Compact Microstrip-Fed Square Loop Antenna for DTV Applications

A design method for a compact square loop antenna fed by a microstrip (MS) line for indoor digital television (DTV) applications is proposed. The proposed antenna consists of a square loop, circular sectors, and an MS line. The square loop combined with circular sectors is printed on one side of a substrate, and a 75 ohm MS line is printed on the other side. The circular sectors are used as a wideband balun or transition to connect the MS line and the square loop. The square loop is used instead of a circular loop in order to reduce the antenna size, and four edge slits are introduced at the corners where the square loop and the circular sectors contact each other to further reduce the antenna size. Performance of a circular loop antenna with circular sectors and performance of the proposed square loop antenna without the edge slits are compared with that of the proposed square loop antenna. A prototype of the proposed square loop antenna operating in the DTV band (470–806 MHz) is designed and fabricated on an FR4 substrate. Experiment results show that the proposed antenna has the desired impedance characteristics in a frequency band of 464–1,220 MHz (89.8%) for a voltage standing wave ratio (VSWR) < 2 covering the DTV band, and a broadside gain of 0.8–3.3 dBi in the DTV band. Keywords—compact, square loop, microstrip-fed, circular sectors, indoor DTV