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In this article, a highly miniaturized absorptive bandpass filter based on a novel topology is presented. The filter topology utilizes a resistor-loaded network to achieve absorptive characteristics while additional capacitive coupling between series resonators is introduced to enhance selectivity. The proposed filter with a center frequency of 2.5 GHz and a 3-dB bandwidth of 2800 MHz is implemented using a GaAs integrated passive device (IPD) technology, exhibiting a small die size (0.7 mm × 1.13 mm), low loss in-band insertion loss (0.9 dB), high out-of-band rejection (8.8 f 0 ¿25 dB), and a wide low-reflection frequency range. The measurement results show good agreement with the simulations. These features show promising applications in highly integrated RF systems. [ABSTRACT FROM AUTHOR]

A novel narrow‐band balanced filtering network using coupled lines loaded with stubs is proposed in this letter. Two Wilkinson power dividers using coupled lines are used to realise the six‐port balanced network. Wideband common mode suppression and power division isolation can be achieved due to the loaded open/shorted stubs. A narrow‐band balanced filtering network for the WLAN band is designed. Good agreements can be found between the simulation and measurement results. [ABSTRACT FROM AUTHOR]

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

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

The fabrication process of an advanced transparent cyclic olefin copolymer (COC)‐based laminate is introduced, along with the laser cutting technology for circuit pattern. Then, a three‐way Gysel divider with an equal power‐dividing ratio is reviewed, designed and measured, based on the proposed COC‐based laminate. The measured results are compared to those from a similar three‐way Gysel divider based on traditional RT/duroid 5880 laminate, from which we can see that COC‐based laminate has the advantage of lower loss, with other advantages such as low cost, easy realization, high‐precision, and even the transparency. This laminate can be an excellent candidate for a substrate at microwave or millimeter‐wave circuits. [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]

In this article, a novel copper clad laminate based on cyclic olefin copolymer (COC) is proposed and manufactured by using lamination process. The loss characteristic of manufactured laminate is investigated by comparing the measured results of two microstrips on proposed COC‐based laminate and traditional Rogers RT/duroid 5880, respectively. Moreover, the SIW/HMSIW baluns operated at X‐band are designed on the proposed laminate, and the measured results verify the inherent out‐of‐phase performance and good amplitude characteristics in broadband frequency range. This work shows a novel type of high‐frequency circuit boards on COC material, which is significantly to be one of the advanced candidates for microwave/millimeter wave circuit applications. [ABSTRACT FROM AUTHOR]

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

This article presents a 23–28-GHz digital-controlled phase-invariant and ultralow gain error variable gain amplifier (VGA) for 5G applications. The mechanisms of gain control and phase variation in CMOS VGA based on single-level transistor structure are analyzed in detail. According to the analysis, an active cross-coupling neutralization (ACCN) technique is proposed. The ACCN technique not only compensates for phase variation, but also makes phase compensation insensitive to the process, supply voltage, and temperature (PVT) variations. For achieving ultralow gain error, an asymmetric capacitive gain resolution improvement (ACGRI) technique is adopted, which realizes a fine gain step with low control circuit complexity. Further to reduce gain error, greatly improving the accuracy and robustness against PVT of gain control is necessary. With regard to this, a current-type digital-to-analog converter (DAC) is also integrated onto the chip. The proposed VGA is demonstrated in 65-nm CMOS technology with a core chip area of 0.14 mm2. Under 5-b digital gain control conditions, the presented VGA achieves a measured linear gain tunability range of 6.2 dB with a 0.2-dB fine tuning step. The measured root mean square (rms) phase error is less than 0.92° across 24–28 GHz with a minimum value of 0.63° at 27.8 GHz. The rms gain error is less than 0.13 dB, with a minimum value of only 0.03 dB at 25 GHz. At the maximum gain state, the proposed CS VGA exhibits a peak gain of 29.4 dB with 3-dB bandwidth of 23.5–27.5 GHz and the minimum noise figure is 4.8 dB at 26 GHz. Besides, the measured OP1dB and OP3dB are 6.3 and 9.6 dBm, respectively. The influence of VT variations on the phase compensation and gain tuning is also measured, and the proposed VGA exhibits strong robustness. [ABSTRACT FROM AUTHOR]

