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An admittance‐inverter‐based two‐section topology is proposed for filtering power dividers in this article aiming at high and wideband output isolation. Different from the classic two‐section Wilkinson power dividers, the bulky quarter‐wave transmission lines are removed and replaced by using two pairs of admittance inverters, which are realized by the input external quality factor (Qe‐in) and coupling coefficient (k12), respectively. Since the electric size of these coupling effects (Qe‐in and k12) are negligible, a significant size reduction is easily realized. In addition, two isolation elements are added between the input resonators and the output ones, respectively. Two‐prefect absorption points are accordingly realized in |S23|, indicating wider and higher output isolation compared with the reported designs using one isolation element. For demonstration, one two‐section filtering power divider is designed and fabricated. The circuit size is only 0.009λg2, while the output isolation exceeds 41.5 dB over the passband. [ABSTRACT FROM AUTHOR]

This article presents an analytical design for millimeter-wave monolithic microwave integrated circuit (MMIC) switches. First, the field-effect-transistor-based (FET-based) resonator is proposed, whose resonant frequency and bandwidth can be controlled flexibly. As a result, the design flexibility of MMIC switches can be highly improved by using FET-based resonators. Second, a fast and flexible impedance matching technique is presented for MMIC switches based on the coupling matrix method. By selecting appropriate coupling parameters, the MMIC switches can be easily designed without designing multistage impedance matching circuits. In this way, low insertion loss (IL) and compact chip size can be accordingly obtained. For design validation, two single-pole single-throw (SPST) switch prototypes are designed and fabricated by using two or four FET-based resonators, respectively. Implemented in 100-nm GaN-on-Silicon HEMT process, high input 1-dB compression point (IP1 dB) of over 30 dBm is realized. The return losses are better than 15 dB, the minimum IL is only 1.1 dB at 30 GHz, and the isolations are higher than 45 dB. The above features indicate the validation of the proposed design method for MMIC switches. [ABSTRACT FROM AUTHOR]

A high gain D‐band hybrid integrated on‐chip antenna (OCA) based on a low‐cost printed circuit board (PCB) packaging technology is analyzed and designed in a standard 40‐nm CMOS process in this paper. The proposed OCA is a hybrid structure of a slotted patch OCA with off‐chip PCB ground and off‐chip dielectric resonator (DR). The proposed OCA exhibits a simulated gain of 3.5 dBi and 53% radiation efficiency at 150 GHz. The simulated impedance bandwidth is 20 GHz. The radiation performance and impedance bandwidth of the OCA are observably improved with the proposed techniques. The proposed OCA occupies 0.52 × 0.56 mm2, and addresses the highly desirable yet challenging overall design of future low‐cost integrated millimeter‐wave (mm‐Wave) and terahertz (THz) systems, which hit the mark on cost and compatibility. [ABSTRACT FROM AUTHOR]

Traditional radome adversely influences the antenna performance besides protecting the antenna from the outside environment. In this work, one co‐design of a millimeter‐wave antenna and radome using parasitic patches is presented, featuring a low profile and high gain. First, the basic influence of radome on patch antenna is investigated on a transparent and low‐loss material cyclic olefin copolymer. Then, the electromagnetic interaction between the patches and the antenna is investigated in detail to reduce the adverse effect of field reflection and phase delay. One prototype of the co‐designed radome and antenna was fabricated for demonstration. The measured results show that the entire profile of the co‐designed radome and antenna is significantly reduced from traditional 0.5–0.2 λg and the gain is enhanced by 2.4 dB. [ABSTRACT FROM AUTHOR]

