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Photonic crystal based sensing technology is the latest technology for various bio-sensing applications. A 2D photonic crystal (PhC) hexagonal shaped ring resonator based biosensor is simulated and designed for the detection of bio-molecules such as glucose, bilirubin, urea and albumin in blood and urine over different concentration ranges. The biosensor structure is created using line and point defect in order to form a ring waveguide and a bus waveguide above the ring structure. If the concentration of bilirubin, glucose, albumin and urea in blood and urine is varied, the refractive index is varied, which in turn changes the output response of the sensor [1] . This principle can be used to identify the aberrant value range of the glucose, bilirubin, albumin and urea in blood and urine. Finite Difference Time Domain (FDTD) tool called Lumericals is used for the modeling and simulation of the biosensor. The resonant wavelength shift, sensitivity, Full-Width Half-Maximum (FWHM) and quality factor (Q-factor) for different concentrations of glucose, bilirubin, albumin and urea are observed and tabulated. The Q-factor obtained for the normal range of glucose, bilirubin, albumin and urea concentration in blood and urine is 310, sensitivity is 400 nm and the resonant wavelength is around 1518.8 nm with the efficiency of 86%.

This paper presents a unique design of a dual-polarized wideband passive beam-switching antenna at millimeter-wave bands for MIMO pattern diversity applications, which exhibits low correlation between the ports and a broad tilt bandwidth. A magneto-electric (ME) dipole fed by a printed ridge gap waveguide (PRGW) as a quasi TE source is considered as the elementary antenna in the Ka-band. To achieve beam deflection in each quadrant, a 4-port MIMO prototype consisting of four ME-dipoles, positioned perpendicular to each other, is integrated with a meta-lens that consists of three layers of 12×12 dual-polarized SRRs offset from the center of each antenna. The beamforming structure is able to generate four fixed beams, one in each quadrant at an elevation angle of ~40° with respect to the broadside direction by exciting each port sequentially while the other ports are terminated. Moreover, the proposed orthogonal structure contributes to low correlation between the four ports, while achieving dual-polarization, which highlights the suitability of the antenna for 5G mm-wave applications. The measured results from a fabricated prototype demonstrate a -10 dB impedance bandwidth of 40% over 24-36 GHz, tilting bandwidth of 32.2%, and a peak gain of 13.4 dBi at 29 GHz, while an isolation better than 30 dB is achieved over the whole frequency band. Moreover, a measured radiation efficiency in excess of 85% is obtained, due to the use of the low-loss PRGW feedlines. This technique allows us to overcome critical limitations of existing beam-switching methods, such as Butler matrices, in particular for applications requiring a wide bandwidth. The diversity performance of the MIMO antennas has also been evaluated through the ECC, DG and TARC parameters, and good results are obtained.

EM enhancement is typically a lensing-type of effect by which a wide input beam couples to spatially localized resonant modes as for example Mie plasmons, void plasmons or Mie modes at high refractive index particles. Accordingly, EM enhancement is inherently a subwavelength phenomenon. Here, we explore a different paradigm for EM enhancement that is based on EM energy being collected over large time intervals by means of an ultra-slow-light waveguide. With ab-initio simulations, we study the dynamic evolution of such EM enhancement. After more than 7000 wave periods we observe that an intensity enhancement of more than 50 can cover an area of more than 15 $\lambda_{free^{2}}$ with $\lambda_{free}$ being the free-space wavelength.

In this communication, we propose a novel feeding scheme to design a wideband filtering patch antenna. The antenna is composed of two substrates: the feeding- and the radiating ones. Two circular patches are etched on the top surface of the radiating substrate as the radiators and a hybrid substrate integrated waveguide (SIW) and spoof localized surface plasmon (SLSP) structure is employed as the feeding scheme. Due to the abundant resonant modes and filtering feature of the hybrid SIW-SLSP structure, the antenna can radiate under the triple-mode resonance with high filtering performance. Moreover, the proposed filtering antenna has an independently adjustable capability of both low-band and high-band radiation nulls. The presented antenna is designed, fabricated and measured. Measured results reveal that the operating bandwidth reaches up to 11.3%, ranging from 7.44 GHz to 8.33 GHz. The peak gain of 10 dBi is obtained in passband with 10 dB gain suppression out of the band. This approach provides a simple way to design wideband filtering patch antenna, which can be easily integrated with planar circuit.

A differential triple-band dual-polarized cavity backed substrate integrated waveguide (SIW) slot antenna is presented in this letter. The hybrid TE130, TE320, and TE140 modes of the square SIW cavity are excited by differential feed for a triple-band realization. The proposed antenna exhibits dual-polarized radiations at 9.06 GHz, 11.86 GHz and 14.23 GHz. An isolation better than 40 dB in all the three frequency bands between the differential ports is obtained. The proposed structure exhibits the differential gain of 5.4 dBi, 10.7 dBi and 9.5 dBi at 9.06 GHz, 11.86 GHz and 14.23 GHz, respectively. To validate the design approach, the proposed antenna is fabricated and its characteristics are measured.