A wideband low-noise amplifier (LNA) with low and flat noise figure (NF) is presented in this article. For conventional wideband noise matching, the noise performance in the high-frequency region of the entire wideband is usually deteriorated due to the frequency-dependent nature of the minimum noise figure (NFmin) for a MOSFET. To address this issue, a novel wideband noise matching approach aiming at noise matching in high band is proposed. This approach can reduce the NF in high band at the cost of a slight NF increase in low band, eventually achieving a low and flat NF and thus a better overall noise performance for a wideband LNA. In addition, the multistage noise matching technique is employed at high frequencies to further reduce the NF caused by the second amplification stage. To validate the proposed techniques, a two-stage LNA prototype was designed and fabricated using a 65 nm CMOS process. The experimental results indicate a peak gain of 16.6 dB with a −3 dB bandwidth (BW) from 7.2 to 27.3 GHz (a fractional BW of 116%). Within the entire band of interest, the simulated NF is low and almost constant (3.3–3.4 dB), while the measured NF falls within the range of 3.30–3.72 dB. Considering the uncertainty of NF measurement, a 0.21 dB NF flatness is one of the best results among the reported millimeter-wave wideband LNAs. The measured third-order input intercept point (IIP3) is −6 dBm at 20 GHz, while the power consumption is 13.2 mW. In addition, only two passive transformers are used in this design, leading to a compact chip core area (0.14 mm2). [ABSTRACT FROM AUTHOR]

An active quasi‐circulator using gallium nitride (GaN) high electron mobility transistors technology is presented. By using two common‐gate and one common‐source transistors, two self‐interference signal paths from transmitting (Tx)‐port to receiving (Rx)‐port are constructed. Due to the features of out‐of‐phase and equal magnitude for the two‐path signals, sufficient Tx‐Rx isolation can be realized through cancellation of the two‐path signals at the Rx‐port. One prototype working at 27–29 GHz was designed and fabricated for demonstration. The measured results indicate maximum isolation of 44 dB at 28.2 GHz and the 30 dB isolation bandwidth of 300 MHz. The measured insertion losses of Tx‐path and Rx‐path are less than 4.5 and 3.6 dB within the operating frequency. Due to the high power density of the GaN devices, the measured IP1dB of the quasi‐circulator is better than 18 dBm. [ABSTRACT FROM AUTHOR]

A dual‐band balanced‐to‐unbalanced filtering power divider by coupled ring resonators is proposed. Two passbands can be easily realised by the two coupled ring resonators. Three transmission zeros near the two passbands are used to improve the selectivity. The common mode can be easily suppressed by the bandstop performance of the open stubs. A fabricated prototype (εr = 2.65, h = 1 mm, tanδ = 0.003) with centre frequencies located at 2.82 and 3.22 GHz is designed and measured to prove the proposed methods. [ABSTRACT FROM AUTHOR]

Two new wideband in-phase and out-of-phase balanced power dividing/combining networks are proposed in this paper. Based on matrix transformation, the differential-mode and common-mode equivalent circuits of the two wideband in-phase and out-of-phase networks can be easily deduced. A patterned ground-plane technique is used to realize the strong coupling of the shorted coupled lines for the differential mode. Two planar wideband in-phase and out-of-phase balanced networks with bandwidths of 55.3% and 64.4% (\vert S{ dd21,31}\vert<4\ {\ {dB}}) for the differential mode with wideband common-mode suppression are designed and fabricated. The theoretical and measured results agree well with each other and show good in-band performances. [ABSTRACT FROM PUBLISHER]

A compact tri-band bandpass filter using input/output cross coupling is proposed. Three passbands can be adjusted by changing the characteristic impedance of the T-shaped structure with a shorted stub. The three passbands are designed to operate at 1.85, 3.5 and 5.2 GHz based on the T-shaped structure. Four transmission zeros are used to realise high selectivity for the passbands. Good agreement can be observed between the measured and simulated results. [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]

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 wideband antenna based on substrate‐integrated suspended line (SISL) platform is presented for the fifth generation (5G) communication applications. The antenna is composed of two dipoles and differentially driven by coupled slot between dipole arms to achieve symmetrical radiation pattern on both E and H plane. Combining with the multilayer feature of the SISL, a metallic cavity under the dipole is formed to improve the antenna bandwidth and radiation performance. To verify the proposed antenna, one prototype was fabricated using the conventional printed circuit board process and a balun structure was designed to provide the differential excitation. The measured results indicate that the proposed dipole antenna with differential feeding network achieves a large −10 dB impedance bandwidth of 58% from 24.5 to 44.5 GHz and a peak gain of 8.2 dBi. The proposed antenna is a promising candidate for 5G communications due to its advantages of wideband, high gain, low cost, and convenient integration with differential active circuits. [ABSTRACT FROM AUTHOR]

