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Two wideband bandstop filters (BSFs) for single and dual-band are proposed and then extended to reflectionless BSFs based on the analysis from input impedance/admittance perspective. Also, topologies of higher-number-stopband input-reflectionless BSF are provided to broaden the design scope. Open/shorted coupled lines are adopted to obtain multi transmission zeros and desired stopband bandwidth by adjusting the even-/odd-mode impedance of coupled lines. Resistor-loaded coupled lines are connected with Port 1 to absorb unwanted signals and obtain input-reflectionless behavior. For validation of the proposed theory analysis, BSFs with corresponding absorptive prototypes are constructed and measured. [ABSTRACT FROM AUTHOR]

A novel 24 GHz circularly polarised metasurface rectenna for wireless power transmission is designed in this study. Based on experimental measurements and retro‐simulation, an effective approach is proposed to extract the parasitic parameters of a Schottky diode. A highly efficient millimetre wave rectifier with a measured efficiency of 63% is constructed based on the exact equivalent circuit parameters of a diode. A circularly polarised metasurface antenna is adopted as the receiving antenna, and the gain is enhanced by introducing metal vias around the metasurface. The antenna and the rectifier are connected directly via a microstrip line. Measurements show that the metasurface antenna has a gain of 11.3 dBic and an axial ratio of 2.5 dB at 24 GHz. The measured conversion efficiency of the rectenna reaches 63% at 300 Ω load when the input power is 15.2 dBm. The rectenna has the advantages of low profile, which can be conformal to the electrical equipment. [ABSTRACT FROM AUTHOR]

In this letter, a novel broadband compact circularly polarized antenna is proposed, which consists of a novel 4 × 4 cross‐layer metasurface (MS) structure and a slanted slot fed through microstrip line. The cross‐layer MS structure is formed by loading several cross‐layer stacked patches along one dimension of traditional square MS structure, and these stacked patches are located below the gaps of the original square patches directly. Compared with traditional square MS structure, the proposed cross‐layer MS structure can be viewed as one polarization‐dependent MS, exhibiting different reflection features in two orthogonal dimensions. Then, by properly tailoring the phase difference of the polarization‐dependent MS structure between the two orthogonal dimensions and combining it with a slanted coupling slot, two degenerate modes can be generated and then a wideband circular polarization radiation can be realized. Furthermore, the proposed antenna has a much compact aperture size of 0.41λ0 × 0.41λ0 due to the cross‐layer stacked patches, which can also enlarge the total capacitance by introducing extra cross‐layer capacitances. Finally, measured results show that the −10 dB impedance bandwidth of the proposed antenna is 39.6% (5.82 ~ 8.69 GHz), and 3‐dB axial ratio bandwidth is 26.3% (6.51 ~ 8.48 GHz) with a peak gain of 5.81 dBi. The simulated and measured results are in good agreement to verify the good performance of the proposed antenna. [ABSTRACT FROM AUTHOR]

A wideband substrate integrated waveguide (SIW) power divider based on half mode analysis is presented in this article. The structure is constructed by two substrate layers and three metal layers. Two symmetrical longitudinal apertures etched on the middle ground are introduced to realize the equal power division, and couple the signal from the SIW to the upper layer output ports simultaneously. Two fork‐type microstrip lines on the top metal layer are used to improve the bandwidth of the power divider. The equivalent circuit based on the half mode analysis method is presented for theoretical analysis and further design of the power divider, and good impedance matching can be obtained accordingly. For demonstration, a power divider prototype with the dimension of 48 × 73 × 1.38 mm3 is designed, fabricated, and measured. Good agreement is observed between the simulated and measured results. The measured return loss of the SIW power divider is better than 12 dB in the frequency range of 6.2 ~ 10.3 GHz, and the insertion loss is around 1.6 dB over the entire frequencies of interest. [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]

