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In this article, a uniform neural network (NN) digital predistortion (DPD) model of radio frequency (RF) power amplifiers (PAs) is proposed for dynamic applications, which is suitable for RF PAs under various operating conditions without updating the coefficients. With the development of communication systems, it is difficult for the DPD to track the nonlinearity of the PA as the operating condition varies frequently. As one of the most promising achievements in recent years, the NN has shown excellent generalization ability, which is applicable to the DPD for scalable applications. In this situation, a uniform neural network model (UNNM), whose structure is a two-stage network, is proposed for scalable output power, scalable bandwidth, or simultaneous scalable power and bandwidth. The experiments are carried out on two sub-6 GHz broadband GaN Doherty PAs (DPAs). The experimental results show that the proposed model can achieve comparable performance without coefficient update in the scalable output power range of about 5 dB and the bandwidth range of 100 MHz, which outperforms the conventional fixed model with better than 3 dB power range and 40 MHz bandwidth range. [ABSTRACT FROM AUTHOR]

In this article, for the first time, we propose a transformer network-based reinforcement learning (RL) method for power distribution network (PDN) optimization of high bandwidth memory (HBM). The proposed method can provide an optimal decoupling capacitor (decap) design to maximize the reduction of PDN self- and transfer impedances seen at multiple ports. An attention-based transformer network is implemented to directly parameterize decap optimization policy. The optimality performance is significantly improved since the attention mechanism has powerful expression to explore massive combinatorial space for decap assignments. Moreover, it can capture sequential relationships between the decap assignments. The computing time for optimization is dramatically reduced due to the reusable network on the positions of probing ports and decap assignment candidates. This is because the transformer network has a context embedding process to capture meta-features including probing ports positions. In addition, the network is trained with randomly generated datasets. The computing time for training and data cost are critically decreased due to the scalability of the network. Due to its shared weight property and the context embedding process, the network can adapt to a larger scale of problems without additional training. For verification, the results are compared with conventional genetic algorithm (GA), random search (RS), and all the previous RL-based methods. As a result, the proposed method outperforms in all the following aspects: optimality performance, computing time, and data efficiency. [ABSTRACT FROM AUTHOR]

Digital predistortion (DPD) is an effective linearization technique for RF power amplifiers (PAs), but conventional full sampling (FS) DPD systems use ADCs with three to five times signal bandwidth, and high-speed ADCs are expensive and power-hungry. In this article, we develop a novel band-limited DPD for reducing feedback sampling rate and acquisition bandwidth based on a general framework for semisupervised learning called manifold regularization (MR), which utilizes the geometry of unlabeled data to construct regularization terms for mitigating the overfitting problem. Considering the properties of DPD, we design a basis MR term and introduce it into the classical MR to obtain the extended MR (ExMR) method. To validate the proposed ExMR DPD method, experiments were conducted on two different RF PAs operating at 2.4 and 39 GHz, respectively. The test results demonstrate that the proposed ExMR DPD can linearize the RF PA with a 40-MHz acquisition bandwidth at 100-MHz input. The proposed method significantly reduces the cost and power consumption of the DPD system in comparison with the conventional FS DPD method, which provides a promising solution for broadband communication systems. [ABSTRACT FROM AUTHOR]

This article presents a novel and cost-effective vector network analyzer (VNA)-based phase-compensated channel sounder operating in the frequency range of 10–50 GHz using radio-over-fiber (RoF) techniques, which can support multilink/channel long-range phase-coherent measurements. The optical cable enables long-range channel measurements with a dynamic range of 115.7 dB at 30 GHz (for the back-to-back connection). The phase compensation scheme is utilized for stabilizing the inherent phase variations introduced by the optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. A novel optical delay line and combiner scheme is proposed and implemented to separate the signals, thereby saving the port resource on the VNA for multilink/channel measurements. The proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with the presence of thermal changes and mechanical stress. The phase change could be maintained within 3° at 10–30 GHz and 7° in 30–50 GHz compared to the over 80° phase variation introduced by the cable effects at 10–50 GHz, demonstrating the robustness and effectiveness of the developed channel sounder in practice. With the proposed optical delay line and combiner scheme, multiple channels can be measured simultaneously with minimal VNA ports, significantly reducing the measurement cost and time for multilink channel measurements. Two multilink indoor channel measurements are conducted and analyzed using a virtual uniform rectangular array (URA) at 28-GHz bands. The results demonstrate the capability of the proposed channel sounder to perform high-fidelity long-range ultrawideband multilink channel measurements. [ABSTRACT FROM AUTHOR]

This work presents a 28/38 GHz dual-band power amplifier (PA) for fifth-generation (5G) communication. In this work, a T-topology-matching network is proposed at the output for its dual-band operation and low insertion loss. Also, a modified dual-LC tank-matching method is proposed for the input and interstage part due to its wideband performance and large-impedance transformation capability. This modified dual-LC tank boosts the transformation ratio to 30 at the interstage matching without trading bandwidth for the 28/38 GHz operation. Furthermore, circular inductors are applied to the matching networks for low insertion loss. This design is fabricated in a 0.25- $\mu \text{m}$ SiGe:C BiCMOS technology with a core area of 300 $\times 770\,\,\mu \text{m}^{2}$. In combination with the proposed methods, this PA achieves 28/38 GHz dual-band operation with high power-added efficiency (PAE). At 28 GHz, the measured peak power-added efficiency (PAE $_{\mathrm {peak}}$) is 25%, the saturated output power ($P_{\mathrm {sat}}$) is 18.8 dBm, and 1-dB compressed power ($P_{\mathrm {1~dB}}$) is 17.8 dBm. At 38 GHz, those are 17.5%, 17 dBm, and 15.8 dBm, respectively. [ABSTRACT FROM AUTHOR]

In this article, we present a novel ultrawideband branch waveguide coupler (BWC) with low amplitude imbalance. This novel design is based on a new structure of branch waveguide obtained by symmetrically increasing the waveguide width. The coupling degree can be independently controlled by the height and width of the new branch waveguide, which significantly increases the design flexibility. In addition, this structure can produce a transmission zero (TZ), and a concept to improve the fractional bandwidth of the BWC with out-of-band TZ is proposed. Based on the analysis, the design guidelines for the novel BWC are provided. For a given center frequency, an n-branch novel BWC can be easily designed. Moreover, because of the larger branch waveguide height, this novel design has greatly eased the machining difficulty. Finally, to verify the design concept, a $W$ -band eight-branch prototype is processed and measured. In full $W$ -band, the amplitude imbalance is less than 0.52 dB, the phase imbalance is less than 2.5°, the return loss (RL) is greater than 21.4 dB, and the isolation is greater than 20.5 dB. The simulation and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