A low-profile single-layer end-fire circularly-polarized (CP) antipodal linearly tapered slot antenna (ALTSA) is proposed and investigated through simulations and experiments. This antenna is a composite structure consisting of a novel width-tapered slotted substrate integrated waveguide (SIW) and an ALTSA fed by the SIW. The former also serves as a radiator to produce vertically polarized radiation, which is crucial to achieve a fully planar end-fire CP antenna when a thin substrate is deployed. Compared to the previous ALTSA fed by the SIW, this proposed antenna utilizes slots on the spare broad walls of the SIW to form an extra slotted width-tapered SIW radiator, which presents an extension of the conventional width-uniform slotted SIW. Moreover, there are no space harmonics in the slotted width-tapered SIW; it is a slow wave that produces the vertically polarized radiation. The proposed antenna is demonstrated at 28 GHz, which is one of the millimeter-wave bands specified for 5G. An experimental prototype of the antenna has an impedance bandwidth of about 9 GHz from 23.8 GHz to 32.8 GHz and an axial ratio bandwidth of about 1.4 GHz from 27.35 GHz to 28.75 GHz, which coincide well with simulated results.

In this communication, a dual-polarized filtering magneto-electric dipole (FMED) antenna and arrays are proposed for 5G n258 (24.25-27.5 GHz) operations. The FMED antenna was devised to incorporate filtering mechanisms using a built-in substrate integrated waveguide (SIW) based filter plus slot-and-notch etching on the dipole element. As such, lower and upper radiation cutoffs and nulls were produced and tuned, independently. To overcome the problem of “high selectivity” of a filtering antenna that has not been correctly quantified and thus has no comparison, a new skirt measure metric named as radiation suppression index is initiated here. Design steps of the FMED element and novel feeding techniques are elaborated, where the SIW-based series-parallel slot-coupled feeders and the slot-coupled differential power divider were conceived for large-size array, to combat with the insertion losses. A prototype of the 4×4 FMED array was implemented and tested for experimental verification. A high gain of 16.8±1.4 dBi with a 3-dB gain bandwidth of 24-27.7 GHz and a radiation efficiency of 78% were accomplished.

A simple decoupling method between two closely-located dual-polarized slot antennas is proposed in this communication. Based on substrate integrated waveguide (SIW), the dual-polarized antenna is realized using cross-shaped slot and U-shaped feed line, and two identical elements are closely located in edge-to-edge space of only 0.031λ0 to form the multiple-input-multiple-output (MIMO) array, where λ0 is the free-space wavelength at the center operating frequency. Wideband characteristics, high dual-polarized isolation, and low envelope correlation coefficient (ECC) are realized by introducing a superstrate with gradient relative permittivity (GRP) above the array. The GRP is obtained using drilling hole arrays on low-cost FR-4 materials. To validate the proposed design, the antenna array is fabricated and measured. The measured result shows that 13 dB and 16 dB isolation enhancements are provided for two orthogonally polarized fields, simultaneously. Moreover, the measured operating bandwidth is from 8 GHz to 10.35 GHz (about 25.6%, the isolation is more than 20 dB), and the ECC between two antennas is less than -52 dB for E1-pol and -62.4 dB for E2-pol over entire operating band. The proposed method has the potential to be used in MIMO wireless systems.

In this paper, a compact and low-profile beam steering circularly polarized folded reflectarray antenna (CPFRA) with low scan loss for wide-angle coverage is proposed and designed. In order to obtain lower scan loss over a wider beam coverage range (BCR), a multibeam optimization method considering the illumination weighting factor is introduced to obtain minimum phase errors for the designed beam direction. To improve antenna compactness and alleviate the mutual couplings among multiple feeding sources, small-size substrate integrated waveguide (SIW) cavity-backed slot antennas are employed as the feeding sources, which are integrated with the single-layer reflector board. An incident angle insensitive circular polarizer is designed and integrated over the antenna aperture to achieve circularly polarized (CP) radiation over a wide BCR. At last, a 15-beam CPFRA working at Ka-band, with size 140 mm × 140 mm is designed, manufactured, and measured to validate the proposed design method. Measurement results show that the designed CPFRA can achieve a rather flat gain, with only a 2.1 dB scan loss, across the wide 3-dB BCR of ±29°. The good CP beams are formed over the entire coverage range without any blind zone. With the advantages of wide-angle coverage, low scan loss, and high integration, the proposed beam steering antenna is promising in applications such as 5G communication, radar imaging, and target recognition.

We report an ultracompact on-fiber multiparameter sensor that employs multiple guided-wave surface plasmon resonances (GWSPRs) and machine learning based signal processing. The sensor structure entails a gold plasmonic crystal cavity covered with a planar dielectric waveguide on the end-face of a single-mode fiber. Incident light on the gold gratings of the plasmonic crystal cavity excites surface plasmon resonances, which are coupled into the waveguide and induce multiple, high-Q GWSPRs. Due to the difference in the field distributions of these resonance modes, the resonance dips in the sensor reflection spectrum have distinctive responses to external stimuli, which enables simultaneous measurement of multiple parameters. To enhance the sensing accuracy, a neural network model is used to demodulate the sensor responses. A proof-of-concept sensor using a UV-curable polymer as a waveguide material is demonstrated for simultaneous measurement of temperature and salinity of salt solutions. Although we only demonstrate the measurement of two parameters, the proposed sensor has the capability to measure more parameters if a multilayer waveguide structure made of different functional materials is used. The proposed sensor can benefit multifunctional analysis in a broad range of biological, chemical, and environmental monitoring applications.

The potential of higher band millimeter waves for characterization of different types of breast tissues based on the dielectric contrast between normal and malignant tissues has been reported. Lowcost phantom samples of normal and malignant tissues have been prepared using naturally occuring components, i.e., agar, water, olive oil and pectin. Waveguide probe based calibration technique was used to extract the complex permittivities of the twocomponent (wateragar) and threecomponent (wateroilagar) phantoms. The twocomponent phantoms were used to study the change in the dielectric properties of phantom with change in agar concentration. Water, agar and varying proportions of oil were used to develop threecomponent phantom mixtures to mimic the dielectric properties of fat, fibrous and malignant breast tissues. Finally, the reflection and transmission properties of tissue mimicking phantoms were tested using the waveguide probe calibration based measurement setup. The difference in the S parameters between the three types of phantoms demonstrate the potential utility of D band based data acquisition setups for tumor margin assessment applications.

