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One kind of cross-layer capacitive-loaded metasurface (MS) structure is proposed and applied to realize miniaturized wideband MS antennas. The proposed MS structure is constructed by loading a thin substrate with several stacked patches above conventional MS structure, where the cross-layer stacked patches are located upon the gaps between the original MS units. Therefore, additional capacitances can be introduced accordingly, and then help decrease the resonance frequency effectively. Based on above strategies, when the resonance frequency remains unchanged, the proposed MS structure with smaller aperture size can provide equivalent capacitive reactance and inductive reactance with conventional MS structure. In this way, the miniaturization can be realized while the wideband feature is still remained. By optimizing the loading structure, symmetrical and asymmetrical MS structures are designed accordingly and different-level miniaturizations are realized, where the element sizes can be respectively miniaturized to 0.067 λ0 × 0.067 λ0 and 0.059 λ0 × 0.059 λ0. For demonstration, onw asymmetrical capacitive-loaded MS structure is used to realize a compact wideband MS antenna, where large impedance bandwidth (∼44.4%) and compact size (∼0.41 λ0 × 0.41 λ0) are obtained. This design method may provide a feasible solution to realize compact wideband MS antennas for broadband wireless communication systems. [ABSTRACT FROM AUTHOR]

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

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

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

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

In this article, permittivity measurement based on open resonator technology is reviewed, and then, the hemispherical open resonator with an enlarged aperture on the curved mirror is proposed for high-frequency applications. A numerical compensate method based on frequency deviation is first proposed in detail for permittivity correction. To verify our idea, an open resonator is designed and fabricated over the frequency from 26 to 40 GHz, and some materials with known characteristics are measured based on proposed technology. The complex permittivity measurement of two transparent materials, polydimethylsiloxane (PDMS) and cyclic olefin copolymer (COC), are studied at 260 GHz. Measured results are compared with previous ones, and the discussion is provided, which shows that the proposed method probably is an efficient way for complex permittivity measurement at high frequency up to terahertz. [ABSTRACT FROM AUTHOR]

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

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

A multiresonance antenna based on a nonperiodic square-ring metasurface (MS) is proposed, which has large bandwidth and stable radiation gain. The nonperiodic MS radiator is formed by several adjustable square-ring patches and fed by a microstrip line through a coupling slot. By properly adjusting the widths of these square rings, different resonance modes can be inspired for the MS according to the characteristic mode analysis. Combined with the resonance mode of the coupling slot, multiple adjacent resonance frequencies occur and thus realize a wideband and consistent radiation. For demonstration, a C-band wideband antenna based on the proposed 4 × 4 square-ring MS units with a low profile of 0.06λ0 is accordingly designed and fabricated. The measured results indicate a large impedance bandwidth of 54% (4–7 GHz) and an extremely stable gain with 2 dB gain bandwidth of 32% (4.76–6.54 GHz). [ABSTRACT FROM AUTHOR]

Recently, 4G and 5G microwave communication circuits and systems have been undergoing rapid development [1], [2]. Signal crosstalk and high costs have seriously limited the fast development of microwave technology and multilayer integrated circuits [3], while radiation power loss of commonmode noise can be up to 25% of the input power in the Ka band (22-27 GHz) [4]. For the past 10 years, different balanced circuits with higher immunity to environmental noise, lower electromagnetic interference, and better dynamic range have attracted increasingly more attention [4], [5]. Balanced filters [6]-[15], balanced power dividers [16]-[22], and crossovers [23]-[27] are the most commonly used planar balanced circuits. In our opinion, for passive balanced circuits, some simple design objectives can be summarized as follows: 1) simpler balanced circuit structures, 2) high passband selectivity and wideband harmonic suppression for the differential mode, and 3) wideband and high-level commonmode suppression. [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]

The characteristics of a modified dual composite right/left-handed (D-CRLH) unit cell is investigated, which can be applied to design bandpass filters. The proposed unit cell is very compact and contains ten structural variables, which provides large design flexibility to realize different frequency responses. To assist the design of D-CRLH unit cells, the resonant characteristics are analyzed, and the design strategies for performance improvements are given accordingly. Furthermore, the design method of D-CRLH bandpass filters is introduced, with which the desired performance can be obtained by dimensions modifications of adopted resonators. For demonstration, three D-CRLH bandpass filters aimed at different performance are designed and experimentally verified. Good agreement between the measurements and design goals can be observed. [ABSTRACT FROM PUBLISHER]

Two novel high selectivity wideband balanced filters based on open/shorted stubs with multiple transmission zeros are proposed in this brief. Two and four transmission zeros near each passband for the differential mode (DM) can be easily achieved for two balanced filters. In addition, the common mode can be suppressed with three and five transmission zeros with an insertion loss greater than 15 dB/20 dB over a wide frequency band. Two prototypes with 3-dB fractional bandwidths of 67.6% and 37.8% for the DM with an insertion loss greater than 15 dB (7.0–12.7 GHz) are designed and fabricated. A good agreement can be observed between the measured results and the theoretical expectations. [ABSTRACT FROM PUBLISHER]

Tunable dual-band filter and diplexer based on folded open loop ring resonators (OLRRs) are proposed in this brief. Two pairs of OLRRs of different center frequencies are utilized to couple with microstrip transmission lines in these two devices, and there is no extra matching network in the diplexer structure. Maximal magnetic coupling and high isolation can be obtained by placing the resonators at proper positions along the feeding lines. The passband/channel frequencies of the dual-band filter/diplexer can be tuned independently by varying dc bias voltages applied to the varactors loaded at one end of the resonators. In addition, a broad harmonic suppression can be obtained by choosing appropriate lumped elements adding to the OLRRs. The performances of the proposed devices can be verified by the simulated and measured results. [ABSTRACT FROM PUBLISHER]

