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This article presents a new design of a differentially fed substrate integrated planar antenna array with dual-polarization. Compared with the traditional dual-polarized antenna arrays, the proposed array antenna has the advantages of simple configuration, high cross-polarization discrimination (XPD), and high gain. The $2\times 2$ -element subarray design with a via-loaded crossover structure is used, which reduces the complexity of the array antenna. The operation bandwidth is improved by generating three resonances in the subarray. An $8\times 8$ antenna array is designed, prototyped, and tested to exemplify its potential applications in large dual-polarized antenna arrays. A planar orthomode transducer is used to achieve differential excitation for the antenna array. The measured results show that the proposed antenna array has an impedance bandwidth of 19.2–20.7 GHz for $|S_{11}| dB and port isolation higher than 20 dB. The array antenna exhibits a high XPD of 43 dB and a flat gain of about 22.2 dBi within the bandwidth.

This communication proposes a novel compact multiple-input multiple-output (MIMO) antenna with low mutual coupling based on a $2 \times 2$ dual-polarized half-mode substrate integrated waveguide (HMSIW). The antenna is printed on a single-layer substrate to provide a low profile and ease of integration with planar circuits. The proposed HMSIW antenna element operates in TE110 mode and can be orthogonally arranged with two slots on the ground between the antenna elements, resulting in low mutual coupling. The edge-to-edge element space is only $0.033\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength). A new miniaturized decoupling structure of neutralization lines is proposed to further reduce the mutual coupling by −10 dB in comparison with the ground slot structure. The $2 \times 2$ MIMO antenna was fabricated and implemented to verify the design. The simulated and measured results were in good agreement. The measured impedance bandwidth of $\vert \text {S}_{11} \vert $ less than −10 dB ranges from 5.025 to 5.135 GHz, and the peak gain is 5.6 dBi on the broadside at the center frequency of 5.08 GHz. The mutual coupling levels between the orthogonal and the parallel antenna elements are −45 and −36 dB, respectively. The envelope correlation coefficient is lower than 0.003 across the operating bandwidth. The overall size of the antenna is only $1.08\lambda _{0} \times 1.08\lambda _{0} \times 0.025\lambda _{0}$ , making the antenna a suitable candidate for upcoming fifth-generation MIMO systems.

This article presents the first report of a circularly polarized (CP) omnidirectional radiation antenna for wireless capsule endoscope (WCE) system applications. The proposed antenna incorporates an integrated design concept, and achieves operation at 0.915 GHz Industrial, Scientific, and Medical (ISM) band (0.902–0.928 GHz) with a compact size of $\pi \times 5.5^{2} \times 22 \text {mm}^{3}$ . The simulation is performed in Ansys HFSS, with the antenna being placed in the center of a cylindrical homogeneous muscle tissue with a size of $\pi \times 55^{2} \times 80\,\,\text {mm}^{3}$ . The simulated results show that the capsule antenna has an impedance bandwidth (BW) ( $\vert S_{11} \vert dB) from 0.82 to 0.99 GHz and a CP BW (AR $\theta $ range (49°–144°) in the elevation plane. The robust CP performance and the integrated design concept make the proposed antenna suitable for advanced WCE systems.

A novel wideband circularly polarized microstrip patch antenna (MPA) with multimode resonance is proposed in this letter. The TM1/2,0 mode, the zeroth-order mode, and the TM1,0 mode are excited by inserting the shorting pins underneath the driven patch and the parasitic patch. Therefore, a wide impedance bandwidth is achieved under triple-mode resonance. By sequentially rotating the triple-mode elements, a circularly polarized MPA is developed with a four-feed network. Additionally, four metallic side walls are employed to obtain desirable radiation performances. For demonstration, a prototype of the proposed antenna is fabricated and measured. The measured −10 dB impedance bandwidth is 96% (1.53–4.39 GHz) and 3 dB axial ratio bandwidth is 86% (1.74–4.36 GHz). Meanwhile, a low profile with the height of 0.037 λ 0 ( λ 0 is the wavelength in free space at the lowest operating frequency) is obtained. Such a wideband, low-profile, and circularly polarized antenna is very promising for modern wireless communication applications.

This article presents a novel dual slant polarized antenna for millimeter-wave (mmWave) base stations. Compared with the traditional slant polarized mmWave antennas, the proposed antenna offers the advantages of high cross-polarization discrimination (XPD), good aperture efficiency, simple structure, and low profile. The corner-fed substrate integrated waveguide (SIW) cavity is adopted to improve the port isolation and XPD of this slot-coupled antenna. Four corner-truncated patches connected by a thin cross strip are placed over the SIW cavity to increase the operation bandwidth. Then, a $2\times 8$ antenna array is designed to exemplify the antenna element performance. To improve the impedance matching, a shorted patch is introduced in designing the series feeding network and the power divider. The experimental results show that the 2 dB-down gain bandwidth of the proposed antenna array reaches 6.0% and the port isolation is better than 20 dB. The gain and XPD of the antenna array measure 16.7 dBi and 25 dB at the center frequency, respectively.

An ultrawideband stacked single-turn spiral antenna with an integrated feeding structure is presented in this communication. The proposed antenna consists of two stacked planar single-turn Archimedean spirals which are wound in orthogonal directions. By connecting these two stacked spirals through two vertical posts, the traveling-wave current path is lengthened and, hence, the operating frequency of Mode 1 is decreased. To reduce the feeding complexity, an integrated tapered microstrip line is used to feed the spiral, which also acts an impedance transformer. It is demonstrated that the proposed antenna can operate across 0.29–5 GHz with |S11| < −10 dB and 0.75–3.64 GHz with axial ratio (AR) < 3 dB. Compared with the single-turn Archimedean spiral with the same radius, the impedance and AR bandwidth of the proposed antenna are enhanced from 5:1 to 17:1 and from 1.6:1 to 4.9:1, respectively, showing that the proposed antenna can be a good candidate for ultrawideband applications.

