This paper presents a notched band ultra-wideband bandpass filter using a single perturbed quint-mode half-mode substrate-integrated waveguide cavity. The cavity is perturbed by loading four stubs at two corners of the magnetic walls of the single cavity. The variable parameters of stubs are selected to move down the first five resonant modes to the predetermined passband during the design process. Meanwhile, microstrip lines with a transition structure located on two loaded stubs are employed to feed the resonator. Moreover, the filter also firstly designs a notched band by introducing a complementary split-ring resonator inside the cavity to mitigate potential interference signals at 8 GHz (satellite communication). Finally, a prototype filter was implemented and measured to verify.

In the present paper, we present a dynamic gate biasing technique applied to a 10 W, S-band GaN amplifier. The proposed methodology addresses class-B operation of power amplifiers that offers the potential for high efficiency but requires a careful attention to maintain good linearity performances at large output power back-off. This work proposes a solution to improve the linearity of class-B amplifiers driven by radio frequency-modulated signals having large peak to average power ratios. An important aspect of this work concerns the characterization of the dynamic behavior of GaN devices for gate bias trajectory optimization. For that purpose, the experimental study reported here is based on the use of a time-domain envelope setup. A specific gate bias circuit has been designed and connected to a 10 W – 2.5 GHz GaN amplifier demo board from CREE. Compared to conventional class-B operation with a fixed gate bias, a 10-dB improvement in terms of third-order intermodulation is reached. When applied to the amplification of 16-QAM signals the proposed technique demonstrates significant ACPR reduction of order of 6 dB along with error vector magnitude (EVM) improvements of five points over 8 dB output power back-off with a minor impact on power-added efficiency performances.

In this paper, an array antenna with asymmetric antenna fed network is presented. Total size of the proposed array antenna (with 2 × 2 elements) is 90 × 90 mm2 and distance between elements (fed by fed) is λ0/2 (λ0 = wavelength in free space). The proposed antenna is fed by coaxial cable that isolated input impedance from impedance of the array antenna feed network. The measured impedance bandwidth of the coaxial fed circular polarization array (S11 < −10 dB) is 47.9% from 4.6 to 7.5 GHz (1.63:1), and the measured 3-dB axial-ratio bandwidth is 42% from 4.7 to 7.2 GHz. The peak gain of antenna is 9.1 dBic.

This paper describes the development of a power amplifier operating over a 2.4–2.5 GHz frequency range with the output power level more than 15 W and 60% PAE. The transistor applied was the 10 W (13 W Psat) power GaN HEMT (CGH40010F from Wolfspeed) recommended up to 6 GHz. A harmonic tuning method was used to achieve even 30% more output power than the CGH40010 transistor was specified to deliver while maintaining high gain and high efficiency. Furthermore, an accuracy analysis of amplifier design was also conducted. It included validation and correction of the available transistor models as well as validation of the models of microstrip circuits implemented in ADS. Finally, it was concluded that both the mentioned sources of errors contributed at a similar level.

A circularly polarized (CP) and high gain Microstrip antenna is designed in this paper using metamaterial concepts. The antenna, built on a metamaterial substrate, showed significant size reduction and less mutual coupling in an array compared with similar arrays on conventional substrates. Demonstrated to have left-handed magnetic characteristics, the methodology uses complementary split-ring resonators (SRRs) placed horizontally between the patch and the ground plane. In order to reduce mutual coupling in the array structure, hexagonal-SRRs are embedded between antenna elements. The procedure is shown to have great impact on the antenna performance specifically its bandwidth which is broadened from 400 MHz to 1.2 GHz for X-band and as well as its efficiency. The structure has also low loss and improved standing wave ratio and less mutual coupling. The results show that a reduction of 26.6 dB in mutual coupling is obtained between elements at the operation frequency of the array. Experimental data show a reasonably good agreement between simulation and measured results.

Propagation modeling of small/big pebbles and air-dry/wet sand environments for wireless sensor networks has not been extensively studied in the 5G frequency band. This study is necessary for the proper coverage planning and efficient operation of wireless sensors in various applications such as monitoring summer sporting activities, and environmental/ground surveillance on coastal pebble/sand environments, or tracking pebble mobility and including the rescue of the flood-type avalanche in Gravel-Bed Rivers. In this study, empirical path loss models are proposed for wireless sensor networks in pebble/sand environments at two discrete frequencies, namely 3.5 and 4.2 GHz. The theoretical models and proposed models are compared to indicate the accuracy of proposed models in predicting the path loss in these environments. Additionally, R-squared and RMSE values of eight different generated models are calculated in the range of 0.931–0.877 and 2.284–2.837, respectively. These comparisons indicate that empirical model parameters have a significant effect on the path loss model.

