This paper shows that the two most common impedance transformation networks for power amplifiers (PAs) can be designed to achieve optimum transformation at two frequencies. Hence, a larger bandwidth for the required impedance transformation ratio is achieved. A design procedure is proposed, which takes imperfections like losses into account. Furthermore, an analysis method is presented to estimate the maximum uncompressed output power of a PA with respect to frequency. Based on these results, a fully integrated PA with a dual-band impedance transformation network is designed and its functionality is proven by large signal measurement results. The amplifier covers the frequency band from 450 MHz to 1.2 GHz (3 dB bandwidth of the output power and efficiency), corresponding to a relative bandwidth of more than 100%. It delivers 23.7 dBm output power in the 1 dB compression point, having a power-added efficiency of 33%.

We propose a definition of the efficiency bandwidth for a power amplifier (PA) using a modulated signal as the signal bandwidth at which the amplifier efficiency has dropped to a level of 90% of the maximum efficiency at small bandwidth. We introduce a Monte Carlo method to calculate the efficiency bandwidth for some popular PA architectures. The method assumes a given modulated signal at the load. From this load signal the wave forms at the drains of the transistors are derived and the energy dissipation in the transistors can be calculated. Using idealized transistors with no output capacitance the maximum realizable efficiency bandwidth of an asymmetrical Doherty amplifier is 60%, which is much larger than that of an outphasing amplifier, which is 14%. More realistic transistors that include output capacitances, need a matching circuit with a high Q-value which decreases the efficiency bandwidth. Using output capacitance values typical for LDMOS transistors, the asymmetrical Doherty amplifier shows an efficiency bandwidth of about 400 MHz for a signal centered at 1 GHz. For a signal at 2 GHz the efficiency bandwidth is found to be 520 MHz. Due to the fixed values of the output capacitances the efficiency bandwidth does not scale with frequency.

Directional modulation (DM) is an emerging technology for securing wireless communications at the physical layer. This promising technology, unlike the conventional key-based cryptographic methods and the key-based physical layer security approaches, locks information signals without any requirements of keys. The locked information can only be fully recovered by the legitimate receiver(s) priory known by DM transmitters. This paper reviews the origin of the DM concept and, particularly, its development in recent years, including its mathematical model, assessment metrics, synthesis approaches, physical realizations, and finally its potential aspects for future studies.

This paper presents a 60 GHz reconfigurable active phase shifter based on a vector modulator implemented in 65 nm complementary metal–oxide–semiconductor technology. This circuit is based on the recombination of two differential paths in quadrature. The proposed vector modulator allows us to generate a phase shift between 0° and 360°. The voltage gain varies between −13 and −9 dB in function of the phase shift generated with a static consumption between 26 and 63 mW depending on its configuration.

This paper presents a detailed trap investigation based on combined pulsed I/V measurements, drain current transient (DCT) measurements and low-frequency dispersion measurements of transconductance (LF Y21) and output conductance (LF Y22). DCT characterization is carried out over a 7-decade time scale. LF Y21 and Y22 measurements are carried out over the frequency range from 100 Hz to 1 GHz. These combined measurements were performed at several temperatures for AlGaN/GaN high electron mobility transistors under class AB bias condition and allowed the extraction of the activation energy (Ea) and the capture cross section (σc) of the identified traps. Extensive measurements of these characteristics as a function of device bias are reported in this work to understand the dynamic trap behavior. This paper demonstrated a correlation between LF small-signal (LF Y21 and Y22) and large-signal voltage steps (DCT) results. These measurements allow identifying the same 0.64 eV deep level, attributed to a native defect of GaN, possibly located in the buffer layer.

