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In this paper, a 2-bit unit chipless radio frequency identification (RFID) tag architecture is proposed through using both the defected ground structure (DGS) and the half-wavelength spiral resonator together. This tag structure with the size of $60\times 40$ mm2 consists of integrated microstrip with spiral DGS as well as ${{{\lambda }}}/{\mathbf 2}$ spiral resonators to realize compact 4-bit design without enlarging the tag size, and these spiral resonators can provide transmission zeros. Through combining the narrow band frequency modulated continuous wave radar, this proposed structure can offer the target location as well. Furthermore, the gap distance effect and the spiral dimension for the provided chipless RFID tag structure are analyzed and explained, and the three experimental results show excellent agreements with the theoretical analysis.

A differential planar microwave resonator permittivity sensor for material characterization is proposed in this paper. The sensor is based on asymmetric terminated cross-shaped resonator (TCSR) to provide multi-band notch frequency characteristics, allowing permittivity measurement of a small dielectric material under test (MUT) with a single resonator. Differential sensing is robust against varying ambient factors that cause frequency variations in the measurements. The dielectric properties of the MUT can be measured from the difference in notch frequencies with the reference material. To illustrate the technique, a tri-band sensor is prototyped using the proposed resonator configuration to measure the permittivity of both solid and liquid samples. The empirical equations for the determination of the MUT permittivity in relation to the notch frequencies have been derived. The sensor operates at 0.97, 1.69, and 2.91 GHz with an average sensitivity of 1.18, 4.45, and 1.22 MHz, respectively. The measured results are in a good agreement with the theoretical analysis.

In this work, we investigate an application of convolutional neural networks (CNNs) using radar signal for recognizing objects and human movements. We suggested 7 scenarios and collected 2000 samples of each one: nothing, a carton, a plastic box inside the carton, a metal plate inside the carton, a man sitting behind the carton, a standing man and a moving man. The numeric radar data is preprocessed to generate image. Then it is sent to a pre-trained CNN (Inception V3) for feature extraction. The model is trained for 30 epochs in a batch of 20 samples. We choose to fine-tune the top 2 inception blocks by training the model once again. After all this training process, it attains validation accuracy of 99.2% and testing accuracy of 99.7%. The model carries through the classification of these 7 scenarios.

The radiation behavior of reader antenna is critical for a compact, low-profile handheld RFID reader. Comparing with the conventional technique, this paper gives a basic review of a novel design approach to planar endfire circularly polarized (CP) antenna, which radiates its main beam in parallel with the printed substrate. To this end, a planar magnetic dipole with vertically polarized component is introduced, while the horizontally polarized counterpart can be realized by a loop or an electric dipole antenna printed on the same substrate. Based on this concept, the combinations with different performances are presented and a summary of some recent advances is given. After that, the mathematical analysis based on parallel complementary dipoles is demonstrated, and the conceptual design configuration is provided accordingly. Finally, an experimental example with low profile and endfire CP characteristic is presented. Experimental validation shows that this new class of planar endfire CP antenna can be a promising alternative for a low-profile handheld RFID reader.

This paper presents the concept and demonstration of harmonic diversity for wireless communication, which makes use of multiple harmonic radio frequency (RF) channels with respect to the carrier frequency. Rather than frequency and space diversities widely used today to improve multipath fading, signal quality and spectral efficiency, the proposed scheme does not require multiple RF transceiver front-ends. The advantages of inherent RF device nonlinear characteristics are harnessed to produce and process harmonics within single transceiver. Even though distinct harmonic channels will exhibit different order of phase shifts, the analysis shows that such phase offsets can be compensated by adjusting the phase of local oscillator (LO) at receiver end. Extending the framework of the Shannon theorem, an $M$ -channel harmonic communication system is shown to reduce the minimum required signal-to-noise ratio (SNR) at the input of receiver by $M$ -times. In addition, this work indicates that the power consumption of transmitter can be significantly reduced up to 66% than the conventional ones. Through the analysis of channel capacity, the harmonic system is proved to outperform the single channel counterpart especially when SNR is low. To validate the correctness of the proposed concept, a series of experiments are carried out to emulate the developed theoretical models. For instance, a three-channel harmonic communication system is prototyped, involving certain RF harmonic components designed for demonstration. The retrieved signal strengths are examined with different phase setting of receiving LO, and various modulation techniques are applied for estimating the system performances. All measured results are in agreement with their simulated counterparts, thereby demonstrating the correctness and usefulness of the proposed theories and techniques for nonlinear communication systems of harmonic diversity.

