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To meet the demand for simultaneously supporting the microwave and millimeter-wave technologies in emerging industrial wireless systems, research on dual-band components with a large frequency ratio has been conducted recently. However, it is challenging to implement independent frequency tunability on bandpass filters with both compactness and high performance. This article presents a dual-band bandpass filter with a large frequency ratio, independently tunable frequencies, and an ultrawide stopband. This is achieved by artfully incorporating a harmonic-controllable varactor-loaded microstrip BPF and a wide-stopband dielectric-loaded cavity BPF with the bandgap-embedded aperture coupling mechanism. Extremely compact size can be achieved without additional filtering elements. Two pairs of transmission zeros can be allocated beside two passbands for good selectivity due to the separate path and cross-coupling in the resonators. For validation, a prototype is designed, fabricated and measured. It can provide two independent tunable frequency ranges (3.22–3.52 GHz and 25–27.06 GHz), exhibiting a large frequency ratio up to 8.3. Mid-band suppression better than 20 dB and ultra-wide stopband up to 32.5 GHz with 20 dB suppression level are achieved. Low insertion loss and good selectivity can also be observed. [ABSTRACT FROM AUTHOR]

With the rapid and extensive development of wireless communication and low power electronics, electromagnetic wireless power harvesting (WPH) draws more and more attention. As the core component for RF-to-DC power conversion, its characteristics determine the performance of the overall WPH system. To obtain as much dc energy as possible, ambient electromagnetic energy with various frequencies should be efficiently rectified. Therefore, it is important to widen the operating bandwidth of the rectifier. According to the theoretical analysis of the Schottky diode, it can be found that if the harmonic components generated by the diode can be fed back through a specific approach for rectifying, the bandwidth of the rectifier will be effectively improved. Therefore, a broadband rectifier has been proposed based on the previous principle. For validation, a wideband rectifier based on Schottky diode SMS7630 had been designed, fabricated and measured. When the input power level is 0 dBm, the conversion efficiency of the implemented rectifier is larger than 40% from 0.4 to 2.6 GHz within a relative bandwidth of 146.67%, exhibiting an ultrawide bandwidth compared with existing state-of-the-art configurations. [ABSTRACT FROM AUTHOR]

To address the issues of the inconvenient fabrication and integration for millimeter-wave (MMW) dielectric resonator antennas (DRAs), a new configuration is proposed. First, a dielectric resonator with artificial electromagnetic boundaries is implemented by introducing the electromagnetic band-gap structure along the four side-wall boundaries of a certain dielectric region on a printed circuit board. The electromagnetic bandgap (EBG) structure is constructed using a printed array of periodic upside-down mushroom-type unit cells. The resonant-mode analysis reveals that the proposed DR can support conventional dielectric resonator modes and dense dielectric patch (DDP) cavity modes simultaneously. To excite the DR, a substrate-integrated gap waveguide transmission line is embedded in the proposed structure for implementing a fully integrated DRA. For demonstration, a fully integrated dielectric resonator antenna (FIDRA) operating at 31 GHz is designed. Simulated results show that the antenna offers an 11.5% −10 dB impedance bandwidth (29.6 to 33.2 GHz), in which a peak gain of 7.85 dBi is obtained. As an extension, a multi-beam antenna array composed of a $1 \times 4$ FIDRA antenna array and a SIGW $4 \times 4$ Butler matrix is designed and fabricated. The experimental results verified the effectiveness of the proposed configuration in integrating the DRA and feeding network. [ABSTRACT FROM AUTHOR]

To satisfy the stringent requirements of the emerging wireless communication system, the dual-band operation and reconfigurability are both desired for the front end. However, few works can realize them simultaneously. In addition, the flexibility of the implemented reconfigurability is limited. In this article, a reconfigurable dual-band quadrature coupler with independently tunable characteristics at the lower band is proposed. Based on the investigation of an ideal model, the design requirements to achieve the previous reconfigurability can be obtained. Thus, the coupled line loaded with varactor is proposed on a patch coupler to implement the desired functionality. By varying the voltages applied on the varactors, the frequency and coupling coefficient at the lower band of the proposed coupler can be tuned independently with the characteristics at the upper band fixed. For validation, a prototype was designed, fabricated, and measured. Measured results show that the frequency of the coupler at the lower band can be tuned from 2.9 to 3.2 GHz. Meanwhile, the corresponding coupling coefficient can be tuned from 3 to 10 dB. During the lower band tuning, 3 dB coupling coefficient and quadrature phase difference can be always maintained for upper band, which is fixed at 4.7 GHz. [ABSTRACT FROM AUTHOR]

The failure of the transistor could make an amplifier useless, bringing the wireless system to a sudden halt. Therefore, an amplifier which can handle this type of fault without introducing additional components is highly demanded in industrial applications. For this purpose, a distributed amplification topology is proposed in this paper. The robustness of the proposed structure was theoretically verified by analyzing the ideal models of the amplifier under normal and failed modes. The possibility for further performance enhancement using tunable components is also theoretically investigated. For validation, a wideband amplifier which covers a bandwidth from 0.75 to 2.4 GHz is designed, fabricated, and measured. To verify the robustness, the cases with one and two field effect transistors (FETs) failed are evaluated. For the case with one failed FET, the implemented amplifier maintained a comparable performance over the operating frequency band. For the case with two failed FETs, the same bandwidth can be maintained with the unavoidable minor degradation in gain and gain flatness. The unique fault-tolerant property of the proposed topology is demonstrated. As a beneficial supplement to the proposed fault-tolerant architecture, the proposed optimization approach is applied to achieve a better tradeoff among return loss, gain, and gain flatness. [ABSTRACT FROM AUTHOR]