In this paper, by combining substrate integrated waveguide (SIW) and microstrip technologies, a novel dual-band filter is proposed to achieve a quasi-elliptic response for both passbands. The dual-mode characteristics of the SIW cavities, namely TE101 and TE201 modes, are used to create two passbands. Different with the conventional inductive windows, two pairs of uniform impedance resonators (UIRs) with electric mutual coupling, which are etched between the two rectangular SIW cavities, are used to couple the TE101 and TE201 modes, respectively. Good merits are achieved in this way, including: 1) Independent coupling paths are created for TE101 and TE201 modes, which would reduce the complexity of numerical optimization; 2) Since the electric couplings are generated between each pair of the UIRs, it would be easy to realize a cross coupling by only constructing inductive windows between the SIW cavities. A filter prototype with central frequencies operated at 8 GHz and 10 GHz is then designed and fabricated for validation, which shows a compact size and high selectivity with controllable transmission zeros.

This communication presents a circularly polarized (CP) antenna array with ultra-broadband characteristics and a high gain for millimeter-wave applications. The CP is achieved by arranging eight linearly polarized (LP) tapered slot antenna elements in a circular arrangement based on sequential rotation techniques. The hybrid structure takes advantage of microstrip line (MSL) compactness in the feeding network and the capabilities of the substrate integrated waveguide (SIW) in antenna element design. A new T-junction MSL-to-SIW transition with a wide range of coupling ratios is used to serve as a wide power divider in the compact sequential rotation-feeding network. A detailed parametric study is carried out to demonstrate the effects of the coupling mechanism between the two transmission lines and to find the optimal configuration for the elements of the proposed antenna array. A trade-off is made between antenna coupling, phase deviation, and overall size to achieve a compact structure with robust performances. An 8 element antenna array prototype is fabricated through the PCB process with a size of 57 × 48 × 96 mm3. Measured results show a 3 dB axial ratio bandwidth of about 49% over the entire 22.8 – 37.7 GHz range and a maximum gain of 18 dBi.

This paper proposes the first on-chip bandpass filter (BPF) based on substrate integrated waveguide (SIW) for W-band applications. Slot-loaded, folded ridge and quarter mode technology is used to reduce the cavity size. The coupling characteristic of two folded ridged quarter mode substrate integrated waveguide (QMSIW) cavities implemented in CMOS technology is investigated. A simplified equivalent lumped-element circuit model of the proposed wide-band BPF approach is provided and applied to study the coupling characteristic of slot-loaded folded ridged QMSIW cavity. Then, a novel coupling method using a defected ground structure is proposed to realize a proper coupling intensity for BPF design. Finally, the proposed BPF design is implemented in a commercial complementary metal-oxide-semiconductor (CMOS) technology, fabricated, and measured. The active size of the proposed cavity resonator is only 405 μm × 185 μm (0.22λg×0.1λg), and the measured insertion loss (|S21|) is 3.15 dB with a central frequency of 85.5 GHz.

Continuous-flow microwave heating is widely used in chemical engineering and other fields. However, during microwave heating, the load's electrical permittivity change will affect microwave heating efficiency. In this article, a WR430 asymmetric propagation waveguide is proposed based on gradient-index metasurfaces (GIMs), which can achieve high-efficiency continuous-flow heating with a large range of permittivity. First, asymmetric microwave propagation is realized in a WR430 3-D waveguide model, and the influence of metasurfaces index, thickness, and discrete element size is analyzed. Second, the asymmetric propagation waveguide is realized by fluted medium based on the permittivity equivalent method. The results show that the microwave inside the waveguide can only propagate along one direction at 2.4-2.6 GHz. Finally, the proposed waveguide is applied to a continuous-flow heating system. Compared with the single-mode cavity, multimode cavity, and waveguide water load, the proposed method can improve heating robustness and efficiency with different loads. Experiments show that the microwave absorption efficiency is stable and greater than 90% in the proposed system when the permittivity of the load changes drastically. The proposed system has a simple structure and strong applicability, which can replace the three-stub tuner and get rid of the circulator and water load for continuous-flow heating.

An ultra-wide-angle frequency beam scanning leaky wave antenna (LWA) with high scanning rate based on spoof surface plasmon polaritons (SSPPs) waveguide is proposed in this communication. A row of elliptical patches is placed periodically near the SSPPs waveguide, which can shift the fundamental mode of SSPPs waveguide to the fast-wave region and radiate electromagnetic (EM) waves. The simulated results show that the proposed LWA achieves an ultra-wide scanning angle range of 172° over a narrow operation bandwidth of 9.8-12.28GHz, which implies a high scanning rate. The simulated average gain of the proposed LWA is 10.13dBi and its average total efficiency is 75.35%. The proposed LWA is fabricated and measured. The measured scanning angle range is 167° in the frequency band of 9.9-12.25GHz, and the measured average gain is 9.73dBi. Good agreements between the simulated and measured results are obtained, validating the proposed design.

