Discrete multiloop, modified multiloop, and plate-loop antennas-multifrequency and wideband VSWR characteristics

Three types of loop antennas are presented: discrete multiloop (ML), modified ML and plate-loop (PL) antennas. The discrete ML and modified ML antennas are composed of N square loops. The N square loops of the modified ML antenna are connected by wires at the loop corners. The PL antenna is regarded as a modified ML antenna with infinite loops (N=∞). The analysis of the discrete ML antenna shows that one of the N loops resonates when its circumference is approximately one wavelength. It follows that the discrete ML antenna has N minima in the frequency response curve of the VSWR. In contrast to the discrete ML antenna, the modified ML has a VSWR with a wide-band frequency response: approximately 16% with N=7, which is more than 2.5 times as wide as that for a single-loop antenna (N=1). Further analysis reveals that the PL antenna has a VSWR bandwidth similar to that of the modified ML antenna. The maximum gain of the PL antenna is approximately 9 dB, which is very close to those of the discrete and modified ML antennas