Lorena Cabria

A PHEMT-Based Phase Conjugator for Full-Duplex Retrodirective Arrays

In this letter, a phase conjugator for full-duplex retrodirective arrays is presented. Properly controlling a PHEMT nonlinear behavior, the modulation of the phase conjugated retransmitted signal is assured without distorting the information contained in the amplified version of the received signal. By means of a balanced architecture, the interrogating and response components are obtained through two mutually isolated output ports, respectively connected to the demodulation unit and the orthogonal feed of the employed aperture coupled patch. Measured results demonstrate the phase conjugator performance in two operating modes: retransmission of a BPSK signal after reception of an amplitude modulated interrogation, or ASK response when the incoming excitation is angularly modulated.

Active Reflectors: Possible Solutions Based on Reflectarrays and Fresnel Reflectors

An overview about some of the recent Spanish developments on active reflectors is presented. In the first part, a novel beamsteering active reflectarray is deeply studied. It is based on implementing in each elementary radiator an IQ modulator structure, in which amplitude and phase control of the scattered field is achieved. Finally, a special effort is made in offering solutions to overcome the active antenna integration problems. In the second part, the active concept is firstly extended to Fresnel reflectors. Thanks to the development of a proper simulator, this special structure can be easily analysed. This simulator allows the study of performance of this kind of reflectors and, applying evolutionary algorithms, to find optimal configurations of reflector in accordance with the given specifications for the conformal radiation pattern.

Speed requirements of supply modulators used in polar architectures

This paper investigates the minimum supply modulator linear processing bandwidth and slew rate (SR) requirements necessary to meet the standard specs of total signal distortion and adjacent signal power ratio in modern polar wireless transmitters. System level simulations, performed under CDMA2000FW and CDMA2000RV excitations, showed that, depending on the filter behavior in the amplitude envelope spectrum main lobe, relaxed bandwidths between 2 and 5 times the original signal are sufficient to guarantee desired specs of 45dB of ACPR and −35dB of NMSE. On what the SR is concerned, we concluded that 1/(2.5) times the maximum AM(t) signal slope is enough to achieve the same desired specs.

A UHF class E 2 DC/DC converter using GaN HEMTs

In this paper, the design of a class E2 resonant DC/DC converter, operating at UHF band, is proposed. Combining the use of GaN HEMT devices, both for the inverter and the synchronous rectifier, with high Q lumped-element multi-harmonic matching networks, a peak efficiency value of 72% has been obtained at 780 MHz with a 10.3 W output power. By means of a Pulse Width Modulation (PWM) over the gate driving envelope, the output voltage may be controlled while keeping low switching losses, with an estimated small-signal bandwidth (BW) and a slew rate of 11 MHz and 630 V/µSeg, respectively.

A linearized polar transmitter for wireless applications

This paper reports on a new design method to overcome the nonlinear distortion associated to polar transmitters. The proposed methodology complements the modulation of drain bias, vDD(t), of conventional envelope elimination and restoration power amplifiers with a proper variation of the input drive level, vg(t). Allowing vg(t) to vanish when vDD(t) goes to zero, it obviates the inherent nonlinear distortion caused by the amplifier carrier feed-through. In addition, and beyond guaranteeing linear operation, such a design methodology is also beneficial for power added efficiency as it prevents the dissipation of instantaneous input power for a desired null instantaneous output power.

A zero-bias single-device balanced E-PHEMT mixer with conversion gain for RFID applications

A zero-bias single-device singly-balanced mixer, using an enhancement mode pseudomorphic HEMT (E-PHEMT) is proposed. The mixer takes advantage of the slightly positive pinch-off voltage in this kind of device, for providing gain conversion with an acceptable linearity and avoiding the use of DC bias. A lab model has been designed to be used in an RFID tag, where a low frequency local data signal is up-converted to the 900MHz frequency band, once the device is excited with an interrogating carrier.

Temperature dependent memory effects on a drain modulated GaN HEMT power amplifier

In this paper, the impact of self heating on the linearity of a drain modulated GaN HEMT power amplifier (PA) is studied. After characterizing the frequency response of junction temperature rise to power dissipation, as well as the effect of this variable on the PA modulation profiles, the dynamic envelope trajectory, under a two-tone test signal, appears to be slightly dependent on frequency spacing. Self heating related effects are shown to be negligible in presence of other nonidealities, as the case of feedthrough. In this way, punching a vector hole in the two-tone I/Q diagram and applying memoryless digital predistortion (DPD), will allow identifying the influence of self heating effects, over adjacent channel distortion. Finally, this long-term memory effect is proved to be responsible for only a minor residual distortion in a linearized EDGE polar transmitter.

Polar transmitter architecture used in a Software Defined Radio context

In this paper, we discuss the available transmitter architectures in a Software Defined Radio (SDR) context and present a suitable polar architecture implementation under three different modulation formats (TETRA, EDGE and CDMA2000FW). Then, we show how its recognized nonlinear impairments can be overcome using appropriate digital amplitude and phase pre-distortion algorithms.

Taking Advantage of a Schottky Junction Nonlinear Characteristic for Radiofrequency Temperature Sensing

This paper presents a cost effective solution for remote radiofrequency temperature sensing, taking advantage of a Schottky junction nonlinear characteristic and the device integration in a properly designed dual-frequency radiator. Once the proposed integrated active antenna is interrogated with a CW excitation, the level and phase of the third harmonic response signal gives information of the tag temperature to be controlled

A novel vector control active patch for beamsteering with linearity enhancement capability

In this paper, a novel integrated vector control active patch is investigated for its Introduction in compact arrays with beamsteering capabilities. A dual-feed aperture coupled microstrip patch is simultaneously used as transmitting antenna and output power combiner of two quadrature-phase PHEMT amplifying branches. Gain and/or phase control can be achieved by properly biasing both devices either on the saturated region or in an attractive low voltage highly linear zone.