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Two printed ultra‐wideband (UWB) elliptical antennas are proposed. The first antenna is a printed elliptical antenna with notch cut fed by a microstrip line. It is designed and fabricated for UWB applications under the band (3.1–10.6 GHz). To obtain sufficient matching bandwidth, a partial ground plane, feed gap, and notch cut are used. The antenna is then modified to obtain frequency band notch function of 5.2/5.8 GHz by inserting a U‐shaped slot beneath the notch cut in the elliptical patch. A parametric study is carried out to optimize the proposed structures. The measured bandwidth for the designed antenna without U‐shaped slot is 8.35 GHz. For the antenna with U‐shaped slot, the measured bandwidth is from 3.08 to 11.00 GHz with band rejection from 4.70 to 5.84 GHz. Good radiation patterns and antenna gains, except in the notched frequency band, have also been obtained. Details of the proposed antenna designs and the measured results are presented and discussed. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 860–864, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24183

Summary Miniaturized transponder systems are under development for monitoring unconventional reservoirs, mapping hydraulic fractures, and determining other wellbore parameters. These gadgets are an extension of radio-frequency identification (RFID) and are known as fracture robot (FracBot) nodes to recognize wireless underground sensor networks (WUSNs) for characterization and mapping of hydraulic breakages in unconventional reservoirs. 3D constellation maps of proppant-bed placement are generated by autonomous localization algorithms as FracBots are injected during hydraulic-fracturing operations. To investigate this model, a FracBot platform was established to explore this concept, and three basic functions have been explained. First, we have developed an innovative cross-layer communication model for magnetic-induction (MI) networks in altering underground environments, coupled with selections of coding, modulation, and power control and a geographic forwarding structure. Second, we have developed an innovative MI-based localization framework to capture the locations of the randomly deployed FracBot nodes by exploiting the exceptional properties of the MI field. Third, we have proposed an energy model for a linear FracBot network scheme that provides reasonable data rates while preserving collected energy limitations. Finally, to examine the functionalities of FracBot nodes in air, sand, and stone media, a physical MI-based WUSN test bed was implemented. Experiments indicated that the constructed FracBots can form a communication link and transfer data over amplitude-shift keying (ASK) modulation with 1.6 kbit/sec as a data rate and a minimum receiver sensitivity of −70 dBm. The performance of near-field-communication (NFC) antennas was affected by sand and stone media, which ultimately affect MI signal propagation and decrease the energy transfer. In sand or stone media, augmented mismatch between transmitter and receiver antennas was detected, leading to the decision that an advanced matching circuit design or an adaptive-frequency feature should be integrated into the FracBot design. This permits an optimal energy transmission and consistent communication link through sand and stone media.