Microstrip ultra-wide band (UWB) delay lines consisting of a novel periodically loaded transmission line (PLTL) are presented, along with discontinuous structured guard lines (DSGLs). The distinctive advantage of the proposed approach is that the far-end crosstalk (FEXT) between the adjacent lines is effectively suppressed comparing to the conventional circuits. Afterward, the crosstalk of connected adjacent lines is effectively suppressed by modifying the DSGLs, since the current distributions are different from the separated adjacent lines. Subsequently, the strong reflection points are eliminated, which seriously deteriorate the performances in amplitude and group delay. Moreover, the serpentine delay line (SDL) and serpentine meandered delay line (SMDL) are studied, respectively, using the conventional microstrip (CMS) and the proposed PLTL with DSGLs. As a result, the SMDL pattern is also demonstrated useful to suppress the near-end crosstalk (NEXT) between the adjacent second-level curves, which in turn reduce the fluctuations in the group delay. In addition, the PLTL SMDL with DSGLs consequently have the superiority of suppressing the NEXT and FEXT simultaneously. Further simulations and measurements indicate that the performances of the PLTL SMDL with DSGLs lines are superior to the conventional method in a UWB range of dc to 25 GHz, including amplitude and group delay flatness, along with high time delay efficiency due to the slow wave property. [ABSTRACT FROM AUTHOR]

A novel miniaturized wideband antenna based on a hybrid L/T‐shaped metasurface structure is proposed, which is fed by an aperture coupling through a microstrip line. To realize the miniaturization of the metasurface antenna, the hybrid L/T‐shaped metasurface structure composed of several L‐shaped metal patches and T‐shaped metal patches is firstly presented. By placing the L‐ and T‐ shaped metal patches with an inverted arrangement, the capacitances caused by interdigital‐like capacitors can be introduced accordingly, which can decrease the resonance frequency and then realize obvious size reduction. The fabricated antenna prototype exhibits a wide impedance bandwidth of 44.0% (5.93 ~ 9.28 GHz) with reflection coefficient ≤ −10 dB and peak gain of 6.57 dBi within a compact radiation aperture size of 0.32λ0 × 0.39λ0. [ABSTRACT FROM AUTHOR]

In this paper, low-profile compact microstrip magnetic dipole antennas with large beamwidth and broad bandwidth are proposed for vehicular applications. At first, by introducing a strip on the bottom layer of microstrip magnetic dipole antenna, the electric current sources are introduced for the enhancement of beamwidth together with the magnetic current source. The operation principle of an equivalent complementary source model is then revealed to provide a physical insight. As seen, the half-power beamwidth (HPBW) can be controllable and effectively enlarged by the electric length of the planar magnetic dipole antenna. Next, by using a stub crossing on the strip, the impedance bandwidth is significantly improved comparing with the unloaded counterpart. After that, the antenna size is miniaturized by etching a pair of slots to extend the length of current path. Experimental results indicate that, under a very low profile of 0.016λ0 and 0.032λ0, the antenna prototypes can still achieve an impedance bandwidth of 14.5% and 20.8%, and a maximum HPBW of 99° (E-plane)/180° (H-plane) and 112° (E-plane)/159° (H-plane). It is also demonstrated that when the antenna size is reduced to 0.442λ0×0.284λ0, the impedance bandwidth up to 14.9% and the maximum HPBW of 93° (E-plane)/231° (H-plane) can be guaranteed with a low profile about 0.032λ0. Comparing with other design approaches, the proposed designs feature a very low profile structure, and superior beamwidth and bandwidth properties, as well as simple configuration and compact size. [ABSTRACT FROM AUTHOR]

