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In this paper, a compact, efficient and easy to fabricate wearable antenna integrated with Artificial Magnetic Conductor (AMC) is presented. Addition of slots and bevels/cuts in the rectangular monopole patch antenna yield a wide bandwidth along with band notches. The proposed antenna is backed with an AMC metasurface that changes the bidirectional radiation pattern to a unidirectional, thus, considerably reducing the Specific Absorption Ratio (SAR). The demonstrated antenna has a good coverage radiating away from the body and presents reduced radiation towards the body with a front-to-back ratio of 13 dB and maximum gain of 3.54 dB. The proposed design operates over a wide frequency band of 2.9 to 12 GHz (exceeding the designated 3.1−10.6 GHz Ultra-Wideband (UWB) band). The band notches were created using slots on the radiating patch in the sub-bands from 5.50 to 5.67 GHz and 7.16 to 7.74 GHz. The overall dimensions of the structure are 33 × 33 × 6.75 mm3. The antenna's radiation performance increased considerably with the addition of the AMC layer. The SAR values for the antenna are reduced by 85.3% when the AMC is used and are 0.083 W/kg which is well below the FCC SAR limits. The simple design, miniaturized profile, low SAR and wide operating bands with multiple band notches make the presented antenna an appealing choice for several UWB wearable body area network (WBAN) applications.

In this study, an ultra-wideband (UWB) monopole antenna with a dynamically reconfigurable notch band, along with the associated RF-triggered power management unit (PMU) that enables the dynamic reconfigurability, are presented. The UWB monopole antenna has a rectangular slot which hosts a J-shaped stub, electrically connected with the radiator using one PIN diode switch. When the diode is OFF, the monopole antenna has a UWB characteristic, while when it is turned ON a frequency notch is created at 5.6 GHz. The diode is fed from a PMU that consists of a rectenna and a DC-to-DC active booster. When the rectenna that consists of a patch antenna and a rectifier receives a −11 dBm or higher 5.6 GHz signal, it rectifies the RF signal into a sufficiently high DC voltage. The rectified DC voltage is applied to the cascaded DC-to-DC booster as enabling signal, and the booster provides at its output terminal sufficient DC power to actuate the PIN diode and thus dynamically reconfigure the UWB antenna. The dynamically reconfigurable notch band is created immediately in response to the reception of an external, −11 dBm RF signal at 5.6 GHz, and it disappears in real time immediately after the external RF signal is removed. 13 12 2046 2052

A novel ring resonator bandpass filter with reconfigurable bandwidth with central frequency at 2.4 GHz is demonstrated. Theoretical analysis for computing the resonant frequencies is shown, and the design approach of implementing $\pi $ -section stubs connected to the ring to obtain the bandwidth reconfigurability is explained. The use of reconfigurable $\pi $ -section allows the alteration of the stub’s effective width and therefore the filter’s bandwidth reconfigurability. p-i-n diodes are used as switching elements to achieve the narrowband/wideband response. Coupled line sections are used for suppressing the higher modes by generating out-of-band transmission zeros, resulting in a significantly enhanced out-of-band rejection. Measurements indicate that the 3-dB fractional bandwidth can be switched from 58.5% to 75% at a fixed center frequency of 2.4 GHz with an insertion loss better than 1.1 dB. Moreover, the −20-dB stopband performance is extended to $2.7f_{0}$ .

Two rectenna designs consisting of a patch antenna and a voltage doubler operating at 5.6 GHz are presented. Rectenna-1 is matched with a varying input impedance active DC-to-DC booster based on Texas Instruments charge pump IC TPS60300. Depending on the biasing conditions the ohmic impedance varies significantly between 4.2-6.7 KΩ which consists of a design challenge for the rectifier matching. Rectenna-2 is optimized to be terminated with a passive ultra-low-voltage self-powered converter with relatively constant 3.9 KΩ input impedance. The passive converter can only be used if the required rectified power is sufficiently small. 1807 1808

A compact planar dual-band antenna for UHF and ISM bands is proposed. The antenna is fabricated on a 45 mm × 80 mm × 0.787 mm Rogers Duroid (R) 5880 substrate and is intended for use in Wireless Power Transfer (WPT) and Power Harvesting (PH) systems. It covers the UHF band from 855-935 MHz making it a suitable antenna for UHF applications worldwide and the ISM band from 2.4-2.5 GHz. In order to exploit the power that can be harvested from the ambient environment, from entirely random directions, omnidirectional behavior was intended. A prototype of the antenna has been fabricated S-parameter measurements, radiation pattern and gain simulations are also presented. 1 5

A practical implementation of a miniaturized crossover is presented using negative-refractive-index transmission-line (NRI-TL) metamaterial lines. NRI-TL metamaterial theory has demonstrated that by loading a conventional transmission line with lumped LC elements, a large phase shift per-unit-length can be achieved. Employing this technique, the conventional microstrip transmission lines in a three-section branch-line coupler crossover are replaced with 90° NRI-TL lines, and thus a compact NRI-TL crossover with an area 47 times smaller than the area of its conventional counterpart is demonstrated. Measured results demonstrate that the proposed NRI-TL metamaterial crossover exhibits a −10 dB |S11| bandwidth of 33% and a |3 dB| |S31| bandwidth of 26% around 1 GHz.

