The lower hybrid current drive ͑LHCD͒ system is an important system in superconducting steady state tokamak ͑SST-1͒. It is used to drive and maintain the plasma current for 1000 s with a duty cycle of 17%. The LHCD system is being designed to launch 1 MW of radio frequency ͑rf͒ power at 3.7 GHz. The rf source is comprised of two high power klystron amplifiers, each capable of delivering 500 kW rf power. In this article, the results obtained during installation and commissioning of these klystrons are presented. Two klystrons ͑model TH2103D͒ have been successfully installed and commissioned on dummy loads, delivering ϳ200 kW power for more than 1000 s. The maximum output power that could be obtained is limited due to the available direct current ͑dc͒ power supply. The test system is comprised of a TH2103D klystron, a low power rf ͑3.7 GHz/25 W͒ source, two high power four port circulators, two high power dual directional couplers, two arc detector systems, and two dummy water loads. To avoid rf breakdown in the rf components of the transmission line, the system has been pressurized with dry air to 3 bar. To energize and operate the klystron, a high voltage dc power supply, a magnet power supply, an ion pump power supply, a Ϫ65 kV floating anode modulator power supply, and a filament power supply are used. An arc detector unit has been installed to detect and initiate action within a few microseconds to protect the klystron, waveguides, and other rf passive components during arcing. To protect the klystron in the event of an arc, a fast responding ͑Ͻ10 s͒, rail gap based pressurized crowbar unit has been used. The entire system is water cooled to avoid excess temperature rise during high power continuous wave operation of the klystron and other rf components. The tube requires initial conditioning. Thereafter, the output rf power is studied as a function of beam parameters such as cathode voltage and beam current.

This paper presents the design and characterization of wide band ohmic microswitch with an actuation voltage as low as 20~25 V, and a restoring force of 14.1 μN. The design of the proposed switch is primarily composed of an electrostatic actuator, bridge membrane, cantilever (beam) and coplanar waveguide, suspended over the substrate. The analysis shows an insertion loss of -0.002 dB at 1GHz and remains as low as -0.35 dB, even at 100 GHz. The isolation loss of the switch is sustained at -21.09 dB at 100GHz, with a peak value of -99.58 dB at 1 GHz and up-state capacitance of 4 fF. To our knowledge, this is the first demonstration of a series contact switch, which works over a wide bandwidth (DC-100 GHz) and with such a high and sustained isolation, even at high frequencies and with an excellent figure of merit (f c =1/2.pi.Ron.Cu= 39.7 THz).

Ever increasing demand for microwave operated applications has cultivated need for high-performance universal systems capable of working on multi-bands. This objective can be realized using Multi-Dielectrics in RF MEMS capacitive switch. In this study, we present a detailed analysis of the effect of various dielectrics on switch performance. The design consists of a capacitive switch and performance is analyzed by changing the dielectric layers beneath the switch. The results are obtained using three different dielectrics including Silicon nitride (7.6), Hafnium dioxide (25) and Titanium oxide (50). Testing of proposed switch yields high isolation (-87.5 dB) and low insertion loss (-0.1 dB at 50 GHz) which is substantially better than the conventional switches. The operating bandwidth of the proposed switch (DC to 95 GHz) makes it suitable for wide band microwave applications.

This paper proposes a metal contact RF MEMS switch which utilizes a see-saw mechanism to acquire a switching action. The switch was built on a quartz substrate and involves vertical deflection of the beam under an applied actuation voltage of 5.46 volts over a signal line. The see-saw mechanism relieves much of the operation voltage required to actuate the switch. The switch has a stiff beam eliminating any stray mechanical forces. The switch has an excellent isolation of -90.9 dB (compared to -58 dB in conventional designs [3]), the insertion of -0.2 dB, and a wide bandwidth of 88 GHz (compared to 40 GHz in conventional design [16]) making the switch suitable for wide band applications.

This paper presents design and simulation of wide band RF microswitch that uses electrostatic actuation for its operation. RF MEMS devices exhibit superior high frequency performance in comparison to conventional devices. Similar techniques that are used in Very Large Scale Integration (VLSI) can be employed to design and fabricate MEMS devices and traditional batch-processing methods can be used for its manufacturing. The proposed switch presents a novel design approach to handle reliability concerns in MEMS switches like dielectric charging effect, micro welding and stiction. The shape has been optimized at actuation voltage of 14-16 V. The switch has an improved restoring force of 20.8 μN. The design of the proposed switch is very elemental and primarily composed of electrostatic actuator, a bridge membrane and coplanar waveguide which are suspended over the substrate. The simple design of the switch makes it easy for fabrication. Typical insertion and isolation of the switch at 1 GHz is -0.03 dB and -71 dB and at 85 GHz it is -0.24 dB and -29.8 dB respectively. The isolation remains more than -20 db even after 120 GHz. To our knowledge this is the first demonstration of a metal contact switch that shows such a high and sustained isolation and performance at W-band frequencies with an excellent figure-of merit (fc=1/2.pi.Ron.Cu =1,900 GHz). This figure of merit is significantly greater than electronic switching devices. The switch would find extensive application in wideband operations and areas where reliability is a major concern.