Aiming at high and wideband output isolation, a new topology of filtering power divider based on complex isolation impedance and surface wave mitigation techniques is proposed. Different from previously published filtering power dividers using pure resistor, an analytical design method by using complex impedance is proposed in this article. To formula the complex impedance, the LC equivalent circuit model is introduced, and the closed-form derivation is given accordingly. Based on the calculated impedance, high isolation can be theoretically realized in circuit level. However, the output isolation is limited below 20 dB in practical EM simulations. To solve this issue, the filtering power divider is further investigated in field level. To reduce the crosstalk between adjacent filtering channels, the surface wave mitigation techniques are investigated. Accordingly, a 16-dB enhancement of output isolation is realized, without sacrificing other filtering specifications. For experimental verification, a filtering power divider is designed, fabricated, and measured. A significant size reduction and 36-dB output isolation with over 500% isolation bandwidth can be observed, verifying the validity of the proposed design method. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mm-wave) monolithic-microwave-integrated-circuit (MMIC) bandpass filters (BPFs) usually feature high insertion loss (IL). To this concern, an analytical method for low-loss MMIC BPFs is presented by using lumped-distributed parameters in this article. To reduce the IL, the enhanced-quality-factor resonator and low-loss coupling topology are both investigated. First, the proposed resonator and filter are realized by combining quasi-lumped elements and distributed mutual coupling. Both compact size and multiple transmission zeroes are accordingly realized. Second, a low-loss coupling topology is further introduced for MMIC filter by using mixed electric and magnetic couplings. For theoretical analysis, the lossy equivalent circuit modeling for mm-wave MMIC BPF is investigated, as well as an analytical parameter extraction. Based on the circuit analysis, a fast synthesis of low-loss mm-wave MMIC filter is presented. For demonstration, two compact MMIC BPFs are designed by using the gallium arsenide (GaAs) process. Low IL of only 0.95 dB, sharp rejection skirt of passband, and wide stopband are simultaneously obtained. The features of the proposed MMIC BPFs indicate promising applications in the fifth-generation (5G) mm-wave systems. [ABSTRACT FROM AUTHOR]

Double-polarized dual-band absorptive frequency-selective transmission structure (AFST) is presented, which has two passbands within a wide absorption band. Equivalent circuit models (ECMs) are presented to assist the structure design efficiently. Based on the verified ECMs, practical AFSTs are then constructed accordingly. One single-band AFST is first designed, which is realized by introducing slot and cross-frame slot (CFS) resonators in the lossy and lossless layers of one broadband absorber, respectively. As a result, one passband is achieved, while the absorption at both sides is maintained. Furthermore, by using multiple slots and CFS resonators with different resonant frequencies, two transmission poles are, respectively, achieved at 3.5 GHz and 4.9 GHz, and the dual-bandpass performance is achieved. Under normal incidence, the operating frequency bands (reflection <−10 dB) of the proposed AFSTs are larger than 110%, while the minimum insertion losses are less than 0.25 dB. For demonstration, one prototype of the dual-band AFST is fabricated and measured, and a reasonable agreement between the simulated and measured results is observed. [ABSTRACT FROM AUTHOR]

In this article, a two-stage broadband GaAs power amplifier (PA) is presented, which consists of an improved Darlington power stage and a drive stage. As the most important part of the two-stage PA, the proposed Darlington power stage can simultaneously achieve large bandwidth and watt-level output power. The circuit analysis of the Darlington structure is carried out for large-size transistors. The bandwidth and gain of the Darlington structure are investigated in three cases with source peaking inductor, interconnection inductor, and compensation inductor. A design procedure for the total PA is developed to provide potential guideline. Furthermore, the total PA was fabricated using 0.15- $\mu \text{m}$ GaAs pHEMT technology. The measured maximum gain in the case of a small signal is 25.9 dB, and the 3-dB bandwidth is from 10.7 to 16.7 GHz (43.8% fractional bandwidth). The maximum power of 36 dBm and the maximum power-added efficiency (PAE) of 46.8% are measured at 13 GHz. To the best of our knowledge, the proposed PA exhibits the highest figure of merit (FOM) when compared with the other previously published works. [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]

In this article, various types of six-port balanced rat-race couplers with wideband common-mode suppression characteristics are presented. In these couplers, the input and output ports can functionalize either as single-ended or differential terminals to realize different operational modes. The power-splitting ratio for these balanced couplers can be flexibly adjusted by means of the values of the characteristic-impedance parameters of their constituent transmission-line segments. Furthermore, the employment of double-sided-parallel-strip-line-(DSPSL)-based 180° phase inverters instead of half-wavelength transmission-line-based ones allows for the considerable enlargement of their operation bandwidth in more-compact circuits with lower in-band insertion-loss levels. For experimental-validation purposes, two microstrip prototypes at $f_{0}=0.9$ GHz with equal and unequal power division are fabricated and characterized. They exhibit common-mode rejection levels higher than 15 dB from 0 to 1.8 GHz (i.e., 0– $2f_{0}$) and differential-to-common- mode-conversion suppression levels above 15 dB within the spectral range 0–1.49 GHz (i.e., 0– $1.65f_{0}$). [ABSTRACT FROM AUTHOR]