To meet the stringent requirements of the emerging wireless communication system, the components should exhibit high flexibility in the control of operating frequency, amplitude characteristics, and also phase characteristics. Among them, the reconfigurability in phase is important but difficult to implement. The existing phase-reconfigurable coupler can only provide a tuning range between 45° and 135°, resulting in limited applications. To solve this problem, a tunable unit consisting of open and shorted stubs and tunable capacitors is introduced between two eighth wavelength coupled lines to construct a compact phase-tunable coupler. For the first time, the continuous tuning range of a phase-reconfigurable coupler is extended to 0°–180°. The corresponding theoretical analysis has been conducted. For the demonstration, two couplers operating at 2.4 GHz were fabricated and measured. Good agreement between simulation and measurement can be observed. Coupler I achieved a phase tuning range from 45° to 135°, maintaining equal power division characteristics. The amplitude bandwidth defined by 10-dB return loss and 1-dB amplitude imbalance was larger than 16.3% for all states. Coupler II provided a tunable phase from 0° to 180° over an amplitude bandwidth larger than 12.5%. These results validate the effectiveness of the proposed structures. [ABSTRACT FROM AUTHOR]

As the most critical component of wireless power transfer (WPT) and wireless energy harvesting (WEH) systems, the rectifier is required to exhibit excellent performance. Most existing works focus on improvement in efficiency and bandwidth for a given input power level. However, in practice, the input power level is usually unpredictable. Therefore, a rectifier which exhibits high efficiency over a wide range of input power is highly desirable. But existing structures can only achieve limited input power range with a complex configuration. A novel cooperative structure using two diodes with diverse characteristics is proposed to solve these problems. Theoretical analysis and a comparison of performances with conventional ones are carried out. For validation in different application scenarios, two rectifiers operating at 2.4 GHz were designed, fabricated, and measured. For the proposed rectifier I, the measured efficiency is larger than 60% over an input power range from 3.5 to 25.2 dBm. While for rectifier II, the measured efficiency remains over 50% with input power from −6 to 26.5 dBm. These results demonstrated the effectiveness of the proposed structure in extending the input power range, especially for the low power region. Furthermore, the application in a WPT system was also demonstrated. [ABSTRACT FROM AUTHOR]

To support different standards simultaneously within a wireless communication system, research on dual-/multi-band components has been conducted extensively. However, the operating frequencies of existing works are usually fixed resulting in a low flexibility. To solve this problem, a highly reconfigurable coupler whose two operating frequencies can be controlled independently is proposed for the first time in this paper. Based on the analysis of a basic configuration, the conditions for realizing the desired independent frequency tuning can be obtained. To realize this unique property, varactors loaded coupled line sections are introduced on a conventional branch line coupler. Owing to the symmetrical structure of the proposed coupler, explicit theoretical analysis can be conducted. For demonstration, two reconfigurable couplers are designed, fabricated, and measured. The first coupler can provide frequency tunability from 3.4 to 4.2 GHz at the upper band with the lower band fixed at 2.4 GHz. The other one can not only provide a tunable frequency from 1.3 to 1.6 GHz at the lower band with the higher band fixed at 3.4 GHz, but also give a tunable higher band from 2.9 to 3.4 GHz with the lower band fixed at 1.55 GHz. The measured results agree well with the simulated results, validating the proposed design methodologies. [ABSTRACT FROM AUTHOR]

In this paper, a balanced bandpass filter (BPF), a balanced-to-balanced filtering power divider (FPD), and a balun filter are implemented using the isosceles right triangular patch element. Two isosceles right triangular patch elements are coupled through an open stub for a triple-mode passband response under differential-mode operation and wide common-mode suppression simultaneously. To further improve the selectivity, an open stub is loaded on each feed-line. Based on these elements, a balanced BPF with excellent performance can be implemented. As an extension, a balanced-to-balanced FPD and a balun BPF are implemented based on the structure of the filter. For validation of the proposed configurations, all the balanced BPF, FPD, and balun BPF have been fabricated and measured. All measured results are found to be in a reasonable agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Total bandwidth of existing wireless communication technologies covers a wide frequency range of over one octave. But most existing power amplifier configurations cannot meet this requirement while at the same time maintaining a high efficiency. Therefore, a new structure that can achieve multioctave bandwidth is proposed in this paper together with the design methodology. The difficulty in realizing a bandwidth larger than one octave lies in the overlapping of fundamental and harmonic frequencies. Regarding this problem, the continuous class-F mode is extended to allow a resistive second harmonic impedance, rather than the pure reactive one. With the relaxed design requirements and overlapping design space of fundamental and second harmonic frequencies, harmonic tuning and fundamental frequency matching networks can be designed separately. More importantly, broadband matching for fundamental frequencies can be implemented simply by considering only three fundamental frequency points using the multiple frequencies matching method. To verify the validity of the proposed methodology, a multioctave power amplifier was designed, fabricated, and measured. Measured results verify a wide bandwidth of 128.5% from 0.5 to 2.3 GHz. Over this frequency range, drain efficiency was larger than 60% with output power greater than 39.2 dBm and large signal gain larger than 11.7 dB. [ABSTRACT FROM PUBLISHER]

