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A novel bandwidth enhancement method using loading multiple parasitic structures to realize broadband miniaturized antenna is proposed. Based on the proposed strategies, one miniaturized wideband dual-polarized dipole antenna covering LTE/CDMA/GSM bands (690–960 MHz) for base-station application is designed. The antenna consists of two folded bowtie-shaped dipoles fed with a pair of crossed baluns, and is further loaded on a ceramic block with high permittivity ($\varepsilon$) for miniaturization. A parasitical square loop is loaded for bandwidth enhancement at a lower frequency. In addition, four split rings with a small square loop are firstly adopted for antenna resonance tuning, the impedance bandwidth is thus improved effectively. The antenna size is only $0.18\,\times \,0.18\,\times \, 0.22\,\,\lambda _{0}$ at the center frequency. The measured result of the fabricated prototype exhibits a relatively large operation bandwidth of 32.73% (VSWR < 1.6) with stable radiation patterns and relatively flat broadside gains. Moreover, to verify the feasibility of the proposed miniaturized antenna element in the base-station application, an array of $2\,\times \, 4$ is further designed. The measured results of the array indicate isolation over 20 dB with an impedance bandwidth of 32%. Due to the good performance and compact feature, the proposed miniaturized broadband antenna element can find large application potential in multiband wireless communication base stations. [ABSTRACT FROM AUTHOR]

A novel coupling-cancellation method by loading planar path is proposed and applied in the millimeter-wave phased array for wide-angle scanning. By employing the improved decoupling stubs with weak radiation first, an extra introduced wideband equal-magnitude and anti-phase path is generated to cancel the inherent coupling path. The principle of the proposed method is investigated by the equivalent circuits and the full-wave simulation. Based on this method, a high-isolation 1-D phased array using low-temperature-cofired ceramic (LTCC) process is designed and fabricated. The planar paths are placed symmetrically between the subarrays and its radiation polarization is coincident with the antenna elements, resulting in high isolation and enhanced boresight radiation null-fill of subarrays. The measured isolation is below 20 dB within the relative bandwidth of 16.7% and the maximum scanning angle is ±60°. Moreover, the proposed method can be expectedly extended to large-scale arrays. [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]

Novel designs of paper-based bandstop frequency-selective surfaces (FSSs) are presented in this article. The characteristics of the paper-based honeycomb structure are investigated first. One folded dipole resonator with first-order bandstop response is analyzed and further printed on the sidewalls of the honeycomb structure accordingly. A second-order response with two cascade FSSs is proposed with controllable bandwidth by the coupling coefficient of the resonators with the aid of the equivalent circuit model. Two paper-based FSS samples were fabricated and measured to demonstrate the validity of the proposed design strategies. Benefiting from the merits of lightweight and strong mechanical properties, the proposed paper-based FSS is a potential candidate for application in radar systems and aircraft. [ABSTRACT FROM AUTHOR]

A low-profile and shared aperture dual-polarized (DP) omnidirectional antenna by reusing the structure of an annular quasi-dipole array is presented. The proposed antenna consists of a center-fed circular patch antenna, an annular quasi-dipole array, a wideband one-to-four power divider integrated with the center-fed circular patch antenna, and two annular strips. The center-fed circular patch antenna is utilized as the driven element for the vertically polarized (VP) radiation. The annular quasi-dipole array fed by the one-to-four power divider produces horizontally polarized (HP) radiation. Simultaneously, it also acts as the VP director to improve VP gain and bandwidth. Besides, the two annular strips enhance the HP omni-directivity and gain. In this way, the VP and HP share the same aperture to improve the profile utilization rate effectively. Due to the symmetry of the basic antenna structure, stable DP donut patterns are obtained within the entire operating bandwidth. For demonstration, a 4.1–5.0 GHz prototype is designed, fabricated, and measured. Under a low profile of $0.13\lambda _{0}$ , the prototype realizes a −10 dB overlapped bandwidth of 20%, high port isolation of above 35 dB, and stable DP donut patterns with horizontal gain larger than 1.8 dBi. [ABSTRACT FROM AUTHOR]

A planar bidirectional circularly polarized (CP) antenna using orthogonal magnetic dipoles (OMDs) without an extra phase shift line is proposed in this work. It consists of a rectangular microstrip magnetic dipole antenna (MMDA) and a loop radiator with two arms directly connected to the open edge of MMDA. The working principle is revealed by the equivalent sources model to provide a clear physical insight at first. The theoretical investigations imply that by controlling the width and the feed locations of the loop antenna on the aperture, the phase and magnitude for CP radiation can be realized in both endfire and backfire directions without introducing an additional phase shift line structure. For demonstration, one antenna prototype is designed and fabricated. The experimental results indicate that an overlapping bandwidth of 5.91% from 2.30 to 2.44 GHz is attained. Compared with the counterpart using OMDs, the proposed antenna exhibits a low design complexity and improved gains of 3.56/1.83 dBic in the endfire/backfire directions. [ABSTRACT FROM AUTHOR]