A differential magnetic field probe based on a balanced filter is proposed to improve electric field suppression. The probe comprises a rectangular metal loop for detection and a balanced filter transmission. Three 1/4λ stepped impedance transmission lines are designed between the detective part and balanced filter for impedance matching. The balanced filter can suppress the common mode signals generated by a normal electric field but has little influence on the differential signals detected by a tangential magnetic field thus, the electric field suppression of the magnetic probe can be enhanced. The measurement results show that the working frequency of the proposed magnetic probe ranges from 10 to 20 GHz, and the electric field suppression ratio is over 35 dB from 10 to 15 GHz. [ABSTRACT FROM AUTHOR]

A wideband and high-efficiency power amplifier (PA) based on a bandpass filtering (BPF) matching network is presented. Composite right-/left-handed (CRLH) cell and dual-CRLH (D-CRLH) cell are employed to realize the wideband BPF matching network with an absorbed bias circuit. The equivalent circuit model of the proposed BPF matching network is given and a synthesized design method is introduced. Furthermore, one wideband gallium nitride (GaN) PA with high efficiency is achieved by using the proposed BPF matching network accordingly. The measured S-parameters of the wideband PA reveal bandpass response from 1.2 to 2.3 GHz with ±1.2-dB gain flatness and one transmission zero (TZ). For large signal performance from 1.25 to 2.4 GHz, the experimental results show that the measured drain efficiency (DE) is between 64.3% and 77.5%, and verifying the validity of the design strategies for the proposed wideband high-efficiency PA. Due to the compact feature of the CRLH and D-CRLH (D/CRLH) matching network, the proposed PA achieves the smallest area in terms of core circuit compared with other published works. The results demonstrate the advantages of the D/CRLH BPF structure for designing wideband high-efficiency PAs. [ABSTRACT FROM AUTHOR]

Two novel high selectivity balanced-to-unbalanced filtering power dividers using ring resonators are proposed. The even-/odd-mode analysis method is applied to obtain the design equations at the operating frequency. The ring resonators can bring two transmission zeros in each side of the passband for the differential mode for the filtering power divider (structure I). Moreover, the three-quarter wavelength transmission lines are applied to produce the additional two transmission zeros of differential mode for structure II, which can further improve the differential-mode harmonic suppression and common-mode suppression. Two fabricated prototypes with 4-dB bandwidths of 11.2% and 11.6% are designed and measured to prove the proposed methods. All the structures show good performances for differential-mode power division and common-mode suppression. [ABSTRACT FROM AUTHOR]

One kind of miniaturized filtering power divider (FPD) with a new topology is proposed. For previously published FPDs, the isolation resistors were usually added with additional quarter-wave ($\lambda $ /4) transmission lines for output isolation. In this paper, $\lambda $ /4 transmission lines are removed, and the resistor is added to the loaded resonator for the miniaturized design. By regarding the input external quality factor ($Q_{e\text {-in}}$) as an admittance inverter, the indispensable 90° delay can be easily realized. To further improve the miniaturization, the dual-composite right-/left-handed (D-CRLH) resonators are adopted; therefore, the overall sizes of the resulting FPDs can be smaller than $0.012\lambda _{g}^{2}$. Moreover, the equivalent circuit of the proposed FPD is investigated for the performance improvement. Input $Q_{e\text {-in}}$ should be double of output $Q_{e\text {-out}}$ for good matching, and good isolation can be obtained by appropriately utilizing $Q_{e\text {-in}}$. For demonstration, three D-CRLH FPDs are designed for narrowband, wideband, and dual-band applications. Satisfactory agreements between the measured results and theoretical expectations are observed, verifying the validity of the proposed design concepts. [ABSTRACT FROM AUTHOR]

Abstract: In some extent, microwave absorbers and receiving antennas have some similarities, for both of them aim at receiving the ambient electromagnetic wave around. The essential difference between them is that the receiving antenna must transmit the EM wave to the loading system, but the microwave absorber just need to dissipate them. In this work, we studied a novel broadband microwave absorber, which is achieved from a wideband folded‐dipole antenna array backed through a quarter‐wavelength spacer by a metal ground. By studying the impedance locus of the folded dipole array on Smith chart, the authors first obtained a wideband folded‐dipole array antenna, and then changed it to an absorber by replacing the excitations with lump resistors. Both simulation and measurement results show that the folded‐dipole array‐based microwave absorber can achieve a wide bandwidth of 100% at the normal incident waves as in mode of antenna array, while the center frequency is at 5.5 GHz. Meanwhile, the −10 dB bandwidth of the absorber can still be over 90% at an oblique incident waves of 30°. [ABSTRACT FROM AUTHOR]