To satisfy the simultaneous requirements of future wireless communication systems on short-range high-speed data transmission and long-distance basic coverage, the coexistence of the millimeter-wave and microwave technologies becomes the inexorable trend. However, it is difficult for the existing dual-/ tri-band filter configurations to achieve a frequency ratio larger than three. In this paper, the new use of aperture coupling mechanism is proposed to combine two bandpass elements for dual-/tri-band operation with large frequency ratio but comparable sizes. For this purpose, a microwave BPF with wide stopband up to millimeter-waveband is implemented based on the complementary frequency response characteristics of the stepped-impedance resonator bandpass filter and low-pass filter. The millimeter-wave BPF can be simply designed using the air-filled substrate-integrated waveguide circular cavities, which exhibit the natural low-frequency cutoff characteristics. Based on the proposed design concept and two BPF elements, the dual-/ tri-band bandpass filters with frequency ratio up to 12.59 and 12.7 were designed, fabricated, and measured. Owing to the independence of the two elements, a diplexer with large frequency ratio can be simply implemented based on the previous dual-band filter. All the simulation and measured results are in good agreement, validating the proposed structures. [ABSTRACT FROM AUTHOR]

The phase-difference performance at two desired frequencies of the generalized dual-band unequal coupler is discussed and presented in this comment as supplementary information. The condition of \ \angle S21 - \angle {S31\ {f_1}} + \ \angle S21 - \angle {S31\ {f_2}} = \pi and the analytical equations for \ \angle S21 - \angle {S31\ {f_1 \,\text{or}\, f2}} are provided. It can be concluded that the dual-frequency output phase differences are constant and equal to 90° when R_2 = R_3, but the values of R_1 and R_4 can be varied. Finally, the calculated results show that the phase-difference variations about \pm 11\% in the whole useful bandwidths of these branch-line couplers are objective and acceptable in common practical applications when {R_2} and {R_3}$ are in the range of 30–100 Ω ({R_2} \ne {R_3}). [ABSTRACT FROM PUBLISHER]

Abstract: A wideband 3 dB branch line coupler with arbitrary phase difference between output ports is proposed. The wideband properties in both amplitude and phase are achieved by utilizing λ/4 coupled line sections. By designing different even and odd impedance of the coupled line matched in different ports, small phase imbalance can be achieved. For validation, two 3 dB couplers with different phase differences (60° and 120°) were designed and fabricated. They were measured to exhibit wide bandwidths of 40.2% and 44.6%, respectively. [ABSTRACT FROM AUTHOR]

The coexistence of microwave and millimeter-wave technologies becomes the inexorable trend of future wireless communication systems. The corresponding components of the system are required to cover these two frequency bands simultaneously. However, it is difficult for the existing dual-band antenna configurations to achieve a frequency ratio larger than 3. In this paper, a novel topology is proposed to solve this problem. For the desired dual-band operation, a signal routing approach is proposed to guide the microwave/millimeter signals to the specific elements, respectively. The classical aperture coupling mechanism is deliberately utilized to block the millimeter-wave signal from feeding to the microwave antenna element and route the millimeter-wave signal into the millimeter-wave antenna element. Meanwhile, the substrate- integrated waveguide (SIW)-based millimeter-wave antenna element has the high-pass nature to reject the microwave signal. Therefore, the antenna elements for microwave and millimeter-wave bands can be designed separately with a high flexibility. First, a dual-band antenna was implemented to support 5.8 and 30 GHz simultaneously by integrating an annular-ring antenna element and an SIW slot antenna element. Furthermore, different radiation properties at the two bands can be easily realized owing to the high flexibility of the proposed approach. For validation, these two antennas were fabricated and measured. [ABSTRACT FROM PUBLISHER]

The existing tunable circuits mainly concentrate on the control of frequency and amplitude. The control of phase characteristics becomes more and more important in the modern system for further performance enhancement. But none of existing coupler configurations can achieve this tunability. A novel hybrid coupler with simultaneous phase- and frequency-tunable characteristics is presented for the first time. Varying the difference between the capacitances for two rows of tunable capacitors loaded on the branch lines can provide different phase differences between two output ports with equal magnitude. Based on the same circuit, a tunable operating frequency can be realized while maintaining the equal power division and desired phase characteristics. This is achieved by simply changing the capacitances for two rows of tunable capacitors in unison. The high flexibility to achieve tunability in phase and frequency simultaneously is implemented. For demonstration purposes, a hybrid coupler operating at 1 GHz is designed and measured to validate the concept. It exhibits a variable phase difference from 45° to 135° while maintaining equal power division. Meanwhile, the same circuit gives a tunable operating frequency extending from 0.8 to 1.1 GHz while maintaining good performance for a 3 dB coupler with a tunable phase difference from 50° to 130°. [ABSTRACT FROM PUBLISHER]

In a conventional differential phase shifter (DPS), to realize arbitrary phase shifts, the reference and main microstrip lines are of different lengths. This difference results in suboptimal integration density, which renders the wireless communication system implementation complex and bulky. This paper presents an equal-length multiway DPS based on metamaterials. The reference lines have identical dimensions and are of equal lengths with the main lines. The proposed structure covers a wide bandwidth by aligning the main line phase slope without degradation in return and insertion losses. A design optimization methodology is presented for wideband DPSs in the 0°–90° range. For demonstration, a six-way DPS has been designed and fabricated. The measurements show that the phase shifters have less than 5° differential phase stability and better than a 10-dB return loss, with an insertion loss less than 1.24 dB from 1.6 to 3.2 GHz. [ABSTRACT FROM PUBLISHER]

