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This article presents a compact, low-power, yet efficient wireless sensing platform to detect the angular displacement of an object with a reoriented complementary split-ring resonator (RCSRR). This RCSRR sensor belongs to the CSRR family, consisting of a 90° feedline on the stator and slots on the rotor. The reflected signal of the sensor experiences a monolithic phase response to the angular displacement because of its asymmetricity. In the platform, the sensor acts as a variable load of the multiport interferometer. The multiport converts the reflected signal into dc voltage readouts representing the real and imaginary parts of the phase of the reflection coefficient. Moreover, this platform operates at a fixed frequency (i.e., 2.4 GHz), and it requires only a biasing power as low as −30 dBm. This platform prevents ponderous system architecture and power consumption. This innovative wireless sensing platform has been designed, implemented, and tested. The experimental results show good agreement with their theoretical counterparts, and the standard deviation of angular displacement uncertainty is only $10^\prime $ .

A distinct usage of the conventional multiport architecture is introduced in this work to explore the compendious scheme of a concurrent dual-band interferometric receiver. Dual RF signals at individual frequency channels are received simultaneously, and only a single low-power local oscillator (LO) source is deployed for frequency translation or conversion to the same intermediate frequency (IF) band. Although these signals are spectrally overlapped, they can be extracted with a simple and efficient algorithm with good channel-to-channel isolations. Compared to the conventional multiport configuration, the power detectors are replaced by analog-to-digital converters (ADCs) to process the signals in this proposed scheme. The underlying physics of the concurrent receiving operation is explained and derived analytically. Some experiments are also presented to investigate various performance indexes, including signal linearity, noise behavior, interchannel interference, and so forth. Lastly, multiple $M$ -quadratic-amplitude modulation (QAM) signals are applied to evaluate the communication behavior of the proposed receiver architecture. Distortions due to frequency drift, channel imbalance, and in-phase and quadrature (IQ) imbalance are studied, and bit-error-rates (BER) are measured and compared with their theoretical counterparts. All obtained results confirm that the proposed interferometric receiver provides good communication performances.

In this paper, the design methodology of a microstrip angular displacement sensor based on an impedance transformer with a quasi-Chebyshev frequency response is proposed. This sensor with impedance transforming function can realize the angular displacement detection by bandwidth sensing, and matching sensing simultaneously. The insertion loss in stopband achieves 24.9 dB to 32.6 dB with an average bandwidth selectivity of 2.25 MHz/degree of the sensor centered at 2.4 GHz with two poles of 1.71 GHz and 2.81 GHz. Meanwhile, the average matching level of return loss for displacement sensitivity are 0.18 dB/degree and 0.15 dB/degree, respectively. It is the first time to apply an impedance transformer into the angular displacement sensor design for both bandwidth and matching level sensing among reviewed literatures. In this design, the load-to-source impedance transformation is designed for 250-to- $50~\Omega $ , and by adding a rotated stub on the proposed microstrip transformer, the sensing function is developed with angular displacement.

In this paper, a wideband bandpass filter (BPF) with simultaneous bandwidth and notch tuning is proposed, by using a dual cross-shaped resonator (DCSR) with parallel-coupled three-line (PCTL) feeding. It is found that three intrinsic transmission zeros can be generated by the proposed DCSR, while two of the zeros are used for the implementation of passband edge zeros and the other one is for a notch. Three varactors are used to implement the bandwidth and notch tuning independently. These innovative integrated functions of both tunable bandwidth and notch in a single architecture are proposed for the first time. On the other hand, the PCTL can provide sufficiently strong coupling in the desired passband. The proposed BPF can achieve the bandwidth tuning with a fixed notch inside/outside the passband, and the bandwidth can also be kept unchanged when tuning a notch within the passband. The prototyped BPF centered at 6 GHz reports that the absolute bandwidth (ABW) can be varied from 2.5 to 5.8 GHz, while the fractional bandwidth (FBW) is tuned from 41.7% to 96.7% together with notch frequency tuning of 5.0 to 8.2 GHz. The experimental measurements are in good agreement with the theoretical analysis.

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.

