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In this paper, a broadband, low insertion loss, and compact folded substrate integrated waveguide (FSIW) phase shifter is proposed for the first time. By loading the complementary split-ring resonators (CSRRs) on the middle metal layer of the FSIW, a closed-type slow-wave transmission line (TL) is obtained, which can provide a wideband phase shift (39%) compared with the equal-length fast-wave one. The enclosed structure of the CSRR-loaded FSIW prevents the CSRRs from radiation as suffered in the previous reported CSRR-loaded TLs, resulting in a low insertion loss. This feature greatly reduces the amplitude imbalance between the main line and the reference line of the phase shifter. In addition, no transition structure is required between the FSIWs with and without CSRRs for broadband impedance matching, which makes the phase shifter more compact and easier to integrate with other FSIW devices. To validate the performance of the proposed phase shifter and to illustrate its ease integration, a novel FSIW 180° directional coupler that consists of an FSIW 90° coupler and an FSIW 90° phase shifter is designed, fabricated, and measured. The measured results agree well with the simulated data.

The earliest intense red hue compound of SiO2@LaOF:Eu3+ core-shell nanostructures (NS) was created utilizing a basic solvothermal technique and heat processing. The produced core-shell particles are spherical, non-agglomerated, and have restricted size dispersion. Photoluminescence (PL) radiation spectra exhibit sharp maximums in 593, 611, and 650 nm, corresponding with 5D0 -- 7FJ (J=0, 1, 2) Eu3+ conversions. The Judd-Ofelt (J-O) hypothesis helps determine the spectrum strength indices and Eu-O ligand activities. The CIE coordinates are x=0.63, y=0.36, nearly equal the NTSC coordinates which are x=0.67, y=0.33. Because of the CCT level of 3475 K, which is lower than 5000 K, this phosphor is appropriate for warm light-emitting diodes. To visualize latent fingermarks both porous and non-porous substrates, the fluorescent labeling marker adapted core-cover SiO2 (coat III)@LaOF:Eu3+ (5 mol%) was utilized. With no background influence, the fingermarks obtained are exceedingly sensible and exclusive, permitting for fingerprint ridge features ranging from level-I to level-III. The findings indicate the significant enhancement in the illumination of corecover NS as a responsive operational nanoparticle for increased forensics and firm status illuminating implementations.

In this letter, a novel dual-band coupler made of only three coupled microstrip-slotline (CMSL) sections is proposed to achieve a tight coupling with a high band ratio in a small size. A desired dual-band operation can be obtained by proper design of the coupling levels of the CMSL sections. Explicit design equations of the proposed coupler were derived by the method of even- and odd-mode excitations, and the characteristics of the CMSL were studied. For demonstration, a 3-dB dual-band CMSL coupler operating at 1 and 3 GHz is designed, fabricated, and measured. The proposed coupler has the advantages of small size, tight coupling, and high isolation.

In this letter, a compact bandpass filtering power divider with tunable bandwidth based on spoof surface plasmon polaritons (SSPPs) and substrate integrated waveguide (SIW) is proposed. The hybrid-SIW-SSPP structure shows good potential to expand the scope of bandwidth control of the device. The bandwidth can be designed in a wide range by simply optimizing its dimensions or loading interdigital structures (ISs). Defected ground structure (DGS) is also introduced on the bottom layer to further improve the out-of-band suppression. And good isolation can be obtained via additional resistors welded across the SSPP slot. A prototype loaded with dumbbell-shape DGS and two resistors is fabricated with an overall size of 45 mm x 18 mm x 0.5 mm. Both $S_{21}$ and $S_{31}$ are around -3.8 dB within the whole X-band. The simulated and measured results agree with each other well.

A low radar cross section (RCS) slot array antenna based on absorptive frequency-selective structure (AFSS) is presented in this letter. The AFSS unit cell is constructed by two lossy layers and four double-sided parallel strip lines (DSPSLs). The radiation performance of the antenna can be preserved due to the transmission window of the lossy layers. Wide absorption bands of the AFSS are achieved due to periodic impedance of the DSPSL and the combination of the lossy layers. The operating principle of the design is demonstrated, and a prototype is fabricated and measured to validate the design. The proposed design features both wide RCS reduction band of the antenna and wide transmission band of the AFSS.