The conventional differential phase shifter configurations usually require different reference lines to provide constant phase shifts over a certain bandwidth. This results in high design complexity, especially for the multiway and poly-phase applications. To solve this problem effectively, a new differential phase shifter configuration based on the parallel stubs loaded transmission line is proposed. The phase of different main lines in the proposed structure can be easily aligned with that of the same reference line by simply changing the position of the loading stubs, which has a linear relationship with the desired phase shift. The new phase aligning approach and the universal reference line bring about simplicity in design and implementation. For demonstration purposes, a group of differential phase shifters is designed, fabricated, and measured. The corresponding constant phase shifts (from 45° to 135° with a step of 15°) are obtained between the main lines and the reference line, over a bandwidth of 55.6% with small insertion loss and phase deviation. [ABSTRACT FROM PUBLISHER]

A new design concept of a generalized dual-band branch-line coupler with unequal power division and four arbitrary terminated resistances is proposed in this paper. By using an external frequency-dependent impedance transformer, a novel dual-band branch-line coupler is obtained with a detailed analytical design method. For ease of design, maximum power-dividing ratio with varying frequency ratio for different terminated impedance values is provided. Owing to the additional design freedom, the calculation of parameters becomes much more flexible. Finally, for experimental validation and convenient measurement, a dual-band unequal microstrip branch-line coupler with four standard ports is designed, fabricated, and measured. Good agreement between the simulated and measured results can be observed. [ABSTRACT FROM PUBLISHER]

For the first time, a patch hybrid coupler that can provide arbitrary power division ratios over two arbitrary frequency bands, is presented in this paper. Complementary split ring resonators (CSRRs) are loaded onto each quadrant of a patch hybrid coupler to enable dual-band operation. The unique property of CSRR was found to give different power division ratios over the two frequency bands, which is difficult to implement using conventional approaches. An equivalent circuit has been extracted and used to describe the operating principles, along with the presentation of parametric analysis. To demonstrate the flexibility in realizing arbitrary power division ratios in two different frequency bands, five dual-band patch hybrid couplers are designed, fabricated, and measured. Good agreement between the simulated and measured results consolidates the work proposed. [ABSTRACT FROM AUTHOR]

ABSTRACT Radiation loss is a major problem of defected ground structures (DGSs) in past decades. This paper presents a novel band pass filter (BPF) employing low radiation spur-line DGS (S-LDGS) resonators and a split ring resonator (SRR). This combination results in compact size and significant reduction in radiation loss. The proposed BPF achieves controllable fractional bandwidth, ranging from 36.2% to 46.5% centered at 2.6 GHz, which covers two Wi-MAX bands. The proposal is verified with a prototype that demonstrates good agreement between simulations and measurements. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2966-2968, 2016 [ABSTRACT FROM AUTHOR]

For the first time, a differential phase shifter with harmonic suppression is proposed. Not only does the proposed structure provide a constant differential phase shift over a wide bandwidth, but it also has good harmonic rejection. Compared to the existing coupled-line phase shifters, the proposed stub-loaded transmission line configurations show good performance, with simplicity in both design and fabrication. Design formulas for the structure are derived using an analytical technique. Optimal design parameters for typical differential phase shifts which are independent of substrate used and operating frequency are provided to allow for a quick design procedure. To illustrate the principles, a broadband 45^\circ phase shifter with harmonic suppression is designed, fabricated, and measured. It achieved excellent performance with small insertion loss, small phase deviation within the desired bandwidth, and good out-of-band rejection. [ABSTRACT FROM AUTHOR]

Traditional two-way passive differential phase shifters (DPSs) are comprised of a reference line and a delay line. To realize a passive multi-way poly-phase DPS, a single reference line is not possible and a cascaded network becomes necessary. This results in both a cumbersome and complex structure, with large phase error that propagates through the network. A novel phase shifter is presented here that allows multi-way and poly-phase differential phase shift using just one common reference line. This phase shifter is constructed using a newly proposed phase-shift component in all element designs, where each element maintains a constant phase shift with adjacent elements. This characteristic for DPSs offers a simple solution to multi-way poly-phase systems, such as those found in phased arrays. To validate the proposed concept, phase shifters are designed as a group of five different elements operating at 2 GHz, with each maintaining a constant phase shift (45^\circ, 90^\circ, 135^\circ, 180^\circ) compared to a reference element. Measured results agree well with the theoretical analysis. Over a 40% bandwidth the achieved phase shifts are \45^\circ \pm \0.9^\circ, \90^\circ \pm \1.5^\circ, \135^\circ \pm \4^\circ, and \180^\circ \pm \4.2^\circ, while amplitude imbalances are all less than 0.25 dB. [ABSTRACT FROM PUBLISHER]