A differentially fed duplex filtering dielectric resonator antenna (DFDRA) is proposed. This DFDRA combines the functions of the duplexer, the filter and the antenna into one highly integrated multifunctional module. A dual-mode substrate integrated waveguide (SIW) cavity working as the common feeding structure operates at two orthogonal modes at the lower and higher channel and is differentially fed by two pairs of differential input ports. The DRA working as the common radiation element operates at two orthogonal modes at two channels respectively and is excited by two cross slots etched on the top of the SIW cavity. High-isolation between the two channels is realized due to the two pairs of orthogonal operating modes of the DRA and SIW cavity. Measured results show that the balanced DFDRA can operate with differential mode 10dB impedance bandwidth of 2.7% (5.07-5.21 GHz) and 2.6% (5.72-5.87 GHz), the peak realized gains of 4.6-4.9 dBi and 4.8-5.1 dBi for two channels respectively. The isolation between the lower and higher channels is greater than 75dB. Good common mode suppression is realized.

In this article a compact planar fed substrate integrated waveguide (SIW) based self-multiplexing (SM) antenna for hexa-band operation is proposed for the first time. Six different patches with planar 50Ω feed lines are designed and attached to the top side of the rectangular SIW cavity. The antenna operates at six different frequencies (5.33 GHz, 5.76 GHz, 6.31 GHz, 6.86 GHz, 7.34 GHz, and 7.8 GHz) simultaneously. The antenna attains 4.5 dBi, 4.94 dBi, 4.9 dBi, 5.12 dBi, 6.12 dBi, and 6.6 dBi peak gain at respective resonant frequencies. Port relocation, stepped patches, and additional vias are exploited to maintain isolation (> 23 dB) between any two ports. The front-to-back ratios (FTBRs) are between 10 dB to 20 dB and Co-Pol to Cross-pol ratios are between 10 dB to 29 dB. The design supports single-variable independent frequency tuning for all six patches and eligible for wide range of applications. The proposed design is fabricated and results are validated through measurement. The antenna is suitable for planar microwave devices.

In this paper, a low sidelobe-level (SLL) circularly-polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal LP structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio (AR). In addition, because of the short waveguide wavelength of the SIIG, this feed line can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBi and the SLL is 19.1 dB.

A wide-angle scanning circularly polarized (CP) antenna array based on a novel polarizer is proposed. The working mechanism is that the linear polarization (LP) substrate integrated waveguide (SIW) slot antenna array can be converted into CP antenna array through the proposed hybrid polarizer. Specifically, the proposed hybrid polarizer consists of a dipole array polarizer with 6 × 6 elements and a metasurface polarizer with 19 × 19 elements. The metasurface polarizer can realize the LP-CP conversion of the beams with a scanning angle range (-55°, 55°) and the dipole array polarizer can realize LP-CP conversion of beams with scanning angle ranges (-60°, -40°) and (40°, 60°) through reasonable design. Based on the complementary characteristics of the metasurface polarizer and dipole array polarizer for different scanning angles, the proposed hybrid polarizer gives the designed CP antenna array have good AR characteristics in the scanning angle range (-70°, 70°). Then, a 6 × 6 Butler matrix is designed to feed the proposed wide-angle scanning CP antenna array. Finally, a prototype of the wide-angle scanning CP antenna array is fabricated. The test results show that the AR of the proposed wide-angle scanning CP antenna array is less than 3 dB, the maximum scanning angle is -60° and the maximum gain is more than 16.5 dBi in the operating frequency range 27.9-28.4 GHz.

A wideband millimeter-wave magneto-electric dipole-like array with low-profile is presented in this letter. The unit is fed by twin lines located on the same dielectric plate as the shorted patches, making the antenna have a low profile (0.13 M). Furthermore, by using the butterfly patch and staggered arrangement, the impedance bandwidth of the designed unit can cover 23.946.75 GHz (64.7%), and the broadside gain is 5.51.1 dBi. Then, a power divider based on the printed ridge gap waveguide (PRGW) is used to excite the 14 array. Finally, the designed array is manufactured and tested. The measured results are in good agreement with the simulated ones, showing that the working bandwidth of the array combined with the feed network can cover 24.540 GHz (48%), while the broadside gain is 7.7312.65 dBi.

A millimeter-wave high-gain dual-polarized antenna array with an enhanced bandwidth is presented. An innovative air-filled differential feeding cavity loaded with a short-ended cross-shaped waveguide is investigated to serve as the feed network and the mode splitter simultaneously of the 2 × 2 dual-polarized sub-arrays. Wideband characteristics and a compact planar size that are desirable for the wideband array design are achieved. Moreover, a wideband dual-polarized waveguide-fed magneto-electric (ME) dipole antenna with a lightweight self-support geometry and wideband H-plane parallel feed networks with modified dual-layered configurations are proposed, which are convenient to connect with the differential feeding cavity directly. With the use of a commercial metallic three-dimensional (3D) printing facility, the proposed radiating elements, feeding cavities, and feed networks can be combined successfully in a whole piece with a lightweight geometry. The printed 8 × 8 array prototype operating in the Ka-band confirms a wide bandwidth of about 30%, a gain of up to 28.5 dBi, and stable unidirectional radiation patterns for the two polarizations. Benefitted from the advantages of the promising wideband dual-polarized radiations and convenience of fabrication, the proposed antenna array would be attractive for millimeter-wave polarization diversity applications.