In this paper, a radio frequency identification (RFID) reader architecture composed of two signal generators, a mixer, an amplifier, and a low-pass filter (LPF) for reading a 2-bit chipless RFID tag is proposed. This tag consists of integrated microstrip and defected ground structure (DGS) with U-slot resonator to realize compact 2-bit design, and these slotline resonators can provide transmission zeros. The reader is a frequency modulated continuous wave (FMCW) radar, which interrogates a tag and decodes the tag’s identification data.

This paper proposed a Ultra-Wide Band (UWB) chipless radio frequency identification (RFID) tag. This tag consists of integrated microstrip and slot cross-shaped resonators with stub to realize compact multi-bit design. These stubs can provide transmission zeros which are controlled independently. A prototype of four-bit chipless tag is fabricated on RO6010 with 10.8 dielectric constant. The simulation and measured results are in good agreement.

In this communication, a novel highly integrated antenna-triplexer on a two-layer printed circuit board is proposed for multiband communication systems. This integrated three-port component operated at triple frequency bands (0.85, 1.65 and 2.45 GHz) simultaneously utilizes a single slot antenna and its rectangular loop as the radiating elements. Good three-port isolations are achieved by the multi-mode excitations including even, odd and bi-directional modes. These modes are intrinsically orthogonal and therefore the isolations are guaranteed. Compared with the conventional counterparts that use additional bandpass filters to assure the port isolations, the proposed antenna-triplexer preserves the simplicity and compactness of the antenna itself, and it is suitable for the practical portable applications. To demonstrate the significance of this new antenna-triplexer, a prototype measured with compact size is implemented and the experimental results show the good agreements with the simulations. The antenna gains of 0.85, 4.00 and 4.23 dBi are obtained and an average isolation in three ports is as good as 22.7 dB at operating frequencies.

In this paper, the resistor effect on isolation bandwidth of a compact Wilkinson power divider is studied. The discussion is based on an equal modified compact power divider on RO4003, with center frequency of 2.4 GHz. In this compact power divider, stepped impedance interdigital coupling sections were introduced to replace the quarter wavelength impedance transformer of Wilkinson power divider to realize the bandpass filtering capability. The theoretical analysis, simulation and measurement results are also discussed in this paper.

This paper describes a ZigBee-based wireless sensor network node for the ultraviolet (UV) detection of flame. The sensor node is composed of a ZnSSe UV photodetector, a current-sensitive front end including a high-gain current-to-voltage amplifier with 120 dB and a logarithm converter, and a transceiver operated at a 2.4-GHz industrial, scientific, and medical band. A passive photodetector is designed to have a cutoff at 360 nm and convert the UV emission of flame into picoamperes. Including mixed signal processing and ZigBee transmission, the speed of flame detection is as fast as 70 ms. The sensor node consumes only an average of 2.3 mW from a 3.3-V supply. The performance of a prototype sensor node was verified when the luminous flame was imaged onto the sensor node with different angles ranging from -30° to 30° and distances of 0.1, 0.2, and 0.3 m enabling effective fire safety applications.

