A dual-band UHF/ISM compact rectenna with wideband UHF matching (855-935 MHz) covering all, EU, US and Chinese UHF RFID standards is presented. The proposed design consists of a compact single-port, dual-band antenna, a 3-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 multi-tone 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.

In this paper, a single-layer reconfigurable reflective metasurface is presented. The proposed metasurface operates at 5.4 GHz and can achieve either absorption or cross-polarization conversion corresponding at two different diode biasing states. The reflective metasurface acts as an absorber for an incident wave when the diodes are forward-biased. Similarly, it changes the polarization state of the reflected wave for a linearly polarized incident wave when the diodes are reverse-biased. The proposed structure maintains the aforementioned performance characteristics for oblique incidence, up to 60° compared to the perpendicular incidence. The proposed metasurface can achieve linear to linear polarization conversion with polarization conversion ratio (PCR) > 95% and absorption, with absorption ratio (AR) > 80% in the same frequency band just by reconfiguring the state of the PIN diodes.

A dynamically reconfigurable dual-layer UWB antenna integrated with an energy harvesting 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. Inside the slot a quarter wavelength linear stub acts as a resonator and it is connected and disconnected using the low-power FET switch. The UWB antenna shares the RF ground with a very compact energy harvesting system, that consists of a planar inverted-F antenna, a very compact voltage doubler rectifier and a passive 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 any external DC power source is made possible when the collected power at the input of the rectifier is higher than -12 dBm.

A two-way tunable power divider for Simultaneous Wireless Information and Power Transfer (SWIPT) is proposed in this paper. The power divider divides the incoming power in such a way that maximum power is utilized for energy harvesting purposes and the rest of the power is used for information decoding purposes. This unequal distribution of power is realized by tuning the varactor diode’s reverse biasing voltages. A good matching performance is attained using the radial and short stubs at the input and one of the output ports, respectively. High isolation is achieved with the help of the resistor used for connecting the output ports of the power divider. The achieved power division ratios vary from 13:1 to 28:1. The tunable power divider is designed and fabricated at 2.4 GHz. The bandwidth measured at 10 dB return loss is 3.2 GHz and the isolation better than 12 dB is achieved between the output ports. The designed structure is compact and good consistency is observed between the simulated and measured results. The designed power divider may be used for future 5G wireless networks.

A reconfigurable bandpass filter (BPF) with constant centre frequency and wide tuning range of bandwidth is presented. The proposed filter is based on the novel configuration of two modified asymmetrical π-sections with folded shorted stubs loaded on a ring resonator. The novel topology allows the implementation of three reconfigurable passband states. A detailed theoretical analysis for calculating the transmission zeros using ABCD parameters is shown, and the design approach of implementing the random offset -x-, asymmetrical π-sections with the folded stubs to get the bandwidth reconfigurability is thoroughly explained. PIN diodes are utilized as switching elements to achieve narrowband/mediumband/wideband response. The measured results indicate an absolute bandwidth tuning range of 1.3 GHz, whereas the -3 dB fractional bandwidth (FBW) can be varied from 37% to 92% while the centre frequency remains constant at 2.4 GHz. The fabricated prototype reconfigurable BPF demonstrates one of the widest 3-dB FBW tuning ranges and one of the highest absolute tuning ranges with a sharp-skirt characteristic. It has also more than 20 dB attenuation in the upper stopband which is extended to 2.7 times the centre frequency.

This paper reports on the RF design and practical development of a non-reciprocal balanced bandpass filter (BPF) that exhibits a highly-selective quasi-elliptic response in the forward direction of propagation that is shaped by four transmission poles and two transmission zeros (TZs). By modulating some of the filter’s resonators with phase-progressed AC signals, a non-reciprocal response is obtained in the differential mode. Its common-mode is also highly suppressed due to the incorporation of a balanced network that results in two additional TZs and resistive loss that are unique to the common-mode. The filter order can be increased by cascading additional resonators. For validation purposes, a microstrip prototype centered at 725 MHz was designed, manufactured, and measured. It showed a high isolation in the differential-mode reverse transmission of up to 62.1 dB. Moreover, the common-mode was suppressed by over 45 dB in a bandwidth greater than one octave.