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

This study presents an low-temperature cofired ceramic (LTCC) V-band cross-coupled band-pass filter using substrate-integrated waveguide cavities. Two antisymmetric U-shaped slots connected by via is proposed to construct the negative coupling structure, which is simple and especially useful for 60 GHz applications. Moreover, the U-slot structure possesses a wide range of realizable coupling coefficients from −0.008 to −0.075. An experimental LTCC fourth-order filter was fabricated for demonstration, achieving a bandwidth of 12% (7.2 GHz) at 59.6 GHz with superior frequency selectivity. [ABSTRACT FROM AUTHOR]

A compact dual-band bandpass filter (BPF) realized with stepped impedance resonators (SIR) and T-shaped line is proposed in this article. By appropriately selecting the impedance ratio of the SIR, a passband around at 5.4 GHz can be achieved by the second harmonic frequency of the SIR. In addition, a T-shaped line is used to replace the quarter-wavelength line between the two SIRs, and another passband at 2.45 GHz is realized between the transmission zeros created by the central open stub of the T-shaped line and the fundamental frequency of the SIR. Moreover, the transmission zeros created by the central open stub and SIR could also be used to improve the skirt selectivity of the proposed BPF. Good agreement can be observed between the measured and simulated results, demonstrating the validity of the design strategies. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2721-2724, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25599 [ABSTRACT FROM AUTHOR]

Two compact planar magic-T structures implemented on the double-sided parallel-strip line (DSPSL) and the slotline coupling are proposed and demonstrated. Due to a metallic ground inserted into the middle of the substrate for the double-sided parallel-strip line, the E-plane DSPSL power divider thus shows an intrinsic 180^\circ out-of-phase characteristic between the two input/output ports. A transition between slotline and DSPSL is utilized to realize the H-plane input/output port of the magic-T. The equivalent circuits are derived for the design of the proposed planar multilayer magic-T. Good agreement between the measured and simulated results indicates that the fractional bandwidths for the two planar magic-T structures are 42.8% and 43.8%, respectively, while the amplitude and phase imbalance are less than 0.22 dB and 1.5^\circ. [ABSTRACT FROM PUBLISHER]

An improved wideband planar inverted-F antenna (PIFA) is investigated in this work. The meander line structure is introduced into the conventional PIFA and significant bandwidth improvement can be observed. Two improved PIFA antennas with different meander line structures are designed and fabricated; the measured results show good agreement with the simulations, demonstrating 23.1 and 40% bandwidth at -10 dB return loss, about 131 and 300% bandwidth enhancement, respectively, compared with the original PIFA (less than 10%). Obviously, the proposed antenna demonstrates good performances (especially in bandwidth), compact size, low profile, and low cost; it is thus expected to find possible applications in wireless communication systems. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 384–387, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24046 [ABSTRACT FROM AUTHOR]

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

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

A wideband low-noise amplifier (LNA) featuring transformer-based wideband input matching is proposed for millimeter-wave applications. By analyzing the properties of conventional series input matching networks, which were widely employed in narrowband LNAs and shunt–series matching networks for bandwidth extension, a novel input matching network possessing the merits of both was proposed. For further bandwidth extension, another peak of input impedance at a higher frequency is introduced for the proposed input matching network. Moreover, it is proved that the proposed input matching network can suppress the gate resistor noise, resulting in significant noise figure (NF) improvement of an LNA. On the other hand, the NF is further reduced by connecting a transformer between the two amplification stages, which helps suppress the noise contribution from the second stage, leading to an LNA design with NF lower than 4.5 dB over a very wide operating bandwidth. To enhance the gain bandwidth, the peak distribution, including both shunt peaking and series peaking, is discussed. By appropriately distributing these peaks, which is also known as the pole-tuning technique, a wider gain bandwidth can be obtained. To validate the proposed techniques, an LNA with two common-source (CS) stages is designed and fabricated using a 65-nm CMOS process, and the overall chip size, including all pads, is only 0.26 mm2. The two CS stages are cascoded for dc biasing to reduce the power consumption. Experimental results show that a peak gain of 13.5 dB is achieved within a −3-dB bandwidth from 19.2 to 42.6 GHz. The measured NF is 3.1–4.5 dB, and the input 1-dB gain compression point (IP1 dB) ranges from −13.54 to −9.89 dBm in the entire gain bandwidth. The input return loss $S_{11}$ is less than −10 dB over a frequency range of 16.8–38.9 GHz. Moreover, benefiting from the current-reuse technique, the power consumption of the LNA is only 6.36 mW. [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]

