1 Introduction

The Engineering Test Satellite VIII (ETS-VIII) is scheduled for launch from Tane-gashima Space Center aboard the H-IIA rocketin summer 2004. The CommunicationsResearch Laboratory (CRL) loaded an on-board processor (OBP) for voice communica-tions [1], an on-board packet switch (PKT) forhigh-data-rate communications [2], and a highaccuracy clock (HAC) [3]. These devices willbe used to carry out mobile satellite communi-cation and broadcast experiments [4], as well atime comparison experiment [5].

An S-band earth station was installed atthe Kashima Space Research Center to form aservice link between the ETS-VIII andground, and is used as a standard station forvarious satellite communication experiments.

This paper reports on the performance andelectrical characteristics of several units con-stituting the S-band earth station.

2 Configuration of S-band earthstation

A block diagram of the S-band earth sta-tion is shown in Fig.1.

The major components of the S-band earthstation consist of an antenna unit, an RF unit,an IF unit, a monitor and control subsystem,and a standard frequency unit.

It is assumed that the satellite uses thelarge-scale deployable reflector (LDR) forcommunication with this earth station. How-ever, if for some reason the LDR cannot beused, the satellite employs a small (1.1-mφ)S-band antenna normally used in time com-parison experiments instead. Since the per-formance of this link becomes significantlylower than the link which used LDR, the earthstation has sufficient performance so that anexperiment can be performed.

As shown in Fig.1, in the experimentwhich used the LDR, attenuators (ATT(LDR)) are inserted in the output side of thepower amplifier and the output side of the

YAMAMOTO Shin-ichi et al. 137

4-2 S-band Earth Station for Mobile Commu-nication

YAMAMOTO Shin-ichi, OBARA Noriaki, and YAMAZAKI Ichiroh

Engineering Test Satellite VIII (ETS-VIII) is scheduled for launch in the summer of 2004.The Communications Research Laboratory (CRL) is planning various mobile satellite com-munications experiment using On-Board Processor, On-Board Packet Switch etc., whichwere carried in the satellite, and the satellite broadcasting experiment. An S-band earth sta-tion was installed in the Kashima Space Research Center, in order to measure characteris-tics which serve as a basis in the communication and the broadcasting experiment,between ETS-VIII and a mobile station.

This paper describes the outlook of an S-band earth station and the electric characteris-tic.

Keywords Personal satellite communication, ETS-VIII, S-band earth station, Service link

138

low-noise amplifier (LNA), and adjust theinput and output level.

Fig.2 shows the antenna unit and the RFunit.

2.1 Antenna unitThe antenna unit consists of an antenna

apparatus and an antenna drive control subsys-tem.

Fig.3 shows the antenna appearance, andTable 1 shows the mechanical performance ofthe antenna unit.

The antenna receives the S-band signal(2500–2540 MHz) from the satellite and pass-es it to the low-noise amplifier (LNA) of thenext stage, and transmits an S-band signal(2655–2660 MHz) output from the 20-W S-band solid state power amplifier (20-W SSPA)of the RF unit to the satellite.

The antenna diameter is 3.6 m, and thefeed system is the front-feed type which useda cross dipole for the primary radiator.

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Block diagram of S-band earth stationFig.1

Appearance of S-band earth stationFig.2

Appearance of antenna unitFig.3Antenna unit RF unit

The antenna drive control subsystem per-forms remote direction adjustment of theantenna, and is composed of an antenna con-trol unit (ACU) and a motor control unit(MOTOR CONT). There are three antennadrive modes: slew, manual, and preset, operat-ed via the ACU. The ACU displays data ofvarious types, including the antenna directionangle. The antenna is also provided with lim-iter switches to protect against excessivedrive.

Table 2 shows the electrical performanceof the antenna unit.

G/T is calculated based on the perform-ance of the antenna unit and the LNA.