Based on characteristic mode theory (CMT), a quad-polarization reconfigurable antenna with suppressed cross polarization is proposed in this article. The proposed antenna is composed of the radiator, excitation units, and feeding network. A square conductive slab (SCS) is used as the main radiator, which is designed elaborately by characteristic mode analysis (CMA). Different modes of the radiator are stimulated selectively by four groups of balanced inductive exciters (BIEs) to realize horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Two p-i-n diodes are embedded into the feeding network to switch the excitation states of the four groups of BIEs, thereby achieving quad-polarization reconfiguration. More importantly, a novel method exploiting the CMA is adopted for achieving low cross polarization. By means of introducing the orthogonal mode, the cross-polarization component of the fundamental mode can be canceled out by the co-polarization component of the orthogonal mode, which greatly reduces the cross polarization from −10 to −40 dB in the two principal planes. The measurement results demonstrate that the quad-polarization agility and a cross-polarization level around −30 dB under all polarization states are achieved simultaneously, verifying the functionality and reliability of the proposed method.

Based on a newly proposed planar Yagi antenna with magnetic and electric dipoles, a compact $1\times 4$ broadband dual-polarized (DP) array with endfire radiation is designed in this paper. The magnetic Yagi antenna operates on the vertical polarization while the electric one operates on the horizontal one. The compact configuration of $0.5\,\,\lambda _{0}\times 0.63\,\,\lambda _{0}\times 0.09\,\,\lambda _{0}$ benefits from the novel half-mode magnetic Yagi antenna and the arrangement with the electric Yagi antenna. The broadband characteristic comes from the directors of the magnetic and electric Yagi antennas and the reflector of magnetic Yagi antenna. The simulation and the measurement verify this design. The measured common bandwidth of $\vert S_{11}\vert < -10$ dB for both polarization ports is 23.8–30.1 GHz (23.7%), and the gains vary between 3 dBi and 4 dBi within 24.2–30 GHz band range. The $1\times 4$ DP array with $0.5~\lambda _{0}$ element space has the beam scanning range of ±43 ° at the endfire direction and the gain of higher than 7.1 dBi. The scanning performances are experimentally validated by two phase-shift feed networks for 0 ° and 30 ° main beam directions. The proposed endfire DP array has the good features of compact structure, a low profile and no clearance requirement, which is easy to integrate in 5G terminals.

A novel method of designing a wideband dual-feed circularly polarized (CP) antenna is presented for different axial ratio (AR) requirements. By analyzing the output characteristic of the feed network for the dual-feed CP antenna, an approximate function is obtained and utilized to calculate the variances of the output magnitude and phase of the feed network under a required AR. Based on the analysis, different branch-line couplers are used for achieving wide AR bandwidths of less than 3, 2, and 1 dB, respectively. Compared to the traditionally used 3 dB coupler, the presented feed method can have an AR peak with the expected value at the center frequency and two AR valleys beside the peak, while the traditional 3 dB coupler can only get an AR valley with narrower bandwidth. Therefore, much wider AR bandwidths for different AR requirements are obtained by using the presented method. The wideband dual-feed antenna fed by these different couplers was simulated, fabricated, and measured for the final performance verification.

This article presents the design and analysis of an ultrawideband (UWB) circularly polarized (CP) antenna element and its array. First, an UWB CP antenna element using circular-arc-shaped monopole (CASM) with asymmetric ground plane is proposed. Characteristic mode analysis (CMA) is used to investigate its CP operating mechanism, providing physical insights into different modes (mode currents and characteristic radiation fields) at various frequencies. The CMA results show that the asymmetric ground plane makes great contribution to produce CP radiation in the lower frequency band, while another upper CP band is generated by CASM. Thus, the overall 3 dB axial ratio bandwidth (ARBW) of the element can be significantly expanded. Furthermore, a $2 \times 2$ UWB CP array is designed based on this element. A gradient artificial magnetic conductor (GAMC) with a metal cone is adopted to realize both a low-profile ( $0.1 \times \lambda $ , where $\lambda $ is the air-free wavelength at lowest frequency) and the high-gain radiation for the first time. To validate this novel configuration, this array is fabricated and measured. The measured bandwidth ( $\vert S_{11} \vert dB, AR < 3 dB) is approximately 92.3% (1.75–4.75 GHz). It also achieves a wide 3 dB gain bandwidth of 72.3%. Both the simulated and measured results demonstrate that this low-profile high-gain antenna array is promising for applications in wireless systems such as mobile satellite communication system.

A novel method of using axial ratio (AR) contour to design a broadband circularly polarized (CP) antenna is presented in this letter. By resolving a radiated CP wave into two orthogonal far-field components, the resulted AR will be determined by the radiated power and phase differences between the two orthogonal components. Therefore, a series of AR contours can be obtained for different AR values of the radiated wave. In the AR contour, details of phase-advance, phase-lag, power-advance, and power-lag can be simultaneously observed along with the resulted AR. Based on these analyses, the AR contour is first utilized to directly design a broadband CP antenna instead of using the traditional AR versus frequency curve to achieve optimal AR bandwidth. Compared to the traditional AR curve, the method of using AR contour to design CP antenna is more effective and informative. The designed broadband CP antenna was also fabricated and measured for the final performance verification.

This paper presents a close-spaced dual-band 2 × 2 multiple-input multiple-output (MIMO) antenna with high isolation based on half-mode substrate integrated waveguide (HMSIW). The dual-band operation of the antenna element is achieved by loading a rectangular patch outside the radiating aperture of an HMSIW cavity. The HMSIW cavity is excited by a coaxial probe, whereas the rectangular patch is energized through proximity coupling by the radiating aperture of HMSIW. The antenna elements can be closely placed using the rotation and orthogonal arrangement for a 2 × 2 array. Small neutralization lines at the center of the MIMO antenna can increase the isolation among its elements by around 10 dB in the lower band and 5 dB in the higher band. A prototype of the MIMO antenna is fabricated and its performance is measured. The measured results show that the resonant frequencies are centered at 4.43 and 5.39 GHz with bandwidths of 110 and 80 MHz and peak gains of 6 and 6.4 dBi, respectively. The minimum isolation in both bands is greater than 35 dB. The envelope correlation coefficient is lower than 0.005 within two operating bands.