A one-parameter family of designs for an exponentially tapered transmission line to match a given resistive load to a real input impedance is derived. Consideration is also given to frequency bandwidth, ripple height, and length of the matching section. Comparisons are made to the Bramham, Hamid & Chen, and Klopfenstein transmission line matching circuits. A careful examination of design trade-offs for this class of structures is made. [ABSTRACT FROM AUTHOR]

In this article, a load-modulation enhanced wideband compact high-efficiency millimeter-wave (mm-wave) gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) synchronous Doherty power amplifier (DPA) is presented. A synchronous DPA architecture is used to ensure the optimal saturation performance at the mm-wave band. Based on the analysis of load-modulation behavior, the bandwidth of the DPA can be extended by decreasing the phase dispersion factor $\alpha $. A simple optimal tuning-based method is proposed to design an equivalent $\lambda $ /4 transmission line (EQWTL) with the minimal $\alpha $ for a given topology. Furthermore, the influence of the power division ratio $\sigma $ on the proposed DPA’s load-modulation behavior has also been analyzed and a proper load modulation can be realized by splitting more power to the peaking branch properly. For verification, a 24–28-GHz GaN MMIC synchronous DPA has been designed using a 0.15- $\mu \text{m}$ GaN on silicon carbide high-electron-mobility transistor process. Both the load modulation and the matching of the fundamental and the second harmonic load impedances can be realized by a modified bandpass-type EQWTL with a minimal $\alpha $ easily. Experimental results show that the fabricated DPA can achieve the output power of 35.4–36 dBm and the power-added efficiency (PAE) of 27.8%–36.8% at saturation. The PAE at 6-dB power back-off (PBO) is 18.3%–30.1% and the 9-dB PBO PAE is higher than 14.3% in the whole frequency band. An average PAE of 27.4% with good linearity is obtained when excited by a 400-MHz modulated signal after linearization. [ABSTRACT FROM AUTHOR]

This article proposes a novel concept of an optically invisible artificial magnetic conductor subarrays for bandwidth improvement of display-integrated antennas in millimeter-wave spectrums. The proposed subarrays consist of two unit-cell types that are arranged as $4 \times 4$ super cells to cover target bands of a slotted dipole antenna with triband resonances. The optical transparency is realized by using thin-metal meshes, and both solid and thin-metal mesh prototypes are fabricated to demonstrate the proposed concept from antenna characteristics standpoints. The mesh prototype exhibits the measured 10-dB matching bandwidth of 25.9% at 28.2 GHz with an average gain of 1.12 dBi, which is similar to 21.1% at 27.5 GHz and 1.25 dBi of the simulated results. These results confirm that the proposed concept is feasible to broaden bandwidths of the triband antenna, while maintaining the optical transparency of 85.1%. [ABSTRACT FROM AUTHOR]

In this article, we propose a nested feedforward noise canceling (NFF-NC) technique for transimpedance amplifier (TIA) in optical link communication. The proposed technique minimizes the noise voltages due to both the first and second stages of the TIA, which provides substantial improvement in its noise performance over conventional noise canceling (NC) topology. Comprehensive analysis and comparison are performed between two techniques. While not degrading other key performance parameters (e.g., bandwidth, gain, and power consumption), our proposed scheme presents 30% noise reduction compared to conventional scheme. The proposed NC architecture provides the improved stability since NFF-NC scheme inherently presents an additional left half-plane (LHP) zero due to the FF-stage. The loop stability performance is verified over several process corners, temperatures, and voltage variations confirming the detailed analysis in its loop gain and loop parameters. The proposed NFF-NC TIA was implemented in a 65-nm CMOS technology. The implemented TIA consumes 10.1 mW of power from a 1.3-V supply and occupies 0.037 mm2 of core area. The measurement results show that the proposed TIA presents dc transimpedance gain of 56.3 dB $\Omega $ and bandwidth (−3 dB) of 6.5 GHz. An average input-referred noise current density, $\overline {i_{n,\text {in},\text {avg}}}$ , is 15.1 pA/(Hz)1/2 over the bandwidth. Eye diagram is also measured with a pseudorandom binary sequence (PRBS) of 27 – 1 with the data rate at 8.5 Gb/s. [ABSTRACT FROM AUTHOR]

A high-data-rate $D$ -band transmitter (TX) module cointegrating a dual-channel TX integrated circuit (IC) in 45-nm CMOS partially deplated silicon-on-insulator (PDSOI) technology and an antenna is presented. The proposed system-in-package is based on an innovative channel-bonding technique and is fabricated using a low-cost printed circuit board process. The IC consists of two upconversion chains, including on-chip millimeter-wave local oscillator generators. The emitted signal is composed of eight channels, each one having 2.16-GHz bandwidth, organized in two sets of four channels at the intermediate frequency (IF) band (around 61.56 GHz) that are upconverted to two adjacent subbands centered at 148 GHz. Then, the two subband signals are combined off-chip using a substrate integrated waveguide diplexer and radiated by a patch antenna array realized on the same package. The output spans from 139.3 to 156.6 GHz. The total equivalent isotropic radiated power is 8.3 dBm. An 84.48-Gb/s data rate is achieved with 64-QAM. The module consumes 600 mW from a 1-V supply and occupies a compact area of 12 $\times $ 6 mm2. [ABSTRACT FROM AUTHOR]

A wideband planar multilayer filtering magic-T is proposed and developed. The proposed magic-T uses coupled microstrip slotlines (CMSs) and microstrip-slot transitions. With the orthogonality of even and odd modes of the CMS, the Chebyshev filtering responses of both the in-phase divider part (H-T) and out-of-phase divider part (E-T) are independent of each other. The microstrip-slot transitions act as a part of filtering structures to realize vertical transmission of energy. With equivalent impedance transformer models, the synthesis processes of a four-pole Chebyshev filtering H-T and a three-pole Chebyshev filtering E-T are derived and analyzed. To verify the proposed concept, a prototype with an operating center frequency of 3 GHz, a 100% equal ripple fractional bandwidth, and a different H-T and E-T in-band ripple are synthesized and implemented on a three-layer printed circuit board. The synthesized, simulated, and measured results show good agreements among them, verifying the feasibility of the proposed planar magic-T. [ABSTRACT FROM AUTHOR]