Fig.4 shows the transmitting antenna pat-tern, and Fig.5 shows the receiving antennapattern.

The figure indicates that the sidelobe char-acteristics are excellent in both transmission

and reception.

YAMAMOTO Shin-ichi et al. 139

Mechanical performanceTable 1

Electrical performanceTable 2

Transmitting antenna patternFig.4

Receiving antenna patternFig.5

140

2.2 RF unitThe RF unit consists of four subsystems: a

power amplifier, a low-noise amplifier (LNA),an up converter (U/C), and a down converter(D/C).

Table 3 shows the main performance ofthe individual subsystems.

The power amplifier is composed of a 20-W SSPA housed in an SSPA enclosure, a har-monic filter, a band pass filter, a coaxialswitch unit with a dummy load, and a coaxialswitch controller.

The S-band RF signal from the U/C passesthrough a directional coupler (for monitoring)and through a VAR ATT (for input signaladjustment), and is input into the 20-W SSPA.The SSPA has a gain 62 dB or more, amplifiesthe RF signal up to a required level, and pass-

es it to the antenna or to the dummy loadthrough the band pass filter and the coaxialswitch.

The output of the 20-W SSPA is branchedby a directional coupler, and this output ispassed to a 2.6/2.5-GHz TRANSLATOR fromthe coupler’s TX MON terminal. This outputis then used to perform the loop test.

The low-noise amplifier (LNA) subsystemis composed of a low-noise amplifier (LNA),a power supply for the LNA (LNA PS), acoaxial switch, and a cold load for calibration(HOT/COLD LOAD).

This system is mounted in an LNA hous-ing enclosure attached to the antenna feedunit, and is used for low-noise amplificationof the S-band (2500–2540 MHz) weak andwide-band signals received by the antenna;these signals are then sent to the D/C subsys-tem in the subsequent stage. The HOT/COLDLOAD is used when measuring the noise tem-perature of the receiving system, and it meas-ures by switching a cold load (COLD) and anormal temperature load (HOT).

The up converter subsystem is composedof an up converter (U/C), a 10-dB directionalcoupler with an RF monitor terminal, and aprogrammable attenuator (VAR ATT). A 140-MHz band IF signal input into the U/C is con-verted into a 2.6-GHz band RF signal, passedthrough the directional coupler and the VARATT, and input into the 20-W SSPA. TheVAR ATT adjusts the level of the transmittingRF signal.

The down converter subsystem is com-posed of a down converter (D/C), a 60-dBdirectional coupler with a TEST IN terminal,and a 40-dB attenuator for the LDR operation.As shown in Table 3, the D/C converts RF sig-nals in the communication or broadcast bandsinto the appropriate IF signals.

The 2.5-GHz RF signal from the LNA issupplied to the D/C after passing through the40-dB attenuator and the directional coupler.The D/C converts the input RF signal into anIF signal in the 140-MHz band or the 176.25-MHz band. The IF signal is then divided intotwo signals by a hybrid device, and the signals

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Main performance of subsystemsTable 3

are output to the IF unit after passing througha bandpass filter.

2.3 IF unitThe IF unit is divided into a transmitting

IF component and a receiving IF component.The transmitting IF component consists of anIF connection panel (IF PATCH) and an IFcombiner (IF COMB). The receiving IF com-ponent consists of a bandpass filter (BPF)built into the D/C, an IF divider (IF DIV), anIF amplifier (IF AMP), and an IF connectionpanel (IF PATCH).

The IF PATCH for transmission has BNCconnectors on the front panel, in order to input140-MHz IF signals, a test signal, etc. fromcommunication terminals.

The IF COMB combines three 140-MHzsignal inputs into one output.

Two BPFs of the receiving IF compo-nent—one for communication in the 140-MHzband and the other for broadcast in the 176-MHz band—are built in to the D/C, andrestrict the frequency band of these two IF sig-nals.

The IF DIV splits one 140-MHz input sig-nal into three output signals.