In this article, a novel millimeter-wave dual-polarized 2-D multibeam antenna array incorporating differentially fed antenna elements is proposed to achieve high cross-polarization discrimination (XPD) when the beams scan to the maximal pointing angles. The antenna element is composed of an SIW cavity with four shorted patches placed inside, and it is differentially excited for dual-polarization by a pair of feeding strips and transverse slots beneath the patches. Differential excitation is realized by a power divider designed on two laminate layers. Two Butler matrices placed perpendicularly with each other in different laminates are employed to generate four tilted beams with dual-polarization. A $2\times 2$ dual-polarized 2-D multibeam antenna array working at 28 GHz is designed, fabricated, and measured. The operation bandwidth of the antenna is 26.8–29.2 GHz. The improvement in the XPD is experimentally demonstrated by far-field measurement. When the beams scan to 30° off the boresight, the measured XPDs are 28 dB at the center frequency and higher than 25 dB over the operation bandwidth, which confirms that the cross-polarized radiation in the 2-D multibeam antenna array is suppressed by using the differential-feeding technique. The measured gain is in the range from 7.6 to 10.5 dBi.

This article presents a polarization-reconfigurable wideband high-gain antenna based on liquid metal tuning. The antenna consists of a center-feed circular patch antenna with a C-shaped slot as the driven element. To broaden the bandwidth and improve the realized gain, a parasitic circular disc and 13 circular directors are employed. The direction of polarization can be tuned by changing the location of the liquid metal alloy contained in the tube. The relationship between the dimensions and the maximally achievable gain has been analyzed. The antenna has exhibited a −10 dB impedance bandwidth from 4.3 to 5.3 GHz (a fractional bandwidth of 21.2%). A 14.4 dBi gain is achieved at 5.3 GHz. The simulation and measurement results show good agreement with each other.

This communication proposes a novel method to design a dual-band circularly polarized (CP) transmitarray (TA) antenna with a linearly polarized (LP) feed. By using this method, a shared-aperture dual-band TA is developed, which forms independent beams with right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) in two frequency bands with a single LP feed antenna. Four different CP TA prototypes operating at 12 and 14.2 GHz with different senses of CP and different beam directions are designed, and two of the prototypes are fabricated to validate the design concepts. A good agreement is obtained between the radiation patterns, gain curves, polarizations, and cross polarization levels measured and computed in both frequency bands. The proposed single-source dual-band CP TA design has advantages of simple structure, lightweight, easy fabrication, low cost, and high performance, making it a good candidate for varied applications.

This paper presents the integration and channel characterization of a highly integrated dual-band digital beamforming space-borne synthetic aperture radar (SAR) receiver. The proposed SAR sensor is a low-cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module ready for the next-generation space-borne SAR missions. In previous works, by the authors, the design and experimental characterization of each sub-system was already presented and discussed. This work expands upon the previous characterization by providing an exhaustive experimental assessment of the fully integrated system. As it will be shown, the proposed tests were used to validate all the instrument channels in a set-up where the SAR sensor was illuminated by an external source minim the ground reflected waves. Test results demonstrate how the system channels are properly operating allowing the reception of the input signals and their processing in the digital domain. The possibility to easily implement a calibration procedure has also been validated to equalize, in the digital domain, the unavoidable amplitude differences between the different channels.

A novel miniaturized ultrawideband (UWB) half-mode Vivaldi (HM-Vivaldi) antenna based on mirror image theory is proposed in this letter. The antenna consists of half a modified radiating arm and two rows of metallized vias, which are equivalent as the perfect electric wall. According to the mirror image theory, the induced current on the electric wall can replace the mirror image current of the radiating arm at its symmetrical position, which will result in the HM-Vivaldi structure. The antenna size of 0.35 λ 0L × 0.54 λ 0L ( λ 0L is the free-space wavelength at the lowest operating frequency) is reduced by 33% compared to the original antipodal Vivaldi antenna size. In addition, the continuous exponential curved edge on the ground is improved to retain the wideband impedance match characteristic. The operation theory and parametric analysis of this HM-Vivaldi antenna are presented with a prototype being measured. An UWB from 5.3 to 40 GHz with the reflection coefficient lower than –10 dB is experimentally achieved except that | S 11| is slightly higher than –10 dB at several frequencies, and the maximum gain reaches 11 dBi.

A novel method of designing a wideband series-fed circularly polarized (CP) differential antenna by using crossed open slot-pairs is presented in this paper. The near-field distributions and input impedance analyses show that the closely spaced open slot-pairs can radiate as the crossed dipoles and have stable radiating resistance with a compact radiator size. Besides, a wideband half-power phase shifter by using open slot is proposed and utilized to realize CP radiation. The proposed CP antenna is composed of a wide slot-pair and a narrow slot-pair. In the antenna design, the narrow slot-pair is not only excited as a radiator, but also elaborately loaded to provide wideband half-power output and quadrature phase excitation to the wide slot-pair. Both the proposed half-power phase shifter and CP antenna are illustrated by the corresponding equivalent circuits. Based on these analyses, the proposed antenna is designed, fabricated and measured. Compared to the simulated traditionally designed counterpart, 2.1 times wider axial ratio bandwidth is achieved for the proposed antenna. The measured overlapped bandwidth for axial ratio 10 dB is 1.95-3.45 GHz (55.6%). Also, the antenna gain and radiation patterns are measured, which agree well with the simulated results.

A wideband high-efficiency millimeter-wave (mm-wave) circularly polarized (CP) array which is constituted by novel planar substrate integrated waveguide (SIW)-fed S-dipoles is presented in this communication. The proposed mm-wave CP S-dipole consists of two rotational symmetric curved arms and is fed differentially through aperture coupling, which features simple configuration and excellent performance. Detailed analysis is given to explain the operating principles of this element. It is noted that superior element performance including a wide impedance bandwidth of 43%, a wide 3 dB axial ratio (AR) bandwidth of 36%, and 1 dB gain bandwidth of 38% is achieved by the planar SIW-fed S-dipole. By feeding 64 in-phase S-dipole elements through a full-corporate SIW feeding network, a planar wideband highly efficient mm-wave $8 \times 8$ CP array is realized. To verify the design concept, a prototype operating at Ka-band is fabricated and measured. The measurement results indicate that the proposed array achieves a wide overlapped bandwidth of 27.6%, a high antenna gain of 25.2 dBic, and a high aperture efficiency of 89.9%. Attributed to the planar and robust array structure as well as its excellent performance, the presented array is a good candidate for various mm-wave applications.