This paper investigates a wideband omnidirectional antenna that possesses 124.7% of fractional bandwidth. The antenna's two crescent‐shaped radiating patches and their ultrawideband matching structures are printed on two laminates that are crossly placed vertically over the ground plane. Simulation shows that the structure on a single laminate radiates an "8"‐shaped pattern on the horizontal plane. The cross formation of the two printed laminates generates an omnidirectional radiation pattern by superimposing two "8"‐shaped patterns perpendicularly. The proposed antenna is fabricated and measured for demonstration. The measured results agree well with the simulation, indicating the omnidirectional antenna works from 1.38 to 5.95 GHz with a return loss of −10 dB. Simulation and measurement also show the gain variation on the xoy plane is 2 dB in the band of interest, which is small if the ultrawide bandwidth is considered. The above features make the proposed antenna a promising candidate for applications in the digital cellular system (DCS1800), long‐term evolution (LTE2300/2600), wireless local area network (WLAN2400), and IEEE 802.11p. [ABSTRACT FROM AUTHOR]

A compact Ku‐band bandpass filter is proposed by using low‐temperature cofired ceramic (LTCC) technology in this Letter. For miniaturisation, the folded dual‐composite right‐ and left‐handed (D‐CRLH) resonator is introduced. By folding the inter‐digital capacitor and microstrip section inductor in multiple metal layers, the circuit size of D‐CRLH resonator can be reduced to one third of the planner one. Furthermore, the additional transmission loss caused by reverse currents is also investigated. To this end, a very compact LTCC filter is designed, fabricated, and measured, with the core circuit size smaller than 0.91 × 0.95 × 0.29 mm3. The minimum insertion loss is 1.95 dB at 13 GHz while with wide stopband suppression from 14.3 to 33.1 GHz. [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]

A novel wideband reconfigurable impedance matching network is presented, which consists of a main transmission line and several switchable branch lines. The proposed network can match different complex loads at different frequency bands. A novel optimization method is proposed to calculate the circuit parameters efficiently. The calculation results indicate that the proposed impedance matching network can match a broad range of complex loads with wideband operation. For demonstration, two prototypes are designed and fabricated. Good agreement is observed between the measured and expected performances. [ABSTRACT FROM AUTHOR]

A millimeter-wave series–parallel patch antenna array is presented, in which the dual-slot feeding structure is handily implemented using the intrinsic field distribution of TE20 mode in substrate-integrated waveguide (SIW). One 28 GHz patch antenna element fed by the TE20-mode SIW is first designed, achieving a 10 dB impedance bandwidth of 10.2% and a simulated peak gain of 6.48 dBi. Based on the antenna element, a $4 \times 4$ array with a compact series–parallel differential feeding network is developed accordingly. Due to the novel compact SIW-based series–parallel feeding network, the antenna array can achieve superior radiation performances, which is the highlight of this communication. The simulation and measurement results of the proposed antenna array are in good agreement, demonstrating a performance of 8.5% impedance bandwidth, 19.1 dBi peak gain, symmetrical radiation patterns, and low cross-polarization levels (−30 dB in E-plane and −25 dB in H-plane) in the operating frequency band of 26.65–29.14 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a novel ultralow-profile transmitarray (TA) is proposed by using multifolded ray tracing principle. The proposed TA unit cell would reflect the incident wave of x-polarization as a ground and transmit the incident wave of y-polarization with arbitrary phase shift in the operating frequency band. A broadband polarization rotation reflection surface based on artificial magnetic conductor with small phase difference in wide range of incidence angle is applied to transform the polarization of incident wave. Two kinds of TA antennas at 28 GHz are studied, where the distances between the source and the TA are, respectively, reduced to 1/3 and 1/4 of the focal length (named as TA antennas I and II), which are much less than that of the conventional TA antennas. The simulated results show that the proposed TA antennas can achieve −1 dB gain drop bandwidth of 5% and cross-polarization level of less than −30 dB, and the maximum aperture efficiencies can achieve 46% and 40%, respectively. For demonstration, the TA antenna I is fabricated and measured. Good agreement can be observed between the measurement and simulation. [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 60-GHz $4 \times 4$ differential -fed patch antenna array using low-temperature cofired ceramic (LTCC) process. Wideband patch with L-shaped feeding scheme is adopted as antenna element, while differential substrate integrated waveguide feeding network with low insertion loss is applied for the integration of antenna array. The differential-fed structure improves the symmetry of radiation patterns and reduces the cross-polarization level significantly. To further suppress the surface wave and improve the gain of the antenna array, one kind of soft surface structure is proposed. The equivalent circuit model of the soft surface is developed for calculating its dispersion diagram and analyzing stopband characteristics. The simulated results indicate that the antenna gain enhancement can be up to 2 dB because of the proposed soft surface. For demonstration, one prototype using LTCC process is fabricated and measured. The measured 10-dB impedance bandwidth of the antenna array is 11.7%. The measured antenna peak gain of 18.62 dBi at 61.5 GHz and symmetrical radiation patterns with a low cross polarization of −25 dB across the whole operating frequency are achieved. [ABSTRACT FROM AUTHOR]