Laterally diffused metal oxide semiconductor (LDMOS) transistors with 10 V breakdown voltage have been implemented in a 65 nm Complementary metal oxide semiconductor (CMOS) process without extra masks or process steps. Radio frequency (RF) performance for Wireless local area network (WLAN) frequencies and in X-band at 8 GHz is investigated by load-pull measurements in class AB operation for both 3.3 and 5 V supply voltage. Results at 2.45 GHz showed 290 mW/mm output power density with 17 dB linear gain and over 45% power added efficiency (PAE) at 4 dB compression at a supply voltage of 5 V. Furthermore, results in X-band at 8 GHz show 8 dB linear gain, 320 mW/mm output power density and over 22% PAE at 4 dB compression. Third-order intermodulation measurements at 8 GHz revealed OIP3 of 18.9 and 21.9 dBm at 3.3 and 5 V, respectively. The transistors were also tested for reliability which showed no drift in quiescent current after 26 h of DC stress while high-power RF stress showed only small extrapolated drift at 10 years in output power density. This is to the authors' knowledge the first time high output power density in X-band is demonstrated for integrated LDMOS transistors manufactured in a 65 nm CMOS process without extra process steps.

A new model is proposed on how to account for the inertia of scatterers in radar-based turbulence intensity retrieval techniques. Rain drop inertial parameters are derived from fundamental physical laws, which are gravity, the buoyancy force, and the drag force. The inertial distance is introduced, which is a typical distance at which a particle obtains the same wind velocity as its surroundings throughout its trajectory. For the measurement of turbulence intensity, either the Doppler spectral width or the variance of Doppler mean velocities is used. The relative scales of the inertial distance and the radar resolution volume determine whether the variance of velocities is increased or decreased for the same turbulence intensity. A decrease can be attributed to the effect that inertial particles are less responsive to the variations of wind velocities. An increase can be attributed to inertial particles that have wind velocities corresponding to an average of wind velocities over their backward trajectories, which extend outside the radar resolution volume. Simulations are done for the calculation of measured radar velocity variance, given a 3-D homogeneous isotropic turbulence field, which provides valuable insight in the correct tuning of parameters for the new model.

This paper presents a compact microstrip tri-band bandpass filter (BPF) using two multimode stepped-impedance resonators (SIRs) with a 0° feed structure. The fundamental odd-mode and even-mode resonant frequencies and the third resonant frequency are utilized to determine the center frequencies of the tri-band filter. The mode-splitting technique is used by combining two SIRs with electrical coupling. Therefore, two modes generate one passband and the bandwidths can be controlled by the electrical coupling strength. The 0° feed network is applied to create one pair of transmission zeros at each side of all the triple passbands, resulting in high selectivity. Finally, a tri-band BPF with the central frequencies of 1.8, 2.4, and 5.8 GHz, and respective fractional bandwidths of 8.9, 12.5, and 5.3% are designed and fabricated. The simulated and measured results show a good agreement.

This paper analyses the effects of receiver non-linearity on the performance of the most commonly utilized signal detectors in cognitive radio systems. The analysis covers both self-modulation products of a single orthogonal frequency-division multiplexing (OFDM) signal and intermodulation (IM) products of two OFDM signals, and also their contribution to the probability of false detections. As a result, this work presents the linearity requirements for the spectrum sensor receiver front-end as a function of the sensitivity of the signal detector. Furthermore, we show that the cyclostationary feature detectors are more robust than the energy detectors against IM products of multiple interferers. Theoretical results are verified in measurements with a cyclostationary feature detector using digital video broadcasting – terrestrial (DVB-T) signals as an example.

In radar receivers, the low noise amplifier (LNA) must provide very low noise figure and high gain to successfully receive very low signals reflected off of illuminated targets. Obtaining low noise figure and high gain, unfortunately, is a well-known trade-off that has been carefully negotiated by design engineers for years. This paper presents a fundamental solution method for the source reflection coefficient providing the maximum available gain under a given noise figure constraint, and also for the lowest possible noise figure under a gain constraint. The design approach is based solely on the small-signal S-parameters and noise parameters of the device; no additional measurements or information are required. This method is demonstrated through examples. The results are expected to find application in design of LNAs and in real-time reconfigurable amplifiers for microwave communication and radar receivers.

An N-band resonator, particularly well-suited for reconfigurability, is presented in this paper together with its synthesis. The resonator is based on the association of an N-band dual-behavior resonator and tunable capacitors. Its topology consists of a parallel association of N + 1 different bandstop structures, each one composed of a stub terminated by a capacitor. N pass bands, separated from each other by a transmission zero, are then obtained. As each bandstop structure independently controls one transmission zero, the use of variable capacitors allows each of them to be tuned independently and then to reconfigure the resonator in terms of transmission zeros and resonant frequencies. After the presentation of the general synthesis, this principle is validated by the realization of a tri-band resonator in microstrip technology.