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 dual-polarized lower-band (LB) antenna element is proposed in this paper. A pair of vertical arms and a pair of horizontal arms are designed with two cross -shaped feeding lines together for 45polarizations. The sleeve arm can suppress the scattering for high frequency electromagnetic wave, and have almost negligible effect on low frequency. Meanwhile, unobstructed space for placing the higher-band (HB) elements is reserved with surrounded scheme. The dual-band antenna (DBA) with four HB elements operating from 1.46~2.43 GHz and one LB element operating from 0.65~1.11 GHz is designed and fabricated. The simulated and measured results show that stable radiation performance and low mutual interference for LB and HB elements are achieved in DBA.

A gain-enhanced antenna consisting of a bandpass frequency selective surface (FSS) and a patch antenna is initially proposed in this communication. By utilizing the reflection characteristic of the FSS, a quasi-Fabry–Perot (F-P) cavity is formed between the FSS and antenna’s ground, which considerably improves the gain of the antenna. Meanwhile, the bandpass FSS has a little phase compensation for oblique transmitting waves, which also slightly enhances the gain. Then a low-radar cross section (RCS) and gain-enhanced antenna is proposed by using absorptive/transmissive frequency selective structure (ATFSS). It is implemented by mounting the ATFSS above a patch antenna. The ATFSS is constructed by stacking a lossy layer above a bandpass FSS. Both antennas are fabricated, assembled, and measured. They achieve a gain-enhancement of 5.27 and 3.84 dB, respectively. Besides, the low-RCS antenna achieves 10 dB monostatic RCS reduction from 5 to 5.33 GHz and from 9 to 13.4 GHz under the TE-polarization, and from 8.4 to 13.5 GHz under the TM-polarization, respectively. Simulated results show it also achieves a good improvement in bistatic RCS reduction as well.

A planar dual-band shared-aperture array antenna for the ${K}$ -/ Ka -band low Earth orbit (LEO) satellite communication is presented in this article. Substrate integrated coaxial line (SICL)-fed bow-tie transverse slots and substrate integrated waveguide (SIW)-fed slot pairs are employed to provide ${K}$ -band horizontal polarization and Ka -band vertical polarization, respectively. The ${K}$ -band and Ka -band radiating elements share a common metallic-via-array, which can effectively improve the port-to-port isolation. Furthermore, the port-to-port isolations in both bands can be also improved by introducing the high-pass characteristic of SIW and out-of-phase cancellation between two current paths. For the sake of achieving low-profile height and compact size, the ${K}$ -band feeding network is subtly buried between Ka -band shielding cavities. As a proof-of-concept example, a shared-aperture dual-polarized array antenna operating at ${K}$ -/ Ka -band is designed and fabricated for verification by using a multilayer printed circuit board (PCB) technology. The measured results show a good concordance with the simulated one, indicating that the proposed antenna has the advantages of wideband, high isolations, low profile, and easy planar integration, which can be adopted for the millimeter-wave (mm-Wave) LEO satellite communication system.

A method to suppress cross frequency band scattering in multiband array (MBA) is proposed in this letter. Due to the short distance between the lower band (LB) elements and the higher band (HB) elements in MBA, the performances of the elements are distorted. By adding three L-shaped branches to each arm of LB element, the induced current can be effectively regulated, which greatly reduces the cross-band scattering ability of the array. Thus, the elements of each frequency band do not interfere with each other and work alone. This method is applied to the MBA with the interleaved scheme, which consists of one LB element with the operating frequency ranging from 0.73 to 0.86 GHz, and four HB elements with the operating frequency ranging from 1.79 to 2.41 GHz. Both simulation and measurement of proposed geometry show that this method is simple, effective, and easy to fabricate. The proposed geometry can be widely used in multiple wireless communication systems due to its high isolation, stable radiation patterns, and lower cross-band scattering.

To enhance the dual-layer remote phosphorus configuration’s color standard help spread its application in the LED devices, the new green-emitting phosphor of Ca7Si2P2O16:Eu2+ is proposed. The sol-gel method is used to dope the Eu2+ ions with Ca7Si2P2O16. Increasing the ion Eu2+ concentration can lead to high thermal stability, color-tunable ability, stronger green emission band, and higher photoluminescence extraction. The dual-layer structure’s color standards, as well as the luminous flux, are examined with different concentrations of Ca7Si2P2O16:Eu2+ in the phosphor layer. Owing to the improved features, the green phosphor Ca7Si2P2O16:Eu2+ has enhanced the emission intensity in the blue and green wavelengths, resulting in better color mixing and distribution. The luminescence shows the enhancement when increasing the concentration of Ca7Si2P2O16:Eu2+. However, the color rendering feature can present a reduction with more than 10% wt. green phosphor within the double-layer phosphorus remote configuration, due to color balance’s loss.