It is a problem when modeling the thin layer of periodic structures with numerical method by directly discretizing the inner part, because the fine mesh applied to simulate the thin layer would result in great computational data. The internal network boundary condition (INBC) incorporated in the transmission line matrix (TLM) scheme is proposed in this paper, to avoid the directly discretization of the thin layer and achieve a high accuracy. The thin layer of periodic structure is regarded as an easily analyzed two-port network. Vector fitting approach is used to approximate the network parameters into a series of rational expressions with either real term or complex conjugate pole–residue pairs. The INBC equation with discrete-time form is derived and then incorporated in TLM scheme by introducing the approximate pole–residue pairs to the TLM update equation. Compared with the extremely fine-discretized TLM unit cell used to deal with the thin layer by the conventional TLM scheme, a much larger coarse TLM unit cell is accurate enough to be used to discretize the structure by the proposed method. Compared with the conventional TLM scheme, substantial savings in computational storage are achieved. A common frequency selective surface (FSS) structure is first analyzed for the validation of the method. Good agreement in scattering characteristics is observed in frequency domain between the proposed method and simulation by HFSS software. To further demonstrate the validity of the proposed method, an aperture-coupled resonator-based FSS is designed and fabricated. Good agreement among the S-parameters from the proposed method, simulation, and measurement is observed, verifying the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel optimization design method for circuit analog absorbers consisting of resistor-loaded square-loop arrays. First, new precise equivalent circuit models (ECMs) for square-loop-array-based absorbers are derived through the synthetic asymptote method. The presented models are applicable for multilayered absorber with printed single or double SLAs on each layer. Then, the combination of this ECM and conventional genetic algorithm (GA) is proposed and provided a fast and efficient way to design broadband and low-profile SLA absorbers. For demonstration, four absorbers are designed and optimized. Finally, the agreement between the simulated and measured reflection coefficients indicates the validity of the presented method. [ABSTRACT FROM AUTHOR]

A novel polarization-reconfigurable mechanism based on a polarization-rotation artificial magnetic conductor (PRAMC) structure is proposed. A new polarization-reconfigurable antenna is designed by combining a PRAMC-based multipolarized dipole antenna with a RFIC switch-based network, in which three polarization states of right-handed, left-handed circular polarization (RHCP, LHCP) and +45^\circ linear polarization (LP) can be realized by controlling the dc bias of the switches accordingly. The multipolarization antenna is well designed for offering three polarization states. A large 3-dB axial ratio (AR) bandwidth of 15.5%, a wide 3-dB AR beamwidth for CP states and a large cross-polarization isolation of more than 50 dB for LP state together with a broad impedance bandwidth of 20.5% are obtained. A switch network is used to generate three feeding modes, and the performance of the RF-integrated circuit (RFIC) switches is experimentally verified. A prototype of the proposed polarization-reconfigurable antenna is fabricated and tested. Good agreements between the measured and simulated results are observed, which indicates good performances of the proposed antenna. [ABSTRACT FROM PUBLISHER]