In this article, a high-isolation power divider with ultrawideband characteristics for simultaneous operation in two adjacent bands is proposed. The power divider is developed based on a four-port coplanar Magic-T. The difference port of the Magic-T consists of a double-ridge gap waveguide (RGW) that supports quasi-TEM mode transmission, which provides the benefit of its broadband characteristics and allows for facilitated assembly. In addition, an inline microstrip line (MSL) containing a probe is inserted into the opposite side of the difference port to form the sum port. This basic configuration has actually achieved high isolation between the output arms and low return loss at each port, and however, its isolation bandwidth is limited by the narrowband matching of the sum port. To overcome this difficulty, a three-port microstrip T-junction is connected in series to the sum port of the Magic-T, resulting in a five-port 3-dB power divider with a wide isolation bandwidth. The process of considering this solution is analyzed and explained in detail in this article and the corresponding simulations and experimental verifications are performed. According to the obtained results, the proposed power divider has excellent overall performance, in particular low loss, ultrawideband, high isolation, and good amplitude/phase consistency. [ABSTRACT FROM AUTHOR]

A novel methodology to perform mode conversion from rectangular fundamental TE10 mode to circular TE $_{n1}$ ($n $ = 2, 3, $4, \ldots $)/TE $_{0p}$ ($p $ = 1, 2, $3, \ldots $)/TE $_{1q} (q $ = 2, 3, $4, \ldots $) modes with similar topologies is presented in this article. The mode converter consists of two sections: a novel H-plane T-junction-based rectangular TE $_{m0}$ ($m $ = 2, 3, $4, \ldots $) mode launcher and a rectangular TE $_{m0}$ -circular TE $_{n1}$ /TE $_{0p}$ /TE $_{1q}$ mode converter. This kind of mode converter possesses good comprehensive performance and is highlighted by three primary advantages: 1) it is flexible to produce various circular TE modes and rectangular TE $_{m\mathrm {0}}$ modes; 2) the mode converter has a relatively simple and easy-to-fabricate geometry, making it especially suitable for the terahertz-band operation; and 3) it possesses a high mode conversion efficiency over a wide bandwidth, which is adequate to satisfy most of the application requirements. The analysis of mode conversion principle, numerical simulations, microfabrication, and experimental measurement of two H-band (220–325 GHz) prototypes are described. Back-to-back measurement results exhibited good agreement with simulation predictions having considered the conductor loss. A 3-dB transmission bandwidth of 56.7 GHz (231.4–288.1 GHz)/42.1 GHz (244.0–286.1 GHz) was experimentally obtained for the ${\mathrm {TE}}^{\square}_{10}-{\mathrm {TE}}_{01}^{\circ}/{\mathrm {TE}}_{31}^{\circ}$ mode converter. [ABSTRACT FROM AUTHOR]

A new class of wideband unequal power divider with enhanced power dividing ratio, fully matching bandwidth, and filtering performance is presented. A leading triple-mode resonator is inserted in front of the power dividing junction to relax the requirement of high impedance and bring in more poles in input return loss (RL) response and isolation response. Therefore, the power dividing ratio is significantly enhanced and bandwidths of input RL and isolation are enlarged. Moreover, the cascade of the leading triple-mode resonator and the following transmission line segments corporately construct Chebyshev filtering performance. Thus, the power divider can be synthesized by the required bandwidth of RL and power dividing ratio. Examples of 4:1 and 8:1 filtering power dividers operating at 2.4 GHz are designed and fabricated. The measured power dividing ratios of two filtering power dividers are 3.8:1 and 8.1:1 with corresponding RL bandwidths of 95.8% and 97.5% ($\vert S_{11}\vert < -10$ dB), and the measured port-to-port isolation bandwidths are 100% ($\vert S_{32}\vert < -14$ dB) and 100% ($\vert S_{32}\vert < -20$ dB), respectively. [ABSTRACT FROM AUTHOR]

In this article, a novel training set optimization method in an artificial neural network (ANN) constructed for high bandwidth interconnects design is proposed based on rigorous probability analysis. In general, the accuracy of an ANN is enhanced by increasing training set size. However, generating large training sets is inevitably time-consuming and resource-demanding, and sometimes even impossible due to limited prototypes or measurement scenarios. Especially, when the number of channels in required design are huge such as graphics double data rate (GDDR) memory and high bandwidth memory (HBM). Therefore, optimizing the training set selection process is crucial to minimizing the training datasets for developing an efficient ANN. According to rigorous mathematical analysis of the uniformity of the training data by probability distribution function, optimization flow of the range selection is proposed to improve accuracy and efficiency. The optimal number of training data samples is further determined by studying the prediction error rates. The performance of the proposed method in terms of accuracy is validated by comparing the scattering parameters of arbitrarily chosen strip and microstrip type GDDR interconnects obtained from EM simulations with those predicted by ANNs using default and the proposed training-set selection methods. [ABSTRACT FROM AUTHOR]

In this article, a new class of tunable filters and diplexers operating in $X$ -band is presented. The proposed circuits are based on an in-line dual-post resonator, which consists of a pair of antipodal partial-height posts. The resonance and coupling characteristics of the proposed resonator can be regulated by the height and height difference of the posts. The most interesting feature of using the in-line dual-post resonator is that the input–output coupling and inter-resonator coupling are inversely proportional to the frequency within the tuning range, which is necessary for maintaining the fixed absolute bandwidth of the tunable filter. A prototype tunable filter is designed and fabricated, showing a low variation ($< \pm 3.9$ %) in the absolute bandwidth over a relatively wide tuning range of about 17%. The waveguide $H$ -plane static $Y$ -junction is designed and cascaded with two channel filters to implement the tunable diplexer. Noncontiguous and contiguous frequency plans can be realized by properly arranging the frequency band of the two channel filters. Measured results show that the tunable diplexer can obtain constant frequency spacing and approximately 10% tuning range with an insertion loss of less than 1.5 dB. [ABSTRACT FROM AUTHOR]

