Ultra‐wideband loop antenna coupled‐FED by a monopole feed for penta‐band folder‐type mobile phone

An ultra‐wideband coupled‐fed loop antenna for penta‐band operation in the folder‐type mobile phone is presented. The antenna comprises a loop strip and a monopole feed; the latter not only serves as a coupling feed for the loop strip to generate a 0.5‐wavelength loop resonant mode, but also provides a 0.25‐wavelength monopole resonant mode for enhancing the operating bandwidth of the antenna. Hence, with an occupied volume of 2.6 cm 3 only, the antenna can provide a very wide operating band of larger than 100% or about 1.7 GHz (from 790 to 2480 MHz), allowing the antenna to cover GSM850/900/DCS/PCS/UMTS penta‐band operation with radiation efficiencies larger than 70% for the folder‐type mobile phone in the open state (talk condition). For the antenna in the close state (idle condition), it can still provide a very wide operating band just by including a matching circuit of a series chip capacitor at the antenna's feeding point, and the radiation efficiencies over the five operating bands are still better than 53%. Details of the proposed antenna are studied. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2706–2712, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23753