A CPW‐fed hexagonal‐shape monopole‐like UWB antenna

Abstract

It is worth to note that a maximum possible number of strain sensors depend on a dynamic measurement range of the OTDR and a discrimination range of the strain sensor. If it is assumed that the commercial OTDR has the dynamic measurement range of 30 dB and while each of sensors based on SMS fiber structure has the discrimination range of 0.5 dB, therefore the maximum number of sensor can be used in this system is about 60 sensors. This feature is useful for quasi-distributed strain measurement in many applications such as to monitor strain in the bridges, buildings or others civil structures.Further investigation on a temperature-dependence on the optical fiber strain sensor needs to be carried out. It is well known that the temperature variations can induce strain measurement errors. According to the references, an accurate strain measurement in the SMS fiber structure sensor can be carried out when the ambient temperature is known using either an external temperature sensor or a self-temperature sensor as reported in Ref. 4, or other technique can be used by choosing core and cladding material with opposite thermo-optic coefficients [8].The proposed strain measurement system offers low cost and simple fabrication process of the sensor based on SMS fiber structure. The interrogator of OTDR is widely used to inspect the optical fiber network in the field makes the proposed strain measurement system is suitable to be developed. Moreover, the quasidistributed strain measurement can also be easily implemented. CONCLUSIONThe SMS fiber structure sensor and the OTDR interrogator for the strain measurement was investigated and proposed. Depending on the MMF length of the SMS fiber structure, the strain sensor characteristic can be varied. It is found that the strain measurement with a range of 0-1000 le with a resolution less than 10 le can be achieved. It is demonstrated as a proof of principle, the quasi-distributed strain measurement using the proposed method. Depending on the dynamic measurement range of the OTDR, tens of sensors can be used simultaneously to perform the quasi-distributed strain measurement for applications such as a structural health monitoring system. ABSTRACT: The analysis of TEM three-section symmetrical directional couplers with tightly coupled section realized as a tandem connection of two coupled-line sections has been shown. The design equations allowing for calculating the required even-mode characteristic Key words: broadband coupled-line couplers; tandem connection of coupled-line couplers; symmetrical couplers ACKNOWLEDGMENT INTRODUCTIONMultisection coupled-line directional couplers are commonly used in modern microwave electronics because they offer very wide bandwidth and relatively small size. They can be realized in either asymmetric or symmetrical structures [1,2]. The major advantage of symmetrical multisection couplers over asymmetric ones is that they provide constant 90 differential phase over entire frequency range. However, it is known that they require much stronger coupling...

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