In this paper, a novel thin, broadband, single polarization capacitive surface-based absorber is proposed and investigated. First, the impedance of a substrate and matching surface are analyzed and used for the determination of the structure parameters of the microwave absorber. Second, by utilizing infinite strip gratings with lumped resistors, a capacitive surface-based absorber is presented with 48.6% thickness reduction and 11.7% bandwidth enhancement in comparison to the Salisbury screen. Finally, a prototype of the proposed absorber is fabricated and measured for validation. The proposed method provides an efficient way for the design of thin broadband microwave absorbers. [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 dual-wideband bandpass filter with controllable bandwidths is presented in this article. Two passbands for the WLAN band are realised based on a multimode resonator with three open stubs. The bandwidth of the two-order passbands with even or odd mode can be adjusted by appropriately selecting the characteristic impedance of the multimode resonator. A planar microstrip dual-wideband bandpass filter prototype with a 3-dB fractional bandwidth of 16.7% and 9.2% is designed and fabricated. High selectivity and good in-band performance can be achieved in the dual-wideband bandpass filter. [ABSTRACT FROM AUTHOR]

A compact single-layer substrate integrated waveguide (SIW) monopulse network for Ku-band tracking system applications is investigated and demonstrated in this work. The feeding network and the monopulse comparator are integrated into a substrate with a structure size of 8.2\lambda0\times 9\lambda0 at center frequency while 32 output ports are welded perpendicularly for connecting active transmit/receive modules. The optimal design of a 3-dB coupler with metallic slots and phase shifter with dual steps is presented. The relative frequency bandwidth (\vert S11\vert, \vert S22\vert, and \vert S33\vert<10\ \ dB) of the network is 6%, in which the phase imbalance of all ports is less than 5.5° [root mean square (rms)], the power imbalance is about 0.5 dB (rms). The insertion losses are about 3–5 dB and the isolations between the three channels are all better than 25 dB. The good performances of this SIW-based monopulse network are validated by measurements, showing the advantages of low cost, light weight, easy fabrication, etc. It presents an excellent candidate for Ku-band tracking systems or up-band millimeter-wave systems. [ABSTRACT FROM PUBLISHER]

Two compact dual-wideband bandstop filters based on open-coupled lines and transversal signal-interaction concepts are proposed in this study. Two transmission paths with a half-wavelength open stub and two open-coupled lines are used to realise two wide stopbands for WLAN bands. Second/third-order stopbands with transmission poles near each stopband can be easily achieved by the two transmission paths. Two planar dual-wideband bandstop filters with 10 dB fractional bandwidths of 40 and 18.2, 61 and 26.8% are designed and fabricated. The theoretical and measured results are in good agreement and show good in-band filtering performance and high selectivity. [ABSTRACT FROM AUTHOR]

This article applies the generalized multimode S‐parameters to multiport antennas and radio frequency (RF) components for CAD applications. Consider the special case of impedance matching which could significantly simplify the multimode representation on port and remove the requirement on calculating port impedance. N single‐ended ports of a network are regarded as one generalized multimode port, supporting N orthonormal modes represented by N orthonormal basis vectors, respectively. By doing this, in antenna and RF component designs, one can only focus on specific modes interested, while ignore others. A multiport network's characteristics could be represented and understood in a much simpler manner because fewer but more intuitive physical quantities are considered. Therefore, this can significantly simplify the analysis, design, and optimization of multiport networks. For better illustration, several examples, including branch‐line coupler, mixed‐mode case, sequential rotation feeding antenna, and monopulse feed are analyzed and designed. Complicated analyses in network design using the single‐ended S‐parameters, including matching, amplitude and phase unbalance, could be converted into much simpler ones from the generalized multimode perspective. [ABSTRACT FROM AUTHOR]