In this paper, a reconfigurable dual-band bandpass filter, using memristive switches, is proposed. The applied memristor is non-volatile and has low-power consumption, which could be potentially us...

A new type of sleeve monopole antenna with a choke structure for broadband applications is proposed in this letter. The antenna consists of a choke structure and a single-sleeve structure, which effectively broadens its impedance bandwidth. Meanwhile, the top-loading technique is applied to reduce the size. The proposed structure is designed, analyzed, and optimized. Parameters study is carried out for its working mechanism. The fabricated antenna is measured, and the measured results have good agreement with the simulated ones. The antenna shows the omnidirectional radiation with a broad impedance bandwidth ranging from 0.24 to 0.95 GHz. The proposed antenna has a potential application in wireless communication.

This article presents a novel class of dual-mode substrate-integrated waveguide (SIW) bandpass filters exploiting perturbed SIW rectangular cavities. By introducing metallized via-holes along the central line of an SIW rectangular cavity, the resonant frequency of TE101 mode can be shifted close to that of TE201 mode, thus creating a dual-mode resonator. This structure implements a doublet, which provides two poles and one or two transmission zeros (TZs). The pass bandwidth, spurious-free bandwidth, and positions of the TZs can be fully controlled by modifying the length of the perturbation, the side ratio of the rectangular cavity, and the offset of the input/output ports, respectively. Eight two-pole SIW filters are designed and investigated to demonstrate the high design flexibility. Moreover, a four-pole SIW filter with the asymmetric response and a five-pole SIW filter with quasi-elliptic response are designed, fabricated, and measured to describe the extension of the proposed approach to higher order filters.

A single-layer dual-circularly polarized cavity-backed patch filtenna with wide axial-ratio (AR) bandwidth is presented in this letter. The degenerated substrate-integrated waveguide (SIW) cavity modes TE120/TE210 cooperating with the patch modes TM01/TM10 are utilized to achieve a wide AR bandwidth. Simultaneously, two radiation nulls, which are inherently introduced by the SIW-cavity mode TE110 and mixed electromagnetic coupling between the cavity and patch, respectively, are realized at both band edges to achieve a bandpass filtering response. For demonstration, a sample was fabricated and tested. The measured results show that the proposed filtenna achieves an operating bandwidth of 12% with the center frequency of 10 GHz, a peak gain of 7.4 dBic, an in-band average gain of 6.7 dBic, and an out-of-band rejection level over −13 dB.

This letter presents a novel class of compact dual-mode bandpass filters based on half-mode substrate-integrated waveguide (HMSIW) cavities. By using both TE102 and TE301 modes of the HMSIW rectangular cavity as resonant modes and TE101 mode as nonresonating mode, a novel HMSIW doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located at one side or both sides of the passband. Therefore, flexible responses can be obtained. A two-pole HMSIW filter with asymmetric response and a four-pole HMSIW filter with quasi-elliptic response have been designed, fabricated, and measured, to demonstrate and verify the proposed structure. Compared with substrate-integrated waveguide (SIW) counterparts, the dual-mode HMSIW filters have the advantage of smaller size.

In this paper, a millimeter-wave (MMW) dual-mode and dual-band switchable Gilbert up-conversion mixer in a commercial 65-nm complementary metal oxide semiconductor (CMOS) process is presented. By simply changing the bias, the proposed CMOS Gilbert up-conversion mixer can be switched between subharmonic and fundamental operation modes for MMW dual-band applications. With a low local oscillator pumping power of 3 dBm and low dc power consumption of 6 mW, the proposed CMOS Gilbert up-conversion mixer exhibits a measured conversion gain of −0.5 ± 1.5 dB from 37 to 50 GHz and 2.5 ± 1.5 dB from 17.5 to 32 GHz for the subharmonic and fundamental modes, respectively.