A compact beam-scanning flat antenna array with high gain based on the substrate- integrated waveguide (SIW) is presented in this article. The radiation elements are the continuous transverse stub (CTS) constructed by SIW, which are arrayed on the substrate. The SIW-CTS array has a 4 dB higher gain than the traditional CTS array with the metal parallel plate waveguide and the theoretical explanation is analyzed. A new compact corporate-feed network consisting of an SIW-horn and a flat lens is also proposed. The flat lens could convert the cylindrical wavefront generated by the feed probe and the SIW-horn to a planar wavefront for feeding the CTS array. The Taylor distribution of the feed level made the array has a low sidelobe and high gain. The beam scanning of the array could be realized by simply moving the small SIW-horn along the line across the focal point. An eight-element array is designed, simulated, and fabricated to verify the design. The measured results show that the scanning range is from −35° to 35° with the highest gain of being 20.6 dBi and the sidelobe level of −25.2 dB at the broadside.

Plane Wave Generator (PWG) has attracted great research interest in the industry and academia for sub-6 GHz massive MIMO base station (BS) measurement, thanks to its low-cost and smaller system setup. One major concern in the small setup is its high reflectivity level inside the anechoic chamber, which might distort the quiet zone performance significantly. Meanwhile, it is critical that the quiet zone performance is insusceptible to system inaccuracies. However, these two aspects are largely overlooked in the plane wave synthesis (PWS) study in the literature. In this article, a new PWS strategy is proposed based on parametrized field distribution over an enlarged sampling area. The proposed method offers robust design and low reflectivity level. The effectiveness and robustness of the proposed PWS strategy is demonstrated in a numerical simulation.

Low-terahertz (Low-THz, 100 GHz-1.0 THz) technology is expected to provide unprecedented data rates in future generations of wireless system such as the 6th generation (6G) mobile communication system. Increasing the carrier frequencies from millimeter wave to THz is a potential solution to guarantee the transmission rate and channel capacity. Due to the large transmission loss of Low-THz wave in free space, it is particularly urgent to design high-gain antennas to compensate the additional path loss, and to overcome the power limitation of Low-THz source. Recently, with the continuous updating and progress of additive manufacturing (AM) and 3D printing (3DP) technology, antennas with complicated structures can now be easily manufactured with high precision and low cost. In the first part, this paper demonstrates different approaches of recent development on wideband and high gain sub-millimeter-wave and Low-THz antennas as well as their fabrication technologies. In addition, the performances of the state-of-the-art wideband and high-gain antennas are presented. A comparison among these reported antennas is summarized and discussed. In the second part, one case study of a broadband high-gain antenna at 300 GHz is introduced, which is an all-metal model based on the Fabry-Perot cavity (FPC) theory. The proposed FPC antenna is very suitable for manufacturing using AM technology, which provides a low-cost, reliable solution for emerging THz applications.

In this paper, a tightly coupled dipole reflectarray antenna as well as a variant-coupling-capacitance method to improve the antenna aperture efficiency is presented. Tightly coupled elements and true-time-delay lines are employed in the design of a wideband reflectarray. The proposed reflectarray can operate from 2 GHz to 5 GHz with the gain varying from 11.3 dBi to 21 dBi. Moreover, we propose a variant-coupling-capacitance method to improve the reflectarray aperture efficiency at lower frequency. By changing the coupling capacitance between neighboring elements according to their positions in the reflecting surface, a more linear equivalent distance delay line is achieved. Hence, phase error is reduced. According to measurement, the reflectarray gain in 2 GHz using the proposed method is increased by 3 dBi compared with the previous design. Aperture efficiency in 2 GHz is improved by 21.6%.

A compact and wideband folded dipole antenna with multi-resonant modes is presented in this paper. Three resonant modes are obtained by using a modified planar folded dipole and its coupled feeding structure. Incorporating the shorting pins and parasitic patches, multiple resonant modes in the antenna are manipulated, shifted, and then combined to increase the impedance bandwidth. Using this concept, a prototype of a multi-mode folded dipole is designed, fabricated, and measured. The experimental results show that the proposed antenna achieves a bandwidth of 80% from 1.57 to 3.68 GHz, while occupying a compact size of $0.3\lambda _{0}\times 0.15\lambda _{0}\times 0.05\lambda _{0}$ ( $\lambda _{0}$ is the wavelength in free space at the lowest operating frequency). Furthermore, a simple and effective design to achieve good omnidirectional radiation performance is developed by placing two proposed folded dipoles back to back. The antenna exhibits a flat gain variation of less than 1.27 dB over a broad bandwidth (82%) in the horizontal plane. Such a compact, wideband, planar antenna is a promising candidate for indoor signal coverage, wireless access points, and micro base stations in 2G/3G/4G/5G and WLAN/WiMAX wireless communication systems.

A novel concept of antenna design, termed differential mode/common mode (DM/CM) design, is proposed to achieve a highly integrated multi-input multi-output (MIMO) antenna unit in mobile terminals. The inspiration comes from a dipole fed by a differential line which can be considered a DM feed. What will happen if the DM feed is transformed into a CM feed? Some interesting features are provided in this article. By symmetrically placing one DM antenna and one CM antenna together, a DM/CM antenna can be achieved. Benefitting from the coupling cancellation of antiphase currents and the different distributions of the radiation currents, a DM/CM antenna can obtain high isolation and complementary patterns, even if the radiators of the DM and CM antennas are overlapped. Therefore, good MIMO performance can be realized in a very compact volume. To validate the concept, a miniaturized DM/CM antenna unit is designed for mobile phones. The 24.2 dB isolation and complementary patterns are achieved in the dimension of $0.330 \lambda _{0} \times 0.058\lambda _{0} \times 0.019 \lambda _{0}$ at 3.5 GHz. One $8 \times 8$ MIMO antenna array is constructed by using four DM/CM antenna units and shows good overall performance. The proposed concept of DM/CM design may also be promising for other applications that need high isolation between closely packed antenna elements and wide-angle pattern coverage.