A highly reconfigurable radio frequency patch hybrid coupler with a simple topology is presented for the first time. Due to the introduction of lumped equivalent circuit and flexibility of varactor loaded patterned ground plane, the complex reconfigurability in port arrangement and coupling coefficient can be implemented. Varying the capacitance across different planes allows the electronic switching between different operating modes of the patch hybrid coupler. When the auxiliary patch and patterned ground plane is placed closer to the two output ports, tunable coupling coefficient can also be implemented by changing the capacitance. This results in wide band reconfigurability for the coupling coefficient range. For demonstration purposes, a patch hybrid coupler operating at 2.4 GHz is designed and measured to validate the port reconfigurable concept. Also, a patch hybrid coupler with tunable coupling coefficient operating at 3.5 GHz is designed, fabricated, and measured. This circuit gives a reconfigurable coupling coefficient ranging from -4.2 to -10 dB while maintaining good performance. [ABSTRACT FROM PUBLISHER]

This paper presents, for the first time, a patch coupler configuration that can be designed with an arbitrary coupling coefficient and phase difference at the output ports. Four circular sector patches are combined to form the patch coupler resulting in ease of design and fabrication. To demonstrate and verify this, a patch quadrature coupler configuration is proposed to realize a wide range of coupling coefficients by adjusting the radii of each quadrant. To extend this concept of an arbitrary coupling coefficient for 180^\circ patch couplers, different patterns are etched underneath the circular patch to realize the required power division ratio while maintaining good impedance matching and desired phase characteristics at the input/output ports. Finally, a circular patch coupler is demonstrated to exhibit an arbitrary phase difference between output ports maintaining an equal power division. [ABSTRACT FROM PUBLISHER]

Previous hybrid couplers have output phase difference that have either been 0^\circ, 90^\circ, or 180^\circ. Other phase differences could only be realized using additional phase-shift elements. This increased circuit size and cost, and also degraded overall performance due to interconnecting mismatch losses. The proposed uniplanar arbitrary phase-difference coupler eliminates these additional components, thereby maintaining small size and good performance. Theoretical analysis is presented here together with measured results for two microstrip couplers for verification. [ABSTRACT FROM PUBLISHER]

This paper presents, for the first time, a method to realize the concept of frequency agility on patch-type circuits, which have found more applications at very high frequencies because of its simple structure. A patterned ground plane has recently been proposed for size reduction of patch-type circuits making them more favorable at lower frequencies. An additional auxiliary patch on the ground plane is proposed in this paper as a mechanism to change the capacitance between the upper patch and ground plane. The patterned ground plane loaded with tunable capacitors is applied to the patch element to realize frequency agility. For demonstration, a frequency-agile rectangular patch hybrid coupler with a varactor loaded patterned ground plane is designed to operate over a frequency range of 50% (from 1.5 to 2.5 GHz) with good return loss, small amplitude imbalance, and quadrature phase characteristics. [ABSTRACT FROM AUTHOR]

A mode-counteraction-based self-decoupling method is proposed for the circularly polarized (CP) multi-input multi-output (MIMO) microstrip patch antenna (MPA) array. The array simply consists of two identical diagonal-fed rectangular MPAs, without any extra decoupling structure. It is found that by properly adjusting the patch dimensions and feeding positions, the orthogonal TM1, 0 and TM0, 1 modes can be simultaneously excited in the active MPA to generate the CP field. Meanwhile, the coupled $E$ -fields of the two modes in the adjacent passive MPA can counteract each other, generating a null-field region. When the feeding probe of the passive MPA is placed within the null-field region, no signal can be received at the port, and consequently, an extremely low mutual coupling of −59.4 dB is achieved, without scarifying any other radiation performance of the MPA. In addition, this self-decoupling method is also applicable to other types of MPA arrays and four-element MPA arrays, exhibiting great versatility and extensibility. [ABSTRACT FROM AUTHOR]

A wideband patch directional coupler is proposed. The coupler is designed based on the non‐uniform mushroom structure with unique characteristics. The current distribution within the patch can be controlled by the mushroom cells underneath for wideband property. An 8 dB directional coupler has been designed, fabricated and measured for verification. It exhibits good return loss, small coupling coefficient variation and quadrature phase difference among the output ports over a wide bandwidth of 74.6% centred at 8.45 GHz. [ABSTRACT FROM AUTHOR]

A frequency-reconfigurable bandwidth-enhanced dielectric patch antenna is investigated in this article. The modified feeding structure and air tunnel are introduced to incorporate the TM10 mode and antiphase TM20 mode, thereby expanding the antenna bandwidth. Meanwhile, the air tunnel provides space for the placement of frequency tuning components. After that, according to the $E$ -field distribution of the modes, two pairs of varactor-loaded microstrip lines are implanted in the air tunnel and sides of the DP resonator to independently tune the TM10 mode and antiphase TM20 mode, respectively. Finally, the approximate synchronous tuning of two modes is realized through the appropriate parameter combination of the frequency tuning structure. During the tuning process of the operating frequency, the bandwidth enhancement characteristic of the resultant antenna is obtained while maintaining high gain, good efficiency, and low profile ($0.06\lambda _{0})$. The fractional bandwidth of each state varies from 7.9% to 13.1%. The −10 dB frequency coverage of the antenna is 22.6% (4.28–5.37 GHz). As the operating frequency shifts down, the peak gain varies from 8 to 6.2 dBi while the peak efficiency changes from 93% to 82%. [ABSTRACT FROM AUTHOR]