This communication presents a new multiband multiarray (MBMA) scattering suppression antenna configuration for a dual-band and dual-polarized antenna array with reduced radiation distortion. The proposed antenna array configuration consists of a low-band (LB) antenna element working in the 690–960 MHz band and four high-band (HB) antenna elements working in the 1.7–2.7 GHz band. The LB antenna introduces U-shape structures to the radiation element to neutralize HB scattering currents. On the other hand, the HB antenna involves an LC resonant structure between its radiation arm and feeding balun to suppress LB scattering currents. An antenna array using the proposed LB and HB elements is designed to achieve MBMA functions. Experimental results show that the radiation distortions in both LB and HB bands are improved significantly. The VSWR of less than 1.5, the isolation of more than 25 dB, and the symmetrical radiation pattern are obtained in both bands. [ABSTRACT FROM AUTHOR]

A novel decoupling method by utilizing one $1\times2$ subarray to provide a pair of phase-reversed coupling paths for coupling energy cancellation is proposed. The newly proposed decoupling approach is implemented by symmetrically loading several U-type, I-type, and cross strips around the antennas to change the original couplings, so that two elements in the $1\times2$ subarray can form a pair of phase-reversed coupling paths into adjacent element in different subarray for coupling cancellation. Then, the couplings from the subarray to adjacent element are effectively suppressed, thus the isolations between different subarrays of the array are promoted. Moreover, the method can be also applied in improving the isolation between different polarizations in the same subarray. In addition, these strips not only have little influence on radiation characteristics of the antenna array, but also can be etched on the antenna layer without extra profile and process. For demonstration, one dual- polarized patch antenna array based on the new decoupling mechanism is designed. The results indicate that all the isolations between the subarrays of the proposed dual-polarized antenna array can achieve a very high level of over 25 dB in an operation band of 3.4–3.6 GHz. Compared with other decoupling methods, the proposed method can simultaneously improve complex multiple-port isolations among different subarrays and different polarizations to realize a very high isolation with less impact on antenna radiation. Due to above features, the proposed decoupling mechanism is expected to find potential applications in 5G dual-polarized multiple-input–multiple-output (MIMO) antenna array. [ABSTRACT FROM AUTHOR]

This article presents a novel broadband dual-polarized filtering patch antenna array using low-temperature cofired ceramic (LTCC) process for 5G millimeter-wave (mmW) applications. The filtering antenna element is implemented using a ± 45° polarized patch antenna fed by two pairs of differential L-type probes. An additional square ring and open strips are connected to each probe, resulting in radiation nulls and realizing the lower/upper stopband rejection level over 24 dB with skirt selectivity. The cross coupling among these structures not only introduces filtering responses, but also contributes to broadening the passband of 24.25–29.5 GHz covering 5G n257/n258/n261 bands. The antenna performance is validated by equivalent circuits based on transmission line models, which reveals clearly the principles of filtering antenna step by step and provides guidelines for further designs. The proposed filtering antenna element is expanded to a $4\times 4$ filtering antenna array with shunt-fed feeding networks. The spacing between elements is $0.48~\lambda _{0}$. The measured results demonstrate that the array performs good filtering characters including high stopband rejection, high selectivity, and wide upper stopband up to 40 GHz, where the antenna efficiency (considering radiations from all the directions) is less than 5%. In addition, the differential feeds provide symmetric radiation patterns with low cross-polarized counterparts. Compared with other reported works, the proposed filtering antenna/array has excellent performances of wideband, high stopband rejection and wide upper stopband for potential 5G mmW applications. [ABSTRACT FROM AUTHOR]

A broadband low-profile folded transmitarray (FTA) is proposed and investigated, in which a novel wideband transmission polarizer (TP) is used to realize low-profile design. The proposed TP, mainly consisting of a differential-fed grid-slotted patch antenna, can realize high-efficiency transmission and polarization selection simultaneously within a wideband frequency range. Moreover, the proposed TP can realize linear transmission phase because of the true-time delay (TTD) technique. Owing to the function of polarization selection and linear transmission phase, the TP can be used as antenna element for a FTA. A 140-element FTA is designed and fabricated by combining the TP with a broadband polarization rotation reflecting surface (PRRS). The measured radiation patterns agree well with the simulated results, and a peak gain of 24 dBi and maximum aperture efficiency of 44.7% are achieved. Furthermore, −1 and −3 dB gain bandwidth with 25.9% and 33.3% are also experimentally demonstrated in the proposed FTA, respectively. [ABSTRACT FROM AUTHOR]

