Development of Solid-State Weather Radar

<>‚P Introduction

Recently, mobile phone is used as personal digital assistance, and the capacity of wireless LAN becomes much larger than before. As a result, demand of frequency resources is growing year after year.  There is not enough allocation of new frequency for a part of frequency band, and weather radar is required to reduce band width of radio wave. Also, it is general for weather radar to operate as radar network, and the running cost of weather radars needed to be inexpensive. 

For resolving these problems, Toshiba develops 5GHz and 9GHz bands solid-state weather radars by globally advanced technology of semi-conductor and sophisticated signal processing technology.  Both radars have high-end function and quality as multi parameter radar, and it is possible to narrow the interval of frequency assignment by one quarter.  Solid-state weather radar reduces running cost because expensive consumables that are magnetron and klystron are not used.  Moreover, it makes to reduce system stop time by the redundancy of transmitting device.  This paper shows about solid-state weather radar developed by Toshiba. <>2Specification of Solid State Weather Rader

5GHz and 9GHz bands solid-state weather radars are developed for decrease of running cost and effective use of frequency resources. Figure 1. and Figure 2.  show appearances of 5GHz and 9GHz bands solid-state weather radars. 5GHz bands solid-state weather radar is stationary type. The radar has an observation performance same as klystron radar of peek power 250kw, and the size became less than one half. The transmitter works as not only horizontal polarization radar, but also dual polarization radar including vertical polarization capability. Returned signals from hydrometeors with dual polarization wave are used by identifying hydrometeors such as rain, snow, and hails and improving precipitation observation accuracy.[1]

Figure 1.    Solid-state weather radar 5GHz band type

Figure 2.     Solid-state weather radar 9GHz band type

9GHz bands solid-state weather radar is a mobile type, and the radar has an observation quality same as magnetron radar of max. power 40kw.  Instillation space is 2m square, and the weight is less than 2t.  Transmitter and receiver are installed near by antenna, and make it reduce loss due to wave-guide.  As a result, power consumption is less than 3kVA.  Both radars can be LAN access to external device.  They can be remotely controlled and transfer observed data by distance.  TABLE I. shows typical specification of solid-state weather radars.
TABLE I.     Typical specification of solid-state weather radar

Transmitting power	More than 3.5kW (5GHz),                  200W  (9GHz) (horizontal and vertical each)
Duty Ratio	Less than 20% (5GHz)                  10% (9GHz)
Minimum receiving power	Less than  -110dBm
Antenna gain	More than 42dBi
Beam width	Less than 1.2deg
Pulse width	1 to 350µsec (variable) (5GHz) 1µsec and 32µsec   (9GHz)
Output Data	Reflectivity factor  Z(dBz) Doppler velocity  V(m/s) Spectrum width  W(m/s) Differential reflectivity  ZDR(dB) Linear depolarization Ration  LDR(dB) Differential phase  ƒ"DP (deg) Specific differential phase  KDP(deg/km) Correlation coefficient  ƒÏHV Rainfall rate  R(mm/h)

<>3 Frequency characteristic of transmitting wave

Solid-state weather radar has precise wave form control possible due to high linearity input-output characteristic. In general, frequency band increases in width as pulse width gets short. Figure 3. shows a worst case, theoretical transmitting wave form in simulation at 1µsec pulse width and Figure 4. the real transmitting wave outputted from transmitter. 

We can determine that transmitting wave form is close to theoretical concept by control it carefully though distortion compared with theoretical transmitting wave form. 

Figure 5. shows transmitting spectrum mixed one to a fewµsec pulse width. As previously mentioned,actually one to a fewµsec short pulse width and from dozens of to a hundredµsec long pulse width transmit alternately in operation. The spurious level 2.5MHz away from center frequency is 62.17dB lower than center frequency That is to say, it can work out at 2.5MHz away frequency and this is impossible over 10MHz away in the past.

Though the transmitting by only short pulse has its characteristic degrade, we have confirmed that the filter for transmitting has suppress over 60dB.

Figure 3.    Theoretical transmitting wave form

Figure 4.    Real transmitter output

Figure 5.    Spectrum of transmission wave (mixture of short pulse and long pulse)
  <>4 Result of precipitation observation

The aim of solid-state weather is radars to observe as original observation as shorten interval of radio frequency assignment. Figure 6. shows a case of distribution of precipitation and Figure 7. shows distribution of Doppler velocity observed by 5GHz band solid-state weather radar.

Figure 6.     Distribution of precipitation reflectivity

Figure 7.    Distribution of Doppler velocity

This is relatively strong precipitation, and we can get right distribution of precipitation compared with existing radar's observation. It also gets right continuous change in velocity.

Actually, compared weather radar installed in field with observational result quantitatively, it measured 0.84 with correlation coefficient. In the case of comparing observational data of weather radar, installed at different place, we can see accurate correlation from the viewpoint of the difference of altitude or time. At this point, missing area of the north is due to hiding by mountain and not related the performance of radar. 

Figure 8.  to Figure 10. show a case of the observation of 9GHz band solid-state weather radar. We can see fine observational result on phase difference between horizontal phase wave, specific differential phase and differential reflectivity.

Figure 8.    Horizontal Reflectivity Factor

(by Nagoya University)

Figure 9.    Specified Differential Phase

(by Nagoya University)

Figure 10.                          Differential Reflectivity

(by Nagoya University) <>5 Conclusion

We developed 5GHz band solid-state weather radar and 9GHz band solid-state weather radar by solid-state element. This radar shortens the interval of radio frequency assignment by 1/4 with keeping high-end system and performance as Multi-Parameter radar. Moreover, it has life cycle cost cut-down without changing like electron tube. We will improve more and lead the world for adoption of solid-state weather radar.