This paper presents an airborne piezoelectric micromachined ultrasonic transducers (PMUTs) operated at low frequency (40–50 kHz) for long-range detection, where the acoustic absorption loss in air is relatively low (0.8–1 dB/m). The PMUTs made with single-crystal Lead Zirconate Titanate (PZT) enables a high piezoelectric coefficient ( ${e} _{31, f} \approx ~16$ - 24 C/ $\text{m}^{{2}}$ ), and a low dielectric constant ( $\varepsilon _{\mathrm {r}}~\approx ~308$ ), achieving high PMUT transceiver efficiency. The $2\times 2$ PMUT array achieves a very high sound pressure level (SPL) output of 109.4 dB at 26 cm distance. Different from conventional PZT PMUTs, this study utilized single-crystal PZT with a low permittivity to achieve a good acoustic reception, demonstrating the sensitivity of 2 mV/Pa. This work reports the PMUT design, modeling, fabrication, characterization, enabling a long-range detection of 4.8 meters in a pulse-echo experiment, which was conducted by a pair of $2\times 2$ PMUT arrays with the matched resonances. [2020-0270]

A dual-polarized broad band-absorptive frequency-selective rasorber (FSR) is proposed in this article. The FSR has a lowpass band with low insertion loss and a broad absorption band. It is a two-layer structure formed by a lossy surface cascaded an absorptive transmission/reflection surface (ATRS), in which the ATRS is constructed by one substrate with a resistive square loop on its top side and a double square loop on its bottom side. The working mechanisms of the proposed ATRS and FSR are completely studied by using their equivalent circuit models. The ATRS retains dual stopbands of the double square loop and suppresses the unwanted transmission pole of the double square loop. Then a broadband absorptive FSR is achieved. A sample of the proposed FSR is fabricated and measured. The measured results show that the proposed FSR has a lowpass band up to 860 MHz ( $\vert S_{21}\vert \ge -1$ dB) and a broad absorption band with bandwidth of 95.3% from 3.84 to 10.83 GHz ( $\vert S_{11}\vert \le -10$ dB and $\vert S_{21}\vert \le -10$ dB).

This communication presents a magnetic-material-loaded 3-D frequency-selective rasorber (FSR) consisting of independent transmission and absorption channels. The main feature of the proposed design is employing both ferrite material and meander line in the absorption channel to obtain a wide absorption band and low-loss transmission band. Detailed analysis of the absorption channel is given with the help of equivalent circuit models to demonstrate the operating principle. The design guidelines are formulated, and a design example is presented with both the simulated and measured results. The proposed FSR features both thin thickness and wide absorption bands. Moreover, no lumped components are required, which greatly facilitates the fabrication and reduces the cost.

A three-dimensional (3-D) structure is proposed in this article for ultra-wideband absorber design. The ultra-wideband absorber is implemented by properly combining two subabsorbers. The first subabsorber operates in its fundamental mode ( $f_{0}$ ) and the third-order mode ( $3f_{0}$ ). Its lossy layer is designed with an infinite impedance at the second-order mode frequency ( $2f_{0}$ ). The second subabsorber is designed to operate in its fundamental mode frequency, which is corresponding to $2f_{0}$ of the first subabsorber. A double-sided parallel-strip line (DSPSL) is employed to produce the required infinite impedance of the first absorber. A simple equivalent circuit model of the DSPSL is established to explain the operating principle. A conventional parallel LC circuit is also provided for comparison to show the advantages of the DSPSL. Single-polarized and dual-polarized ultra-wideband absorbers are designed by combining these two subabsorbers, and their simulated fractional bandwidths (FBWs) of 151.6% and 150.9% are achieved, respectively. A prototype of the dual-polarized ultra-wideband absorber is fabricated and measured to validate the design concept. Its measured absorption band from 1.50 to 12.31 GHz with an FBW of 156.6% is in a good agreement with the simulated one. The proposed absorber features a wide absorption band and few lumped elements, which makes it more useful in practical applications.

In this letter, a 24-GHz high-isolation ON–OFF keying (OOK) modulator with reduced input impedance variation in a 65-nm CMOS technology is proposed. A modified magnetic coupled triple-cascode configuration with a series inductor and two shunt transistors, which can simultaneously improve the ON/OFF isolation and reduce the input return loss variation between the ON- and OFF-states, is designed and analyzed for the first time. Based on this configuration, the OOK modulator achieves a 45.7-dB ON/OFF isolation and maintains better than 10-dB return loss for both the ON- and OFF-states. In addition, a data rate of 3.3 Gbps is achieved.