This paper presents a novel hybrid design technique to minimize the number of layers of the transmitarray (TA) panel while maintaining 360° phase shift range. Two types of unit cells, the receive–transmit unit cell and the frequency selective surface (FSS), are placed in the same aperture. The resulting TA panel is very thin but does not sacrifice the radiation efficiency of the array. The receive–transmit unit cell is an aperture-coupled square patch, and the FSS unit cell is a novel wide bandpass FSS. Both types of unit cells have three conductive layers and are printed on two substrates with a total thickness of $0.07\lambda _{0} $ . The developed hybrid TA shows better gain than a homogeneous TA using the same elements. Meanwhile, it has comparable radiation performance but with a much lower profile compared to the conventional FSS-based TA designs that use several substrates separated by air layers. To verify the design concept, two hybrid TAs of different sizes with central frequency at 13.3 GHz were designed and fabricated. The measurements show that the TAs have at least 6.7% 1 dB gain bandwidth and higher than 30% aperture efficiency. Compared to the existing ultrathin designs of similar panel thickness, the presented TAs do not suffer from the phase quantization loss and achieve better or similar bandwidths.

A novel antipodal Vivaldi antenna operating at an ultra‐wideband of 5.2 to 40 GHz with high gain and miniaturized size is presented in this article. By introducing a pair of radiation arms with maple‐leaf edge shape, the antenna gain is increased by 1 to 3 dB over the upper operation band (10‐40 GHz) compared to the normal antipodal Vivaldi antenna (AVA). To remain the beamwidth while increasing the gain, two rows of specialized symmetrical metallized vias are loaded on the two inside edges of the exponentially slot. By loading the resistors between the top and the bottom planes, the side lobe level at E‐plane is reduced by 3 dB. This proposed maple‐leaf antipodal Vivaldi antenna (MAVA) has the miniaturization size of 0.66λg × 0.68λg × 0.003λg. According to the simulated results, the relative bandwidth of the reflection coefficient less than −10 dB is 154%, and the gain is higher than 10 dBi over the 22 to 40 GHz band with the maximum value of 14.3 dBi. The antenna design is validated by the measurements

In this communication, an orbital angular momentum (OAM) mode-reconfigurable antenna based on a uniform circular array (UCA) is presented. To realize multiple switchable operating states while maintaining a relatively simple structure, a simplified feeding scheme is developed. By introducing a set of optimal reference phases for different OAM modes, the tunable phase states for the entire array are degenerated, which leads to a reduction in the total number of required phase states. Then, the excitation phases are decomposed into two parts and generated by the reconfigurable radiators and reconfigurable feed network, respectively. In addition, p-i-n diodes are selected as switches to control the operating states of the radiators and feed network. Therefore, OAM-mode switching capability can be obtained by altering the direct current (dc) bias configurations of the diodes. The antenna design is validated by both simulation and measurement. Results indicate that the proposed eight-element array antenna produces six operating states corresponding to OAM modes l = ±1, ±2, and ±3. The measured overlapped band among the states with $\vert \text{S}_{\mathbf {11}}\vert dB covers 2.33–2.73 GHz. Moreover, the proposed antenna also features the advantages of easy fabrication and low cost.

This letter presents a compact dual-polarized over-the-air testing antenna with low radar cross section (RCS) for the fifth-generation and emerging wireless communication systems. The proposed antenna design is achieved by slotting two orthogonal Vivaldi antennas in a cross-shaped form into a two-part three-dimensional printed radome and loading microwave-absorbing materials (MAMs) at the antenna's outer edges. The proposed antenna has a rocket-nest shape with a diameter of 63.4 and 113.68 mm length. The −10 dB impedance bandwidth ( S 11) is obtained from a range of 2.1 up to 6 GHz. The two-part radome is formed by polylactic acid and acrylonitrile butadiene styrene dielectric materials, respectively. Their respective dielectric constants are approximately 2.6 and 4.5 within the −10 dB impedance bandwidth. The MAMs geometry and distribution location are optimized to suppress induced current over the antenna. An antenna prototype has been fabricated and measured. The measured results agree reasonably well with the simulated results. The results show that the use of the two-part radome enables the achievement of low RCS with compact form factor. Furthermore, a low bistatic RCS of between 2 and 6 GHz is observed in simulation for angular ranges of ${{\boldsymbol \theta }} \in [ { - {\text{30}^\circ }, + {\text{30}^\circ }} ]$ and $\boldsymbol{\Phi } \in [ { - {\text{90}^\circ }, + {\text{90}^\circ }} ]$ .

A novel self-diplexing aperture-shared dual-band dual-sense circularly polarized (CP) antenna array is proposed for transmitting/receiving (Tx/Rx) applications in X-band satellite communication systems. The antenna is capable of receiving the left-handed CP (LHCP) signals in the low band while transmitting the right-handed CP (RHCP) signals in the high band. First, a dual-port cavity-fed linearly polarized (LP) patch antenna with high isolation is developed as the element of the array. The element is composed of a slotted patch, a U-slot loaded substrate integrated cavity (SIC), and two groups of split-ring resonators (SRRs). The LHCP and RHCP operations are achieved by employing two sequentially rotated feeding networks which are isolated by a ground plane. To reduce the mutual coupling between the radiators, narrow slots are etched out in the center of the patches. Importantly, the sharing of patches at different bands (i.e., common aperture) enables a compact footprint to be achieved for the array, which is beneficial for suppressing undesirable grating lobes due to the reduced interelement spacing. The measured results of a fabricated prototype agree well with the simulations, showing an impedance bandwidth of 7.2–7.75 GHz (7.85–8.4 GHz), 3 dB axial ratio (AR) bandwidth of 7.4–7.7 GHz (7.95–8.32 GHz), and gain of 14 dBic (14.2 dBic) at the low band (high band). The channel isolation is over 27 dB and the sidelobe levels are below −15 dB in both bands. The demonstrated low-profile dual-band, dual-sense CP antenna array can be a good candidate for satellite communication.

A broadband polarization-reconfigurable slot antenna and 2 × 2 array with compact feed network are proposed in this letter. The wide circle slot, etched on the ground, serves as the radiation aperture with a wideband characteristic. A novel compact microstrip (MS)–slot line–coplanar waveguide feed network on the top side is proposed to realize reconfigurable-polarization senses. Three p-i-n diodes are loaded on the MS for generating the linear polarization (LP), left- and right-hand circular polarizations (CPs) in the wide circular slot. Based on the compact feed network, a 2 × 2 polarization-reconfigurable antenna array with two dielectric layers is suggested. The feed networks are printed on the bottom and top metal planes, while the wide slots are on the middle one. To further improve the directivity, a reflector is loaded at the back of the array. A prototype operating at S -band is fabricated and measured. The measured 10 dB impedance bandwidth is 10.8% for the LP operation. The overlapped 10 dB impedance and 3 dB axial-ratio bandwidths are 14.5% for the CP operations. The peak gain reaches 14.7 dBi, which comes from the low loss and compactness of the novel feed network. The design can be extended to a larger array without increasing the structure complexity.