We present single- and dual-frequency antennas based on the shorted helical slot in hepatic microwave ablation. The single-frequency antenna is designed by lathing a helical slot on shorted traditional semirigid coaxial cable, which is expected to be operated at the frequency of 2450 MHz, and the dual-frequency antenna is designed with the combination of an annular slot and a helical slot, which can be operated at 915 and 2450 MHz. We use full-wave electromagnetic simulation and transient thermal simulation to analyze the performance of the proposed ablation antennas. Both the proposed antennas are fabricated and used in ex vivo ablation experiments at different frequencies with a power level of 23 W for 2 or 5 min. We observe that the proposed single-frequency antenna with helical slot has more concentrated specific absorption rate (SAR) pattern than those antennas with conventional slots does at 2450 MHz, and the dual-frequency one has the capability to control the roundness of ablation zone from 0.34 to 0.63 under the different combination of frequencies and operation times. The proposed microwave ablation antennas are expected to lead to a potential solution of curing the liver cancers with various characteristics. [ABSTRACT FROM AUTHOR]

A novel method to realize positive phase response of antenna element is proposed conceptually and applied in ±45° dual-polarized dual-beam series-fed metasurface antennas (MSAs). It takes the features of stable beam angle within the relative bandwidth of 10% and dual-polarized dual beams. Benefiting from the positive phase response zone of the antenna, the long-line effect is eliminated and the phase response between the elements is reshaped as expected. Therefore, a stable beam of series-fed array oriented at specific angle is guaranteed accordingly. To achieve the ±45° dual-polarized dual-beam performance, a four-port MSA element with interwoven feeding network is designed and used for further array design. For demonstration, one prototype of MSA array is designed. Considering the band of 4.7–5.2 GHz (10%), the beam angle of the MSAs based on positive phase response control (PPRC) method is oriented to 30°, and the variation versus frequency is less than 6°, which is smaller than the variation of 19° for traditional array. The simulation and measurement results show that stable beam angle is achieved for the dual-polarized series-fed MSA array, indicating a promising candidate for base-station application. [ABSTRACT FROM AUTHOR]

A novel method of dual-band dual-beam control (DDC) is proposed and applied in metasurface antennas (MSAs). Based on this DDC method, the feeding network employed in MSAs can realize independent forward and/or backward radiation of two bands. Combining the metasurface cells and feeding network, the desired bands and the corresponding beam angles of MSAs can be controlled. The symmetrical two-port feeding network consists of uniformly spaced slots in the ground and a bent microstrip line beneath the slots, so that two identical beams are realized. The radiation direction of the two bands can be implemented independently by adjusting the distance of the slots and length of the bent line simultaneously. To verify the design strategies, two prototypes (MSA A and MSA B) with different performance are designed, respectively. As a result, the proposed MSAs can achieve independent beam angels of two bands with low profile and compact design. The above good features make the proposed MSAs potential candidates in base-station antennas of high-capacity wireless communication system. [ABSTRACT FROM AUTHOR]

This article presents an antenna array to produce a circularly polarized (CP) isoflux beam for CubeSat earth coverage applications. Distinguished from conventional arrays formed by identical elements, the proposed one is based on sequential rotation-fed concentric annular aperture elements. By adjusting the excitation phase, magnitude, and polarization of each annular aperture element, the radiation patterns of the array can be shaped to form isoflux beams. Radiation pattern modeling method is developed to obtain array radiation parameters. Besides, to effectively characterize the impedance matching of the radiators of the array with multiple excitations, an overall reflection coefficient is deduced from signal decomposition. A prototype operating at $C$ -band (5 GHz) is designed, fabricated, and measured. It consists of a radiator and a feeding network. The radiator is formed by two annular aperture elements, of which the inner one is realized by a circular patch antenna while the outer one is formed by eight planar inverted-F antennas (PIFAs). The feeding network drives annular aperture elements in the manner of sequential rotation. In this way, a CP isoflux beam array with a low profile ($0.078~{\lambda }_{0})$ , lightweight, and ease-of-integration for CubeSat is realized. The proposed array can also be extended to realize other shaped beams. [ABSTRACT FROM AUTHOR]

A novel frequency-reconfigurable method using vanadium dioxide (VO2) is proposed. VO2 is one kind of phase change material (PCM) which can be electrically switched between the states of insulator and metal. By integrating the VO2 film into a uniplanar compact photonic-bandgap (UC-PBG) structure, a frequency-reconfigurable metasurface (FRMS) structure with frequency ratio of 1.78 is constructed accordingly. Moreover, the active VO2-based FRMS is used as radiation element to design a high-gain millimeter-wave frequency-reconfigurable metasurface antenna (FRMSA), which is excited by a stepped waveguide through two slots of different lengths. In order to electrically activate the VO2 films of the antenna, a simple dc bias co-planarly localized with the FRMS is well designed. Benefiting from the convenient connection of the UC-PBG, only simple connection with two sides of the antenna is required for the dc bias, thus causing little impact on radiation due to far from the radiation region. One prototype is fabricated and measured for demonstration. When the VO2 film is activated to insulating state, the measured results show that the proposed FRMSA can operate in 23.25–24.3 GHz with the maximum gain of ~8.7 dBi, while it can work in 37–39.8 GHz with a peak gain of ~7.6 dBi when driven to metallic state. The ratio of two frequencies is about 1:1.61. Compared with other reported VO2-based antennas, the proposed antenna exhibits a larger frequency ratio and higher gain in millimeter-wave bands. [ABSTRACT FROM AUTHOR]