This article presents a broadband three-stage pseudoload modulated balanced amplifier (P-LMBA) with enhanced power back-off efficiency. Unlike the conventional LMBAs, one of the balanced PA pairs of the proposed P-LMBA is modified to serve as the carrier amplifier, while the other one and the control amplifier (CA) are working as the peaking amplifiers. A new load combining network is designed to dynamically modulate the load impedance of the three PAs. Thus, the three PAs working in voltage saturation achieve peak efficiency at two different back-off and saturation points. This new load modulation mechanism enables the P-LMBA to greatly extend the back-off range and significantly enhance the power back-off efficiency. Based on the proposed theory, a three-stage P-LMBA operating from 1.6 to 2.0 GHz (22%) is designed and measured. Under the continuous-wave excitation, the measured 10-dB back-off, 6-dB back-off, and saturation efficiencies are 49%–62%, 52.4%–64.8%, and 65%–75%, respectively. The measured 10-dB back-off gain and saturation gain are 8.5–9.7 and 7.2–9.7 dB, respectively. When driven by a 20-MHz long-term evolution (LTE)-modulated signal with a 10.32-dB peak-to-average power ratio (PAPR), the proposed P-LMBA achieves an average efficiency of 42.8%–54.6% and the adjacent channel power ratios of −23.5 to −30.76 dBc. [ABSTRACT FROM AUTHOR]

In this article, we propose a hybrid glide-symmetric metasurface which presents an electromagnetic bandgap (EBG) behavior at the $Ka$ -band. The innovative part of this work is the hybrid nature of the periodic structure, which is implemented with holes on two different technologies: printed circuit board (PCB) and metallic waveguide. These holes avoid propagation in an undesired parallel plate created between a PCB and a metallic waveguide. To demonstrate the potential of this concept, a hybrid glide-symmetric configuration was placed surrounding a PCB–waveguide transition at the $Ka$ -band to reduce the leakage created by undesired air gaps. A prototype was manufactured and measured to corroborate the effectiveness of this technique to reduce losses and crosstalk. [ABSTRACT FROM AUTHOR]

The great challenge in fabrication is one of the most significant factors for hindering the development of subterahertz sheet beam traveling wave amplifiers (SB-TWAs). Therefore, it is in great demand to develop power coupling structures and slow wave structures with easy-to-fabricate and compact geometries for SB-TWAs. In addition, it is desirable that their heights are as small as possible, thus conducive to the focusing of the sheet electron beam. In this article, two novel power coupling structures are designed, which are based on an $H$ -plane short-slot and multiple branch waveguides, respectively. The former one is highlighted by its compactness, and the latter one has a wider frequency bandwidth. Two proof-of-concept prototypes of the proposed power coupling structures were microfabricated and tested, showing excellent agreement between experimental measurements and design simulations. Reflection coefficient <−13.6 dB, isolation coefficient <−15.4 dB, and transmission coefficient >−2.2 dB were experimentally obtained across the band of 220.0–273.4 GHz (53.4 GHz). Hopefully, a wider measured frequency bandwidth will be obtained if the operating frequency range of the vector network analyzer could be extended to lower frequencies. [ABSTRACT FROM AUTHOR]

Traditional methods for radio frequency (RF) beamforming require significant amounts of power, making them difficult to deploy in some low-power applications. A detailed analysis of RF beamforming utilizing transmission-line transformers (TLTs) and balanced impedance phase shifters (BIPSs) is presented. This technique enables ultralow-power RF beamformers by: 1) leveraging the RF feed lines to implement a low-loss TLT for signal combining and 2) using the balanced impedance tuning of shunt passives to implement simple, low-loss phase shifters. We highlight some of the key advantages of this beamforming approach for low-power systems and show how this idea can be expanded to arrays of more than two antenna elements by introducing a crossover switch into the phase shifters to extend the beam-steering range. In addition, a thorough comparison between the theoretical and measured performances of a simplified prototype system is provided for key system metrics, including loss and bandwidth. The prototype system is a fully passive 2-GHz two-element RF beamformer, utilizing TLTs and BIPS, realized with off-the-shelf components and a standard FR4 PCB. [ABSTRACT FROM AUTHOR]

This article presents a 2.4-GHz low-power compact integer- $N$ ring oscillator-based phase-locked loop (PLL) for Internet of Things (IoT) applications. The proposed integer- $N$ PLL is based on a dual loop Offset-PLL topology to achieve a fine frequency resolution similar to conventional fractional- $N$ PLL. Not using a delta-sigma modulator (DSM) allows an expanded PLL bandwidth without deteriorating the overall noise performance. Implemented in 28 nm CMOS fully depleted silicon on insulator (FD-SOI) technology, the proposed architecture requires a 22-MHz internal reference frequency while achieving a 2-MHz frequency resolution and a 3-MHz PLL bandwidth. Measured prototypes perform −43.9 dBc reference spur, as an average value over all the bluetooth low energy (BLE) band and numerous tested dies, a jitter Figure-of-Merit of −229.6 dB for a power consumption of 0.87 mW and a core area of 0.0256 mm2. [ABSTRACT FROM AUTHOR]

The high phase noise (PN) of CMOS millimeter-wave oscillators has encouraged the adoption of wide loop bandwidth for an integer- $N$ phase-locked loop (PLL). This article proposes a quadrature sampling phase-frequency detector (QS-PFD) to disengage the tradeoff between spur rejection and loop bandwidth. With the introduction of an auxiliary path for phase detection, the spur generated by the main path is canceled without incurring extra power or degrading the loop stability. The high gain of the QS-PFD attenuates its jitter contribution to the loop. The QS-PFD enables fast frequency detection and lock detection. Implemented in 40-nm CMOS technology, the proposed PLL shows a −75-dBc reference spur, −101.5-dBc/Hz PN at a 1-MHz offset, and a minimum integrated jitter of 121.9 fsrms (10 kHz–100 MHz) at 38.2 GHz with a division ratio of 128. The lock detection time is at the microsecond level. The proposed PLL consumes 23.6 mW from a 1.1-V power supply, leading to a figure of merit (FoM) of −245 dB. [ABSTRACT FROM AUTHOR]

This article presents a new method to design dual-band three-way Doherty power amplifiers (DPAs). A novel modified load modulation network (LMN) is constructed for enabling dual-mode Doherty operation with three-way configuration, providing enhanced high efficiency range in both modes. Moreover, a parallel load compensation network (LCN) is employed in the proposed three-way DPA to provide wideband performance in each operation band. A three-way dual-mode DPA using commercial gallium nitride high electron mobility transistors (GaN HEMTs) is then designed and manufactured to verify the proposed architecture. Frequency bands of 1.45–1.9 GHz in Mode I and 0.75–1.0 GHz in Mode II are achieved by the DPA, respectively. The fabricated DPA has a 9-dB output back-off (OBO) efficiency of 42.8%–57.7% and a saturated efficiency of 55.4%–70.1%. When driven by a 20-MHz long term evolution (LTE) modulated signal with 8-dB peak-to-average ratio (PAPR), the adjacent channel power ratio (ACPR) of the fabricated DPA is better than −49.9 dBc after digital predistortion at 0.9 and 1.7 GHz with average efficiency of 45.7% and 54.6%. [ABSTRACT FROM AUTHOR]