A dual-polarized (DP) flat antenna array with passive 2-D beam-scanning capability is presented in this paper. The array consists of a DP continuous transverse stub (CTS) array, a flat Risley prism (FRP), and a line source generator. Two sets of CTSs, being constituted by the substrate-integrated waveguide (SIW), share a common aperture and are arranged orthogonally for the DP operation. A novel compact long line source is proposed for exciting this DP-CTS array. The FRP is realized by two linear phase progression phase-shifting surfaces (LPP-PSSs) and is placed above the DP-CTS array. The beam-scanning capability in the azimuth and in the elevation can be realized by rotating simultaneously the two LPP-PSSs in the same and in the opposite directions, respectively. A six-element array prototype is simulated and fabricated. According to the measured results, beam-scanning ranges of 40° in the elevation and 360° in the azimuth are achieved with the maximum gain of 17.8 dBi. The novel contributions from this paper include: 1) a novel compact long line source and 2) the first passive DP 2-D beam-scanning flat antenna array. This array can be extended easily to a higher gain or a circular polarization application.

A novel differentially driven dual-polarized patch antenna is presented in this communication. The proposed antenna is a low-cost design with a simple configuration, which avoids using the conventional high-cost multilayer PCB technology. The antenna is composed of two intersected open-loop resonators, which are connected to each other at the center. By using the electric coupling from the intersected resonators, two orthogonal radiating modes are excited from the top radiating patch. With the even- and odd-mode current distributions on the intersected resonators, high port isolation and low cross-polarization level are obtained. The external quality factor of the resonator is illustrated by using the analytical model of a double-loaded resonator. To demonstrate the design method, the proposed antenna and array are designed, fabricated, and measured. Compared to the traditionally designed capacitively coupled antenna, two times wider impedance bandwidth is obtained for the proposed antenna with high isolation (>38.5 dB) and low cross-polarization level (< −33 dB). The antenna array is designed for 5G base stations, which features the compact size and low reflection coefficient (< −15 dB). In addition, beam scanning performance of the antenna array is also investigated for base-station applications.

A robustness-enhancing technique without additional computational cost in antenna optimization design is presented. The robustness is implemented by minimizing the variances of the gains, axial ratios, and VSWRs over the required frequency band. It is demonstrated that the new technique has two obvious advantages. One advantage is that it can ensure the antenna robustness without the extra computational overhead. The other advantage is that it is possible to broaden the bandwidth of the antenna. We apply this technique to design a microstrip antenna at 2.4 GHz. The experimental results show that, by adopting this new technique, the evolved antenna is more robust than by using two other techniques.

This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system.

This letter presents a novel low-cost leaky-wave antenna (LWA) with the fixed-frequency beam-scanning capability. An improved half-mode corrugated substrate integrated waveguide structure is proposed as the guiding wave structure to reduce the transverse size of the antenna. A novel electronic phase-shifting structure, composed of fan-shaped open stubs with different sizes and PIN diodes, is proposed for beam scanning. This LWA uses interdigital slots as radiating elements, and the phase-shifting structure is placed between the adjacent radiating elements. By changing the switching states of these PIN diodes, the phase difference between the adjacent radiating elements can be controlled. To verify the concept, one prototype of the 2 × 6 array antenna at C -band is designed, simulated, fabricated, and measured. The antenna demonstrates a beam-scanning range of 25° (34°–59°) at fixed frequency, a peak gain of 12.4 dBi with the gain variation less than 2.3 dB. The antenna has low cost and can be easily fabricated using standard printed circuit board process.

In this paper, a compact, broadband, planar array\ud antenna with omnidirectional radiation in horizontal plane is\ud proposed for the 26 GHz fifth-generation (5G) broadcast\ud applications. The antenna element is composed of two dipoles and\ud a substrate integrated cavity (SIC) as the power splitter. The two\ud dipoles are placed side-by-side at both sides of the SIC and they\ud are compensated with each other to form an omni-directional\ud pattern in horizontal plane. By properly combing the resonant\ud frequencies of the dipoles and the SIC, a wide impedance\ud bandwidth from 24 to 29.5 GHz is achieved. To realize a large\ud array while reducing the complexity, loss and size of the feeding\ud network, a novel dual-port structure combined with radiation and\ud power splitting functions is proposed for the 1st time. The\ud amplitude and phase on each element of the array can be tuned,\ud and therefore, the grating lobes level can be significantly reduced.\ud Based on the dual-port structure, an 8-element array with an\ud enhanced gain of over 12 dBi is designed and prototyped. The\ud proposed antenna also features low profile, low weight and low\ud cost, which is desirable for 5G commercial applications. Measured\ud results agree well with the simulations, showing that the proposed\ud high-gain array antenna has a broad bandwidth, omni-directional\ud pattern in horizontal plane, and low side-lobes.

A dual-band ten-element MIMO array based on dual-mode inverted-F antennas (IFAs) for 5G terminal applications is presented in this paper. The proposed dual-mode IFA is composed of two radiators, which are etched on the outer and inner surfaces of the side-edge frame. The outer part of the antenna generates the low-order mode at 3.5 GHz, while the inner part radiates another one-quarter-wavelength mode at 4.9 GHz. In this way, the IFA can achieve dual-band operation within a compact size of 10.6 × 5.3 × 0.8 mm3. Based on the proposed antenna, a dual-band ten-element multiple-input and multiple-output (MIMO) array is developed for 5G terminal applications. By combining neutralization line structures with decoupling branches, the isolations between the elements are improved. To validate the design concept, a prototype of the ten-element MIMO array is designed, fabricated, and measured. The experimental results show that the proposed antenna can cover the 3.3-3.6 GHz and 4.8-5.0 GHz bands with good isolation and high efficiency. Furthermore, the envelope correlation coefficient (ECC), and channel capacity are also calculated to verify the MIMO performances for 5G sub-6GHz applications.