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

A novel wideband dual‐circularly polarized orbital angular momentum (OAM) antenna array using metasurface is proposed. The proposed antenna array composed of four antenna elements generates OAM beams in a simple configuration. Each antenna element is placed perpendicularly to the adjacent one, and fed by an in‐phase excitation with equal amplitude. Each antenna element is based on corner‐truncated polarization‐rotation metasurface (PRMS) cells and excited by a dual‐feeding structure through a cross‐like slot, which can realize wideband dual circular polarization (RHCP, LHCP). The proposed antenna array produces dual‐mode OAM mode waves (l = ±1) and exhibits good dual‐circularly polarized performances in a low profile of 0.068 λ0. The measured results show wide impedance bandwidths of 30% for LHCP and 26.6% for RGCP. Also, the large axial ratio bandwidths ARBWs of the OAM antenna array are 20% for LHCP and 14% for RHCP. [ABSTRACT FROM AUTHOR]

A novel topology for designing 60 GHz duplexers is presented. Both the receiver (Rx) and transmitter (Tx) filters of the duplexer, which were constructed using dual‐mode substrate‐integrated waveguide (SIW) cavities, can exhibit a single‐sided transmission zero. The transmission zeros were arranged to achieve high channel isolation and frequency selectivity. The results confirm that the fabricated duplexer can achieve an Rx/Tx isolation higher than 30 dB. [ABSTRACT FROM AUTHOR]

A novel microstrip diplexer for global system of mobile (GSM) and wireless local area network (WLAN) bands using common shorted stubs is proposed. Two transmission zeros on both sides of the passband response can be easily realised for each passband. Additional transmission zeros created by the shorted stubs are introduced to suppress the harmonic of the microstrip diplexer. A microstrip diplexer with high isolation and selectivity can be achieved by locating the transmission zeros of each channel. A microstrip diplexer prototype with 30 dB isolation from 0.1 to 6.0 GHz has been designed and fabricated. [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]

In this article, a novel polarization‐dependent metasurface (PDMS) structure is presented and applied to realize a wideband high‐gain antenna with multiple resonances. The PDMS element is obtained by cutting slots into the square patch unit cell of conventional metasurface (MS). Very different from the conventional MS structure, the proposed PDMS element exhibits different reflection phases and resonance frequencies, depending on the polarization state of the incident plane wave. By properly tailoring the reflection‐phase curves under different polarizations, a proper PDMS structure is introduced. Then, by arranging the PDMS elements along different orientations, a multiresonance radiator can be realized. When applying the proposed radiator to the slot‐coupled MS antenna, one broadband PDMS‐based antenna with multiple adjacent resonance frequencies can be realized by the combination of coupling slot‐mode and PDMS modes. For verification, a PDMS radiator with 4 × 4 unit cells is designed accordingly and applied to realize one C‐band broadband PDMS‐based antenna in a low profile (0.06 λ0). The measured results of the fabricated prototype PDMS‐based antenna exhibit a large –10 dB impedance bandwidth of 55% (4.31‐7.58 GHz), a maximum available gain of 10.898 dBi, and a 2‐dB gain bandwidth of 30.81% (5.1‐6.96 GHz). [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]

This study proposes a compact structure of the three‐way Gysel power divider with arbitrary power dividing ratio, which has a significant difference from existing N‐way ones with a common node in the centre of the circuit. First, existing equations are reviewed, and new analytical closed‐form equations are derived according to the proposed structure. The frequency bandwidths, affected by the parameters of isolation networks are investigated in detail and optimised for performance balance. For verification, the proposed three‐way Gysel power dividers are calculated, optimised and fabricated at the centre frequency of 3.5GHz with different dividing ratios of 1:1:1 and 1:2:3, respectively. Moreover, the equations are derived to design the N‐way Gysel power divider. [ABSTRACT FROM AUTHOR]

A novel high-performance wideband balanced bandpass filter based on transversal signal-interference techniques is proposed in this article. Two signal-propagation paths consisted of coupled lines structure are used to realize two transmission zeros for the differential mode passband. Folding coupled lines are used to reduce the size of the balanced filter, and the source–load cross-coupling lines can generate additional transmission zeros to suppress the common mode signal. To validate the design, a prototype with center frequency at 2.2 GHz for long-term evolution (LTE)-band with 3-dB fractional bandwidths of 65.4% for the differential mode is designed and fabricated. [ABSTRACT FROM AUTHOR]