The serpentine delay line (SDL) is commonly used as one kind of typical true time delay lines (TDLs) with periodic strong reflection points (SRPs). However, the Hilbert fractal curve delay lines (HFCDLs), with the same circuit area and the same spacing between the adjacent segment lines, are proven to have quite different SRPs with improved performance. An analytic analysis model is used to investigate the SRPs of the two-order and three-order HFCDLs, respectively, in which the structure symmetry is fully considered to make the relevant adjacent structure equivalent to a pair of parallel dual lines. Thus, the accumulated far-end crosstalk (FEXT) is derived in the HFCDLs, and the implicit periodic SRPs are revealed. Furthermore, the iterated two-order and three-order HFCDLs are investigated to validate the analysis model. Subsequently, the periodically loaded transmission line (PLTL) with and without strategic discontinuous structured guard lines (DSGLs) is, respectively, utilized in the three-order and two-order HFCDLs, and thus, the proposed structures possess better wideband cancelation of the FEXT accordingly. In the ultrawideband (UWB) range of dc–51 GHz, the typical return loss (RL) is less than 20 dB for the proposed two-order HFCDL and less than 15 dB for the proposed three-order HFCDL. Meanwhile, the fluctuations are eliminated in the group delay (GD) for the proposed two-order HFCDL. For the proposed three-order HFCDL, the delay fluctuations are observed at the high end of the UWB due to the enhanced near-end crosstalk (NEXT), while the delay fluctuations less than 72.2 ps are still obtained in the range of dc–35 GHz. [ABSTRACT FROM AUTHOR]

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]

Hepatocellular carcinoma is one of the common tumors in the world, which leads to more than 600,000 deaths per year.Microwave hyperthermia has been widely used in hepatocellular carcinoma treatment, whereby the cancer cells are heated and killed by making use of the different thermal sensitivity of the cancer cells and normal cells. Monopole is used to be microwave radiator in recent years; however, the ablation region is elongated along the antenna insertion direction so that the skin and normal tissue around the tumor is also heated unexpectedly. It is desirable to generate a heating region in the vicinity of the antenna tip in a spherical manner. To solve the issue, a coaxial-slot antenna with choke is proposed in the article, the specific absorption rate (SAR) distribution around antenna is computed by means of the finite difference time domain method. By comparison with the SAR distribution caused by monopole antenna, it is clear that no unnecessary heating region is generated near the surface of the body when the improved antenna is used. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 54:405-409, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26553 [ABSTRACT FROM AUTHOR]

This article presents a compact microstrip dual-band bandstop filter (BSF), in which one λg/4 defected ground structure (DGS) pair is utilised to realise one stopband while two stepped impedance resonators (SIRs) help obtain another stopband and suppress the spurious harmonics. The design strategies and the equivalent circuits are introduced in detail. The measured results indicate 43.8% and 18.7% fractional bandwidth in the two stopbands (2.4 GHZ and 5.2 GHz) respectively, and the return loss is greater than 15 dB in the whole passband. In addition, size reduction can be conveniently achieved by adjusting the length of the SIRs and DGS. [ABSTRACT FROM AUTHOR]

An H-plane horn antenna constructed into SIW (substrate integrated waveguide) is proposed. It has a dielectric arc lens for better directivity and a simple microstrip transition as feed. The horn, the lens and the transition share the same substrate. The resulting formula from optical principles shows that the suitable dielectric lens can improve the directivity of the antenna significantly. A prototype was fabricated; the antenna size is 39.175 × 14 × 2 mm3. The frequency band is from 25.5 to 28.5 GHz. The measured gain of this antenna is about 9 dB; the bandwidth, at 10 dB return loss, is over 12%. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007. [ABSTRACT FROM AUTHOR]

The propagation characteristics of double-layer SIW structures have been investigated in this paper. On the basis of the theory of resonance cavity and SIW, the simple theoretical formulas for the lower and upper frequencies in the passband have been found. The theoretical analyses have indicated that these two frequencies have much dependence on the width of SIW and the length of the coupling slot, the fractional bandwidth of the double-layer SIW structures can be controllable. Agreement between the simulation data and the calculated results from the formulas can be observed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1459–1463, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22469 [ABSTRACT FROM AUTHOR]

This mini-special issue of the IEEE Transactions on Microwave Theory and Techniques includes seven expanded articles from the sixth IEEE MTT-S International Wireless Symposium (IEEE IWS 2019) held on May 19–22, 2019, in Guangzhou, China. [ABSTRACT FROM AUTHOR]