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) array using a multi-slot decoupling technique for the fifth generation (5G) mobile communication. By employing a compact dual-loop antenna element, the proposed array obtains two broad bandwidths of 12.2% and 15.4% for sub-6GHz operation. To reduce the mutual coupling between antenna elements, a novel dual-band decoupling method is proposed by employing a multi-slot structure. The proposed MIMO array achieves 15.5-dB and 19.0-dB isolations across the two operating bands. Furthermore, three decoupling modes generated by different bent slots can be independently tuned. Zero ground clearance is also realized by the coplanar arrangement of the antenna elements and decoupling structures. The proposed MIMO array was simulated, fabricated, and measured. Experimental results agree well with the simulations, showing that the dual-band MIMO array has good impedance matching, high isolation, and high efficiency. In addition, the envelope correlation coefficient and channel capacity are calculated and analyzed to validate the MIMO performance of the 5G terminal array. Such a dual-band high-isolation eight-element MIMO array with zero ground clearance is a promising candidate for 5G or future mobile applications.

This paper introduces an ultra-wideband circularly polarized (CP) asymmetric-S antenna with wide axial ratio beamwidth (ARBW) for C-band applications. The proposed antenna is realized by bending a linearly polarized dipole into asymmetric-S shape with variable trace width, which achieves CP radiation. Unlike the reported symmetric-S antenna, the proposed antenna is constituted with two unequal curved arms to enhance the bandwidth and beamwidth performances. Compared with the symmetric-S antenna, the proposed antenna demonstrates much wider AR bandwidth and wider ARBW over broader frequency range. A prototype is fabricated to verify the design principle. The measured and simulated results are very consistent and both indicate that the proposed antenna has a wide impedance bandwidth (VSWR

A dual-polarized communication rectenna array with high isolation and low cross polarization for simultaneous wireless information and power transmission (SWIPT) is presented. It consists of a 2 × 2 element receiving antenna array and a high efficiency rectifier based on voltage doubler topology. The receiving element is corner-fed to achieve high isolation of more than 20 dB between the dual-polarized ports, which guarantees low mutual interference between the communication and the rectifying ports. To receive enough electromagnetic (EM) wave for rectifying and meanwhile meet the communication sensitivity, this 2 × 2 array uses its 2 × 2 vertical polarization ports and 1 × 2 horizontal polarization ports for power rectifying, and the rest 1 × 2 horizontal polarization ports for communication. For the communication port, the measured gain is 10.9 dBi and the cross polarization is less than -20 dB. The performance of the whole communication rectenna array has been measured, where a 2 × 4 circularly-polarized array with a gain of 17.5 dBi, settled 1 meter away is used as the transmitter. Measured results show that the system achieves a peak microwave - direct circuit (mw-dc) conversion efficiency of 74.9 % for the CW signal, and 67 % for the QPSK signal with 10 MHz channel bandwidth on the load of 345 Ω at 2.58 GHz operating frequency.

This paper presents a novel Circularly Polarized (CP) microstrip array antenna with circular shape and slotted by an elliptical ring for X-band communication. This array antenna consists of 4 paths. Each patch is designed with a unique model, and the purposed antenna is mainly circular-shaped. An elliptical ring slot is set at the center of the circular-shaped patch. And a pair of triangle shapes employed as truncation factor is placed at the edge of the circular-shaped antenna. This microstrip array antenna is developed by 2 × 2 patches in a sequential rotation mode with relative phases 0˚, 90˚, 180˚ and 270˚. Total dimension of this array antenna is 60.92 mm × 60.92 mm. The simulated result shows a good agreement with minimum requirement. The center frequency of the antenna design is 8.2 GHz with low-frequency at 8 GHz and high frequency at 8.4 GHz. The proposed antenna produced under -10 dB S11 of 21.9%, maximum gain of 12.47 dBic at the center frequency, and axial ratio bandwidth obtained 12.2%. Simulated result has been validated by fabrication and measurement, then the structure of the antenna design is fabricated on NPC-H22A with a thickness of 1.6 mm and dielectric constant of 2.17. Complete investigation and experimentation are presented in the next sections.

The design of a novel planar wideband phased antenna array operating over 7.5-19.5 GHz has been presented. The array radiator consists of a feeding patch and a couple of shorting patches which are connected to the ground plane with shorting vias and isolating vias. Good impedance matching can be obtained due to the shorting vias while the common-mode resonance is eliminated by the isolating vias. Both the infinite unit-cell model and the finite simulation model have been implemented to investigate the performance of the proposed antenna array. The obtained results have shown that the active VSWR is less than 2 for wide scan in the E-plane while the active VSWR is less than 3 for 45° scan in the H-plane. The whole thickness of the radiator is 3.4mm, indicating the possibility for low-profile applications.

This paper proposes a compact rectifier design method for utilizing harmonics. Based on total reflection generated by pure reactance loads at the second harmonic (2nd) and open circuit at the third harmonic (3rd), a compact DC-pass filter is designed to effectively utilize the 2nd and 3rd harmonics excited by the rectifying diode. The amplitudes of the harmonics can be controlled by adjusting the input impedances of the DC-pass filter at harmonics. A prototype operating at 5.8 GHz fundamental frequency is implemented and measured to validate the scenario. When the input power is 18.3 dBm, the measured rectifying efficiency is 71.3%, while the 2nd and the 3rd harmonic amplitudes are −2.4 dBm and 0.1 dBm respectively. This method could also be extended to design a rectifier only utilizing the 2nd or the 3rd harmonic.

