Comb Beam Transmission by Phased-Array Antenna for Troposphere-Adaptive Observation

Angular imaging technique is useful for realizing a fast scanning weather radar. It was originally proposed in [1] for researching spatiotemporally complicated structures of tornadoes. Recently, a phased array weather radar (PAWR) using the angular imaging technique has been developed in Japan firstly for practical uses, and it is expected to reduce social damages caused by severe weather phenomena or to support weather safeties on airport operations by its fast scanning capability of 10—30 sec refresh rate [2].

Angular imaging technique normally forms a (elevationally) broad transmission beam and forms multiple narrow reception beams. Because the multiple narrow reception beams can be “simultaneously” formed, azimuthal scan speed can be increased. This technique is called digital beam forming technique (DBF), and the DBF of the PAWR is detailed in [3]. However, since transmitting electric power density in a unit solid angle is reduced by broadening transmitting beam, an elevational range which is simultaneously observed is limited. For example, the PAWR observes simultaneously for a range of roughly 10 deg in elevation. That is, in order to observe an elevational range of 30 deg as current weather radars, the normal broad beam needs to be transmitted three times to cover.

This work proposes comb transmission beam that is multiple sharp transmission beam sparsely covering a wide range of elevation. An example of broad and comb beam transmissions is shown in Figure 1. The broad transmission beam covers an elevational range of 0—10 deg. It needs to be re-transmitted by changing its center angle to observe at elevation angles more than 10 deg. On the other hand, the comb beam transmission, which is realized by designating phase shifts on transmitting elements of an array antenna, observes at elevations at 0—30 deg. Although the elevational range is covered sparsely, it has already very well demonstrated by current weather radar that the sparse covering efficiently observes weather phenomena. Moreover, as shown in Figure 1, gains of upper combs can be adaptively reduced. Typical weather radars do not need a power at higher elevation because of altitudes of troposphere (10—15 km). Thus, the comb beam transmission is efficient also on power consumption.

In the presentation, principles and simulations of the comb beam transmission will be discussed.

Fig. 1 Example of normal broad beam and proposed comb beam.
Comb beam transmission sparsely covers a wide range of angles, and designate gains of comb’s teeth adaptively for troposphere (reduces gains at upper elevations).

[1] Wurman, J., and M. Randall, 2001: An inexpensive, mobile, rapidscan radar. Preprints, 30th Int. Conf. on Radar Meteorology, Munich, Germany, Amer. Meteor. Soc., P3.4.

[2] F. Mizutani, T. Ushio, E. Yoshikawa, S. Shimamura, H Kikuchi, M. Wada, S. Satoh, and T. Iguchi, 2018: Fast-Scanning Phased-Array Weather Radar with Angular Imaging Technique, IEEE Trans. Geosci. Remote Sens., vol. 56(5), pp. 2664—2673.

[3] E. Yoshikawa, T. Ushio, Z. Kawasaki, S. Yoshida, T. Morimoto, F. Mizutani, and M. Wada, 2013: MMSE Beam Forming on Fast-Scanning Phased Array Weather Radar, IEEE Trans. Geosci. Remote Sens., vol. 51(5), pp. 3077—3088.