A novel leaky wave endfire filtering antenna based on spoof surface plasmon polaritons (SSPPs) is proposed. The structure of leaky wave antenna consists of multiple radiating elements and one double-sided parallel strip line (DSPSL), and the filtering performance is realized by adding stubs with via holes. The structure with a periodic arrangement of the radiating elements has similar dispersion curves of SSPPs, which has low-pass transmission characteristic and also can radiate energy to the free space. According to the measured results, a peak gain of 8.65 dBi at a center frequency of 7.7 GHz and a bandwidth of 36.36% can be achieved for the leaky wave endfire filtering antenna based on SSPPs. The out-of-band rejection is over 13 dB. [ABSTRACT FROM AUTHOR]

A wideband reflectarray antenna consisting of single‐layer dipole element attached with T‐shaped stubs is proposed. By varying the lengths of the T‐shaped stubs, the unit cell can provide a linear phase curve covering about 420°. Critical design parameters are analyzed to understand its wideband operating mechanism. Using this novel type of unit cells, a 441 element 25° offset‐fed reflectarray with grid spacing of λ/3 at 10 GHz is designed, fabricated, and measured. The experimental results show that the proposed reflectarray can achieve 1‐dB gain bandwidth of 24% and 1.5‐dB gain bandwidth of 37%. In addition, aperture efficiency of 66.6% and cross polarization level of 29 dB are obtained at 10 GHz, respectively. [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]

In this article, a novel differential bandpass filter based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. It consists of a pair of double-layer SSPPs using double-sided parallel-strip line (DSPSL), a pair of single-layer SSPPs, and a 180° phase inverter. The transmission characteristics of the proposed SSPPs’ structure are analyzed by the differential-mode and common-mode method, and also applied to design the differential filter. To validate the design concept, a differential filter sample has been designed, fabricated, and measured. The simulated and measured results indicate a 3-dB fractional bandwidth of 25.5% (frequency 5.5 GHz), and a wide 20-dB common-mode suppression from 2.9 to 8 GHz can be achieved for the differential filter. [ABSTRACT FROM AUTHOR]

This article presents a method for analyzing the coupling between two adjacent substrate-integrated waveguides (SIWs) sharing a common row of metallic cylinders, which is based on the concept of equivalent circuit and wavenumber calculation. When the specific sizes of two adjacent SIWs are known, the scattering parameters of the shared common row of metallic cylinders can be derived, and the equivalent transmission line model of the SIW coupling structure is extracted. The even-and odd-mode wavenumbers in both transverse and propagating directions are calculated for this equivalent circuit. For an ideal forward-wave directional coupler, the transmission and coupling coefficient are then derived directly from the wavenumber and the length of the structure. Based on the proposed method, three SIW directional couplers with different coupling levels are designed and fabricated for verification. Good agreements between the calculated and simulated coupling parameters are observed. The proposed method provides a simple and accurate approach to estimate the coupling between two closely spaced SIWs sharing one common row of metallic cylinders and is expected to use for the design of millimeter-wave SIW-based circuits and systems. [ABSTRACT FROM AUTHOR]

Two novel classes of high-selectivity input-reflectionless bandpass filters (BPFs) with narrow- and wide-band characteristics and out-of-band transmission zeros (TZs) are presented. These input-reflectionless BPFs, which are based on a complementary-duplexer approach, respectively, exploit intercoupled short-/open-ended dual- behavior resonators (DBRs) and coupled line/T-stub two-path transversal filtering stages in their main BPF channel. Their absorptive auxiliary channel is made up of a resistively terminated dual-band bipath transversal filtering cell, whose dual passbands are allocated in the stopband regions of the main BPF channel. Thus, the RF-input-signal energy that is not transmitted by the main channel in its attenuated bands is dissipated by the loading resistor of the auxiliary one. Hence, input-reflectionless properties are attained in the whole BPF architecture. The theoretical design principles of the conceived narrow- and wideband input-reflectionless BPF approaches are described. Furthermore, their experimental usefulness is verified through the development and characterization of two microstrip sharp-rejection BPF prototypes centered at 2 GHz. [ABSTRACT FROM AUTHOR]