A new kind of compact dual-mode dual-composite right-/left-handed resonators is proposed. Dual-band bandpass filters (BPFs) are consequently designed with over 88% size reduction. To assist the filter design, an analytical design method is further presented, with which one filter can be designed flexibly according to the desired frequencies and bandwidths (BWs). To alleviate the design difficulties, a synthesis design technique and a feedback-based optimization process are both employed. In addition, the independent control of frequencies, BWs, and coupling coefficients are also realized, which provide large freedom for designing BPFs. To ensure the feasibility of the design method, the valid ranges of center frequency and BW ratios are first determined. Furthermore, four compact BPFs are designed with a large/small center frequency ratio (3.11/1.6) and a large/small BW ratio (2.52/0.52). Good agreement between the measurements and simulations are observed, indicating the validity of the proposed design method. [ABSTRACT FROM PUBLISHER]

This paper presents a varactor- and stub-loaded dumbbell-shaped resonator (VSDSR) for application in differential dual-band bandpass filter, which possesses a tunable lower passband and a fixed upper passband. Under differential-mode (DM) bisection, the VSDSR behaves as a ring resonator with four resonant modes, which can be categorized into two independent groups for constructing two passbands. At the same time, the common-mode (CM) equivalent circuit of the VSDSR generates multiple CM resonant frequencies and some of them inevitably overlap with the DM ones. Accordingly, the traditional CM suppression methods such as adding shunt stub or lumped element are disabled. To suppress the CM signals in both DM passbands, the defected ground structure (DGS) units are embedded underneath the adjacent edges of the two rings directly to form a CM suppression filter without increasing the circuit size. Meanwhile, they have almost no effect on the DM responses. Benefitting from the bandstop and slow-wave effects of the employed DGS units, the CM noises in both DM bands can be rejected effectively. In particular, the level of the CM suppression in the DM lower passband can be improved by adjusting the location of the DGS units. Furthermore, the proposed CM suppression scheme is adaptive in the tunable lower DM passband. [ABSTRACT FROM PUBLISHER]

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

A new frequency-agile scheme for the loaded stepped-impedance resonator (SIR) is introduced, which can be employed for designing a wideband tunable bandpass filter (BPF). Two identical capacitors are added to the two open ends, and a capacitor is added to the center of the SIR. By properly controlling their respective values, the even-mode resonant frequency (f_\mathrmeven) can be bidirectionally tuned, resulting in a wideband tuning range (approximately double those of the traditional tunable resonators). However, in such frequency range, the odd-mode resonant frequency (f_\mathrmodd) functions as a spurious resonance would appear. To overcome this, the feed line is attached to the center of the SIR where it is always short-circuited for f_\mathrmodd and its odd-order harmonics, which cannot be excited accordingly. Thus, the wideband tuning range of the passband (f_\mathrmeven) in the proposed BPF is validated to be meaningful, and the selectivity of the passband is improved due to the suppression of odd-mode spurious near the passband. For demonstration, a wideband tunable BPF is designed, and the simulated and measured results are presented, showing good agreement. The results showcase that the tuning range of passband reaches 84.4%, i.e., from 0.77 to 1.42 GHz with insertion loss from 3.1 to 1 dB. [ABSTRACT FROM PUBLISHER]

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

A novel kind of tri-band bandpass filter (BPF) is presented, which is based on the dual composite right- and left-handed resonator. The proposed tri-band BPF is very compact with over 30% size reduction over the previously published ones. The center frequencies and bandwidths can be controlled independently with large flexibility. In addition, the return losses can also be adjusted independently, resulting in the optimal impedance matching for the proposed designs. Finally, one tri-band BPF is designed for demonstration, which simultaneously exhibits compact circuit size and preferable in-band performances. Good agreement between the measured and simulated results is observed, verifying the validity of the design strategies. [ABSTRACT FROM PUBLISHER]

A novel dual-band microstrip bandstop filter with multiple poles using open/shorted coupled lines is proposed in this paper. Nine transmission poles near the two stopbands can be easily realized by conventional coupled lines and transmission lines. The two center frequencies of the dual-band bandstop filter can be adjusted flexibly by only changing the even/odd-mode of the coupled lines. The planar microstrip dual-band bandstop filter ( $\varepsilon r = 2.65$ and $h = 0.5$ mm) with nine transmission poles is designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filter. [ABSTRACT FROM PUBLISHER]

Two novel wideband differential bandpass filters based on a T-shaped structure are proposed in this paper. Broad passband and wideband harmonic suppression for the differential/common mode can be easily achieved for the wideband differential filter without cross coupling, due to the controlled resonator frequencies of the shorted/open T-shaped structure. In addition, another more compact differential filter using cross coupling is proposed with two transmission zeros close to the passband to improve the selectivity for the differential mode. To verify the presented concept, two prototypes (\varepsilon r = 2.65, h = 0.5~\ mm) with 3-dB fractional bandwidth of 70% and 70.7% for the differential mode and insertion loss greater than 13.5 dB for common mode (0–19 GHz) are designed and fabricated. Good agreement can be observed between measured results and theoretical expectations. [ABSTRACT FROM AUTHOR]