This study presents a novel dual-band antenna design methodology utilising a dual-frequency impedance transformer with defected ground structure (DGS). The proposed dual-frequency DGS impedance transformer generates a second resonant frequency from a conventional single-band antenna, resulting dual-band operation. Simulation studies illustrate that the adopted design achieves versatile configurations for arbitrary operating frequencies and diverse input impedance ranges in planar antenna structures. To experimentally verify the proposed design methodology, a dual-frequency DGS impedance transformer was implemented for a 2.4 GHz monopole antenna to obtain a 900/2400 MHz dual-band antenna. Measurement shows that the 10 dB return loss bandwidth in 900 MHz band is 34.4 MHz, whereas that in 2400 MHz band is wider than 530 MHz. Typical monopole radiation patterns are observed at both operating bands.

This paper presents a new concept of simultaneous data transfers with existence of multiple harmonic frequency channels. Contradictory to conventional approaches of multiband communication systems, which generate the desired operating frequencies with multiple local oscillators and communicate in time division basis, this proposed harmonic communication system reuse the intermodulation products generated by the intrinsic property of nonlinear devices, primarily the up-/down-converting mixers in the transceiver. In this case, duplicated data can be transferred through multiple frequency channels. Moreover, compact multiband components can be used to replace those single-band circuits in conventional multiband systems and therefore limiting the cost of such transceiver. In theoretical analysis, the optimal signal-to-noise ratio (SNR) performance can be enhanced by 3-dB whenever the number of frequency channels is doubled. As the consequence, the bit-error-rate (BER) performance can be improved, or in another point of view, the minimum required SNR for the receiver can be relaxed. The simulation results show good agreements with the theoretical ones and therefore demonstrate the usefulness of proposed harmonic frequency channels concept.

In this paper, a novel differential bandpass filter (BPF) with dual-band filtering response is proposed. The equivalent circuits of proposed dual-band filter are illustrated and analyzed in both differential-mode and common-mode. By controlling the electrical length of an open stub in the differential-mode, two passbands operating at the desired frequency ratio can be designed. Also, the spurious response within the passbands can be suppressed by the over-coupling technique. In the common-mode operation, the short-ended meander line enhances the common-mode suppression. From the measurement results, the dual-band BPF operates at 854 MHz and 2.40 GHz, with 3-dB fractional bandwidth 7.17% and 3.71% respectively. A transmission zero is recorded at 1.79 GHz to suppress the spurious passband. The measured common-mode suppression is better than 18.5 dB in two passbands is achieved.

In this paper, a novel wireless sensing network node with 2.4 GHz communication and flood detection with 0.02 volt/mm sensitivity is presented for flood monitoring of distribution substation of electrical utilities in low-lying area. The sensor node is as compact as 8 cm × 6 cm and a low power consumption of 860 mW. When a liquid level detector detects an abnormal water level near the substation room, a signal can be transmitted in 115 kbps via a Zigbee module to a control center. It may reduce the risks of damage of the substation and subsequently ensure the power supply safety.

In this paper, a tunable microstrip antenna-filter is proposed based on a double U-shaped defected ground structure (DGS) and compact tunable square-loop dual-mode bandpass filter using capacitively loaded resonator. The antenna structure consists of a simple trapezoid monopole with a DGS microstrip feedline for excitation and this also yields a broaden impedance bandwidth covering 0.8 GHz to 2 GHz for UHF RFID operation and electromagnetic emission of partial discharge of traditional power facilities. In addition, the capacitively stepped impedance resonator of the filter allows frequency tuning between 1.2 and 1.6 GHz so as to steer the principal emission detection of partial discharge.

In this paper, a dual-mode bandpass filter using square-loop resonator is proposed for wideband applications. By introducing two capacitive stepped-impedance inner arms along the square-loop resonator, a wide passband response is achieved. In addition, the degradation of the insertion loss over the passband can be enhanced by a pair of tight coupling feed lines located at two perpendicular positions of the square ring. In order to demonstrate the performance of the proposed filter structure, a prototype filter is designed at 5 GHz with 74% fractional bandwidth. Good agreement is obtained between simulations and measurements.