The IF AMP amplifies the 140-MHz bandIF signal, and can carry out variable gain up to40 dB.

The IF PATCH of the receiving IF compo-nent outputs 140-MHz and 176-MHz IF sig-nals, and a monitor signal and a test signalfrom BNC connectors on the front panel.

2.4 Monitor & control subsystemThe monitor & control subsystem is com-

posed of a TX path selector (TX PATH SEL),an RX coaxial switch controller (COAX SWCONT), a monitor & control device (M&C),and an alarm monitor (ALM MONITOR).

The TX PATH SEL and the COAX SWCONT each control coaxial switches to selectthe path of the transmitted signal and of thereceived signal. There are two control modes,local control and remote control, in this switchcontrol, and remote control mode is normallyselected, which is controlled by the M&C.

The M&C is monitoring the status ofdevices installed on the S-band earth station,and displays the status of the remote operationof the coaxial switches, and thetransmission/reception routes, and NOR-MAL/FAULT of devices. Fig.6 shows thefront panel of the M&C.

As can be seen in the layout of the frontpanel, the M&C is designed to monitor thestatus of each device along the signal path. Interms of the transmitting system, the panelallows visual confirmation of IF signal inputto the IF PATCH, through the AMP, combina-tion by the COMB, and connecting to the U/Cand the 20-W SSPA. The LED indicates anyfault occurring in the AMP. In the U/C andthe 20-W SSPA, a green LED is activated dur-ing normal operation and a red LED lights inthe event of fault. When a route switch buttonon the display is pushed, the COAX SW exe-cutes remote control of the PATH SEL toswitch the signal route. The current route isdisplayed on the button.

In the receiving system and the antennadrive control subsystem, monitoring and con-trol are similarly performed by M&C.

The ALM MONITOR indicates alarm out-put from any of the devices installed in the S-band earth station via lighting or flashingLEDs and activation of a buzzer. The ALMMONITOR also relays the alarm message tothe M&C. Twelve alarms can be displayedand there is a function to memorize the gener-ated alarm.

2.5 Testing device subsystemThis subsystem is equipped with a pro-

YAMAMOTO Shin-ichi et al. 141

Front panel of monitor & control deviceFig.6

142

grammable attenuator (VAR ATT) and a2.6/2.5-GHz test translator (TEST TRANS-LATOR), which are used in various waysaccording to the specific test purposes.

The VAR ATT is installed between theU/C and the 20-W SSPA, and is used to atten-uate the transmitted RF signal in accordancewith the testing purpose. An attenuator can bevaried, in increments of 1 dB or 10 dB, up to amaximum value of 85 dB.

The TEST TRANSLATOR carries outtesting by looping an output signal back fromthe SSPA without establishing a communica-tion channel to the satellite; this device con-verts a 2.6-GHz band input signal into a 2.5-GHz band output signal.

3 Overall electrical characteris-tics

The input-output characteristics of the 20-W SSPA are shown in Fig.7.

The component gain is 62.1 dB and a satu-ration output power is +43.5 dBm.

Fig.8 shows the amplitude-frequency char-acteristics of the transmitting system.

The amplitude-frequency characteristic ofthe transmitting system is measured along theroute from the IF PATCH to the TX MON. Aninput signal of 140 MHz ± 2.5 MHz at －10 dBm results in an output signal fluc-

tuation of 0.19 dBp-p.Fig.9 shows the spurious of the transmit-

ting system.The spurious of the transmitting system

input the signal of 140 MHz and －10 dBmfrom the IF PATCH, and measured it in theDIP input.

Fig.10 shows the input-output characteris-tics of the LNA.

The gain is 38.3 dB, and the 1-dB com-pression point is －39 dBm in input level.

Fig.11 shows the amplitude-frequencycharacteristics of the receiving system forcommunication band, and Fig.12 shows theamplitude-frequency characteristics of thebroadcast band.

