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A dual-band UHF/industrial, scientific and medical (ISM) compact rectenna with wideband UHF matching (855–935 MHz) covering all, EU, U.S., and Chinese UHF radio frequency identification (RFID), standards is presented. The proposed design consists of a compact single-port, dual-band antenna, a three-port dual-branch matching network, and two voltage doubler rectifiers implemented with Schottky diodes and terminated with a common 10 kΩ load. For each band, the measured RF-to-dc efficiency is around 60% for a −5 dBm unmodulated signal. The wideband behavior of the rectenna supports harvesting of multitone signals. The use of a six-tone signal increases the maximum RF-to-dc efficiency of the dual-band rectifier, from approximately 60% for a single-tone UHF signal (890 MHz) to 80% for a six-tone signal for a received RF power of −5 dBm in both cases. A signal generator is used to generate a six-tone signal of equally weighted and equally spaced (10 MHz separation) monochromatic tones, with a total bandwidth of 50 MHz. The measurement results demonstrate that the dc voltages rectified from the two separate RF signals are effectively superimposed on the load, providing a clear advantage compared to single-band rectennas. The single-layer, compact design with a size of 80 × 45 mm2, with a high RF-to-dc efficiency, is an excellent candidate for wirelessly powered RFID tags. [ABSTRACT FROM AUTHOR]

In this article, a dynamically reconfigurable dual-layer ultra-wideband (UWB) antenna integrated with an energy harvesting (EH) system for powering a GaAs FET switch is presented. The UWB antenna dynamically creates a notch band in the presence of an interfering signal at 5.6 GHz and it goes back to normal UWB operation when the interferer is removed. For the switching operation, the FET switch is powered using only harvested energy carried by the interfering signals. The UWB antenna on the front layer is a microstrip-fed monopole with an embedded elliptical slot. A quarter wavelength linear stub acts as a resonator inside the slot, which is connected and disconnected using the low-power FET switch. The UWB antenna shares the RF ground with a very compact EH system that consists of a planar inverted-F antenna, a very compact voltage-doubler rectifier, and a passive direct-current (dc)-to-dc boost converter. The boost converter elevates the rectified voltage to above the 3.3 V threshold, which is the minimum voltage needed for the actuation of the FET switch. The dynamic notch-band reconfiguration of the UWB antenna without the need for an external dc power source is made possible when the collected power at the input of the rectifier is higher than −12 dBm. [ABSTRACT FROM AUTHOR]

This communication presents a compact reconfigurable phase shifter based on negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Two interswitchable NRI-TL metamaterial unit cells are collocated within the same board area, and can be reconfigured based on the biasing polarity of embedded p-i-n diodes to provide two discrete phase states. The p-i-n diodes are located on the shunt branches of the metamaterial line in order to reduce losses in the direct signal path. Design limitations in terms of return loss and insertion loss are discussed in relation to the two phase states. A proof-of-concept module with a size of 17.8 \times 21.6~ \text mm^2 is designed at 1 GHz, with measured insertion phases of −14.5° and +58.5° in the two phase states leading to a differential phase shift of 73°, while exhibiting insertion losses of 1.43 and 0.89 dB, respectively. The combined bandwidth for which the reflection coefficient in both states remains simultaneously below −10 dB is 0.46 GHz (46%), from 0.83 to 1.29 GHz. [ABSTRACT FROM PUBLISHER]

This communication presents a novel cactus-shaped ultrawideband (UWB) monopole antenna fabricated on liquid crystal polymer (LCP). The proposed antenna is a very compact design, since it can be fabricated on a board with dimensions only $20\times28$ mm ^{2} , while the three linear segments that comprise the cactus-shaped monopole provide a direct control on antenna matching. The proposed antenna is operating from 2.85 to 11.85 GHz and it presents very consistent omnidirectional patterns throughout the UWB frequency range. Return loss and pattern measurements are presented and the operation principles are discussed in detail. The simplicity of this topology, with the easily controllable return loss, allows for its easy implementation for various UWB subband designs, just by building suitable monopole versions, for which the only difference is the length of the three linear segments. [ABSTRACT FROM AUTHOR]