This paper presents a new compact wideband bandpass filter (BPF) with an extremely broad stopband consisting of two parallel coupled-line sections and multiple open-ended stubs, for S-band applications. Due to symmetry of the design, even- and odd-mode analysis method is applied to analyze the proposed filter structure. To further enhance the upper stopband, additional TZ's are generated by attaching two open stubs at the input/output feed lines and a third one in the middle of the structure. The fabricated prototype filter covers the whole S-band frequency range, and has 3-dB fractional bandwidth (FBW) of 66%. The measured insertion loss within the passband is less than 0.8 dB and the measured return loss is greater than 15 dB within the entire passband. In addition, the proposed filter has an appealing compact size of ${0.09\lambda_{\mathrm{g}}}^{2}$ with the upper stopband extended up to $5.96f_{0}$ , for suppression level greater than 20 dB.

This paper presents a compact reconfigurable phase-shifter based on negative-refractive-index transmission-line (NRI-TL) metamaterial unit cells. Two inter-switchable NRI-TL metamaterial unit cells are collocated within the same board area, and can be reconfigured based on the biasing polarity of embedded PIN diodes to provide two discrete phase states. The PIN 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 × 21.6 mm2 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 dB 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 GHz to 1.29 GHz.

The use of a tunable power splitter (PS) as a constituent component of a simultaneous wireless information and power transfer (SWIPT) system is discussed. Two varactor diodes are used to achieve a tunable output power ratio P2 : P3 varying from 1 : 1 to 1 : 10 under good matching conditions. The SWIPT system that operates at 2.4 GHz consists of a typical patch antenna, cascaded with the tunable PS, and a voltage doubler rectifier. The constituent components were implemented and tested as stand-alone devices and were subsequently combined in a measurement system using interconnectors. The effect of the tunable PS was explored with respect to the SNR measurements on the port that is intended for the information decoding receiver and the DC voltage measurements on the termination load of the rectifier that is connected directly on the energy harvesting port of the tunable PS. A spectrum analyzer is used for the SNR measurements while the input power is controlled using a signal generator. Both wireless power transmission and on-board measurements verify that the harvested energy can be maximized by using the minimum SNR at the information decoding branch at the expense of DC power consumption required for the biasing of the varactor diodes.

This study presents a simulation and measurement test-bench to investigate the antenna detuning, impedance mismatch and losses in through-body communications. These parameters are relevant to the efficient design of wearable and implantable antennas for biomedical sensors. The study was carried out using finite-difference-time-domain electromagnetic simulations using realistic high-resolution numerical human body phantom models. S-parameter measurement corresponding to the simulation setup was carried out when an implantable antenna connected to a Vector Network Analyzer was placed in the armpit of a human subject and communication was established with an external wearable antenna. The measured results verified the reliability of the proposed simulation test-bench for biomedical sensor applications. 1 4

Antennas for UWB Applications chapter deals with an overview of ultrawideband (UWB) antennas used for different applications. Some fundamental and widely used radiators, such as fat monopole, microstrip-fed and coplanar waveguide (CPW)-fed slot antennas, and tapered end-fire antennas are presented. Selected antenna designs are presented in relation to the UWB applications and their dictating radiation and operation principles. The demonstrated UWB antennas include antennas for handheld devices used for personal area network (PAN) communications; antennas for localization and positioning; UWB antennas for radio-frequency identifications (RFIDs); radar antennas for through-wall imaging, for ground-penetrating radar (GPR), and for breast tumor detection; and more generally, UWB antennas used for sensing. For some of the aforementioned applications, UWB antennas with special characteristics are needed, and they are presented and associated with the relevant applications. These include reconfigurable UWB antennas, metamaterial-loaded UWB antennas, and conformal UWB antennas. The usefulness of these special characteristics in comparison with the claimed advantages is critically evaluated. For the UWB applications presented in the chapter, one type or UWB antenna is recommended.

A novel ring resonator bandpass filter with reconfigurable bandwidth with central frequency at 2.4 GHz is demonstrated. Theoretical analysis for computing the resonant frequencies is shown, and the design approach of implementing π-section stubs connected to the ring to obtain the bandwidth reconfigurability is explained. The use of reconfigurable π-section allows the alteration of the stub's effective width and therefore the filter's bandwidth reconfigurability. p-i-n diodes are used as switching elements to achieve the narrowband/wideband response. Coupled line sections are used for suppressing the higher modes by generating out-of-band transmission zeros, resulting in a significantly enhanced out-of-band rejection. Measurements indicate that the 3-dB fractional bandwidth can be switched from 58.5% to 75% at a fixed center frequency of 2.4 GHz with an insertion loss better than 1.1 dB. Moreover, the -20-dB stopband performance is extended to 2.7f₀.

Wireless Power Transfer (WPT) is promoted as a key enabling technology (KET) for the widespread use of batteryless Internet of Things (IoT) devices and for 5G wireless networks. RF-to-DC rectifiers are essential components for the exploitation of either ambient RF power or wireless transmitted power from a dedicated source. There are several alternative rectifier topologies which can be selected depending on the desired wireless charging scenario and may include one or more diodes. For full rectification, a minimum of two diodes are needed. The current chapter discusses various implementations of voltage-doubler designs, which revolve around the basic topology of two diodes and two capacitors. Schottky diodes are usually used, in combination with lumped capacitors. Off-the-shelf diodes include both separate diodes and integrated voltage-doubler topologies in a single package. Rectifiers are inherently narrowband, non-linear devices, and the RF-to-DC efficiency, which is usually the figure of merit, depends non-linearly on both the termination load and the received RF power. The bandwidth of the rectifier depends on the preceding matching network.