The amplitude-frequency characteristic ofthe receiving system for communication bandwas measured along the signal path from theLNA input to the IF PATCH. A signal of2502.5 MHz ±2.5 MHz and －66.3 dBm inputinto the LNA resulted in an IF PATCH outputsignal fluctuation of 0.69 dBp-p.

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

Input-output characteristics of 20-WSSPA

Fig.7

Amplitude-frequency characteristicsof transmitting system

Fig.8

Spurious of transmitting systemFig.9

The amplitude-frequency characteristic ofthe receiving system for broadcast band wasmeasured along the signal path from the LNAinput to the IF PATCH, as in communicationmeasurement. A signal of 2,538.75 MHz

±1.25 MHz and －66.3 dBm input into theLNA resulted in an IF PATCH output signalfluctuation of 0.24 dBp-p.

Fig.13 shows a level diagram of the trans-mitting system.

When the LDR was used, the value of theVAR ATT was set to 12 dB. When the HACwas used, the value of the VAR ATT was set to2 dB, and the 20-dB fixed ATT inserted in thestage following the 20-W SSPA was removed.

Fig.14 shows a level diagram for commu-nication of the receiving system.

When using the LDR, a 40-dB ATT isinserted in the IFL. The broadcast band takesa different path in the IF PATCH. The gain ofthe AMP for the broadcast band differs fromthat of the communication band, the AMP isthus configured so that PATCH output levelcorresponds to the level of the communicationband.

4 Concluding remarks

We have discussed the configuration, per-formance, and electrical characteristics of anS-band earth station designed for mobile com-munication experiments. The launch of the

YAMAMOTO Shin-ichi et al. 143

Input-output characteristics of LNAFig.10

Amplitude-frequency characteristics(communication) of receiving system

Fig.11

Amplitude-frequency characteristics(broadcast) of receiving system

Fig.12

Level diagram of transmitting systemFig.13

Level diagram of receiving system(communication)

Fig.14

144

ETS-VIII is scheduled for the summer of2004, and this earth station will play a centralrole in mobile communication experimentsinvolving the satellite. Going forward, wewill continue in our preparations, involving

verification of the interfaces to be used inexperimental communication terminals, toensure that these experiments will proceedsmoothly.

Journal of the National Institute of Information and Communications Technology Vol.50 Nos.3/4 2003

References1 Y. Hashimoto,"3-7 The On-Board Processor for a Voice Communication Switching", This Special Issue of

NICT Journal.

2 S. Taira, "3-8 Onboard Packet Switch for High-Data-Rate Satellite Communications", This Special Issue of

NICT Journal.

3 H. Noda, K. Sano, and S. Hama, "3.9 High Accuracy Clock", This Special Issue of NICT Journal.

4 S. Taira, S. Hama, S. Yoshimoto, and N. Hamamoto, "5-1Plan of Experiments for Mobile Satellite Communi-

cations and Broadcasting", This Special Issue of NICT Journal.

5 Y. Takahashi, M.Imae, T. Gotoh, F. Nakagawa, M. Fujieda, H. Kiuchi, and M. Hosokawa, "5-2 Experimental

Plans using Time Comparison Equipment", This Special Issue of NICT Journal.

6 T. Iida, "Wave Summit Course:Satellite Communications", Ohmsha, Ltd. 1997.

YAMAMOTO Shin-ichi

Senior Reseacher, Mobile SatelliteCommunications Group, WirelessCommunications Division

Mobile Satellite Communications

YAMAZAKI Ichiroh

Senior Researcher, International Coop-eration Group, Research AllianceOffice, Strategic Planning Division

Satellite Communication Technology

OBARA Noriaki, Ph. D.

Senior Researcher, Ionosphere andRadio Propagation Group, AppliedResearch and Standards Division

Mobile Satellite Communications,Polar Area Satellite Communications,Antenna and Propagation