The series-fed subarray still plays a critical role in a partially-corporate-fed array, which has advantages over the corporate feed one in terms of both beam steerability and freedom in array sizes. In this paper, two techniques are presented for the wideband design of series-fed waveguide slot arrays. Firstly, the overload technique is adopted to design standing-wave fed 1 × 4-element arrays of both coupling slots and radiating slots. The simulated bandwidths for |S 11 | < -15 dB are enhanced to 8.1% and 12.2%, respectively.Secondly, the open-cavities, namely decoupling structures above radiating slots, are introduced to suppress the mutual couplings among a 4 × 4-element array. Its bandwidth for |S 11 | < -15 dB is significantly improved from 5.1% to 11.3%. For demonstration, a 4 × 4-element array is designed in the X-band, and is fabricated by Direct Metal Laser Sintering technique. The measured bandwidths for |S 11 | < -12.5 dB and the antenna efficiency higher than 70% are as wide as 12.4% and 9.5%, respectively. The validity of those wideband design techniques is verified.
Abstract:Because the traditional transmission line method treats electromagnetic waves as excitation sources and the cavity as a rectangular waveguide whose terminal is shorted, the transmission line method can only calculate shielding effectiveness in the center line of the cavity with apertures on one side. In this paper, the aperture coupling effect of different sides was analyzed based on vector analysis. According to the field intensity distribution of different transport modes in the rectangular waveguide, the calculation model of cavity shielding effectiveness in any position is proposed, which can solve the question of the calculation model of shielding effectiveness in any position in the traditional method of equivalent transmission methods. Further expansion of the equivalent transmission lines model is adopted to study the shielding effectiveness of different aperture cavities, and the coupling effect rule of the incident angle, the number of apertures, and the size of the cavity is obtained, which can provide the technical support for the design of electromagnetic shielding cavities for electronic equipment.
We propose an instantaneous frequency measurement (IFM) scheme featured with unambiguous measurement utilizing a Sagnac loop with an embedded bi-directional phase modulator and an optical filter with a linear frequency response. The frequency of the microwave signal to be measured is instantaneously estimated by calculating an amplitude comparison function (ACF) of photocurrents from the upper and lower branches of the proposed structure. Compared to previous IFM schemes, the ACF in the proposed scheme is monotonic, by which the frequency of the unknown microwave signal can be uniquely confirmed without ambiguity. Only one laser source and a phase modulator are needed, which simplifies the measurement system. In addition, the monotonous ACF can guarantee measurement accuracy in a wide range, from low frequency to high frequency. The IFM system has robustness in optical and RF power shifts. Simulation results show that frequency measurement over the range of 30 GHz with a measurement error of 0.4 GHz is achieved.
In the present contribution, we investigated possible reaction mechanisms for the direct conversion of methane into methanol and acetic acid over a mononuclear rhodium species anchored on a zeolite support (Rh-ZSM-5) by density functional theory (DFT) calculations. To elucidate the role of CO, we systematically compared the reaction mechanisms in the absence/presence of CO. The most favored mechanism is shown to be via a CO-assisted oxygen activation, and the formation of the CO–O bond is found to be the rate-determining step. It is clearly shown from our calculations that the presence of CO will promote the formation of a more active Rh-oxo species, which can easily catalyze the conversion of methane so that the direct transformation of methane can be achieved under mild conditions. Apart from forming a stable catalytic precursor and promoting the formation of the active Rh-oxo species, CO can also be directly involved in the reaction, resulting in the formation of acetic acid.
This paper develops a circuit theory on bandpass negative group delay (NGD) topology. The NGD active lumped circuit uses a low noise amplifier (LNA). An S-parameter model is formulated. Unfamiliar, NGD function analysis is introduced by analytically defining the NGD value, bandwidth, and central frequency as a function of the topology parameters. The synthesis formulas enabling the calculation of cell parameters as a function of the targeted bandpass function specifications. To validate the circuit theory, an NGD proof of concept (PoC) is designed, simulated, and tested. As expected, simulations and measurements are in good agreement. Calculated model, simulated and measured results showing NGD level of about −10 ns around the centre frequency 0.5 GHz over the bandwidth 50 MHz validate are obtained.
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