A novel microstrip low-pass filter (LPF) using radial patched resonator and modified T-shaped resonators is designed to achieve ultra-wide stop-band. Also, the designed LPF has successfully addressed the problems of compactness and insertion loss, simultaneously. LC equivalent circuit of the proposed filter is calculated and equation for the sharpness in transition band is obtained based on LC equivalent circuit and transfer function. The proposed filter not only exhibits a very wide stop-band of 168%, but also is able to suppress the 11th-harmonic response in conjunction with a small size of 0.147 × 0.052λg, where λg is the guided wavelength at 1.47 GHz. It is shown that the simulated results are highly consistent with the measured data.

This paper reports on a novel voltage-mode class-S power amplifier for the 450 MHz band, based on GaN–HEMT monolithic microwave integrated circuits (MMICs). It achieves a peak output power of 3.4 W for a single tone at 400 MHz, encoded in standard band-pass delta-sigma modulation with 1.6 Gbps sampling frequency. The corresponding efficiency is 38%, peaking at 52% for 0.5 W output power. In order to demonstrate the influence of coding efficiency, additional measurements using a periodic square-wave signal were performed (class-D operation), which yield a maximum output power of 7 W with 64% efficiency. To the author's knowledge, these are the best results in this frequency range achieved so far with the voltage-mode class-S configuration. The paper discusses behavior at power back-off and the influence of the loss mechanisms.

Implantable antennas have recently been receiving substantial attention for medical diagnosis and treatment. In this paper, a coplanar waveguide-fed monopole antenna for industrial, scientific, and medical (ISM) band biomedical applications is proposed. The antenna has a simple structure is placed on human tissues such as muscle, fat, and skin. The designed antenna is made compatible for implantation by embedding it in an FR4 substrate. The proposed antenna is simulated using the method of moment's software IE3D by assuming the predetermined dielectric constant for the human muscle tissue, fat, and skin. The antenna operates in the frequency of ISM bands, 2.4–2.48 GHz. Simulated and measured gains attain −7.7 and −8 dBi in the frequency of 2.45 GHz. The radiation pattern, return loss, current distribution, and gain of these antennas were examined and characterized.

This paper presents a systematic comparison of the relationship between transmission line characteristic impedance and Q-factor of CPW, slow-wave CPW, microstrip, and slow-wave microstrip in the same CMOS back-end-of-line process. It is found that the characteristic impedance for optimal Q-factor depends on the ground-to-ground spacing of the slow-wave transmission line. Although the media are shown to be similar from a mode of propagation point of view, the 60-GHz optimal Q-factor for slow-wave transmission lines is achieved when the characteristic impedance is ≈23 Ω for slow-wave CPWs and ≈43 Ω for slow-wave microstrip lines, with Q-factor increasing for wider ground plane gaps. Moreover, it is shown that slow-wave CPW is found to have a 12% higher optimal Q-factor than slow-wave microstrip for a similar chip area. The data presented here may be used in selecting Z0 values for S-MS and S-CPW passives in CMOS that maximize transmission line Q-factors.

Radar absorption structures made of an active frequency selective surfaces (AFSS) have enormous potential in the aviation, naval, and other industries. In this research paper, a systematic review (SR) is carried out in the field of the AFSS to bring uncertainties, obstacles, challenges, classifications, applications, and design issues that arrive in the development of the sub-6 GHz architecture. To bias the AFSS component, as per the signal requirements, a unique set of circuits (PIN diode) is required, with ON and OFF state and a transmission zone. The bandwidth of which is determined by the bias voltage supplied. It can behave as a complicated hybrid impedance structure by providing ON and OFF biasing voltage to a PIN diode embodied in an FSS structure. Higher manufacturing costs of AFSS components, more significant complexities involved, a large amount of power consumption, and reactive impedance losses are some common limitations faced while implementing and designing an AFSS. Many envisioned problems are corrected with the AFSS design, current or creative implementations, and processing parameters are investigated progressively. It implies that new AFSSs will be an alternative to regular FSSs in the future. This paper is based on Kitchenham’s three-phase review procedure and supplements it with results, views, and recommendations from other leading experts in the field.