One kind of interembedded metasurface (MS) structure is proposed and applied to realize miniaturized wideband MS antennas (MSA). Different from conventional MSA, the proposed interembedded MSs are formed by etching slots on the radiating patch with various sawtooth schemes rather than rectangular gaps. Consequently, the resonance frequency of MSA can be decreased due to introducing those interdigital-like capacitances, while obvious miniaturization can be realized accordingly. By optimizing the parameters of the sawtooth radiating slots, a miniaturized antenna using cross-shaped interembedded MS is proposed, achieving an impedance bandwidth of 35.08% and a high gain of about 8.25 dBi with a compact overall size of 0.66 λ0 × 0.66 λ0. Moreover, one further miniaturized antenna using modified cross-shaped interembedded MS is also presented, realizing a larger impedance bandwidth of 41.35% and a high gain of about 6.62 dBi with a smaller aperture of 0.48 λ0 × 0.48 λ0. Compared with conventional MSA, 42% overall size reduction and larger bandwidth can be obtained. The design approach may provide a feasible solution to realize compact MSAs with the unique advantages of large bandwidth, low profile, low cost, and easy fabrication. Due to above good features, the proposed antenna can be a promising candidate for applications in modern wideband wireless communication systems. [ABSTRACT FROM AUTHOR]

A high-transmittance all-dielectric focusing metasurface (MS) with polarization-controllable focus is proposed and experimentally applied in the $Ku$ -band. The MS is based on a single-layer dielectric structure consisting of cross-shaped dielectric elements. Without the use of any metallic unit, the dielectric element shows a high transmission magnitude of up to 0.95 and a nearly full phase-control coverage of about 330°. Moreover, the element is polarization-sensitive, capable of providing different phase gradients for the orthogonally polarized incident waves. As a result, two spatially separated foci can be obtained for the orthogonal polarizations through the focusing MS, and the focal positions can be independently controlled by tuning the lengths of the two orthogonal arms of the cross-shaped dielectric elements. For verification, a prototype of the dielectric focusing MS is fabricated and measured. A separation of more than two wavelengths between the two polarization-dependent foci is obtained. The high levels of polarization sensitivity, design freedom, and transmittance (89%) make the proposed all-dielectric MS a promising material for use in polarization detection, wireless communication, and power transfer systems. [ABSTRACT FROM AUTHOR]

A half-power beamwidth (HPBW) extended patch antenna with harmonic suppression is proposed in this article. The antenna consists of one driven patch and two parasitic patches. The parasitic patches are placed parallel to the two adjacent edges of a driven patch. By introducing four sets of shorting pins near the outer edges of the patches, surface currents on the patches flow through the pins to the edges of the ground plane periodically, making those edges radiate as electrical dipole elements. Huygens’-like radiation with extended HPBW and low back-lobe level is formed by the interaction of dipole and patch-like radiation sources. On the other hand, the resonance at the second harmonic frequency is suppressed, and resonances at higher order modes are shifted away from the third harmonic frequency because of the joint effect of introducing shorting pins and coupling between patches. The mechanism of the antenna is analyzed. A verifying prototype is implemented. In the measurement, the antenna operates at 5.23 GHz. HPBWs of 135°/132° are found, while front-to-back ratios of 13.5/13.3 dB are achieved in the XoZ/YoZ-plane. Resonances at the second and third harmonic frequencies are successfully suppressed. [ABSTRACT FROM AUTHOR]

A novel wideband polarization rotating element based on a metasurface antenna is proposed. To achieve high polarization isolation and low cross polarization, a wideband differential-driven dual-polarized metasurface antenna is designed accordingly. By connecting the two differential ports of the dual-polarized metasurface antenna, a wideband polarization rotating metasurface element (PRMSE) is realized, while a large polarization rotating bandwidth of 27.6% can be achieved. In addition, combining the true-time delay (TTD) microstrip lines, the PRMSE can achieve linear phase response and can be applied to the folded reflectarray design. Based on the PRMSE, a 140-element center-fed folded reflectarray (FRA) is designed and fabricated. The measured radiation patterns of the FRA are stable within the frequency range from 26 to 32 GHz. The measured −10 dB impedance bandwidth is 25.4% from 25.4 to 32.8 GHz. Furthermore, the measured 1 dB gain drop and 3 dB gain drop are 20.7% and 34.5%, respectively. The measured sidelobe levels are below −13 dB and the cross-polarization levels are below −30 dB at the broadside direction within the entire operating band. [ABSTRACT FROM AUTHOR]