The mobile communication systems have evolved rapidly in recent decades, from the 1st generation (1G) in the 1980s to the 2nd generation (2G) in the 1990s, 3G in the 2000s and 4G in 2010s. We are now in the transition period from 4G to 5G, and there are already lots of research activities investigating the 6G technologies. A variety of frequency bands have been employed in mobile communications. Figure 1 illustrates typical frequency bands of 2/3/4/5G mobile communication base station. The 2/3/4G systems occupy a wide frequency range including 698 to 960 MHz and 1710 to 2690 MHz, while 5G employs several different frequency bands such as 3.3-3.6 GHz, 4.8 - 5.0 GHz, 37 -43.5 GHz, etc. Hence the co-existence of 2/3/4/5G becomes a hot topic. In particular, it is important to investigate the development of base-station antennas which can have a compact size and can achieve a very wideband impedance matching performance for covering the frequency bands of 2/3/4G. The antenna also needs to achieve dual polarization with high isolation between two input ports, high polarization purity, stable radiation patterns and constant beamwidth across the frequency range. In addition, the antenna needs to be immune to the inferences from radio signals of 5G systems [1]–[2]. This invited talk has two parts. First, a review of recent development in wideband dual-polarized antennas for base stations will be provided, and different antenna technologies will be discussed. Then, three examples of wideband dual-polarized antennas for base station applications, recently developed at the University of Kent, UK, will be presented. These include a wideband dual-polarized antenna which achieves a compact size by using a shared dipole approach, a compact-size highly integrated shared-dipole antenna with wideband dual polarizations, and a compact dual-polarized antenna with the configuration of the equivalent electric and magnetic dipoles and using the parasitic strips and shorting sheet to realize wideband harmonic suppression. These three antennas are verified by both the simulated and measured results, including the S-parameters and radiation patterns. Good agreements are achieved to show that these antennas can be the good candidates for the base station applications. Figure 2 shows one of the wideband dual-polarized antennas and its radiation pattern. During the talk, the designs of these three antennas and their simulation and measurement results will be discussed. Finally, a discussion of future challenges will be given at the end.

Based on the current technical approaches, a microwave power transmission demonstration system has been proposed to simulate the operating mode of MPT for the future Space Solar Power Station (SSPS). Several key technical parts are emphatically considered in the system design, namely high efficiency microwave power amplifier, transmitting antenna array, rectenna array and beam steering control technology. Each module of the microwave power transmission system is designed and optimized in this paper. The operating frequency of the MPT system is 5.8 GHz. The diameters of transmitting antenna and rectenna arrays are about 1.2 m and 2 m respectively, correspondingly the transmission distance is about 55 m. The transmitting microwave power is about 1600 W, the output DC power is expected to be larger than 300 W, and the accuracy of beam control is better than 0.4°. This work can provide technical support for the MPT system demonstration towards SSPS.

In this paper, a polarization-insensitive metasurface, harvesting electromagnetic (EM) energy with high efficiency and frequency stability over a wide range of incidence angles, is proposed. The previously reported metasurfaces suffer from their maximum efficiencies shifting with the frequency when the incidence angle increases. By introducing a square-shaped metal via ring around the elements, the mutual coupling among adjacent cells is reduced so that the proposed metasurface can maintain maximum efficiency at the fixed operation frequency over a wide range of incidence angles. Furthermore, with one single harvesting via in the proper position for the connection of a harvesting load, the metasurface can collect EM energy effectively with both transverse electric (TE) and transverse magnetic (TM) polarizations in one single harvesting load. Compared with the reported metasurfaces, this proposed metasurface has a higher efficiency and fixed operation frequency within a wide incidence range. The energy distribution, harvesting efficiency, and surface current are simulated to investigate the operation mechanism of the proposed metasurface. The simulation results show that the maximum harvesting efficiency is 91% at 5.8 GHz for both TE and TM polarizations at the normal incidence. When the incident angle increases to 75&deg, the maximum efficiency is achieved at 5.79 GHz (0.19% shift), and the maximum efficiencies of TM and TE polarizations are 91% and 68%, respectively. A 5 &times, 5 array is fabricated and tested. The experimental results are in good agreement with the simulated ones.

Plane Wave Generator (PWG) has recently attracted great attention from industry and academia for over-the-air (OTA) testing of base station (BS) antennas in the fifth-generation (5G) wireless communication systems. This paper aims to reduce the scattering from the PWG to the antenna under test (AUT), which might be problematic in the near-field OTA testing. First, we introduce a low monostatic radar cross section (RCS) PWG array element design. The PWG is also loaded with pyramidal microwave absorbing material (MAM) to suppress the multi-reflections between the AUT and the PWG. Furthermore, unlike coplanar PWG design generally reported in the literature, a novel non-coplanar design is proposed to realize the destructive interference of the scattered signals from the PWG, thereby significantly reducing the multiple reflections. PWG elements in the non-coplanar design are placed in the propagation direction according to planar and non-planar field distribution on the PWG radiated from the BS AUT. To validate our proposed design, a $4\times 4$ PWG array with a 108 mm element spacing and a non-coplanar structure is developed and experimentally validated. The measured results show that the second incident wave of the proposed non-coplanar PWG array structure based on non-planar field distribution is 7.9 dB lower than that of the classical coplanar PWG design from 2.3 GHz to 3.8 GHz, and 1.9 dB lower than that of the proposed non-coplanar PWG array structure based on planar field distribution, which demonstrates the effectiveness and robustness of our proposed design.

In this paper, a novel H-plane substrate integrated waveguide (SIW) horn antenna loaded with tapered periodic leaky-wave strips (TPLS) and a dielectric slab is proposed. The mismatching between the horn aperture and free space caused by the thinness of the substrate, leads to narrow impedance bandwidth and poor radiation performance for SIW horns. To enhance the bandwidth and gain performances, the TPLS are printed in front of the horn aperture, which guide and leak the electromagnetic waves gradually along the dielectric slab. Moreover, an extended dielectric slab placed in front of the TPLS further enhances the realized gain by more than 5 dBi. Simulated results illustrate that an impedance bandwidth of 60.8% is obtained from 20.6 GHz to 38.6 GHz with the return loss |S 11 | below -10 dB. Meanwhile, a peak realized gain of 19.1 dBi is achieved at the frequency of 29 GHz, with the realized gain more than 9 dBi across the whole operating band. In addition, stable radiation patterns in both E-plane and H-plane are observed over the entire operating band.

This paper presents a compact circularly polarized (CP) substrate-integrated waveguide (SIW) leaky-wave antenna (LWA) with consistent gain and high total efficiency at millimeter-wave frequencies. The proposed antenna consists of two layers. The lower layer is a conventional slotted SIW LWA, while the upper layer is an S-dipole array. The S-dipole layer is introduced to achieve circular polarization and improve the total efficiency of the antenna. Simulated results demonstrate that the proposed antenna operates from 24.5 to 29.5 GHz and exhibits a continuous 32° CP beam scan with a realized gain variation between 13 and 14.2 dBic. Moreover, the axial ratio is maintained below 3 dB throughout the operating frequency band. The average realized gain and total efficiency are about 13.7 dB and 93%, respectively.