This work introduces a new design of Fabry-Perot cavity (FPC) antenna with great filtering response based on a novel filtering feeding scheme. Unlike the traditional method of adopting frequency selective surfaces to achieve filtering characteristic, the proposed strategy focuses on the feeding source. We can obtain an excellent filtering response by utilizing a performance-improved filtering antenna to act as the source of the FPC antenna. To validate the concept, we first propose a new substrate-integrated-waveguide-fed (SIW-fed) filtering antenna element working in 60-GHz band. By using the slotted radiating patches, two radiation nulls are firstly generated respectively on each side of the operating band. We then design a stepped-impedance waveguide feeding structure and a pair of U-shaped hairpin lines to introduce another two radiation nulls to improve the suppression level in the stopband. The proposed filtering antenna prototype shows a -10-dB impedance bandwidth of 57.5-66.6 GHz as well as a maximum gain of 7.9 dBi. Based on such feeding source, an FPC antenna is developed and validated. It achieves a 3-dB gain bandwidth from 58-65.6 GHz, peak gain of 15.8 dBi, and suppression level of over 24 dB. The proposed antennas are good candidates in 60-GHz sensing or communications systems.

A novel compact fan-shaped folded waveguide resonator (FSFWGR) is proposed in this article. The resonator can reduce the size by 87.5% compared with the waveguide cavity while retaining a high unloaded quality ( $Q_{{u}})$ value (>1500). Due to these advantages, a high-quality (-Q) fourth-order bandpass filter centered at 6.0 GHz with a 6.67% bandwidth is designed first. Novel slots cross-coupling is presented to produce a pair of transmission zeros (TZs) while avoiding support structures that traditional metal probes often used. Then compact deformed folded antenna is designed to integrate with the filter. Compared with published works where the last resonator of the reference filter often needs to be detuned, all parameters here do not need to change by introducing a metal probe between the feeding point of the filter and antenna. Therefore, the integrating process is more straightforward. The integrated filter/antenna achieves the same filtering function as the reference filter and a high gain of 6.7 dBi. For experimental demonstration, metal 3-D printing technology was used to fabricate models with only two pieces that significantly reduced the assembly loss. The final measured results agreed well with simulated ones.

In this communication, a novel dual-polarized (DP) epsilon-near-zero (ENZ) antenna is proposed with its operating frequencies independent to lengths for both polarizations. To obtain a DP implementation of ENZ antenna, an anti-phase epsilon-near-zero (AP-ENZ) mode is used based on a slot-fed substrate-integrated waveguide (SIW) antenna at its cutoff frequency, in which the electric field presents a sign function-like distribution, presenting a fixed operating frequency independent on length. The proposed DP length-irrelevant antenna design is composed by a cross-shaped SIW operating on two orthogonal AP-ENZ modes, which are excited by a cavity-backed cross-shaped slot with good port isolation. The SIW lengths for both polarizations can be tuned independently without disturbing the operation frequency with controllable radiation patterns. To be specific, we study two cases of different lengths where sidelobe elimination and high gain radiation are realized, respectively. To verify this design, two antenna prototypes Ant. 1 and Ant. 2 are fabricated and tested, exhibiting agreements between simulation and experiment. The proposed Ant. 1 presents no sidelobes at 2.42 GHz while Ant. 2 shows a high gain of 10.56 dBi from 2.45-2.55 GHz. The proposed design method enables antennas with a variety of radiation patterns to be designed at a fixed frequency and both symmetric and asymmetric patterns for DP antennas. It also inspires the design of a flexible antenna with unchanged operating frequency when folded in both dimensions.

A millimeter-wave dual-polarized beam-scanning SIW phased array is proposed for the 5G communications. The principle of the proposed antenna radiating element is first analyzed with the characteristic mode analysis (CMA) to obtain a wide operating bandwidth. Then, the horizontally and vertically polarized radiations are excited by a differentially-fed substrate integrated waveguide (SIW) cavity and a linearly tapered microstrip line through the coupled slots, respectively. To further validate the proposed design, a 1x4 phased array is fabricated and tested. The experiment results show that the 11.0% overlapped dual-polarization bandwidth is from 25.8 to 28.8 GHz with the return loss larger than 10 dB, and the isolation between the dual-polarization is higher than 31.5 dB. The measured far field patterns demonstrate that the beam-scanning ranges can cover 44 and 41 at 28 GHz for the horizontal and vertical polarization, respectively.

We design and fabricate the suspended silicon microring with racetrack and spiral structure to exploit the resonantly enhanced stimulated Brillouin scattering (SBS). The designed photonic-phononic waveguide can provide the independent control on the optical and acoustic modes by introducing the silicon ridge waveguide into the phononic crystal slab as a line defect. We demonstrate efficient forward SBS in the two kinds of microrings and extract the characteristic Brillouin parameters through the heterodyne four-wave mixing measurement. The stronger inhomogeneous broadening effect in the spiral microring due to the structural variations is also observed. In addition, our microrings show the single mode transmission spectrum and high quality factor, which is beneficial to the enhanced intramodal forward SBS. This design can readily extend to other silicon-based platforms and paves the way toward on-chip photonic-phononic signal processing and Brillouin amplifier technologies.

This paper presents a gain enhanced wide azimuth beam automotive antenna using half-mode substrate integrated waveguide (HMSIW) cavity for automotive applications. The antenna is separated into two HMSIW cavities by electrical via walls. The two HMSIW cavities are excited through differential feeding, including a 180 delay line in the center of the antenna. The antenna was operated in TM11 mode and investigated using aperture theory based on the cavity model. The antenna size is small enough to mount in the rear-view mirror, which has a long rectangular shape. For comparison, the proposed antenna and a conventional 1 2 microstrip square patch antenna array were fabricated to the same dimensions. Then, these antennas were tested to provide validation. The tested results were consistent with the simulation results. The tested results show that the antenna, with the overall dimensions of 70 mm 35 mm 1.52 mm (1.380 0.690 0.030), operates at 5.9 GHz. The gain of the antenna is 9.49 dB, and the azimuth beam width is 74.0. The proposed antenna has a wider azimuth beam width (74.0) than a conventional 1 2 square patch array antenna (42.0) with similar gain and size.