New electromagnetic (EM) structures are demonstrated to realize low-radar-cross section (RCS) antennas by making effective use of frequency-selective absorber (FSA). According to the well-known reciprocity principle, the two-layered FSA can be considered as an actual receiving antenna and then transformed to a circularly polarized (CP) antenna. At the radiation state, a truncated patch resonator on the bottom layer is fed by a coaxial probe so as to produce CP wave, and it further excites the slots on the upper layer, resulting in its radiation toward free space, and when the antenna at the stealth state, the detective incident wave can be effectively absorbed outside the radiation band, thus achieving RCS reduction. The design strategies are then explained and verified with the aid of the corresponding equivalent circuit models. Two examples of $2 \times 2$ and $4 \times 4$ antenna arrays were designed to validate the flexibilities of the proposed design method. Finally, the $4 \times 4$ antenna array was fabricated and measured, and reasonable agreement is achieved. [ABSTRACT FROM AUTHOR]

A novel compact differential-fed dual-polarized filtering patch antenna is proposed. Specific filtering response with radiation nulls is firstly realized for the dual-polarized antenna element by symmetrically loading defected ground structures (DGSs), a cross slot, and eight shorting pins without extra circuits. The DGS with pins can generate a lower edge radiation null for a sharp roll-off rate and simultaneously introduce extra in-band resonance for wide passband. Meanwhile, the cross slot with pins can offer an upper edge null and an in-band resonance. Combining with inherent higher order-mode null of the patch itself, the skirt selectivity and stopband suppression at upper band can be significantly improved. Meanwhile, the $\vert $ Sdd $11\vert $ at the upper and lower stopbands is close to 0 dB to achieve high stopband suppressions. As a result, a compact high-gain dual-polarized filtering patch antenna is readily constructed. Thanks for complete symmetry of above structures, the proposed method is very suitable for dual-polarized antennas, where all the performance for both polarizations are identical. For demonstration, a prototype of the proposed antenna is fabricated and measured. Good agreements between the measured and simulated results are observed, indicating good performance with a large bandwidth of about 23% and a peak gain of up to 8.9 dBi within the passband, as well as out-of-band suppression levels of more than 20 dB. Compared with other reported filtering antennas, the proposed filtering patch antenna not only exhibits good wideband dual-polarization radiation but also features high gain in a compact structure for very high aperture efficiency and ultralow cross-polarization level due to the differential feeding and complete symmetry. [ABSTRACT FROM AUTHOR]

A simple, compact filtering patch antenna with wide out-of-band suppression is presented, where the filtering mechanism is first analyzed and implemented based on mode analysis of a conventional patch antenna. According to the mode analysis, undesired higher-order modes can be effectively suppressed by selecting a proper length ratio of two sides of the patch and the feeding position, thus realizing a wide upper stopband. To further enhance the filtering response, another two simple filtering structures loaded on the patch antenna are also proposed. First, a split-ring-shaped slot is etched on the patch to generate a radiation null at the lower-band edge for improving skirt selectivity. Second, a U-shaped strip is etched underneath the patch and connected with the feeding probe, which can introduce another null at the upper band edge. As a result, a high suppression level of 23 dB in lower and upper stopbands can be realized, respectively, for the proposed filtering antenna, while the upper stopband can extend up to $2.3 f_{0}(f_{0}$ is the center frequency of the antenna). Furthermore, wide passband response can also be achieved by the extra in-band resonances existing in the slot and the strip. A filtering antenna prototype is fabricated and measured for demonstration. Good agreements between the simulated and the measured results are observed, indicating a large impedance bandwidth of 22.6%, high antenna efficiency of 95.6%, and an average gain of about 7.4 dBi. Compared with the reported filtering antennas, the proposed filtering antenna can achieve better wideband filtering response but with a simpler configuration. [ABSTRACT FROM AUTHOR]

A novel filtering method based on the metasurface antenna (MSA) with radiation nulls is proposed without loading extra circuits. Due to the specific multiunit structure of MSA, the filtering method is first realized on each radiating metasurface (MS) unit by introducing a multifolded U-shaped slot and a defected ground structure to generate lower edge radiation nulls. Meanwhile, coplanar parasitic patches are loaded around the MS units to provide upper edge nulls and simultaneously introduce extra in-band resonances for wide passband. Thus, a low-profile, wideband, and high-gain filtering antenna is readily constructed. To verify the concept, a prototype with a low profile of only $0.04\lambda _{{0}}$ is designed and fabricated. The simulated and measured results agree well, demonstrating a good performance with large impedance bandwidth of about 20%, high average gain of 8 dBi, and high aperture efficiency of about 90%, together with high out-of-band suppression levels of about 20 dB. In addition, the radiation patterns are symmetric in both the E- and H-planes with cross-polarization suppressions of over 20 dB. Compared with the reported filtering antennas, the proposed filtering MSA can achieve the wideband filtering response in a low profile, as well as high gain with high aperture efficiency. [ABSTRACT FROM AUTHOR]