A passive waveguide component with circular input and output ports that converts the incident TE1,1 mode polarization from circular to linear and vise versa (a polarizer) is under investigation. Compared with a number of previous researches on this topic, including structures with elliptical, rectangular, truncated cross sections, and rectangular waveguides with periodically perturbed walls, the problem of realization of an ultralow cross-polarization factor (below −40 dB) within the maximum bandwidth is theoretically analyzed in detail based on dispersion evaluation. The solution in the form of a rectangular structure with a pair of corrugated walls with precise mechanical adjustment was manufactured and measured yielding the bandwidth of 16%. A polarizer with such characteristics is extremely important when served as an element of a microwave system for input–output through one window of a high-power high-gain gyrotron traveling-wave tube (gyro-TWT) with a helically corrugated waveguide. [ABSTRACT FROM AUTHOR]

This article presents a novel method of extending the high-efficiency range of Doherty power amplifiers (DPAs) by utilizing multiple output power back-off (OBO) parameters. The OBO extension techniques of the DPAs, such as complex combining load (CCL), virtual stub (VS), and out-phased current combining (OCC) methods, were defined, and a general expression for these OBO extension techniques was derived. Using the general expression, three OBO extension methods were comparatively and comprehensively analyzed. Based on the analysis, the DPA with an extended OBO can be designed by simultaneously employing multiple back-off techniques with a high degree of freedom. To verify the general expression and its analysis, a DPA design for the frequency band of 3.45–3.75 GHz with GaN HEMTs was conducted using multiple OBO extension techniques of VS and OCC methods for a large OBO of 8.5 dB. Using a long-term evolution (LTE) signal with a signal bandwidth of 20 MHz and a peak-to-average power ratio (PAPR) of 8 dB, the drain efficiency (DE) of 38.9%–56.8% was achieved at the average output power levels of 34.4–36.8 dBm while satisfying ACLR of no larger than −45 dBc with digital predistortion (DPD) linearization. Under excitation of a 5G new radio (NR) signal with a signal bandwidth of 100 MHz and a PAPR of 8 dB, the DE of 38.5%–50.2% was achieved at the average output power levels of 34.6–36.8 dBm with an ACLR of under −24.6 dBc without DPD linearization. [ABSTRACT FROM AUTHOR]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

A millimeter-wave (mmW) range enhancement imaging technique for multistatic planar arrays is presented. The echo in an active mmW imaging system that contains both amplitude and phase information, and the latter can be potentially exploited for improving imaging performance in the range direction. With the help of a two-dimensional (2-D) phase unwrapping scheme, and the multi-input–multi-output range migration algorithm (MIMO-RMA) for a multistatic planar array, along with the requisite pretreatment processes such as target extraction and phase error correction for the reconstructed image region, a reconstructed image having a finer range profile could be achieved. The underlying principle of the phase information exploitation to achieve finer range distance information is discussed, the range enhancement imaging implementation steps are outlined, and the necessary pretreatment processes in simulation and experiment are introduced. The efficiency of the proposed approach is analyzed theoretically and demonstrated experimentally. Numerical simulation and experimental results show that the reconstructed image using the new range enhancement imaging technique contains the promised finer range distance information. [ABSTRACT FROM AUTHOR]

In this article, we study closed-loop digital predistortion (DPD) systems and associated learning algorithms. Specifically, we propose various low-complexity approaches to estimate and manipulate the inverse of the input data covariance matrix (CM) and combine them with the so-called self-orthogonalized (SO) learning rule. The inherent simplicity of the SO algorithm, combined with the proposed solutions, allows for remarkably reduced complexity in the DPD system while maintaining similar linearization performance compared to other state-of-the-art methods. This is demonstrated with thorough over-the-air (OTA) mmW measurement results at 28 GHz, incorporating a state-of-the-art 64-element active antenna array, and very wide channel bandwidths up to 800 MHz. In addition, complexity analyses are carried out, which together with the measured linearization performance demonstrates favorable performance–complexity tradeoffs in linearizing mmW active array transmitters through the proposed solutions. The techniques can find application in systems where the power amplifier (PA) nonlinearities are time-varying and thus frequent or even constant updating of the DPD is required, good examples being mmW adaptive antenna arrays as well as terminal transmitters in 5G and beyond networks. [ABSTRACT FROM AUTHOR]

A circular TE0n mode content analysis technique based on the multi-mode coupler with high mode selectivity is proposed. To improve the mode selectivity, a deformed waveguide, entitled the quad-polar waveguide, which discriminates the azimuthally symmetric TE-mode on the waveguide wall, is introduced. The influence of deformation on the TE01 and TE02 modes’ field pattern, the corresponding transmission loss, and the power capacity in the quad-polar waveguide are analyzed. Based on the analysis, a dual-mode coupler of the circular TE01 and TE02 modes, consisting of an oversized deformed circular waveguide coupler and a pair of circular-to-quad-polar waveguide transitions, is designed for a high-power Ka-band gyrotron traveling-wave tube system. To verify the high mode selectivity of a quad-polar waveguide, a simple coupling with equal-radius and equal-interval holes are used. A prototype is fabricated and measured, and the results show that the coupling coefficient is −40 dB with the directivity of 27 dB for the TE01 mode, suppressing the unwanted mode TE02 mode with 53 dB. For the TE02 mode, the coupling coefficient is −40 dB with the directivity of 25 dB and suppresses the unwanted mode TE01 mode with 75 dB from 30 to 40 GHz. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive analysis of the terahertz (THz) rectification process with modern high-speed silicon–germanium (SiGe) heterojunction bipolar transistor (HBT) devices to enable low-power and close-to-optimum detector sensitivity in a near-THz fractional bandwidth. The influence of all major device internal parasitics on the detector responsivity and noise equivalent power (NEP) is analyzed in detail as a function of the device bias point and the operating frequency. By analogy to the cold MOSFET operation, the fundamentals of the detector operating in weak and deep saturation are studied and compared with the forward-active region, indicating its potentially superior NEP performance with a suitable readout path. The antenna’s broadband radio frequency (RF) power coupling aspects are further elaborated and related to the device bias conditions to maximize the internal base–emitter driving voltage. A set of single- and dual-polarized antenna-coupled detectors with close-to-optimum detector operation in a near-THz fractional bandwidth and a state-of-the-art optical performance was implemented in a 0.13- $\mu \text{m}$ SiGe HBT technology with $f_{t}/f_{\text {max}}$ of 350/550 GHz and extensively characterized across 200–1000 GHz to support the underlying analysis. For the forward-active operation, the following maximum optical current responsivity and minimum optical NEP values have been demonstrated: 5 A/W, 1.9 pW/ $\sqrt {\text {Hz}}$ at 300 GHz and 0.65 A/W, 19 pW/ $\sqrt {\text {Hz}}$ at 900 GHz. The corresponding NEP values for deep saturation (with unbiased collector) are 5.1 pW/ $\sqrt {\text {Hz}}$ and 45 pW/ $\sqrt {\text {Hz}}$ but they are largely limited by the noise floor of the consecutive external amplifier. [ABSTRACT FROM AUTHOR]