This paper presents a planar monopole backed with a $2 \times 1$ array of electromagnetic bandgap (EBG) structures. The reflection phase of a single EBG unit cell has been studied and exploited toward efficient radiation of a planar monopole antenna, intended for wearable applications. The shape of the EBG unit cell and the gap between the ground and the EBG layer are adjusted so that the antenna operates at 2.45 GHz. The proposed antenna retains its impedance matching when placed directly upon a living human subject with an impedance bandwidth of 5%, while it exhibits a measured gain of 6.88 dBi. A novel equivalent array model is presented to qualitatively explain the reported radiation mechanism of the EBG-backed monopole. The proposed antenna is fabricated on a 68 \times 38 \times 1.57$ mm ^{3} board of semiflexible RT/duroid 5880 substrate. Detailed analysis and measurements are presented for various cases when the antenna is subjected to structural deformation and human body loading, and in all cases, the EBG-backed monopole antenna retains its high performance. The reported efficient and robust radiation performance with very low specific absorption rate, compact size, and high gain make the proposed antenna a superior candidate for most wearable applications used for off-body communication. [ABSTRACT FROM PUBLISHER]

An overview of design requirements and novel approaches for improved performance UHF radio frequency identification (RFID) tags is presented. Two matching techniques, an inductively coupled structure and a serial stub structure are discussed. Different miniaturized antenna topologies are proposed, focusing on low-profile, high efficiency and high directivity in very compact (less than 3 in x 3 in) configurations. [ABSTRACT FROM AUTHOR]

Two CPW-fed elliptical monopoles were fabricated on liquid crystal polymer (LCP) with reconfigurable rejection band (band-notch) characteristics in the frequency range between S and 6 GHz. The first antenna uses a λ/2 long, U-shaped slot and the second antenna uses two symmetrically placed λ/4 long, inverted L-shaped stubs as resonating elements. Microelectromechanical system (MEMS) switches are used to activate and deactivate the resonating elements without the need of dc bias lines due to a novel design of the switch geometry. Transmission line models and surface current distributions are used to explain the effect of the added resonating elements. Reflection coefficient radiation pattern and gain measurements are presented to verify the design concepts featuring a very satisfactory performance. [ABSTRACT FROM AUTHOR]

A single-feed circular microstrip antenna with reconfigurable polarization capability is proposed. This antenna has a simple structure, which consists of a radiating circular patch, five switches (PIN diode), three matching stubs, and a 50 Ω) microstrip feed line. It can be switched between 4 different states: two states (low-frequency and high-frequency) for linear polarization (LP), one state for left hand circular polarization (LHCP) and one for right hand circular polarization (RHCP) by controlling the bias voltage of two PIN diodes. At the same time, three switchable matching stubs are used for matching every polarization state. Simulation results and experimental results show that the pro- posed antenna demonstrates a low cross polarization level, good impedance bandwidth, and a very good axial ratio in the circularly polarized states. [ABSTRACT FROM AUTHOR]

This paper presents the use of pin diodes to reconfigure the impedance match and modify the radiation pattern of an annular slot antenna (ASA). The planar antenna is fabricated on one side of a Duroid substrate and the microstrip feeding line with the matching network is fabricated on the opposite side of the board. The central frequency is 5.8 GHz and, by reconfiguring the matching circuit, the antenna was also designed to operate at 5.2 and 6.4 GHz. Pin diodes are also used to short the ASA in preselected positions along the circumference, thereby changing the direction of the in the plane defined by the circular slot changes. As a proof of concept, two pin diodes are placed 45° on both sides of the feeding line along the ASA and the direction of the is shown to align with the direction defined by the circular slot center and the diode. Consequently, a design that is reconfigurable in both frequency and radiation pattern is accomplished. Return loss and radiation pattern measurements and simulations are presented, which are in very good agreement. [ABSTRACT FROM PUBLISHER]