High-gain Millimeter-wave Planar Array Antennas with Traveling-wave Excitation

High-gain and large-aperture antennas with fixed beams are required to achieve high S/N ratio for point-to-point high-speed data-communication systems in the millimeter-wave band. Furthermore, beam-scanning antennas are attractive to cover wide angle with high gain for applications of high-speed data-communication systems and high-resolution sensing systems. High-gain pencil-beam antennas are used for mechanical beam-scanning antennas. Although high antenna efficiency can be obtained by using dielectric lens antennas or reflector antennas (Kitamori et al., 2000, Menzel et al., 2002), it is difficult to realize very thin planar structure because they essentially need focal spatial length. By using printed antennas such as microstrip antennas, the RF module with integrated antennas can be quite low profile and low cost. Array antennas possess a high design flexibility of radiation pattern. However, microstrip array antennas are not suitable for high-gain applications because large feeding-loss of microstrip line is a significant problem when the size of the antenna aperture is large. They are applied to digital beam forming (DBF) systems since they consist of several sub-arrays, each of which has small aperture and requires relatively lower gain (Tokoro, 1996, Asano, 2000, Iizuka et al., 2003). Slotted waveguide planar array antennas are free from feeding loss and can be applied to both high-gain antennas and relatively lower-gain antennas for sub-arrays in beam-scanning antennas. Waveguide antennas are more effective especially in high-gain applications than low-gain since a waveguide has the advantage of both low feeding loss and compact size in the millimeter-wave band even though the size of the aperture is large (Sakakibara et al., 1996). However, the production cost of waveguide antennas is generally very high because they usually consist of metal block with complicated three-dimensional structures. In order to reduce the production cost without losing a high efficiency capability, we propose a novel simple structure for slotted waveguide planar antennas, which is suitable to be manufactured by metal injection molding (Sakakibara et al., 2001). We have developed two types of planar antenna; microstrip antenna and waveguide antenna. It is difficult to apply either of them to all the millimeter-wave applications with different specifications since advantages of the antennas are completely different. However, most applications can be covered by both microstrip antennas and waveguide antennas. Microstrip antennas are widely used for relatively lower-gain applications of short-range wireless-systems and sub-arrays in DBF systems, not for high-gain applications. Waveguide antennas are suitable for high-gain applications over 30 dBi.