In this letter, a millimeter-wave (mm-wave) dual-band bandpass filter is proposed with large bandwidth ratio by using gallium arsenide (GaAs)-based integrated passive device (IPD) technology. To realize small chip size, one dual-mode on-chip resonator is designed by using quasi-lumped capacitors and microstrip lines. In addition, multiple transmission zeroes are generated by further introducing both the electric and magnetic couplings between adjacent resonators. To realize large bandwidth ratio of two passbands, the external quality factors are investigated at both passband, and can be independently controlled. For demonstration, a 28-/50-GHz dual-band bandpass filter is designed, fabricated, and measured. The fractional bandwidth ratio is 7.8, which is much larger than the reported on-chip filters. Meanwhile, very low insertion loss of 0.58-dB is realized for the lower passband at 28 GHz, indicating the proposed dual-band bandpass filter a promising application in mm-wave wireless systems. [ABSTRACT FROM AUTHOR]

A novel wideband low‐profile antenna using a hybrid metasurface (MS) structure is presented. The proposed hybrid MS radiator consists of metal patches of different shapes or arrangements, and is fed by a microstrip line through a coupling slot etched on the ground plane. Several resonance modes can be excited for the hybrid MS radiator when a linearly polarized incident plane wave reaches, while one more resonance mode can be introduced by the coupling slot. As a result, wideband and stable radiation can be obtained. The results of the fabricated antenna prototype indicate a large bandwidth of 57.4% (5.23 ~ 9.44 GHz) and a stable gain with a 2‐dB gain bandwidth of 39.2% in a low profile of 0.09λ0. The performances are demonstrated by both simulated and experimental results. [ABSTRACT FROM AUTHOR]

A half-air-filled substrate-integrated groove-gap waveguide is proposed for millimeter-wave and terahertz applications. The waveguide is constructed by a ball grid array using a flip-chip technique without metallic vias with lightweight and low profile. The possible leakage perpendicular to the groove is prevented by solder balls as modeled by an equivalent circuit. Besides, an inline transition between the proposed waveguide and a microstrip line is proposed, fabricated, and measured. The design concept and working mechanism are explained. Good agreement between simulation and measurement is observed. The simulation shows that the proposed waveguide can cover the entire ${W}$ -band (70–118 GHz), and the measurement demonstrates that the proposed transition can operate at 90–98.8 GHz. [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]

This paper introduces a direct sputtering technology for fabricating flexible and transparent microwave microstrip line. The polydimethylsiloxane (PDMS) is used as the substrate, to realize the characteristics of flexible, stretchable, and transparent microwave circuit, and the solid metallic lines are replaced by the mesh metal. In particular, direct sputtering technology is used on the PDMS substrate to fabricate these transmission lines, which is an efficient candidate for fabrication of microwave or millimeter-wave circuits and is potentially a significant method for multilayer circuits. The fabricated transmission lines with different metallic meshes are measured under conditions of the normal state, 30° inside bending, and 130% stretch, respectively, with acceptable electrical performances up to a frequency of 20 GHz. [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]

Half-mode substrate integrated waveguide (HMSIW) switchable unit, built by HMSIW section with loaded single or multi-microstrip shunt stub(s), was proposed in this work. Both shorted and opened stubs were studied, investigated and compared, bandwidth enhancement method for proposed switchable units was proposed and demonstrated. Based on these switchable units, narrowband and broadband HMSIW single-pole-single-through (SPST) switches, SIW SPST switch and SIW/HMSIW-based single-pole-double-through (SPDT) switch were designed, fabricated and measured. Good performances were observed experimentally for these proposed circuits, showing the advantages of proposed concept and an excellent candidate for switchable or reconfigurable SIW/HMSIW circuits or systems. [ABSTRACT FROM AUTHOR]

Two novel wideband balanced networks with wideband common mode suppression and arbitrary power-dividing ratio are proposed in this paper. The differential/common mode equivalent circuits of the balanced networks can be easily reduced based on the matrix transformation. Microstrip-slotline 180° phase inverters loaded with four isolation resistors are used to realize high isolation for the power division output ports. Two planar wideband equal and unequal power division balanced networks with bandwidths of 33% of (1:1, equal) and 39% (1:2.22, unequal) for the differential mode and over 120% common mode suppression (0.96–3.6 GHz, |Scc21, 31| < –10 dB) are designed and fabricated. [ABSTRACT FROM AUTHOR]

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]