Beamforming techniques are widely used in antenna array systems. One of the most popular beamforming networks (BFNs) is Nolen matrix, which can achieve flexible phase progression. However, due to the lack of analysis on phase slope alignments between internal components, the conventional topology-based Nolen matrix exhibits narrow bandwidth. To overcome this shortage, an analytical design method based on signal flow graphs (SFGs) and complex exponential signal is proposed. With the use of this analytical design method, rigorous relationships of phase slope alignments between couplers and phase shifters within the operating band in the traditional $4\times $ 4 Nolen matrix topology can be derived. Based on this, a novel $4\times $ 4 Nolen matrix topology composed of couplers and differential phase shifters (DPSs) with specific phase difference slopes is proposed. For verification, a broadband $4\times $ 4 Nolen matrix based on the proposed topology centered at 1.8 GHz, is designed, fabricated, and measured. Simulated and measured results are in good agreement. The measured bandwidths of ports 1–4 defined by return losses and isolations (15 dB for $S_{i1}$ , 10 dB for $S_{ij,i = 1-4, j = 2-4}$) and 1 dB amplitude imbalance are 41.49%, 46.21%, 40%, and 48.24%, respectively. Phase errors are within ±5° for 0° and ±90° phase progressions and vary within the range from −10° to 5° for 180° phase progression. The proposed Nolen matrix exhibits the widest bandwidth and the flattest phase progression among Nolen matrices in existence, which verifies the validity of the proposed analytical design method. [ABSTRACT FROM AUTHOR]

To avoid the performance deterioration caused by the changing placement angle of a receiving antenna, a wireless power transmitter with uniform power transfer coverage is preferred. The utilization of a transmitting antenna with flat-top radiation patterns is the most effective approach. However, the existing antennas with flat-top radiation patterns usually are complex structures and bulky sizes. To mitigate these problems, a rectangular dielectric resonator antenna (DRA) is proposed to obtain flat-top radiation patterns for the first time. Flat-top patterns are realized in both the E and H planes by combining the TEy119 and TEy133 modes of a rectangular DRA. For validation, both linearly polarized (LP) and circularly polarized (CP) flat-topped DRAs operating at 5.2 GHz were designed, fabricated, and tested. Reasonable agreement between the measured and simulated results is observed. For the LP design, stable flat-top patterns can be maintained from 5.18 GHz to 5.24 GHz. Across the operating frequency band, the measured 3-dB beamwidths are 86° and 58° in the E and H planes, respectively, with the side lobe levels lower than –13.9 dB. For the CP design, similar flat-top radiation patterns can be found. To demonstrate the effectiveness of the proposed transmitting antenna, the LP design is used to construct a wireless power transmitter, which can provide more power and also uniform power coverage within the desired angular sector. [ABSTRACT FROM AUTHOR]

A simple decoupling method of using specific higher-order modes to improve the isolation of dielectric resonator antenna (DRA) elements is investigated. The higher-order modes have the feature that they can be excited by the active (source) DRA while unexcitable by means of the feeding network. As a result, the coupled fields in the passive (coupled) DRA are unable to reach the feeding port, leading to a very low mutual coupling level. When the coupled modes in the passive DRA have the same radiation characteristics with the mode that excited in the active DRA, the distortion of radiation patterns can also be avoided. This method is found effective for reducing both the E-plane and H-plane coupling. As no extra decoupling element is needed, the entire antenna system is very simple. For verification, an E-plane-coupled $1\times 2$ multiple-input-multiple-output (MIMO) DRA array has been fabricated and measured. The results show that using a proper mode, the isolation can be enhanced from about 15 to 45 dB at 5.25 GHz. [ABSTRACT FROM AUTHOR]

A novel decoupling method is investigated for the multi-input multi-output (MIMO) microstrip patch antenna (MPA) array. This method makes use of the TM10 and TM02 modes, which are simultaneously excited in the rectangular MPA. It is found that by adjusting the frequencies of the two modes, their $E$ -fields coupled to the adjacent passive MPA can counteract each other to generate a specific null-field region. When the feeding position of the passive MPA is located in the null-field region, the MPA cannot be excited effectively, and hence an extremely low mutual coupling is obtained without requiring any extra decoupling structure. To validate the feasibility of this decoupling method, an E- and an H-plane-coupled $1\times 2$ MIMO MPA arrays are respectively simulated, fabricated, and measured. The isolation of the E-plane-coupled array is enhanced from ~11 to 57 dB, while that of the H-plane-coupled array is improved from ~18 to 51 dB. [ABSTRACT FROM AUTHOR]

A polarization-dependent transmissive and reflective phase-gradient metasurface (PGMS) is investigated and experimentally verified in the $Ku$ -band. The PGMS is based on a single-layer substrate-integrated element, which consists of a cross-shaped dielectric unit and a couple of metallic strips/patches that are printed on the dielectric unit. Taking advantage of both the dielectric and the metallic components, the proposed element can transmit or reflect the linearly polarized (LP) incident wave depending on its polarization. Moreover, the phase of the transmitted or reflected wave can be independently controlled by different phase-control parameters. As a result, two independent foci can be obtained on the transmission and reflection sides of the PGMS for two orthogonal LP waves. For demonstration, a prototype of the PGMS is fabricated and tested. Both the transmissive and reflective foci are observed at the target positions. Also, the PGMS is shown to be able to manipulate the wavefronts independently on its two sides by adjusting the phase distributions. These features make the proposed PGMS a great choice for use in polarization identification, near-field energy transfer, or far-field wireless communication. [ABSTRACT FROM AUTHOR]