A compact single M-shaped probe fed circularly polarised filtenna (filtering antenna) without extra filtering circuit is presented in this study, in which three pair slots with different lengths are etched on its parasitic patch to produce radiation nulls at both band edges of its operating band. Furthermore, a single M-shaped probe feeding structure is used to improve the selectivity, especially for the lower band edge. By merging the filtering circuit into a radiating element, a good selectivity in the gain response can be realised without influencing the operation band aperture efficiency. A sample is fabricated and results show that the proposed filtenna has an operating bandwidth of 13% (| S 11

A novel wideband high-gain planar antenna array for $E$ -band backhaul applications is presented in this article. The antenna element is composed of a substrate integrated waveguide (SIW) cavity-backed patch and a stepped waveguide horn. The SIW cavity-backed patch is worked as wideband waveform and impedance transformer to excite the stepped waveguide horn on the upper layer. The stepped waveguide horn is employed to enhance the gain of the antenna element by increasing the radiation aperture. Based on the proposed antenna element, a $2 \times 2$ subarray with element spacing larger than a wavelength is designed. A groove, which works as secondary radiation source, is etched between the elements to improve the gain and suppress the high sidelobes of the $2 \times 2$ subarray. By taking the advantage of the groove, the $2 \times 2$ subarray achieves a maximum boresight gain of 17 dBi and an −10 dB impedance bandwidth of 21.8% from 70 to 87 GHz. For further enhancing the gain, a prototype including $16 \times 16$ elements is manufactured and measured. The experimental results confirm that the proposed antenna achieves the −10 dB impedance bandwidth of 22.4% from 71 to 88.5 GHz and a peak gain of 28.8–30.9 dBi. With the merits of a wider operating bandwidth, high gain, low profile, and low cross-polarization, the proposed antenna array is suitable for application in the $E$ -band wireless backhaul systems.

In this paper, air-coupled piezoelectric micromachined ultrasonic transducers (PMUTs) using 36% scandium-doped aluminum nitride (ScAlN) thin-film are presented. ScAlN is known to exhibit higher piezoelectric properties compared to pure AlN leading to significant performance improvements in various piezoelectric micro-electromechanical systems (MEMS) applications including PMUTs. Here, the concentration of Sc in the actual sputtered 1- $\mu \text{m}$ -thick ScAlN film was 36%, which is slightly below the maximum at the phase boundary. The ScAlN PMUTs were fabricated from an SOI wafer, where the dry etching of ScAlN film was optimized. The frequency response and displacement sensitivity of the PMUTs were characterized in the air using laser Doppler vibrometry confirming $2\times $ higher transverse piezoelectric coefficient than AlN. The acoustic transmission and reception of the PMUTs were evaluated from a high-sensitivity microphone and pulse-echo measurements. The PMUTs were designed to operate below 100 kHz in order to mitigate the absorption loss, which resulted in a high transmit pressure of 105-dB sound pressure level (SPL) at 10 cm and only 30-dB attenuation at the 2-m range. Through implementing 36% ScAlN film, the presented PMUTs exhibited a large displacement and consequently, a high SPL compared to the state-of-the-art PMUTs and the bulk transducer considering the size and the excitation voltage.

A novel frequency-selective rasorber (FSR) with a broad absorption band is proposed in this letter. The proposed FSR is realized by vertically cascading a two-dimensional (2-D) lossy layer with a 3-D band-stop frequency-selective structure (FSS). The 2-D lossy layer is composed of meandered square loops loaded with lumped resistors, and the 3-D band-stop FSS is constructed by parallel-plate waveguide arrays (PPWAs) stacked along the TE polarization direction (linear polarization perpendicular to the PPW). The band-absorptive FSR exhibits an absorption band (| S 11| ≤ –10 dB and | S 21| ≤ –10 dB) from 7.85 to 12.85 GHz and a low-pass band (| S 21| ≥ –1 dB) up to 3.8 GHz. Its transition efficiency of the transition band (FRap) is 2.1. A prototype is fabricated, and its measured results show that the proposed FSR has a low loss and flat low-pass band, a wide absorption band with high selectivity, and a steep transition band between the low-pass band and absorption band.