An ultra-wideband transition from microstrip line to ridge gap waveguide (GWG) is proposed for W-band system integration with antenna array and a transceiver. Substrate integrated waveguide bridge is used in the proposed transition for electromagnet wave propagation between microstrip line and ridge GWG, which can realize impedance matching for a wideband frequency range. Back-to-back transition prototypes are fabricated by the low-temperature co-fired ceramic (LTCC) technique, and the probe measurement results show that the transition can work at W-band. Moreover, the application of the proposed transition in a LTCC slot antenna array with magnetic coupling ridge GWG feeding network operated at 77/79 GHz is studied comprehensively. The antenna performance measurements demonstrate that the proposed transition has a potential massive application in the GWG active antennas. [ABSTRACT FROM AUTHOR]

In this paper, two 24 GHz horizontally polarized $1 \times 8$ patch antenna arrays were developed for automotive radar applications. The proposed antenna arrays offer the advantages of wide fan beams and high gain. The far-field radiation patterns are widened in the E-plane by disturbing the near-field distribution of each driven patch. In Design I, the driven patch is loaded with a parasitic loop, which functions as a director in the E-plane. Due to the directing effect, the E-plane beamwidth can be increased. The experimental verification prepared for Design I showed that a beamwidth of 130° and a gain of 12.2 dBi can be achieved through this method. To further enhance the beamwidth, another array with each patch loaded with parasitic mushroom-like elements was proposed by Design II. The PMLEs are 180° out of phase to their corresponding driven patch. The cancelation effects can be properly managed to slightly sacrifice the gain of the array in return for a wider beamwidth in the E-plane. Design II exhibits a wider beamwidth of 150° and a lower gain of 11.1 dBi. [ABSTRACT FROM AUTHOR]

A novel steerable dual-beam metasurface antenna (MSA) with controllable feeding mechanism is proposed. The proposed MSA consists of $7 \times 10$ square metasurface cells and is fed by a completely symmetrical controllable network, which includes three dumbbell-shaped coupling slots etched on the ground and two-port stepped impedance line beneath the ground. The network can flexibly control the magnitude and phase of the coupling energy from the feeding line to the radiated metasurface cells via the slots, so as to realize two desired symmetrical beams. Owing to good directional radiation of the MSA, the beams of the proposed MSA exhibit better front-to-back ratio, higher gain, and higher channel isolation than those of traditional traveling-wave slot antennas. Moreover, benefiting from the controllable feeding mechanism, impedance matching, sidelobe suppression, and isolation of the ports can be further improved. Consequently, the two achieved beams are, respectively, oriented at ±30°in azimuth plane with 10 dB beamwidth of about 120°, high-peak gains of 12.8 dBi and cross level at two beams junction of about −10 dB; meanwhile, the isolation of the two ports is over 15 dB within the band of interests (5.23 and 5.40 GHz). For demonstration of the design strategy, one $1 \times 2$ dual-beam MSA array with gain of 14.8 dBi and similar beam performance is designed and fabricated. Due to the controllable steerable beams and the simple mechanism without complex beamforming networks, phase shifters or large footprint, the proposed steering dual-beam MSA array can be expected to find potential applications in multibeam base stations. [ABSTRACT FROM AUTHOR]

In this paper, a novel wideband and low-profile discrete dielectric lens (DDL) antenna is presented. The proposed unit cells of DDL with the square-pyramid structure can realize wideband antireflection at an air–dielectric interface. By increasing the phase compensation range, the DDL antenna with very large gain bandwidth but large DDL thickness would be achieved. Furthermore, based on the large gain bandwidth technology, a novel multifolded lens structure is proposed to realize the low-profile design, in which a broadband polarization rotation reflection surface is proposed, while a polarized grid is used appropriately. Finally, the proposed multifolded DDL antenna can achieve a very large gain bandwidth, while the thicknesses of the DDL unit cell and the total antenna can be greatly reduced. For demonstration, the proposed multifolded DDL antenna is fabricated and measured. The fabrication was implemented by using a simple and low-cost 3-D printing technology. The results show that the proposed lens antenna can realize a 1 dB gain drop bandwidth of 43%, thickness of less than 1/3 focal-length-to-diameter ratio, and maximum aperture efficiency of 32%. Good agreement can be observed between the measurement and simulation. [ABSTRACT FROM AUTHOR]