In this paper, a novel patch resonator is proposed to realize wideband and dual‐band bandpass filter (BPF) with small frequency ratio. The introduction of metallic vias and slots on the patch enables the flexible control of the resonant frequencies of TM01, two degenerated modes of TM11, and TM21. Two stubs loaded on the patch and coupled with I/O feeding line can introduce two additional resonant modes, and facilitate the control of input/output coupling strength. Owing to the different coupling relationships between the stub modes and two degenerated modes of TM11, the transmission zeros (TZs) located at the center of passband can be eliminated or generated by altering their resonant order, thus realizing wideband or dual‐band operation. For demonstration, two prototypes are simulated, fabricated and measured. Good agreement can be observed between simulation and measurement. The implemented wideband BPF has a passband from 1.85 GHz to 3.03 GHz with six transmission poles (TPs). While the implemented dual‐band BPF operates at 1.8/2.45 GHz with three TPs within each band and two TZs between two bands. Small frequency ratio of 1.33 is achieved. Wide upper stopband and low insertion loss can be observed for both prototypes. [ABSTRACT FROM AUTHOR]

The coexistence of microwave (MW) and millimeter wave (MMW) technologies is considered as the development tendency of the future 5G wireless communication system. In this paper, a single-port, single-layer, dual-band antenna with large frequency ratio is proposed to support the MW and MMW applications. This antenna mainly consists of a stub-loaded microstrip line in the center, two slot-loaded rectangular patches on the lateral sides, and two thin microstrip lines in-between which connect the former two. The stub-loaded microstrip line works as a series-fed MMW linear array at 26 GHz, and simultaneously it serves as the feed line for the MW patches operating at 4.85 GHz. The connection lines are elaborately designed to isolate the MW patches from the MMW signal, guaranteeing the radiation performance of the antenna at the two bands without requiring complicated filter. For verification, a prototype is fabricated and measured. The measured results show that the antenna has an impedance bandwidth of 3.1% and a peak gain of 8.93 dBi at the 4.85-GHz MW band, while an impedance bandwidth of 19% and a peak gain of 13.57 dBi at the 26-GHz MMW band. [ABSTRACT FROM AUTHOR]

A series-fed millimeter-wave (mm-wave) microstrip linear array with single-layer structure and wide operating bandwidth is proposed and investigated. The antenna array simply consists of a microstrip line and a series of short stubs that are periodically introduced on one edge of the microstrip line, at an interval of about one guide wavelength. Owing to the perturbation of the additional stubs, the original symmetrical E-field distributions on the two opposite edges of the microstrip line become asymmetrical, and the intensities of the equivalent magnetic currents are unequal and unable to cancel each other out as in a pure microstrip line. As a result, the stub-loaded microstrip line can radiate effectively, producing broadside radiation patterns. The introduction of stubs can also generate an extra resonant mode, which combines with the resonant mode of the microstrip line, yielding a wide bandwidth of over 20%. In addition, the microstrip array is simply fed by a coaxial probe, without involving any complex feeding network. Therefore, the array configuration is very simple and compact. For demonstration, a $1 \times 4\,\,1$ -D microstrip linear array operating at 27 GHz is fabricated and tested. The measured results show that the array has an impedance bandwidth of 21.40%, an average realized gain of 12.18 dBi, and a first sidelobe level (FSLL) of about −13 dB. Moreover, the FSLL can be decreased to −28.4 dB by tapering the width of the microstrip line. Finally, the design is extended to realize a $4 \times 4\,\,2$ -D microstrip planar array. This planar array can achieve an impedance bandwidth of 19.15% and an enhanced gain of 18.30 dBi. [ABSTRACT FROM AUTHOR]

A planar angled-dipole antenna is investigated in this communication. The angled dipole has an intersection angle of 60°, radiating quasi-isotropic pattern with a gain difference of about 6.4 dB over the entire spherical radiating surface. To improve the isotropy of the antenna, two near-field parasitic elements (NFPEs) are further introduced. The NFPEs function as supplementary radiators and they help to enhance the radiation in the weak region, decreasing the gain difference significantly to 1.57 dB. For demonstration, a prototype operating at 2.4 GHz is fabricated and measured. The prototype shows a high efficiency of 90%, and the roundness is less than 2.59 dB across the entire impedance passband (2376–2526 MHz). [ABSTRACT FROM AUTHOR]

Teaching–learning-based optimization (TLBO) has been widely used to solve global optimization problems. However, the optimization problems in various fields are becoming more and more complex. The canonical TLBO is easy to be trapped in the local optimum when dealing with these problems. In this paper, a new TLBO algorithm with collective intelligence concept introduced is proposed, namely collective information-based TLBO (CIBTLBO). CIBTLBO uses the information from the top learners to form CITeachers and uses the neighborhood information of each learner to form NTeachers, and these teachers help other learners learn in the teacher phase. Furthermore, CITeacher also helps in the learner phase. To demonstrate superiority of the proposed algorithm, experiments on 28 benchmark functions from CEC2013 are carried out, and the benchmark functions are set to 10, 30, 50 and 100 dimensions, respectively. The results show that the proposed CIBTLBO algorithm outperforms the other previous related algorithms. [ABSTRACT FROM AUTHOR]