In this article, we present a novel application of glide symmetry to differential lines with common-mode (CM) rejection filter properties. Two different topologies are investigated. First, glide symmetry is applied to a pair of differential lines where ground-connected mushrooms are employed as a CM rejection structure. The same idea is also used in a pair of differential lines where defective ground structures are introduced to stop the CM propagation. It is demonstrated that the CM rejection bandwidth is drastically increased when glide symmetry is exploited in both topologies when compared with their corresponding structures without glide symmetry. Furthermore, we show that the differential-mode propagation is hardly affected by the use of glide symmetry, ensuring the good integrity of the transmitted information. Experimental demonstration for both mushroom and defected ground structure is provided. Good agreement between simulations and measurements results is observed. [ABSTRACT FROM AUTHOR]

Mode converter is one of the most important devices in the high-power microwave (HPM) applications. To conduct an in-depth research for the orthogonal mode converter, a novel 90° compact TM01-TE11 circular waveguide converter working at 9.7 GHz is proposed in this article. This design innovatively integrates the traditional mode converter with 90° bend techniques based on the mode coupling theory, which ensures a compact structure and high-power handling capacity. Calculated and simulated results illustrate that the maximum conversion efficiency of the converter at central frequency reaches 99.4% when the structure length is 535 mm, and the bandwidth reaches 680 MHz when the conversion efficiency exceeds 95%. For demonstration, a prototype is fabricated, and the corresponding experiments are investigated. According to the $S$ -parameter measurement, it has a high conversion efficiency at central frequency. Meanwhile, the high-power performance is conducted by connecting it with a relativistic backward oscillator (RBWO), and the converter works stably under a maximum output power of 4 GW. The good agreement of the theoretical analyses, simulations, and experimental results indicates the feasibility of the proposed converter. [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]

We demonstrate a broadband near-100%-efficiency ultrathin metasurface operating at microwave and millimeter-wave frequencies. We develop and employ two orthogonally polarized metallic gratings to form a Fabry–Perot cavity and incorporate a subwavelength metallic double-split-ring resonator at the center of each unit cell. It allows arbitrary amplitude-phase combinations with no coupling between amplitude and phase or between transmitted and reflected waves, leading to the design of an ultrathin but highly efficient broadband metasurface with multiple functionalities. Furthermore, the proposed metasurface can generate diffractive beams with different orders and vortex beams with different orbital angular momentum (OAM) modes in reflection and transmission spaces simultaneously. Both numerical and experimental results verify that the proposed metasurface has superior performance to its counterparts that are based solely on phase control. The proposed metasurface presents a lightweight, low-cost, and easily deployable flat device for microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A novel memory-grouped method is proposed for digital predistortion (DPD) of power amplifiers (PAs) with constrained acquisition bandwidth (BW) and extremely low sampling rate. By grouping the basis functions with different memory delays, a two-step algorithm can reduce overfitting in the constrained-BW technique. As a result, excellent DPD performance can be achieved even when the acquisition BW is constrained to several times narrower than the BW of the original input signal. Thus, using the memory-grouped method, a very low-speed analog-to-digital converter (ADC) can be used to sample the constrained feedback signal without aliasing, significantly reducing the cost of configuring a high-speed ADC. The performance of the proposed method is compared with the existing methods in different scenarios. Experimental results show that when the feedback BW is less than the BW of the original input signal, the proposed method can still achieve good performance, while the traditional methods fail to work. The experiment results also imply that the memory-grouped method can reduce the sampling rate by more than ten times. [ABSTRACT FROM AUTHOR]

This article proposes a method to excite the TM11 mode in circular waveguides. The principle of synthesizing a circular TM mode is deduced based on the electric dipole moment theory first, and the output mode and its purity are analyzed theoretically. Then, a mode conversion scheme to convert the rectangular TE10 into circular TM11 mode via a pair of out-of-phase quasi-TEM mode is proposed. In order to achieve the broadband excitation in a compact size, the ridge gap waveguide is used as a medium between the rectangular and cylindrical waveguide. Simulation results present that the proposed exciter has a propagation bandwidth up to 10 GHz in Ka-band with a mode purity over 98%. A prototype is manufactured and measured, and the presence of TM11 mode and the mode purity are confirmed by a port radiation pattern measurement. The mode exciter features high mode purity, broad bandwidth, and a compact size, which provides a low-power generator for the research of novel gyrobackward-wave devices and devices in the high-power transmission line. [ABSTRACT FROM AUTHOR]

An under-sampling digital predistortion based on a multi-tone mixing feedback technique (MTM-DPD) is presented in this article. In contrast to the under-sampling digital predistortion (DPD) based on conventional receivers, the proposed method could simultaneously reduce the sampling rate and acquisition bandwidth using a multi-tone mixing (MTM)-based feedback channel. The MTM-DPD is implemented with an evolved direct learning architecture, where the coefficients of a predistorter are estimated based on the aliased feedback signal, preprocessed input signal, and preprocessed kernels of the DPD model. To preprocess the input signal and kernels, the behavioral model of the MTM-based feedback channel and its corresponding identification algorithm are analyzed in detailed. Experimental results show that for a gallium nitride (GaN)-based power amplifier (PA) with 40-MHz input, under the excitation of a 17 tone LO signal with frequency interval 7.68 MHz, the MTM-DPD with sampling rate 15.36 MSPS and acquisition bandwidth 15.36 MHz could improve the adjacent channel power ratio (ACPR) from −30.1 to −46.5 dBc and the error vector magnitude (EVM) from 9.13% to 1.76%. Compared with the conventional full sampling DPD (FS-DPD), the MTM-DPD could reduce the cost of analog-to-digital converters (ADCs) in feedback channel significantly while maintaining satisfactory linearization performance. [ABSTRACT FROM AUTHOR]