A combined class-AB and a Doherty power amplifier conceived for microwave backhaul in the 7 GHz frequency band are here presented and compared. They are fabricated in the same GaN monolithic process and have identical total active device periphery. For the given application, the linearity-efficiency trade-off for the two architectures is discussed. The two modules have been thoroughly characterized in linear and non-linear continuous wave conditions. Then, to evaluate linearity under the actual operative conditions, a system level characterization has been carried out, applying a modulated input signal and comparing the spectral responses of the two amplifiers with and without digital predistortion. A saturated output power of 40 dBm has been achieved by both circuits. At 6 dB of output back-off, the Doherty amplifier shows an efficiency of 33%, 10 points higher than that of the class-AB module. On the other hand, system level measurements show that, adopting the same predistorter complexity to comply with the reference standard emission masks, the Doherty amplifier needs at least 1 dB of extra back-off. This negatively affects its efficiency, therefore reducing the advantages it can claim with respect to the class-AB amplifier in continuous wave condition.

In this paper, a 1.8–2.6 GHz wideband rectenna is designed for radio frequency (RF) energy harvesting in the context of wireless sensor nodes (WSN). To assess the feasibility of ambient RF energy harvesting, the power density from RF base stations is analyzed through statistical measurements. Power density measurements are also performed close to Wi-Fi routers. Using these results, a methodology based on impedance matching network adaptation and maximum power transfer is proposed to design the wideband RF harvester. Using this method, three RF bands, i.e. GSM1800, UMTS and WLAN, are covered. The theoretical analysis is confirmed by simulations and measurements. From measurements results, the prototype RF-to-DC conversion efficiency is 15% at −20 dBm from 1.8 to 2.6 GHz. It is shown that with three RF sources in the chosen bands, each emitting at 10 dBm, the RF-to-DC conversion efficiency is 15% better compared to that measured with a single RF source. Finally, 7 µW is harvested at 50 m from a GSM1800 and UMTS base station. This value confirms the RF harvester workability to supply small sensors.

We introduce a new technique for the design of an output combiner for Doherty power amplifier (DPA) and its effective exploitation for the development of a wideband laterally diffused metal oxide semiconductor (LDMOS) DPA. The design is enabled by a two-line impedance inverter for the DPA back-off operation, which is capable of 52% of fractional bandwidth. The technique is validated by the development of a DPA prototype for Ultra high frequency terrestrial digital video broadcast (DVB-T) applications, with optimized peak power and efficiency over 470–806 MHz. The prototype delivers between 40 and 53% of average efficiency across the band, at 49 dBm output power in average across the bandwidth, and supporting DVB-T signals with 8 MHz bandwidth and a peak-to-average power ratio of 10.5 dB. It achieves the target adjacent channel power ratio of −52 dBc at 750 MHz if digital pre-distortion is applied, and provides 47.8 dBm of output power with a drain efficiency of 44.3%.

This paper presents the development of two dual-band radio-frequency (RF) harvesters optimized to convert far-field RF energy to DC voltage at very low received power. The first one is based on a patch antenna and the second on a dipole antenna. They are both implemented on a standard FR4 substrate with commercially off-the-shelf devices. The two RF harvesters provide a rectified voltage of 1 V for a combined power, respectively, of −19.5 dBm at 915 MHz, −25 dBm at 2.44 GHz, of −20 dBm at 915 MHz, and −15 dBm at 2.44 GHz. The remote powering of a clock consuming 1 V/5 µA is demonstrated, and the rectenna yields a power efficiency of 12%.

Wireless network has been emerged as one of the most promising technologies for sensor-integrated applications so far. The ever-increasing demand in long-term chronic monitoring of vital or essential signals is driving a technology revolution in dealing with critical issues of clinical, healthcare, fitness, and wellness, creating multidisciplinary collaborations to benefit mankind. The voltage-controlled oscillator has been one of the important building blocks in this regard. In this paper, we report on study concerning the design and implementation of such a key circuit, with particular emphasis on a μW-level low-power design. All the aspects regarding the oscillator are detailed. The proposed circuit structure and experimental results justifying our work are given as proof of concept.