This communication presents novel compact linearly/circularly polarized metasurface antenna arrays based on higher mode substrate integrated waveguide cavities. The linearly polarized antenna is realized by an array of patch cells with similar TM resonant modes as traditional patch antennas, while the circularly polarized one is newly designed based on the proposed polarization-rotation metasurface structure. Moreover, the periodic metasurface antennas are modified with complemental boundaries to further enlarge effective radiation apertures for about 1.5 dB gain enhancement. In addition, a simple TE220 higher mode cavity is employed as a compact and symmetrical feeding network to provide perfectly uniform four-way excitations, resulting in relatively uniform radiation aperture for high gain. The simulation and measured results both indicate that the proposed linearly/circularly polarized metasurface arrays can, respectively, achieve very high directional gains of about 10.75/10.66 dBi with aperture efficiencies of about 90% and low cross-polarization suppressions. In addition, 3 dB axial ratio beamwidths of the circularly polarized array can be up to 68° and 57° at two pitch planes of $\varphi = 0^{\circ }$ and 90°. [ABSTRACT FROM AUTHOR]

A millimeter-wave series–parallel patch antenna array is presented, in which the dual-slot feeding structure is handily implemented using the intrinsic field distribution of TE20 mode in substrate-integrated waveguide (SIW). One 28 GHz patch antenna element fed by the TE20-mode SIW is first designed, achieving a 10 dB impedance bandwidth of 10.2% and a simulated peak gain of 6.48 dBi. Based on the antenna element, a $4 \times 4$ array with a compact series–parallel differential feeding network is developed accordingly. Due to the novel compact SIW-based series–parallel feeding network, the antenna array can achieve superior radiation performances, which is the highlight of this communication. The simulation and measurement results of the proposed antenna array are in good agreement, demonstrating a performance of 8.5% impedance bandwidth, 19.1 dBi peak gain, symmetrical radiation patterns, and low cross-polarization levels (−30 dB in E-plane and −25 dB in H-plane) in the operating frequency band of 26.65–29.14 GHz. [ABSTRACT FROM AUTHOR]

This communication presents a compact 94-GHz 2-D multibeam antenna using the low-temperature co-fired ceramic (LTCC) technology. A good 2-D substrate integrated waveguide (SIW) beam-forming network (BFN) for eight beams is proposed, where four-phase shifters are properly introduced to increase the flexibility of the beams. Benefiting from multilayer LTCC, the BFN is compactly implemented in a completely symmetrical structure by using two multifolded SIW Butler matrixes with 50% reduction of the longitudinal size, and four couplers placed on different layers with interlaced signal routes to avoid overlaps or crossovers. Combined with a $2 \times 4$ SIW slot antenna array, the multibeam antenna can realize eight symmetric scanning beams on 2-D with stable gains for a wide coverage. For demonstration, the two single-port antennas with different pitch-angle beams are fabricated and measured, and good agreements with the expectations are observed. The differences of the beam orientations are less than 5°, while the measured peak gains of the beams are about 8.5 dBi. [ABSTRACT FROM PUBLISHER]

In this paper, a novel ultralow-profile transmitarray (TA) is proposed by using multifolded ray tracing principle. The proposed TA unit cell would reflect the incident wave of x-polarization as a ground and transmit the incident wave of y-polarization with arbitrary phase shift in the operating frequency band. A broadband polarization rotation reflection surface based on artificial magnetic conductor with small phase difference in wide range of incidence angle is applied to transform the polarization of incident wave. Two kinds of TA antennas at 28 GHz are studied, where the distances between the source and the TA are, respectively, reduced to 1/3 and 1/4 of the focal length (named as TA antennas I and II), which are much less than that of the conventional TA antennas. The simulated results show that the proposed TA antennas can achieve −1 dB gain drop bandwidth of 5% and cross-polarization level of less than −30 dB, and the maximum aperture efficiencies can achieve 46% and 40%, respectively. For demonstration, the TA antenna I is fabricated and measured. Good agreement can be observed between the measurement and simulation. [ABSTRACT FROM PUBLISHER]

This communication presents dual-orthogonally polarized patch antennas using nonperiodic rectangle artificial magnetic conductor (RAMC) structure, which take the features of high efficiency and high isolation. The artificial ground composed of several nonperiodic RAMC cells is first theoretically analyzed by projecting it onto a cylindrical surface. It is found that the nonperiodic plane can be similarly equivalent to a cylindrical metal reflector for strongly focusing electromagnetic waves to realize an extremely directive antenna with high aperture efficiency. Based on the above analysis, a novel spherically projected nonperiodic RAMC plane is proposed, and two differentially fed dual-polarized patch antennas using the newly proposed plane are well designed accordingly. Both simulated and measured results demonstrate dual-polarized radiations with very high aperture efficiencies of about 90% and low cross-polarization levels of less than −20 dB at each state, as well as high polarization-isolations of over 30 dB. Compared with 3-D physical reflectors, the proposed artificial grounds not only have similar strong reflections for high-efficiency antennas, but also exhibit a low-profile planar structure, which would be more easily integrated with antennas for applications in wireless communication systems. [ABSTRACT FROM PUBLISHER]

