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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 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.

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 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 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.

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.