A multi-layer interleaved folded half-mode substrate integrated waveguide (HMSIW) dual-band filter is proposed. The TE 101 and TE 102 mode of the HMSIW resonators form dual-band response by vertical coupling, and the bandwidth of the two passbands can be independently designed by adjusting the coupling apertures. Moreover, three transmission zeros (TZs) are obtained to improve out-of-band rejection, and the TZs can be flexibly designed below or above the passband. By vertically superimposing the HMSIW cavity, the HMSIW filter can be extended to multi-pole dual-band filters. A dual-band filter with centre frequency of 3.05 and 4.7 GHz was fabricated and measured to verify the proposed method. The simulated and measured results are in good agreement.

Miniaturised band-absorptive frequency selective rasorbers (FSRs) with wide absorption bands for single-polarised and dual-polarised applications are proposed here. These FSRs are both constructed by a lossy layer and a lossless layer, in which I-type metal strips are utilised to reduce the size of the unit cell of the FSRs. The equivalent circuit models (ECM) of the FSRs are presented and analysed. A prototype of the dual-polarised band-absorptive FSR is fabricated, assembled, and tested. The measured results show that a wide absorption band (| S 21 |≤–10 dB and | S 11 |≤–10 dB) from 3.93 GHz to 8.07 GHz with a bandwidth of 69%, and a low-pass band (| S 21 |≥–1 dB) with frequency lower than 880 MHz has been achieved for the dual-polarised band-absorptive FSR.

Consisting of 6 radiating elements and a 3×3 Butler matrix, a novel tri-beam antenna system is proposed in this paper. The radiating element consists of two U-shaped arms and coupled strips, which shows a wide impedance characteristic. Three branch line couplers and four -90° phase shifters are combined into 3×3 Butler matrix as a beam-forming network (BFN). In order to avoid the crossover of transmission lines, one main line of a 1.76dB coupler is designed and located between two 3dB couplers. With this arrangement, the signal from one input port can be divided into three output signal with equal amplitude and specify phase differences of 0°, +120° and -120°. Furthermore, a 2×3 antenna array is connected with this BFN for three orthogonal beams. Measured results show that three beams at θ=0°, 40° and -40° are produced when different input ports are excited.

The coprime array provides the possibility of resolving more signals than the sensors for the direction-of-arrival (DOA) estimation application. However, the non-consecution of its virtual array raises challenges for making full use of the degree of freedom (DOF). In this paper, we propose a new underdetermined DOA estimation method with coprime array where the non-consecutive virtual array can be converted into a virtual uniform linear array (ULA) with the same aperture. Firstly, all elements in the vectorized signal covariance matrix corresponding to the same virtual array positions are averaged to construct the output signals of the virtual array. Then, an atomic norm minimization (ANM) based optimization problem is formed for denoising the output signals of the virtual array and for interpolating the missing signals at the virtual array holes. At last, the ANM problem is solved by the semidefinite programming (SDP) and the DOAs are obtained by applying the subspace method on the reconstructed signal covariance matrix of the interpolated virtual ULA. The proposed algorithm is gridless and makes full use of the DOF and the information provided by the coprime array. The simulation results compared with the other representative methods are given to demonstrate the superiority of the proposed method with respect to the resolution and estimation accuracy.

This study develops a differential-fed filtering patch antenna, which features superior frequency selectivity, compact size, low cross-polarisation, and symmetrical radiation patterns. The proposed antenna consists of a rectangular patch on the top layer, which is differentially fed by a balun bandpass filter on the bottom layer. A pair of rectangular coupling slots were etched on the middle layer for energy coupling. The patch antenna performs not only as the radiator but also as the last resonator of the whole filter circuit for compactness. A prototype of the proposed filtering antenna operating at 2.45 GHz was fabricated and tested. The measured in-band peak gain is 5.9 dBi with steep roll-off at band edges, and the out-of-band gain is less than - 25 dBi. Moreover, symmetrical radiation patterns and low cross-polarisation levels of - 22 dB are also realised for the proposed filtering antenna.

A horizontally polarized (HP) wideband antenna is designed and analyzed for wireless communication in this communication. The HP antenna is a combination of four quarter-wavelength slot elements, and fed by a wideband power divider with equal amplitude and zero phase difference output signals. Equivalent to the current loop, four slot elements rotate around the center of proposed structure, which gives rise to a monopolar radiation pattern. A prototype is designed, fabricated and measured. The results show that a deep null more than 20 dB appears in the broadside of the elevation plane radiation pattern. And a small ripple less than 2 dB in azimuth plane radiation pattern is obtained. The antenna has a wide impedance band of 33.3% for S11