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The occurrence of passive intermodulation (PIM) is inevitable in high-power microwave devices. It interferes with wireless communication and radar systems, resulting in severe deterioration of receiving performance. So far, narrowband PIM analyzers have been realized for different business bands. However, they are incapable of testing wideband systems. To solve this problem, rack-mounted analyzers piled with multiple narrowband analyzers were implemented. While such solutions significantly increase the volume, cost, and power consumption, they cannot provide a wide, continuous bandwidth for PIM localizations. Aiming to solve this problem, we propose a novel solution for realizing ultrawideband PIM analyzers. Based on the principle of cooperative radio frequency and baseband (RF-BB) nulling, we demonstrate an experimental prototype working within a continuous frequency band covering three octaves, exhibiting promising potential in PIM testing applications. [ABSTRACT FROM AUTHOR]

Personal devices such as smartphones and tablets are rapidly becoming personal communication, information, and control centers. Apart from multitouch screens, human gestures are considered as a new interactive human–smart device interface. In this work, we propose a noncontact solution to implement hand gesture recognitions for smart devices. It is based on a continuous wave, time-division-multiplexing (TDM), single-input multiple-output (SIMO) Doppler radar sensor that can be realized by slightly modifying existing RF front ends of smart devices, and a machine-learning algorithm to recognize predefined gestures by classifying deterministic Doppler signals. An experimental setup emulating a smartphone-based radar sensor was implemented, and the experimental results verified the robustness and the accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

To date, 3-D radar imaging of moving objects in a multipath coordinate space close to antennas remains a technical challenge. In this work, we demonstrate the implementation of such 3-D motion imaging based on a continuous-wave, multiple-input multiple-output (MIMO) Doppler radar sensor (DRS). Working with a time-division-multiplex (TDM) scheme, this portable, cost-effective DRS is a bistatic system with one transmitting and one receiving channels, and a radio frequency (RF) switch in each channel toggling between two antennas. Assisted by algorithms specifically derived for the TDM-MIMO architecture, highly sensitive 3-D imaging performed in a multipath indoor environment was experimentally implemented. Numerical simulations and experimental demonstrations verified the effectiveness and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

We investigate a non-Foster element implemented with a radio-frequency operational amplifier theoretically and experimentally, showing that its full-range frequency response exhibits an inverted Lorentzian resonance, and thus a high-frequency non-Foster response can be observed on the right side of the resonance region. This can be used to overcome the technical difficulty in achieving high-frequency non-Foster elements. [ABSTRACT FROM AUTHOR]

Short-range continuous-wave Doppler radar sensors have been mainly used for noncontact detection of various motions. In this paper, we investigate the feasibility to implement the function of a remote mouse, an input device of a computer, by recognizing human gestures based on a dual-channel Doppler radar sensor. Direct conversion architecture, symmetric subcarrier modulation, and bandpass sampling techniques are used to obtain a cost-effective solution. An arcsine algorithm and a motion imaging algorithm are proposed to linearly reconstruct the hand and finger motions in a 2-D plane from the demodulated Doppler phase shifts. Experimental results verified the effectiveness of the proposed architecture and algorithms. Different from the frequency-domain “micro-Doppler” approach, the proposed remote gesture recognition based on linear motion reconstruction is able to recognize definitive signatures for the corresponding motions, exhibiting promising potential in practical applications of human–computer interaction. [ABSTRACT FROM PUBLISHER]

The state-of-the-art phased array-based digital beamforming systems suffer from disadvantages of high power consumption, high cost, and system complexity due to the massive use of transmitter/receiver (T/R) modules and high-speed digital and digital–analog mixed devices. In this paper, we point out that by proposing a new concept “complex domain” radio frequency (RF) frontend, the relatively slowly changed waveform delay information required to accomplish adaptive beamforming can be separated from wideband RF signals, based on which a self-contained beamforming system can be implemented with a low-speed baseband. By introducing vector RF multipliers in the proposed frontend, the amplitude and phase of RF signals can be simultaneously controlled by the real and imaginary parts of complex numbers, such that beamforming algorithms derived in complex domain can be directly applied without any form of transformation. By doing so, the massive use of conventional T/R modules and high-speed baseband devices can be avoided. Theoretical analysis and experimental demonstration based on commercial components have validated the proposed approach. Our method is able to significantly simplify the realization and decrease the cost of wideband digital beamforming systems, and can be widely used in low cost, power efficient beamforming applications. [ABSTRACT FROM AUTHOR]

Terahertz technology is one of the research fronts in the microwave society. Among many technical challenges, achieving high-power terahertz radiation has been attracting many efforts. In this paper, we investigate the possibility of power synthesis at low-end frequencies of the terahertz gap based on discrete sources. We show that by applying precision digital phase control, such a power synthesis can be achieved, overcoming the difficulty of phase alignment at these frequencies. For demonstration, we implement a 110-GHz prototype system employing solid-state impact avalanche and transit time diodes. Using a simulation- and measurement-based design methodology, the impedance matching of the designed cavity is able to be simultaneously obtained at both the RF bias and the 110-GHz frequency without using any absorbing material. Detailed design, simulation, and measurement of the prototype are introduced and the experimental results comply well with analytical expectations. Analysis shows that with increased wide digital bit width, the proposed approach is able to provide sufficient phase control precision, making it possible to be used in the power synthesis applications at low terahertz frequencies. [ABSTRACT FROM AUTHOR]

In this article, we propose a design and on-board measuring approach for the realization of micro-sized differential antennas for the 2.4-GHz mobile payment (MP) applications. Exampled by a complete realization of a 3 × 11 mm-sized differential antenna driven by a commercial 2.4-GHz transceiver integrated inside a 15 × 11 mm-sized micro-SD card, such design and testing approach is described in detail. The experimental measurements of the micro-sized antenna show that the impedance of the designed micro-sized differential antenna well matches the complex impedance of the transceiver, and, therefore, ensure the stability of the radio frequency performance required by the MP applications. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1419-1422, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25957 [ABSTRACT FROM AUTHOR]