In this paper, a mixed topology for high efficiency, broadband Doherty power amplifier (DPA) is proposed. The transistor gate biases are set to deep Class-AB for the carrier device and deep Class-C for the peaking device, which enable the DPA to achieve its high efficiency. However, this biasing scheme leads to an inadequate back-off range, which in the past limited applicability. To compensate for this reduced back-off range, a “ $\pi $ -type” harmonic injection network (HIN) is integrated into the DPA thereby allowing the second harmonic to be injected between the two active devices. This achieves waveform engineering, which enhances the output power of the peaking amplifier. However, the use of this HIN leads to a reduction in bandwidth due to a mismatch at the fundamental frequency. A bandwidth compensation technique is then proposed, thereby reducing the peaking device drain impedance variation. This mitigates the reduction in bandwidth as a result of the HIN. A high-efficiency DPA is prototyped based on two identical 10-W gallium nitride HEMTs. Measurement results show that a drain efficiency of greater than 60% is achieved at 5.3–6-dB output back-off power from 1.4 to 2.1 GHz. [ABSTRACT FROM AUTHOR]

A center-fed, single-layer, planar antenna with unilateral radiation patterns is investigated. The antenna consists of a turnstile-shaped patch and a slotted ground plane, which function as a vertical magnetic dipole and a horizontal electric dipole, respectively. By combining the two orthogonal dipoles with the same radiation intensities and antiphases, unilateral patterns with wide beamwidth and high front-to-back (F/B) ratio are achieved. As the unilateral radiation pattern can be easily steered in the horizontal plane by changing the slot location, a pattern reconfigurable antenna is further designed by using p-i-n diodes to control the connection states of the radial slots on the ground plane. Four steerable beams are obtained, capable of covering the entire azimuthal plane. For demonstration, both the unilateral and pattern reconfigurable antennas operating at 2.4 GHz WLAN band (2.40–2.48 GHz) were fabricated and measured. The measured overlapping bandwidths, with $\vert S_{11}\vert <-10$ dB and F/B ratio >15 dB, are given by 7.0% (2.33–2.5 GHz) and 6.3% (2.32–2.47 GHz), respectively. [ABSTRACT FROM AUTHOR]

In this paper, a novel $4 \times 4$ Butler matrix with wide bandwidth and compact size is presented. The existing coupled-line-based quadrature coupler cannot be used to construct a Butler matrix due to the location of output ports. To solve this problem, a swap is introduced in a vertically installed planar structure to implement the quadrature coupler and a crossover required by a Butler matrix. For demonstration, the proposed coupler and crossover and the corresponding Butler matrix operating at 1.8 GHz are designed, fabricated, and measured. The implemented Butler matrix exhibits a wide bandwidth of 56.4% defined by 10-dB return loss and 1-dB insertion loss variation, by occupying a circuit size of $0.25\lambda _{g}\times 0.74\lambda _{g}$. Simulated and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

A low-profile wideband circularly polarized (CP) crossed-dipole antenna that has both wide axial-ratio beamwidth (ARBW) and half-power beamwidth (HPBW) is presented in this paper. The crossed dipoles are composed of four trapezoidal patch arms, and they are fed by a pair of vacant-quarter printed rings to generate CP radiation. Four identical parasitic elements that consist of a horizontal triangle patch and a vertical metallic plate are symmetrically intervened between the crossed dipoles and the ground plane. It has been found that the parasitic elements can effectively decrease the antenna profile, increase the operating bandwidth, and simultaneously enhance the ARBW as well as the HPBW. A prototype was fabricated and measured to verify the design. The measured results show that the prototype has a low profile of $0.1\lambda _{0}$ , a −10 dB impedance bandwidth of 78.3% and a 3 dB AR bandwidth of 63.4%. Moreover, a 3 dB ARBW of more than 120° and an HPBW of more than 110° are achieved simultaneously within a wide passband of 50.7%. [ABSTRACT FROM AUTHOR]

A simple structure composed of four rotated metallic plates is proposed to enhance the bandwidth of circularly polarized (CP) crossed-dipole antenna. The metallic plates are vertically added on the ground plane in a sequential rotation way, surrounding the primary radiator of the crossed-dipole antenna. Owing to the coupling with the radiator, orthogonal currents can be induced on the metallic plates. Additional impedance and axial ratio passbands can, therefore, be generated beside the original operating band, enhancing its bandwidth substantially. As the metallic plates are mounted on the ground plane, no extra footprint is needed, making the area of the wideband antenna very compact. Simulation and measured results show that by using this simple structure, the operating bandwidth of CP crossed-dipole antenna can be enhanced significantly from ~30% to 106.1%. The structure is also applicable to the intrinsically narrowband patch antennas. [ABSTRACT FROM AUTHOR]

An endfire periodic leaky-wave antenna (LWA) with high gain is presented in this communication, which consists of a series of rhombic elements based on double-sided parallel stripline (DSPSL). The endfire mechanism of the proposed antenna is illustrated by the phase difference of the far field of each arm in the rhombic element. Meanwhile, a tradeoff between the tilted angle $\theta _{0}$ and the width $w$ is found, which assures an optimum transverse aperture for achieving high-gain endfire radiation. Moreover, the improved Hansen–Woodyard (IHW) condition is applied to predict the optimum endfire phase constant. Finally, a prototype is fabricated and tested. The maximum endfire gain of 19.8 dBi is measured at 11.4 GHz, which is close to the simulated and predicted results. The proposed periodic rhombic antenna provides more choice for the modern communication system. [ABSTRACT FROM AUTHOR]