In this study, a series of wideband bandpass filters (BPFs) with reconfigurable bandwidth and two fixed notch bands are presented. The fundamental topology is based on a new terminated cross-shaped resonator (TCSR), which has three poles and four zeros. With the assistance of two symmetrical parallel coupled-lines, another four poles and two zeros are introduced. As such, a notched-band bandpass filter with multiple transmission poles and zeros are achieved. To realise the reconfigurable bandwidth, four PIN diodes are used. By controlling the status (switching on/off) of these PIN diodes, three reconfigurable-bandwidth states can be implemented while the notch bands and centre frequency are maintained unaltered. Meanwhile, it is also found that the lower bandwidth edge of the proposed filter can be independently reconfigurable by inserting a capacitor into the lower stub of the novel TCSR, while the notch bands are kept unchanged. For validation, three prototypes are designed, fabricated, and measured. The measured results agree well with theoretical analysis and therefore verify the simple designing approach of reconfigurable BPFs.

Based on a novel microstrip terminated cross-shaped resonator (TCSR), the dual-band bandpass filters (DB-BPFs) with fixed and reconfigurable bandwidths are proposed in this brief. In addition to the basic TCSR’s three poles and four zeros, the extra four poles and three zeros can be introduced with the help of a pair of symmetrical parallel-coupled lines and open-ended stubs. Therefore, a planar DB-BPF with multiple transmission poles and zeros can be realized. To achieve the reconfigurable bandwidths, a capacitor is inserted into the basic TCSR’s lower stub. It is found that the lower bandedge of the first passband can be tuned while the other three bandedges are kept unchanged. Two prototypes, including fixed-bandwidth filter (Filter I) with 3-dB fractional bandwidths (FBWs) of 20.8% and 17.3%, and reconfigurable-bandwidth filter (Filter II) with 3-dB FBW variation from 22.5% to 34.7% for the first passband and 19.8% for the second passband, are designed, fabricated, and experimentally characterized. The experimental characterizations of these two filters verify the proposed design.

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.

In this paper, a class of reconfigurable wideband bandpass filters based on dual cross-shaped resonator (DCSR) is studied. The proposed DCSR consists of shunt opened stubs loaded at the end of their parental shunt stub. This configuration can effectively produce additional poles and zeros to the wideband bandpass filter, and therefore providing an overall good in-band response with simultaneous shape cut-off. By introducing some tunable devices (i.e. pin diodes, varactors), the bandwidth of proposed filter can be easily adjusted to accommodate specific applications. In addition, a controllable notch is generated in the passband to reduce the strong interfering signal happened in wideband operation. A DCSR bandpass filter operating at 6 GHz is designed, fabricated and measured. The fractional bandwidth (FBW) centers around 102.2% with ±19% tuning range. Meanwhile, the notch can lie between 3.0 GHz to 7.9 GHz.

This paper addresses a new Frequency Modulated Continuous Wave (FMCW) Doppler radar contactless sensor system for slow moving target detection. The system employs monostatic radar with single-antenna, twice down-conversion and DFT algorithm, which is operating on 5.8-GHz with 10 MHz bandwidth to improve the detection accuracy. The sinusoidal-moving reflector can measure the velocity of 0.057 m/s for evaluating the short range moving target. According to the result analysis, the frequency shift is influenced by Doppler Effect and beat frequency, which are 2 Hz and 10.4 Hz, respectively.

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.

In this letter, a simple and compact Yagi–Uda antenna with good antenna gains is proposed for multiband radar applications. The prototype operates in three different frequency bands, namely 1.9, 2.5, and 3.5 GHz. The drivers are designed on the basis of classical dipole configuration with embedded L-shaped slotlines. On the other hand, directors and reflector are deployed to achieve good directivity over frequency bands of interest. From measurements, the prototype demonstrates high performance of the designed multiband Yagi–Uda antenna and also shows a good agreement between measurements and simulations. Measured operating frequencies are 1.89, 2.54, and 3.51 GHz, respectively, and the realized antenna gains are 6.29, 4.63, and 6.77 dBi, correspondingly. Measured front-to-back ratios are better than 10.8 dB, hence making the design suitable for radar applications.

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.