In this article, a new technique is presented to dramatically enhance the bandwidth of a postmatching Doherty power amplifier (PM-DPA). This technique is based on a coupled-line phase compensation network (PCN). Theoretical analysis shows this coupled-line PCN results in wideband impedance matching by reducing the external $Q$ -factor in the peaking branch. Finally, when augmented with suitably selected peaking amplifier impedances, the proposed technique gave improved peak efficiency and output power over an extended bandwidth. For experimental verification, a DPA based on commercially available GaN HEMT devices (Cree CGH 40010F) was designed and fabricated. Measured results of the proposed DPA show 6-dB back-off operation between 1.3 and 2.3 GHz (55% fractional bandwidth) with efficiency in excess of 41%. [ABSTRACT FROM AUTHOR]

This article introduces a new type of contact-less electromagnetic bandgap (EBG) structure in the form of an embedded bed of nails. Compared with the traditional bed of nails structure, the smooth upper metal plate originally used to provide the perfect electrical conductor (PEC) boundary is replaced by periodic defect grooves, and the metal pins on the base block are embedded in these grooves without any electric contact. One of the advantages of the embedded EBG structure is that it has a robust tolerance for the height of the air gap. Therefore, this structure provides a cost-effective parallel plate mode suppression solution because it allows a low-precision manufacturing process level while maintaining the stability of the bandwidth. On the other hand, the proposed EBG structure can achieve a stopband range of several octaves. This characteristic makes it indeed suitable for wideband gap waveguides (GWs) to provide horizontal open boundaries. To verify the feasibility of the proposed approach, the new ridge gap waveguide (RGW) (with an embedded bed of nails) and the classic RGW (with a traditional bed of nails) with two 90° bends are designed, fabricated, measured, and compared. The experimental and simulation results are quite consistent and indicate that the embedded RGW has prominent advantages in bandwidth and robustness. [ABSTRACT FROM AUTHOR]

In this article, a compact and broadband microstrip line-to-rectangular waveguide (MSL-to-RWG) transition using the magnetic coupling resonator and ground resonators is proposed. The circuit size of the transition occupies only one-eighth of the guided wavelength, while the fractional bandwidth of the transition is 42.7%, which covers the frequency range from 8.2 to 12.6 GHz, encompassing the whole frequency range of the X-band (8.2–12.4 GHz). In this frequency range, the reflection coefficient is smaller than −15 dB, while the transmission coefficient is larger than −0.18 dB. In order to verify the simulation results, the MSL-to-RWG transition is fabricated and measured where the measurement results are in reasonable agreement with the simulation results. [ABSTRACT FROM AUTHOR]

This article describes the development and characterization of wideband millimeter-wave noise sources based on SiGe BiCMOS amplifiers. Two single-ended three-stage amplifier-based noise sources reached excess noise ratio (ENR) values over 20 dB from 120 to 220 GHz with 20 mA of the bias current from a 2.3-V supply. We also introduce a novel switchable noise source employing the Lange coupler for providing wideband matching in both ON and OFF configurations of the noise source. The Lange coupler-based noise source has better than 12-dB matching from 90 to 270 GHz with an ENR of better than 15 dB from 125 to 235 GHz. [ABSTRACT FROM AUTHOR]

This article presents a wideband ultralinear fully integrated power amplifier (PA) in 22-nm fully-depleted silicon-on-insulator (FD-SOI) technology for phased array-based $E$ -band backhaul networks. A novel amplitude to phase modulation (AMPM) compensation technique called NP (N-type P-type) matrix is presented. The performance of the proposed amplifier compared to a traditional N-type common-source (CS) PA is demonstrated in simulation across the corners and wide frequency range. The proposed PA occupies 0.084 mm2 core area and achieves peak 13.1-/13.7-dB gain, 61.8–83.7 GHz (21.9 GHz) 3-dB small signal bandwidth with 0.8 V/1 V supply. At 78 GHz, 13.8-/15.4-dBm peak saturated output power ($P_{\text {SAT}}$) with 13.1%/17% PAE from 0.8 V/1 V supply is measured, respectively. AMPM distortion at the output referred 1-dB compression point ($\text{OP}_{\text {1dB}}$) is less than 3.6° from 65 to 90 GHz. It achieves 18-/24-Gbit/s data rate with 10.7-/8.5-dBm average output power and 8%/4.9% average PAE at 73 GHz with 64/256 QAM modulation and a 0.8-V supply. [ABSTRACT FROM AUTHOR]

In a conventional frequency-modulated continuous-wave (FMCW) radar, the target distance is estimated by the beat frequency, which is obtained from dechirping the received signal with the transmitted one. The challenge to achieve fine-range sensing is limited by the inaccuracy of beat frequency caused by the nonlinearity of sweeping chirps. In this work, instead of determining the accurate beat frequency, a novel dual-phase-term tracking (DPTT) method is introduced for high-accuracy range sensing even in a severe nonlinear situation. By tracking the phase of the beat signal and observing the phase difference over the up or down period of a triangular chirp, two distinct featured phase terms $\phi _{o}$ and $\Phi _{B}$ are extracted. The phase $\phi _{o}$ represents the carrier round-trip phase delay at $f_{\mathrm {o}}$. Although $\phi _{o}$ is free of the nonlinear chirping effect, the range estimation based on $\phi _{o}$ suffers from the range ambiguity problem. The phase term $\Phi _{B}$ represents the phase change over the first half chirp period and it is monotonically increased across the range ambiguity zones of $\phi _{o}$. Therefore, by combining these phase terms to determine the target range, both the frequency chirping nonlinearity and the range ambiguity can be effectively eliminated such that the range accuracy of tens of micrometers can be achieved even with an extremely narrow chirp bandwidth. To validate the proposed method, a 24-GHz FMCW radar with a 400-MHz chirp bandwidth and a 10-ms chirp period has been designed and implemented for demonstration. At a distance of 0.6 m, the measured range accuracy is $40.1~\mu \text{m}$ for the weak nonlinearity factor of 0.3%. For the severe nonlinear chirp case with a 25.3% nonlinearity factor, the range accuracy of $137.5~\mu \text{m}$ is also successfully obtained, validating the robustness of this proposed DPTT method. [ABSTRACT FROM AUTHOR]

