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In the Second World War, the German Army used small-loop antennas for battlefield communication equipment. Because the radiation field associated with an antenna is a space integral of antenna current over distance, small antennas with large currents are capable of producing the same field intensity as large antennas with relatively small currents. A small circumference for the small-wire loop antenna will result in a small radiation resistance which is purely inductive. A series-resonant circuit may be constructed by adding a capacitive element to the small-loop antenna. Because such an addition will nullify the effects of the reactance, leaving only a small resistance to oppose the flow of currents in the small-loop antenna, therefore, large currents can be made to flow in the antenna which can result in relatively large fields from small structures. In small-loop antennas, the currents around the loop are nearly in phase and the loop antenna can be treated as a magnetic dipole. This places a limit on the antenna circumference to about one quarter of the wavelength at the highest frequency of operation. As the frequency of operation increases, it becomes harder to match the radio equipment to the antenna because the impedance at the feed-point becomes extremely reactive and rather large. Hence, matching the small-loop antenna to the radio equipment becomes a challenge. However, at the higher frequencies, the small-wire loop provides gain and radiation patterns that are very similar to a half-wavelength dipole which is much bigger and more difficult to construct as well as requiring far greater effort to maintain. At lower frequencies, the efficiency of the small-wire loops deteriorates substantially and there is a requirement for constantly tuning the antenna. Hence, apart from mobile civilian radio equipment, small wire loops are used extensively for high frequency military communications over a theatre. The armies of Norway, China and Russia use small-wire loops extensively.
Small-loops are, therefore, important when it comes to antenna design for rugged and highly mobile radio equipment. These antennas are relatively insensitive to near field electric sources such as sparks which may have been created by electrical machinery and hence they are attractive for reception in noisy environments for reception from distant sources. Small loop antennas respond far better to the H-fields as compared to the E-fields and because the emission from close interference sources is mostly of the E-field type, therefore the small-loop antenna remains relatively insensitive to these interferences. In this dissertation, an attempt has been made to analyse the small-wire loop and investigate the matching networks that are required for such antennas.