In this letter, a novel miniaturized integrated filter-antenna (IFA) module with dual-band filtering response is proposed. By controlling the open stub of the bandpass filter (BPF) over the antenna slot, its intrinsic band-gap characteristic helps suppressing the high-order spurious. A prototype IFA is designed and experimentally characterized. The dual-band BPF of the proposed IFA is arranged in an arc structure and is operated at 870 MHz and 2.42 GHz with fractional bandwidth 10.3% and 3.9%, respectively, leading to 62.3% size reduction compared to the conventional structure. The impedance bandwidth of the slot antenna is 3.9% with center frequency of 4.06 GHz. The antenna slot provides a good suppression of the spurious passband at 3.57 GHz around 17.3 dB.

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.

A novel miniaturized parallel coupled-line bandpass filter with suppression of second and third harmonic frequencies is demonstrated in this paper. This new filter is based on the capacitive termination on the conventional parallel coupled line to achieve size minimization, while the spurious responses are eliminated by the over-coupling approach. These features offer the classical parallel coupled-line bandpass filter simultaneous compactness and wide stopband performance. The simulations and measurements of a 900-MHz prototype bandpass filter are presented. The measured results agree well with the simulation. Compared with the conventional parallel coupled-line bandpass filter, the measured second and third spurious responses are suppressed to -64 and -55 dB, respectively. In addition, the circuitry size of the prototype filter can be reduced up to 25%.

A microstrip balun-bandpass filter (BPF) using capacitively loaded square-loop dual-mode resonator is proposed; it realizes not only simultaneous size reduction and spurious response suppression in filtering but also overall good differential performance of the balun. The phase and amplitude imbalance improvements due to the loaded resonator are also studied and verified by a prototype balun-BPF operated at 2.55 GHz with 3.5% fractional bandwidth. The experimental results reveal that size reduction of 47% and spurious suppressions of 30 dB beyond 1.5 f0 are achieved as compared to that of the conventional structure. The loading effect of the prototype balun-BPF reports 180.8° and 0.97 dB as phase and amplitude imbalances at the operating frequency respectively.

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, an integrated power divider/ bandpass filter component is proposed for simultaneous size reduction and harmonic suppression. A stepped impedance interdigital coupling element is used to replace the conventional quarter wavelength impedance transforming section of the Wilkinson power divider, yielding not only selective bandpass response but also good power splitting performance. From the experimental results, the insertion loss of a 2.4 GHz prototype is kept as low as 3.3 dB in the passband, and the isolation is 20.6 dB. The first spurious passband is recorded at 3.4f0. These indexes show the significance of the proposed integrated component.

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.

A novel parallel coupled-line bandpass filter with suppression at the 2/sup nd/ harmonic frequency is presented in this paper. This structure offers a simple design methodology and corresponding implementation. An example of a 900 MHz prototype bandpass filter is used to demonstrate the performance of the new structure. The measured results agree well with the simulation, where, up to 40 dB suppression is recorded at the 2/sup nd/ spurious response, whilst the matching achieves an interesting level close to 29 dB.

In this paper, a novel dual-mode bandpass filter using square-loop resonator is proposed. The capacitive stepped impedance inner arm is studied so as to achieve simultaneous size reduction and spurious response suppression for the dual-mode bandpass filter. By introducing this new inner arm at the four inner corners along the square-loop resonator, it is found that an effective spurious response suppression measure at 2nd harmonic and 3rd harmonic can be taken. In order to demonstrate the performance of the proposed filter structure, a prototype filter is designed @ 900 MHz with 1% fractional bandwidth. Significant suppressions up to 37 dB and 31 dB are measured @ 1.8 GHz and @ 2.7 GHz respectively. Moreover, a circuitry size reduction of 40% is achieved when compared with that of the conventional structure.

In this paper, a novel linear predictive method (SELP) for speech spectra modelling is proposed. This method allows one to develop an all-pole filter which combines p+1 consecutive even preceding samples of the speech signal x(n) into p pairs for linear extrapolation. In addition, a weighting selective scheme is employed to obtain high signal-to-error ratio (SER). Comparing to the traditional LPC modelling, the proposed filter's order is then raised to 2p+2 when both filters are with p-normal equations. In order to demonstrate the proposed method usefulness, this new model is simulated at 22.05 kHz speech spectra. Experimental results show that at least 10 dB SER improvement is obtained with p=5 when compared with that of LPC modelling.