In this article, we present a simple, low-cost solution for the gain enhancement of a conventional pyramidal horn antenna using additive manufacturing. A flat, metamaterial lens consisting of three-layer metallic grid wire is implemented at the aperture of the horn. The lens is separated into two regions; namely epsilon-positive and epsilon-near-zero (ENZ) regions. The structure of the ENZ region is constructed accounting the variation of relative permittivity in the metamaterial. By the phase compensation property imparted by the metamaterial lens, more focused beams are obtained. The simulated and measured results clearly demonstrate that the metamaterial lens enhances the gain over an ultra-wide frequency band (10–18 GHz) compared to the conventional horn with the same physical size. A simple fabrication process using a 3D printer is introduced, and has been successfully applied. This result represents a remarkable achievement in this field, and may enable a comprehensive solution for satellite and radar systems as a high gain, compact, light-weighted, broadband radiator.

This study deals with a non-exhaustive overview of location systems operating in the 60 GHz frequency band. Both impulse and frequency hopping topologies are considered and the performances of the two realized systems are presented. For each system, a specific signal processing has been implemented to prevent the degradation of the location error from the impact of the multipath propagation.

In this study, a novel microstrip antenna sensor with defected ground structure is investigated to detect the presence of other substances in liquid food samples. The proposed antenna sensor is rake-shaped which has been designed using time domain solver in three-dimensional simulation software Computer Simulation Technology Microwave Studio. The proposed antenna sensor has been fabricated using an FR4 material, having overall dimensions of 30 × 27 mm2 with dielectric constant 4.4, substrate thickness 1.57 mm, and loss tangent 0.0025. Furthermore, the Q-factor of the proposed antenna sensor is 485 showing a maximum sensitivity of 700 MHz and having accuracy 98%. In the present work, water and juice are considered as liquid samples in which the presence of foreign substances is detected in terms of reflection coefficient and shift in resonant frequency with the help of the suggested microstrip antenna sensor. Through experimentation, it has been observed that with the increase in the percentage of adulterant in the considered samples, the dielectric property of solution changes which results in shift of reflection coefficient and resonant frequency, thus making an allowance for the proposed antenna sensor a valid tool to detect adulteration in liquid samples.

This manuscript presents a 50 Ω microstrip-fed quad-element high isolated ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with band-notched characteristics. The overall area of the proposed structure is 0.33λo × 0.33λo mm2 (where λo depicts the free space wavelength corresponding to the lower cutoff frequency, i.e. 2.54 GHz), etched on an FR-4 substrate of thickness 0.8 mm. The top layer has four semicircular disc-shaped radiating elements that are identical and orthogonal to obtain better inter-element isolation and compactness. A reverse two-shaped slot is etched onto the radiating patches to attain a band-rejection capability. Moreover, a decoupling structure is also placed at the top layer to suppress the unwanted surface waves. The bottom layer consists of a ground plane, which is further modified with quasi-self complementary and meandered line slots. A rectangular slot is also etched below the feed line to better match the impedance near the lower cutoff frequencies. The simulated reflection coefficients (S11) of the proposed antenna are less than −10 dB over 2.54 to 10.74 GHz frequencies except at 3.37 to 4.15 GHz (WiMAX/C band), and the simulated inter-port isolation (S21) is greater than −15 dB over the entire UWB range of frequencies (3.1 to 10.6 GHz). Also, the measured S-parameter results well agreed with the simulated ones. Furthermore, the simulation study of the 20-element UWB-MIMO antenna is also investigated using the proposed quad-element structure.

In this paper, double-walled carbon nanotubes (DWNTs) network layers were patterned using inkjet transfer printing. The remarkable conductive characteristics of carbon nanotubes (CNTs) are considered as promising candidates for transmission line as well as microelectronic interconnects of an arbitrary pattern. In this work, the DWNTs were prepared by the catalytic chemical vapor deposition process, oxidized and dispersed in ethylene-glycol solution. The DWNTs networks were deposited between electrodes contact and then characterized at DC through current–voltage measurements, low frequency, and high frequency by scattering parameters measurements from 40 MHz up to 40 GHz through a vector network analyzer. By varying the number of inkjet overwrites, the results confirm that the DC resistance of DWNTs networks can be varied according to their number and that furthermore the networks preserve ohmic characteristics up to 100 MHz. The microwave transmission parameters were obtained from the measured S-parameter data. An algorithm is developed to calculate the propagation constant “γ”, attenuation constant “α” in order to show the frequency dependence of the equivalent resistance of DWNTs networks, which decreases with increasing frequency.