Radar imaging using the synthetic aperture radar (SAR) principle is a common method to obtain information about e.g., the surface of a target. However, most image formation algorithms for such systems assume (quasi-)static measurements. This may lead to errors in the processed images if the sensor is moving during the measurement process. This is especially the case for frequency-modulated continuous-wave (FMCW)-based sensors since the signal duration is longer than in a pulsed system and the achievable bandwidth is much larger and introduces additional challenges. Motion compensation in the context of radar imaging is usually related to the correction of deviations from an ideal trajectory. In contrast, this article presents a method to take the sensor movement during a single FMCW ramp into account and therefore addresses the effects caused by a continuous path during the transmit/receive process. Hence, faster movement can be achieved during the scanning of the synthetic aperture without being bound by stop-and-go approximations. In addition, it will be shown that the algorithm is suitable to reduce systematic errors due to aliasing caused by spatial sampling below the Nyquist rate. For this purpose, this article presents simulations and measurement results, obtained by an ultrawideband $D$ -band FMCW radar operating between 122 and 170 GHz. [ABSTRACT FROM AUTHOR]

We report on the realization of a multichannel imaging radar that achieves uniform 2-D cross-range resolution by means of a linear array of a special form of leaky-wave antennas. The presented aperture concept enables a tradeoff between the available range resolution and a reduction in the number of channels required for a given angular resolution. The antenna front end is integrated within a multichannel radar based on stepped-carrier orthogonal frequency-division modulation, and the advantages and challenges specific to this combination are analyzed with respect to signal processing and a newly developed calibration routine. The system concept is fully implemented and verified in the form of a mobile demonstrator capable of soft real-time 3-D processing. By combining radio frequency (RF) components operating in the $W$ -band (85–105 GHz) with the presented aperture, a 3-D resolution of less than ${1.5}^\circ \times {1.5}^\circ \times $ 15 cm is demonstrated using only eight transmitters and eight receivers. [ABSTRACT FROM AUTHOR]

A radar transceiver with two transmitters (TXs) and two receivers (RXs) is reported in 22 nm fully depleted silicon-on-insulator (FDSOI) CMOS. It includes a novel 200 MHz bandwidth 80 GHz phase-locked loop (PLL) based on a single-sideband (SSB) upconverter and an 11 GHz bandwidth phase-frequency detector to achieve >8 GHz locking range with record phase noise of −97, −103, and −113 dBc/Hz at 100 kHz, 1 MHz, and 10 MHz offset, respectively, and rms jitter < 40 fs. Stepped-frequency chirps with orthogonal frequency-division multiplexing (OFDM) modulation covering the 152–160 GHz range were demonstrated in a through-the-air loopback link along with a record settling time < 30 ns, limited by the test equipment. The RXs have an IIP3 of −8 dBm, SSB noise figure between 7.5 and 10 dB and a conversion gain of 15 dB, controllable from the LNA back gate over a range of 12 dB. The OP1 dB and $P_{\mathrm {SAT}}$ of the power amplifier (PA) in each TX are 5 and 9 dBm, respectively. The IQ amplitude mismatch and phase error of each RX are < 0.5 dB and 1°, respectively, while the $P_{\mathbf {out}}$ mismatch between the TXs is < 1 dB. The sensor consumes 1.13 W, with 300 mW by the PLL, 275 mW by the 160 GHz local oscillator (LO)-tree, 190 mW by each TX, and 87.5 mW by each RX. [ABSTRACT FROM AUTHOR]

Emerging applications in D-band (110–170GHz) demand amplifiers with high gain-bandwidth (GBW) products. In this frequency range, the cascode stage offers superior available gain, thanks to the high output impedance, but the design of the output matching network entails a GBW tradeoff. The issue is deeply investigated in this work. Simple, closed-form equations for gain and bandwidth as a function of the load reflection coefficient are derived, leading to the following design insights: 1) for maximum gain and bandwidth, the output matching network should be implemented with positive (magnetic) reactances; 2) with lossy reactances, an optimal load reflection coefficient exists to maximize the power gain, ${\Gamma '_{L-{\mathrm{ opt}}}}$ ; and 3) by selecting ${\Gamma '_{L} < \Gamma '_{L-{\mathrm{ opt}}}}$ , the bandwidth increases quickly with a marginal gain penalty, finally enhancing the GBW product. Leveraging the results of the analysis, single-stage and multistage stagger-tuned amplifiers are implemented in SiGe BiCMOS technology. Two- and three-stage amplifiers demonstrate more than 60GHz bandwidth with 20 and 28dB gain, respectively, corresponding to 700GHz and 1.7 THz GBW. Normalizing gain and bandwidth to the number of stages and technology $f_{\max }$ , the resulting figure of merit is remarkably higher than previously reported silicon amplifiers in the same band. [ABSTRACT FROM AUTHOR]

This article presents a dual-mode power divider (PD) that offers new working mechanism, compact size, significant design freedom, wide working bandwidth, arbitrary power division, and ultrawide isolation between the two output ports. The structure is simple in comparison with conventional Wilkinson PDs in that only two composite right-and left-handed (CRLH) transmission lines (TLs) grounded through two resistors are used. Different from previous CRLH-TL-embedded studies in that almost all CRLH-TLs operate at quarter-wavelength phase responses, in the present work, the zero-degree property is noted and used to modify the impedance variation curves. Additionally, because of the use of grounded resistors, the proposed PD can operate in two modes, such that when high-value resistors are used, the PD operates in a lossless mode, while when low-value resistors are used, the PD operates in an attenuated mode. Because working power has been significantly improved due to progress in modern RF system development, more attenuation elements are required. This means that attenuated PDs will become very useful in the future. For verification, two PDs operating in different working modes and power divisions are designed and fabricated. Based on the experimental results, both PDs demonstrate good performance over more than 60% of the bandwidth with reference to the 15-dB S11, ultrawide isolation, full port matching, and compact size. [ABSTRACT FROM AUTHOR]

A new electromagnetic band gap (EBG) structure based on the soft and hard surfaces for gap waveguide (GW) technology is introduced in this article. The proposed EBG structure consists of a soft surface and a hard surface in parallel with a gap between them, where the ridges/corrugations of the two surfaces are perpendicular to each other or with an angle near 90°. Compared with the contactless bed of nails EBG, the most widely used EBG structure in GW technology, the structural strength of the new EBG structure is increased significantly, which makes it very suited for high-frequency applications. Another advantage is that with the varying of the angle between the ridges/corrugations of the two surfaces, the stopband shifts in a wide frequency band, which makes the stopband tunable after the EBG is fabricated. The stopband performance of the proposed EBG is investigated. Straight and bended groove GWs (GGW) employing this new EBG are designed, manufactured and tested. The isolation performance with different columns of ridges/corrugations is also tested. The measured results show the proposed GGWs have excellent transmission performance. [ABSTRACT FROM AUTHOR]