon slot ground plane is initially investigated. The CP characteristics are realized based on unbalanced feeding and loading of irregular slot structure. To increase the gain and yield ultrawideband operation, a 2 × 2 antenna array with a sequential rotational feeding method is introduced. To further reduce the total profile of the proposed antenna array to 0.15λ0, an artificial magnetic conductor array reflector is loaded between the antenna array and the feeding network. The measured 10‐dB impedance bandwidth of the proposed antenna array was 82.6% (8.31–20.0 GHz), and its corresponding CP bandwidth was 65.4% (8.61–16.98 GHz), and the radiation efficiency of the antenna is also higher than 80%. Besides exhibiting very good axial beams across the wide CP bandwidth, a peak gain of up to 11.1 dBic is also achieved. Thus, it is suitable for X‐band and Ku‐band satellite communication applications. [ABSTRACT FROM AUTHOR]

In this letter, a wideband efficiency-enhanced transmitarray is proposed using a variety of phasing elements based on the magneto-electric (ME) dipole structure. Several different ME-dipole geometries and excitation mechanisms are investigated to realize the receive-and-transmit type elements that have same multilayer configuration, wide common bandwidth, and stable transmission phase differences. A number of different phase adjustments can be provided within a wide bandwidth by the proposed elements. A 16×16 transmitarray antenna working from 21.5 to 33 GHz (42%, defined according to 3 dB variation in aperture efficiency) is designed, fabricated, and tested, which confirms a peak gain of 26.8 dBi and a peak aperture efficiency of 41%. Comparing to the original 1-bit ME-dipole transmitarray, where only two transmission phases can be used, the presented hybrid-element design demonstrates a pronounced improvement in aperture efficiency with nearly the same bandwidth and element thickness. [ABSTRACT FROM AUTHOR]

We describe a planar ultrawideband (UWB) dual-polarized tightly coupled bowtie antenna array for ground-based polar ice-sounding radar. The array operates over 180–620 MHz with a bandwidth ratio of 3.4:1. The broadband performance is benefitted from the tightly coupled antenna elements. By carefully integrating the impedance matching network into one arm of the bowtie antenna and using a ferrite core for common-mode suppression, this coplanar side-fed array avoids the use of vertical balun and external antenna matching network. The size of the full array is 2.8 m $\times2.8$ m with a weight of only 90 kg, including 24 power distribution boards and 288 feed cables. The thickness of the array is 12.7 cm, which is only about $0.08\lambda $ at the lowest operating frequency. This antenna array was deployed to Greenland in summer 2019 as a part of a surface-based UWB ice-sounding radar to measure and characterize the Greenland ice sheet. [ABSTRACT FROM AUTHOR]

This article introduces an amplitude and phase independently adjustable transmitarray aperture with a thin profile and low cost to fabrication characteristics, and a transmitarray antenna (TA) featuring the high gain and low sidelobe level (SLL) is realized based on it. The TA is made up of a standard feed horn and a transmitarray aperture, each of which comprises a three-layer metasurface that is well-designed to tune the transmitted phase and amplitude on its own. As a result, the transmitarray aperture can cover the 360° phase range required for phase compensation while also realizing the amplitude distribution calculated by the Taylor design, contributing to the low SLLs. The advantage of independently controlling the amplitude and phase not only enables the proposed TA to be easy to realize and less cost on optimization but also improves the performance of high gain and low SLLs with a low profile and easy fabrication. Theoretical analyses and simulations are carried out, and a prototype is fabricated and measured. At 10 GHz, the measured peak gain is 21.16 dBi, with SLLs of −31.21 and −29.93 dB in the H- and E-planes, respectively. As a result, the tight agreements between measurement and simulation validate the design concept. [ABSTRACT FROM AUTHOR]

In this communication, a broadband substrate integrated waveguide (SIW)-fed circularly polarized (CP) cross-dipole antenna is proposed for millimeter-wave (MMW) applications. Its radiation parts consist of a cross dipole and reflecting ground, which are etched on two substrates. The antenna is fed by an SIW through a double-sided parallel-strip line (DSPSL). In addition, zigzag edges and L-shaped etches are utilized to expand the impedance bandwidth (IBW) and axial-ratio bandwidth (ARBW), respectively. By these methodologies, the antenna prototype possesses a measured IBW of 34.6% from 22.5 to 31.9 GHz, an ARBW of 23.1% from 24 to 30.25 GHz, and a peak gain of 8.8 dBic at 29.5 GHz. In comparison to general coaxial-line-fed cross-dipole antennas with a nonplanar topology and high profile of $0.25\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at the center frequency), the proposed antenna with PCB process maintains broadband and owns a low profile of $0.16\lambda _{0}$ , which makes it more desirable for MMW integrated circuits. [ABSTRACT FROM AUTHOR]

A novel low-profile wideband dual-circularly polarized metasurface antenna based on a traveling-wave sequential feeding mechanism is proposed. It consists of 4 × 4 rectangle metasurface cells and is excited by a simple two-port traveling-wave feeding network, which includes four rotated Z-shaped slots etched on the ground and a ring feeding line, to provide stable sequential phases of 0°, 90°, 180°, 270° for realizing dual-circular polarizations. By changing the width of four Z-shaped slots, the equal amplitude of two orthogonal electric fields can be achieved and good right- and left-handed circular polarization (RHCP, LHCP) can be realized accordingly in a wideband. Moreover, a metasurface is utilized as a radiator to improve the impedance bandwidth (IMBW) as well as radiation performance. For demonstration, one prototype with an overall size of 0.88λ0 × 0.88λ0 × 0.06λ0 centered at 5.3 GHz is fabricated and measured. The measured results show that the proposed low-profile antenna realizes a large 10-dB IMBW of 38.4% (4.33–6.39 GHz) and 46.6% (6.17–6.70 GHz), 3-dB axial-ratio bandwidth of 38.4% and 39.3%, respectively, for RHCP and LHCP states. In addition, the polarization isolation is over 12 dB in the entire band of interest. [ABSTRACT FROM AUTHOR]

This letter presents a compact dual-band dual circular polarization feed chain consisting of only three metallic layers. The minimum number of layers are accomplished by applying an asymmetric architecture based on an enhanced ortho-mode junction (OMJ) with single quad-ridge waveguide machined in one layer. This solution achieves the compactness of the feed chain while maintaining outstanding electrical performance. The feed chain in the band of 17.7–21.2 GHz and 28.2–31.4 GHz is designed and measured. The measured results show that the reflection coefficient of the common port is less than 19.2 dB, the reflection coefficient in both operative bands is better than 25.5 dB, the left-hand circular polarization (LHCP) to right-hand circularly polarization (RHCP) isolation is higher than 20.3 dB, the transceiver isolation is higher than 40 dB, and the axial ratio is below 0.35 dB. The measured results are in great agreement with predicted ones. [ABSTRACT FROM AUTHOR]