A wideband circularly polarized (CP) endfire planar magneto-electric dipole (ME-dipole) antenna based on substrate integrated waveguide (SIW) is proposed for millimeter-wave (mm-wave) applications. The antenna mainly consists of an open-ended rectangular SIW radiating like a magnetic dipole, a parallel electric dipole, and a double-sided parallel-strip line (DSPSL) which connects the two dipoles and provides 90 o phase difference between them to generate CP radiation. To increase the axial ratio (AR) bandwidth, a pair of triangular slots are etched at the end of the upper and lower broad walls of the SIW, and moreover, a specific bowtie-shaped electric dipole is used instead of the traditional linear one. It has been shown that both the slots and the bowtie-shaped electric dipole can regulate or tune the magnitude of the radiation field of the electric dipole, making it tend to balance with radiation field generated by the magnetic dipole and hence leading to a good CP performance. The antenna has a single-layer planar structure, and it shows a -10-dB impedance bandwidth of over 50%, a 3-dB AR bandwidth of 36.6%, and a peak gain of 9.3 dBic.

A dual wideband antenna with a large beam steering angle through endfire radiation and frequency scanning radiation in each band is proposed for the first time. The antenna utilizes a double-layer spoof surface plasmon polaritons (SSPPs) structure, which exhibits stronger field confinement and lower cut-off frequency than the single-layer SSPPs structure. The modulated double-layer SSPPs structure can excite the space harmonic distributing in the fast-wave region and retains transmission in the slow-wave region. By combing the modulated double-layer SSPPs waveguide and the Vivaldi radiator, both the slow-wave radiation (endfire mode) and the fast-wave radiation (frequency scanning mode) can be aroused in the two operating bands. An example antenna is designed and fabricated. In the slow-wave range from 3 GHz to 9 GHz, the antenna works in the endfire mode with the beam direction of 90° and the realized gain varying from 3.55-8.24 dBi. Within the fast-wave band from 13 GHz to 34 GHz, the antenna operates in the frequency scanning mode, accomplishing beam scanning from -90° to ±42.5° with the realized gain of 9.45-15.67 dBi. Thus, the proposed dual-band antenna can achieve two operating bands and two radiation modes, which offers a 1800 beam changing angle in total.

In this paper, a dual-band substrate integrated waveguide (SIW) filtering antenna with improved out-of-band rejection is presented. It consists of two dual-mode rectangular cavity resonators integrated with the slot antenna. Four metal-insulator-metal (MIM) capacitors are designed in the first cavity to realize circuit miniaturization and wide upper stopband. The second slot-loaded cavity achieves a miniaturized dual-band radiation by cutting the currents of TE110 and TE210 modes. Three radiation nulls are obtained due to the multiple coupling paths between the resonating and spurious modes. The radiation nulls locations can also be adjusted by changing the feeding position. For verification, a SIW filtering antenna operating at 3.6/4.1 GHz (f1/f2) is designed and fabricated. The measured peak gain and 10-dB bandwidth at low band of 3.57 GHz (high band of 4.12 GHz) are 4.84 dBi (4.85 dBi) and 2.3% (1.6%), respectively. The measured >30dB inner stopband suppression and 20-dB upper stopband suppression up to 1.46f2 are achieved.

In this study, a novel coupling structure based on half‐mode substrate‐integrated waveguide (HMSIW) is proposed with a small size and broad bandwidth. The HMSIW coupler is realised by connecting their equivalent magnetic walls with metal strips, which avoids exposing the semi‐enclosed magnetic walls outside. Hence, it has greater anti‐interference capability than the existing HMSIW couplers. The directional coupling principle is introduced by analysing the proposed single connecting strip coupler. In order to lower return loss and higher isolation, a 3 dB directional coupler working from 10.8 to 16.8 GHz is designed with two connecting strips. Finally, a six‐port circuit is achieved by utilising this compact 3 dB directional coupler. Furthermore, a broadband HMSIW power divider is optimised to satisfy the performance of this six‐port circuit. The proposed coupler with metal strips helps to increase bandwidth and reduce size, which makes it more applicable to demanding systems with complex requirements such as detecting and transceiver systems. The 3 dB coupler and six‐port circuit are fabricated and measured. The measured results are in accordance with the simulated data.

The transverse linearly-polarized beam can maintain its polarization when reflected, which is important for a detection system. Most of the existing planar Bessel beam generators are implemented in a central feeding radial topology and hard to generate the Bessel beam with the transverse linear polarization. In this communication, a substrate integrated waveguide (SIW) slot array antenna is proposed to generate the transverse linearly-polarized Bessel beam. The desired phase and amplitude distribution of the Bessel beam can be easily realized by such an array. With the inherent 0°/180° output phase of the comb-like divider considered, the desired 0°/180° phase distribution is implemented by placing adjacent slots on the opposite (0°) or the same side (180°) within a linear array and by employing adjacent linear arrays with the inverse (180°) or the same (0°) slot offset direction accordingly. The offset of the slot, as well as the tuning metalized vias within the comb-like divider, is modulated to generate the desired amplitude distribution. After reducing the influence of the rectangularly-truncated aperture by adding a Gauss-tapered amplitude distribution, a transverse linearly-polarized Bessel beam SIW slot array antenna is designed with more than 100 mm depth-of-field (DoF) and less than -25 dB cross-polarization. To the best of our knowledge, it is the first design to generate the transverse linearly-polarized Bessel beam by a planar array antenna.