The propagation and loss characteristics of the substrate-integrated rectangular waveguide (SIRW) at microwave and millimeter-wave bands are investigated. The results further verify that the substrate-integrated rectangular waveguide has nearly the same waveguide characteristics as conventional rectangular waveguides, and it can be analyzed as a rectangular waveguide with effective width of the SIRW. The insertion loss of SIRW and its equivalent rectangular waveguide agree well with each other. However, it is observed that the derivation of the propagation characteristics of the SIRW and its equivalent rectangular waveguide indicates the frequency dependency. At the X-, K-, and Ka-bands, the effective width of the equivalent rectangular waveguide given by the empirical formula [7] should be slightly increased in order to obtain the propagation characteristic that agrees better with that of the SIRW, about 2%. In addition, at the U-band, when the effective width of the equivalent rectangular waveguide is increased 5% or so, the propagation constant of the rectangular waveguide in the whole band agrees well with that of the rectangular waveguide. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 588–592, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21059 [ABSTRACT FROM AUTHOR]

A planar low‐temperature cofired ceramic helical bandpass filter with a compact size is presented. The proposed filter is constructed from short‐circuited λg/4 helical resonators, while the size is reduced significantly by winding resonators vertically. Two single‐sided transmission zeros can be created by the proposed mixed electric and magnetic coupling structure. A prototype with size of 6.2 × 4 mm2 (0.049 × 0.032λg2) has been fabricated for demonstration. The measured fractional bandwidth is 5.9% at 0.845 GHz, and two transmission zeros are observed at 0.90 and 1.07 GHz. [ABSTRACT FROM AUTHOR]

Substrate integrated waveguide (SIW) matching terminations or loads are proposed for low‐cost integration in SIW circuits and systems. The principles of narrowband and broadband SIW terminations are demonstrated and discussed. Both narrowband and broadband terminations are optimised, fabricated and measured over the frequency range of 6–15 GHz. Relative frequency bandwidths (|S11| < 20 dB) of the narrowband and broadband terminations are 7.6 and 42.6%, respectively. Good agreement between the measured and simulated results validates the feasibility of the proposed design strategies of SIW terminations. [ABSTRACT FROM AUTHOR]

One high efficiency second harmonic tuned (2HT) power amplifier (PA) with a compact multi‐harmonic tuning network is presented. The proposed design method can drive the third harmonic impedance to short‐circuit condition to achieve an ideal 2HT PA operation. Then the second harmonic impedance is controlled to proper position to improve the PA efficiency. Meanwhile, the fundamental impedance is also transferred to 50 Ω load by making the most of this tuning network. Consequently, the proposed output network can be designed to a compact size and is suitable for high frequency PA applications. For demonstration, a PA using Cree CGH40010 GaN high‐electron‐mobility transistor is designed and fabricated at 3.5 GHz. The measured results show that the PA achieves peak power added efficiency of 72.8%, output power of 41.3 dBm and drain efficiency of 80.2% at 3.3 GHz. [ABSTRACT FROM AUTHOR]

One dual‐band high‐efficiency power amplifier (PA) based on a D‐CRLH structure is presented. The D‐CRLH cell is employed to realize one dual‐band second harmonic trapping for the two operation frequency bands. Based on above design strategy, high PA efficiency at two frequency bands can be achieved by transferring the fundamental and second harmonic impedances to appropriate positions on the Smith chart. For demonstration, one prototype is designed at 2.3 and 3.5 GHz by using the proposed design strategy. The results indicate one peak output power of 40 and 40.8 dBm at the measured frequency of 2.2 and 3.2 GHz, respectively, while the maximum power‐added efficiencies (PAE) are 73.9% and 64% at the two frequencies. [ABSTRACT FROM AUTHOR]

We present single- and dual-frequency antennas based on the shorted helical slot in hepatic microwave ablation. The single-frequency antenna is designed by lathing a helical slot on shorted traditional semirigid coaxial cable, which is expected to be operated at the frequency of 2450 MHz, and the dual-frequency antenna is designed with the combination of an annular slot and a helical slot, which can be operated at 915 and 2450 MHz. We use full-wave electromagnetic simulation and transient thermal simulation to analyze the performance of the proposed ablation antennas. Both the proposed antennas are fabricated and used in ex vivo ablation experiments at different frequencies with a power level of 23 W for 2 or 5 min. We observe that the proposed single-frequency antenna with helical slot has more concentrated specific absorption rate (SAR) pattern than those antennas with conventional slots does at 2450 MHz, and the dual-frequency one has the capability to control the roundness of ablation zone from 0.34 to 0.63 under the different combination of frequencies and operation times. The proposed microwave ablation antennas are expected to lead to a potential solution of curing the liver cancers with various characteristics. [ABSTRACT FROM AUTHOR]