This paper presents a 60-GHz $4 \times 4$ differential -fed patch antenna array using low-temperature cofired ceramic (LTCC) process. Wideband patch with L-shaped feeding scheme is adopted as antenna element, while differential substrate integrated waveguide feeding network with low insertion loss is applied for the integration of antenna array. The differential-fed structure improves the symmetry of radiation patterns and reduces the cross-polarization level significantly. To further suppress the surface wave and improve the gain of the antenna array, one kind of soft surface structure is proposed. The equivalent circuit model of the soft surface is developed for calculating its dispersion diagram and analyzing stopband characteristics. The simulated results indicate that the antenna gain enhancement can be up to 2 dB because of the proposed soft surface. For demonstration, one prototype using LTCC process is fabricated and measured. The measured 10-dB impedance bandwidth of the antenna array is 11.7%. The measured antenna peak gain of 18.62 dBi at 61.5 GHz and symmetrical radiation patterns with a low cross polarization of −25 dB across the whole operating frequency are achieved. [ABSTRACT FROM AUTHOR]

A straight parasitic strip, closely and horizontally placed above a perfect electrical conductor ground plane, is used to greatly enhance the radiation of a horizontally positioned center-fed half-wave dipole through the phase compensation from the strip. The method is discussed and validated by both full-wave electromagnetic simulation and experiments. Using the parasitic strip, a horizontal dipole with a height of 1/20 wavelength above the ground exhibits an input resistance of 62 $\Omega $ and gain of 7.8 dBi while the dipole without the strip and a dipole with a height of a quarter wavelength above the ground realize the resistance of 5/72 \Omega $ and the gain of 4.3/7.8 dBi across a \vert S_{11}\vert \leq -10 -dB bandwidth of 0.6%, respectively. [ABSTRACT FROM PUBLISHER]

A novel polarization-reconfigurable mechanism based on a polarization-rotation artificial magnetic conductor (PRAMC) structure is proposed. A new polarization-reconfigurable antenna is designed by combining a PRAMC-based multipolarized dipole antenna with a RFIC switch-based network, in which three polarization states of right-handed, left-handed circular polarization (RHCP, LHCP) and +45^\circ linear polarization (LP) can be realized by controlling the dc bias of the switches accordingly. The multipolarization antenna is well designed for offering three polarization states. A large 3-dB axial ratio (AR) bandwidth of 15.5%, a wide 3-dB AR beamwidth for CP states and a large cross-polarization isolation of more than 50 dB for LP state together with a broad impedance bandwidth of 20.5% are obtained. A switch network is used to generate three feeding modes, and the performance of the RF-integrated circuit (RFIC) switches is experimentally verified. A prototype of the proposed polarization-reconfigurable antenna is fabricated and tested. Good agreements between the measured and simulated results are observed, which indicates good performances of the proposed antenna. [ABSTRACT FROM PUBLISHER]

A novel polarization rotation technique based on an artificial magnetic conductor (AMC) structure is proposed. A new polarization rotating reflective surface (PRRS) is designed using a newly proposed AMC as the unit cell. The height of the so-constructed PRRS is only 0.04 \lambda0. Our theoretical analysis shows that the polarization rotation property of the new PRRS is due to an impedance imbalance which can be analyzed using an equivalent circuit model. In addition, two polarization rotation bands and a large polarization rotation bandwidth of 29.1% can be achieved by using the new PRRS. Moreover, the new PRRS is applied for the first time to design a low-profile dipole antenna for the generation of circular polarization radiation. Three polarization states are readily achieved. Both simulation and measurement results demonstrate good right-handed circular polarization with a broad axial ratio bandwidth and a large axial ratio beamwidth in both the x o z and y o z planes. [ABSTRACT FROM PUBLISHER]

This paper presents a wideband 60-GHz antenna array with a dual-resonant slot-patch structure. A multilayered low-temperature co-fired ceramic substrate was used for antenna fabrication. A half-wavelength resonant slot was designed with a backed substrate-integrated waveguide (SIW) cavity to enhance the front radiation. The inverted microstrip center-fed structure was designed for easy signal excitation and superior impedance matching. A parasitic patch was also applied to enhance for bandwidth and gain enhancement. The effects of the SIW cavity-backed slot antenna with and without parasitic patches were empirically examined. The simulated results show that adding parasitic patches increased the resonance of the poles and improved antenna gain by 1.85 dB and bandwidth by 9%. A 2\,\times\,2 dual-resonant slot-patch antenna array was designed to further enhance the gain and bandwidth. The equipment setup for on-chip measurements of gain and radiation patterns was established. The measured S11 showed a wide bandwidth of 23%. The measured gain for the four-element antenna array was 9 dBi with slight fluctuations over the 57–64-GHz frequency range. [ABSTRACT FROM AUTHOR]