This communication proposes a novel fully metallic multibeam Luneburg lens antenna which can simultaneously support the radiation of horizontal polarization (H-pol) and vertical polarization (V-pol). The proposed Luneburg lens consists of a parallel plate waveguide with varying spacing and a series of loaded metallic nails with graded heights. Seven OMTs are employed as the feeder. The measured results show an H-pol/Vpol peak gain is higher than 10.9 dBi/13.8 dBi from 28 GHz to 32 GHz. The dual-polarized beam scan loss is lower than 1.1 dB from −48° to +48°. The results show its potential for application in the MMW multibeam and multi-polarization system.

In this letter, a low-profile and wideband substrate integrated waveguide (SIW) antenna is proposed and validated for full-duplex systems. The proposed antenna operates at 4.9 GHz and 5.8 GHz Wireless Local Area Network (WLAN) bands. Each resonator of the antenna consists of a modified half-mode SIW (HMSIW) cavity, and excited by a 50 $\Omega$ coaxial probe. The wideband response is achieved by coupling the fundamental TE\textsubscript{10} mode with the perturbed TE\textsubscript{10} mode of the HMSIW cavity. The compactness of the proposed design is obtained using two rectangular slots near the closed-ends of the cavities. By properly optimizing the overall geometry, the proposed design exhibits a 10-dB fractional bandwidth of 8.2 \% (4.78--5.2 GHz) and 7.7 \% (5.70--6.16 GHz) in the lower (4.9 GHz) and upper frequency band (5.8 GHz), respectively. The bandwidths of both frequency bands can be controlled by adjusting the coupling between modes. A high isolation ( $>$ 30 dB) between the two ports is observed due to series of metallic vias between them. This antenna has compact size (0.34 $\lambda_{g}^{2}$ ) with high gains of 5.24 dBi and 5.37 dBi at 4.9 GHz and 5.8 GHz, respectively.

In this paper, a new type of Vivaldi antenna with heat dissipation enhancement is proposed and manufactured based on three-dimensional (3-D) printing and printed circuit board (PCB) technologies. A longitudinal slot on substrate integrated waveguide (SIW) is employed to feed Vivaldi radiation structure, which replaces the balun structure of traditional Vivaldi antennas. The measured 10-dB bandwidth of antenna element reaches up to 34.48% (21.77-30.39 GHz) and the in-band realized boresight gain is 6.5-8.8 dBi. The 1×4 Vivaldi antenna array with 28.72% (21.63-28.81 GHz) bandwidth and a gain range of 10.5-12.5 dBi is achieved. The fin-shaped structure of the antenna array further enhances the heat dissipation while increasing the gain up to the range of 13.4-15.5 dBi. The measured results are in good agreement with the simulated ones. The proposed antenna array has important application potential in 5G millimeter-wave systems.

A compact asymmetric waveguide orthomode transducer (OMT) with broad bandwidth and high isolation is presented in this letter. A novel combined transition-bending structure is proposed within the common arm in the design of the OMT branching T-junction. It implements the E-/H-plane 90° waveguide bends and the square-to-rectangular waveguide transition for both polarization sidearms. Its multiple roles help to reduce the geometry discontinuities and improve the matching bandwidth. The measurements demonstrate that the OMT achieves higher than 50 dB isolation level between the two modes and better than 18 dB return loss from 30.3 to 36.3 GHz (18%). Furthermore, the isolation level is typically 60 dB over 50% of the operation bandwidth. The insertion loss of each polarization is below 0.23 dB for a single OMT. The overall size of the OMT functional section is reduced to 1.55 λ₀x 1.45 λ₀x 0.78 λ₀.

A beam-tilted circularly-polarized (CP) corporate-fed waveguide slot array is accomplished in the 60-GHz band. The main-beam tilting in the 45° cut-plane is achieved by introducing a corporate feeding circuit with a linearly-tapered phase distribution. The T-and H-junctions with nonidentical output waveguide widths are newly proposed to realize progressive output phases. By cascading asymmetric T-and H-junctions into a 16×16-way power divider, we design a 32×32-element array consisting of 256 2×2-element CP subarrays. The simulated tilt angle coincides with the theoretical one over the whole frequency band. The test antenna is fabricated by the diffusion bonding of thin copper plates. Stable beam directions and wideband operations are verified by the experimental evaluations. The overall reflection is sufficiently suppressed below -14 dB over the 56–67 GHz frequency band. The realized gain higher than 37 dBic is achieved over the frequency range of 59–64 GHz, while the AR is suppressed below 3.5 dB over the frequency range of 57.25–66.75 GHz.

This paper proposes a shared-aperture self-diplexing antenna using the composite parallel-plate waveguide (PPW). The long-straight slots (LSS) etched on the top surface of the PPW are utilized as the common radiation aperture for two operating bands. At the high frequency band, the proposed antenna, excited by the alternative-phase TE10-mode wave, operates as a leaky-wave antenna (LWA). Meanwhile, it serves as a continuous transverse stub (CTS) array antenna when excited by the TEM wave at the low frequency band. Two kinds of feeding networks are adopted to generate the alternative-phase TE10-mode wave and TEM wave, respectively. To verify the proposed method, a millimeter-wave prototype is designed, fabricated and measured. The measured results show that -10 dB fractional bandwidths are 3.42% (76.25-78.9 GHz) and 14.5% (83.2-96.2 GHz), respectively, and the port isolation is higher than 40 dB. Additionally, the peak gains are 27.1 dBi at 78.5 GHz and 25.3 dBi at 90 GHz, respectively. The proposed antenna can be used to develop compact frequency-division system without using duplexers and multi-band wireless systems.