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

In this article, the design and implementation of two 28-GHz millimeter-wave on-chip high selectivity bandpass filters with coupled dual-behavior resonators are proposed. The proposed bandpass filters consist of coupled dual-behavior resonators with open/shorted stubs. Two and three out-of-band transmission zeros can be realized for the two bandpass filters. Two on-chip millimeter-wave bandpass filters are designed and fabricated for verification. The measurement results show that the insertion losses are both less than 2.2 dB at the center frequency. The sizes of the designed filters are $2.556\,\,\text {mm}\times 1.23$ mm and $3.155\,\,\text {mm}\times 1.47$ mm, respectively, including the pad. [ABSTRACT FROM AUTHOR]

A bandpass push–pull high power amplifier (PA) based on substrate integrated waveguide (SIW) filtering balun power divider is proposed in this article. The filtering characteristic of the PA is realized by the complementary split rings resonators (CSRRs) defected in the balun based on the SIW. Inherent to the middle metal plane of the SIW balun, the 180° phase difference power division can be achieved. Due to the natural differential characteristic of the balun, the proposed design can produce second-harmonic suppression. Greater output power is obtained owing to the filtering balun power combiner. For the fabricated bandpass push–pull PA, it exhibits high-selectivity bandpass response and good PA performance with the peak power-added efficiency (PAE) of 48.7% at 38.5-dBm output power. [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]

In this article, a compact dual‐band crossover using dual‐mode ring resonators by Coplanar‐Waveguide (CPW)‐Fed scheme is proposed. It contains 2 homocentric square ring resonators on the top layer to obtain the dual‐band responses. CPW feeding lines and open stubs are placed on the bottom layer to feed the ring resonators and adjust coupled strength. The center frequencies and bandwidths for each passband can be individually controlled easily. To prove the design concept, a compact dual‐band crossover operated at 1.57 and 2.45 GHz is designed and fabricated. The measured results show good agreement with the simulation ones results a wide frequency range. [ABSTRACT FROM AUTHOR]

Two novel high selectivity wideband balanced filters based on coupled lines with multiple transmission zeros/poles are proposed in this article. Four and six transmission zeros out of the passband for the differential mode can be achieved and adjusted by the loaded coupled lines independently, resulting in over 15 dB/20 dB out‐of‐band rejection, respectively. In addition, the common mode can be suppressed >15 dB/20 dB over a wide frequency band with five and seven transmission zeros. Two prototypes with 3 dB fractional bandwidths of 56% and 42.7% for the differential mode are designed and fabricated. Good agreements can be observed between measured results and theoretical expectations. [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering antenna based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. Double-sided parallel-strip line (DSPSL) is used to realize the wideband property for the double-layer SSPPs. Filtering performance can be realized by adding via holes and ring resonators in the double-layer SSPPs. The simulated and measured results indicate the high gain of 9.38 dBi and bandwidth of 10.44% can be achieved for the antenna with via holes and ring resonators, the out-of-band rejection is over 17 dBi. Meanwhile, the gain variations are less than 1 dBi in the whole frequency band. Good agreements can be observed between the measured and simulated results, which indicate good potential applications in the communication systems and integrated circuits. [ABSTRACT FROM AUTHOR]

This paper presents an automatic impedance transforming technique to extend the radio frequency rectifier input power range with high conversion efficiency. The rectifier employs two branches of subrectifier, each achieving impedance matching at high and low input power ranges. Then, the two branches are connected by a $\lambda/4 $ T-junction power divider. With such configuration, the input impedance of the two subrectifiers are transformed automatically, allowing the impedance matching over a wide input power range. In this way, the injected power can be optimally delivered to the subrectifiers, achieving a high efficiency over this wide input power range. This scheme manages to eliminate the power detetor for branch selection and can be applied to both single- and dual-band rectifiers with a reduced design difficulty. For validation, a single-band rectifier working at 915 MHz and a dual-band rectifier at 915/2450 MHz are implemented. Design analysis on the single- and dual-band rectifiers is carried out. The measurement results show that 68% maximum efficiency is achieved for the single-band (915 MHz) rectifier, and the input power range for the efficiency >70% of the peak efficiency is from −5 to 31 dBm. Besides, the dual-band rectifier shows 66% and 58% peak efficiencies at 915 and 2450 MHz, respectively. The input power range is from −6 to 33 dBm for the efficiency >70% of its peak value at 915 MHz, while from 10 to 32 dBm at 2450 MHz. These indicate that the input power range with high efficiency is extended. [ABSTRACT FROM AUTHOR]