The design of mixed-technology quasi-reflectionless planar bandpass filters (BPFs), bandstop filters (BSFs), and multi-band filters is reported. The proposed quasi-reflectionless filter architectures comprise a main filtering section that determines the power transmission response (bandpass, bandstop, or multi-band type) of the overall circuit network and auxiliary sections that absorb the reflected radio-frequency (RF) signal energy. By loading the input and output ports of the main filtering section with auxiliary filtering sections that exhibit a complementary transfer function with regard to the main one, a symmetric quasi-reflectionless behavior can be obtained at both accesses of the overall filter. The operating principles of the proposed filter concept are shown through synthesized first-order BPF and BSF designs. Selectivity-increase techniques are also described. They are based on: (i) cascading in-series multiple first-order stages and (ii) increasing the order of the filtering sections. Moreover, the RF design of quasi-reflectionless multi-band BPFs and BSFs is discussed. A hybrid integration scheme in which microstrip-type and lumped-elements are effectively combined within the filter volume is investigated for size miniaturization purposes. For experimental validation purposes, two quasi-reflectionless BPF prototypes (one- and two-stage architectures) centered at 2 GHz and a second-order BSF prototype centered at 1 GHz were designed, manufactured, and measured.

In this contribution, a design methodology for octave-bandwidth power amplifiers (PA) for 5G communication systems using surface mount dual-flat-no-lead packaged gallium-nitride high-electron-mobility transistor devices is presented. Systematic source- and load-pull simulations have been used to find the optimum impedances across 75% fractional bandwidth for S- (1.9–4.2 GHz) and C-band (3.8–8.4 GHz) PAs. The harmonic impact is considered to improve the output power and efficiency of the PAs. Utilizing the characteristic behavior of the transistors leads to modified optimum fundamental load impedances for the low-frequency range, which have higher gain compared with high-frequency range, and minimize the influence of the higher harmonics. Continuous wave large-signal measurements of the realized S-Band PA show a power added efficiency (PAE) of more than 40% from 1.9–4.2 GHz and a flat power gain of 11 dB while achieving a saturated output power of 10 W. The measured performance of the C-Band PA demonstrates a delivered power between 3.5 and 5 W across the frequency range of 3.8–8.4 GHz. A flat power gain of around 9 ± 0.5 dB with 26–40% PAE is achieved.

A low profile super-wideband polarization diversity printed monopole antenna with dual band-notched characteristics is presented the first time. The designed antenna comprises two arched shaped radiating elements with two triangular tapered microstrip feed lines (TTMFL) and two arched shaped partial ground planes, which covers an enormously wide impedance bandwidth (BW) from 1.2 to 25 GHz (ratio BW of 20.8:3) for reflection coefficient |S11| < −10 dB. To ensure the high port isolation (better than − 30 dB) between two feeding ports over the whole bands, two analogous antennas have been kept perpendicular to each other at a distance of 1 mm. In addition, the dual band-notched performance in wireless local area network (5–6 GHz) and X-band (7.2–8.5 GHz) is generated by employing a pair of open-circuited stubs (L-shaped stub and horizontal stub) to the TTMFL. Envelop correlation coefficient has been computed to study the polarization diversity performance. Finally, the proposed antenna was fabricated and tested successfully. Measured results indicate that the proposed antenna is an appropriate candidate for the polarization diversity applications. The proposed antenna has a compact size of 40 × 70 × 0.787 mm3, high isolation, and occupies a small space compared with the existing antennas.

This paper presents a new design of a reconfigurable miscrostrip patch antenna based on a substrate-integrated waveguide (SIW). The antenna is resonant at the millimeter-wave (mmWave) 5G spectrum. The tuning technique consists of using a nematic liquid crystal (K15). An adjustable frequency band from 30.191 to 32 GHz is obtained, giving a tunable range of Δfr = 1.809 GHz. The maximum gain and efficiency reach the values of 7.61 and 9.07 dBi and 93 and 94%, respectively. The proposed SIW antenna loaded with liquid crystal was fabricated and tested. The experimental results correlated well with the simulation; however, the measured reflection coefficient plot shows a shift of the tuning range of 284 MHz, which is an acceptable outcome compared to simulation. A new approach of adopting the magnetic field as a technique to tune the resonance frequency has been used. The structure is characterized by its design simplicity, compactness, and fabrication process. The proposed antenna proves that the liquid crystal improves the performance of the antenna in the Ka band for 5G applications and satellite communication systems.