A switched‐line substrate integrated waveguide 1‐bit phase shifter is designed and measured at 28 GHz. Reconfigurability is achieved through a set of floating metallized vias whose connection to the waveguide top and bottom layers can be controlled using PIN diodes. The reconfigurable vias are used to dynamically create alternative paths having different phase delays. A three‐metal layer printed circuit board stack‐up is employed to fully integrate the diode biasing network and to ease the routing of the bias signal. The high integration of the proposed configuration makes it well suited for the implementation of reconfigurable Butler matrices. The phase shift offset between the two states of this digital 1‐bit phase shifter equals 262° at 28 GHz, leading to a measured figure of merit of 161°/dB, and input 1‐dB compression point over 20 dBm. The total area is 13.72 × 10.9 mm without feeding lines and bias.

In this article, a 1×12 millimeter-wave (mmW) linearly tapered slot antenna (LTSA) array, fed by high-order waveguide modes, is introduced. Due to the antiphase characteristic between adjacent channels of a power divider based on the TE2n,0 mode waveguide, the cross-polarized E-field components can cancel each other out in an end-fire direction, even in the case of a relatively thick substrate. Moreover, the electric separations between the adjacent channels employed in a traditional substrate integrated waveguide (SIW) power divider can be removed without affecting the field distributions. This facilitates in improving robustness to avoid fabrication errors. Additionally, a general condition of generating a single high-order mode with symmetrical protection is outlined. By combining two antiphase TE30 mode waveguides, an equivalent TE60 mode waveguide with six identical output channels is realized. To feed a 12-element array, two equivalent TE60 mode waveguides are employed as an equivalent TE12,0 mode-feeding network. Instead of the complex 1-to-n-way power divider and relatively thin substrate featured in previous works, the high-order mode-fed LTSA array introduced in this study is able to operate over 26.5b–30 GHz with substrate height of 2 mm (0.19λ0), yielding a cross-polarization level of less than -15 dB.

This paper presents a novel unequal power divider based on an inverted microstrip gap waveguide. This new geometry can achieve a large power ratio of the two output ports and a small phase difference less than 5°. Based on this novel geometry, a few distinctive unequal power dividers with different output power ratios were proposed for designing a low sidelobe array antenna at 39 GHz. To verify the design, a 16×16 antenna array was designed and measured. The measurement results indicate that the entire array antenna achieves a -10 dB impedance bandwidth of 18.5% (in the range of 35.9-43.2 GHz), a gain greater than 29 dBi from 37.5 to 41.8 GHz and an antenna efficiency greater than 50% over the entire operating frequency band. Based on the application of the newly invented distribution network, the proposed array antenna is below -23 dB on both the E-and H-planes at 37-42 GHz. Furthemore, the radiation pattern of the entire array complies with the ETSI-Class II standard for all azimuth angles.

In this paper, a wideband filtering antenna based on substrate integrated waveguide (SIW) structure for millimeter-wave (mm-Wave) applications is proposed and studied. The proposed antenna is developed using multilayer printed circuit board (PCB) technology. It consists of an SIW feeding structure with a coupling slot, differential-fed L-shaped probes as well as radiating patches. Such architecture provides wide impedance bandwidth along with good filtering characteristic in the lower stopband. Simultaneously, by introducing a pair of open slots on the individual radiating patch as well as two shorting loops on top of the coupling slot, good filtering response in the upper stopband is obtained. The suppression level in the lower stopband is then further improved by introducing a pair of shorted stubs in the coupling slot region. The proposed filtering antenna features no extra filtering circuits, wide bandwidth as well as low profile. To verify the proposed structure and design philosophy, antenna array prototypes have been designed, fabricated and measured. It achieves a 29% bandwidth from 23.5 to 31.5 GHz. Good agreement is achieved between simulated and experimental results. The proposed antenna array is particularly suitable to be applied in 5G (the fifth generation) mm-Wave backhaul communications.

Two planar quasi-isotropic antennas are presented in this letter, and the filtering response is implemented on the second antenna. Firstly, a printed shorted patch which can be equivalent to a magnetic dipole is utilized with a fan-shaped monopole serving as an electric dipole to achieve quasi-isotropic radiation. A lumped capacitor, a pair of near-field parasitic elements (NFPEs) and a slot are introduced to improve the roundness. Ultimately, the gain deviation is reduced to 3.5 dB. Further, a half mode substrate integrated waveguide (HMSIW) is applied to achieve the magnetic dipole for the second antenna. The filtering response is obtained by introducing a uniform impedance resonator (UIR). A radiation null is obtained above the operating band, while a quasi-isotropic radiation is achieved in band with a gain deviation of 7.3 dB.

In this letter, two compact and high-performance filters based on multilayer slow-wave empty substrate-integrated waveguide (SW-ESIW) are presented. SW-ESIW, which contains the air cavity and a bottom layer including several rows of internal metallized via holes, provides a compromise between insertion loss and footprint. It is the first time that SW-ESIW is used to implement compact filters with multilayer air cavity. The proposed filters are simulated, fabricated, and measured. The measurements are consistent with simulations, indicating that the proposed filters can be reduced more than 35% in dimension compared to the same filters in ESIW. Based on the SW-ESIW technology, the proposed multilayer filters realize the advantages of low insertion loss and miniaturization, and express the tremendous potential on applications to complex and high-performance microwave circuits and systems.