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![A Gunn diode oscillator (100-120 GHz) followed by a Schottky diode doubler and tripler has been used to simulate a spurious signal. It has been coupled to the input beam by means of a 12 micron thick Mylar beam splitter (BS1) and a HDP lens (L1). The output frequency of the RF source has been fixed throughout whole experiment at 642 GHz and its output power adjusted regulated by means of a polarizing grid mounted in a computer controlled rotating fixture. The peak output power of several tens of microwatts can be regulated to approximately -40 dB relative power level referred to the input of the mixer. An ALMA band 9 prototype has been used as a tunable frequency LO source. This LO is a combination of power amplifiers and frequency multipliers with a final stage of ×6 (integrated 2×3) multiplier with output frequency range of 600-712 GHz. This source has been made at NRAO in Charlottesville. The output power of the LO has been adjusted by a grid polarizer (G2) and coupled to a receiver beam by means of a 12 micron Mylar beam splitter (BS2) and a HDP lens (L2). It was possible to achieve an optimum pumping level of the SIS mixer throughout whole ALMA band. RF and LO signals that pass through beam splitters or reflect from grids (G1, G2) were terminated in signal absorbers (not shown in the figure). A switchable hot/cold load with temperature levels of 80 K (liquid nitrogen) and 300 K (room temperature) has been used to measure receiver noise temperature and gain under different conditions. The SIS mixer, its associated cold optics (M1, M2) and cold IF components have been mounted in a vacuum space of a Infrared Labs HDL-8 liquid helium cryostat at 4.2 K. Two GoreTex® sheets of 1 mm thickness were used as 4 K and 80 K infrared filters and high performance anti-reflection coated quartz plate was used as vacuum window of the cryostat. The cold IF coupling scheme uses a 4-12 GHz cryogenic isolator [13], and an InP type 4-12 GHz IF amplifier [14] of 30 dB gain and 4.6 K noise temperature. The warm IF chain consisted of two MITEQ IF amplifiers, a set of attenuators, a computer controlled tuneable YIG filter (with a bandwidth of 40 MHz) and an Agilent power meter. Particular care was taken to avoid saturation of the IF amplifier chain at all input conditions by choosing an appropriate attenuation level. This set-up allowed us to measure gain and noise temperature of the mixer versus IF frequency.](profile/Tm-Klapwijk/publication/228873102/figure/fig1/AS:339553996034048@1457967389062/A-Gunn-diode-oscillator-100-120-GHz-followed-by-a-Schottky-diode-doubler-and-tripler.png)
A Gunn diode oscillator (100-120 GHz) followed by a Schottky diode doubler and tripler has been used to simulate a spurious signal. It has been coupled to the input beam by means of a 12 micron thick Mylar beam splitter (BS1) and a HDP lens (L1). The output frequency of the RF source has been fixed throughout whole experiment at 642 GHz and its output power adjusted regulated by means of a polarizing grid mounted in a computer controlled rotating fixture. The peak output power of several tens of microwatts can be regulated to approximately -40 dB relative power level referred to the input of the mixer. An ALMA band 9 prototype has been used as a tunable frequency LO source. This LO is a combination of power amplifiers and frequency multipliers with a final stage of ×6 (integrated 2×3) multiplier with output frequency range of 600-712 GHz. This source has been made at NRAO in Charlottesville. The output power of the LO has been adjusted by a grid polarizer (G2) and coupled to a receiver beam by means of a 12 micron Mylar beam splitter (BS2) and a HDP lens (L2). It was possible to achieve an optimum pumping level of the SIS mixer throughout whole ALMA band. RF and LO signals that pass through beam splitters or reflect from grids (G1, G2) were terminated in signal absorbers (not shown in the figure). A switchable hot/cold load with temperature levels of 80 K (liquid nitrogen) and 300 K (room temperature) has been used to measure receiver noise temperature and gain under different conditions. The SIS mixer, its associated cold optics (M1, M2) and cold IF components have been mounted in a vacuum space of a Infrared Labs HDL-8 liquid helium cryostat at 4.2 K. Two GoreTex® sheets of 1 mm thickness were used as 4 K and 80 K infrared filters and high performance anti-reflection coated quartz plate was used as vacuum window of the cryostat. The cold IF coupling scheme uses a 4-12 GHz cryogenic isolator [13], and an InP type 4-12 GHz IF amplifier [14] of 30 dB gain and 4.6 K noise temperature. The warm IF chain consisted of two MITEQ IF amplifiers, a set of attenuators, a computer controlled tuneable YIG filter (with a bandwidth of 40 MHz) and an Agilent power meter. Particular care was taken to avoid saturation of the IF amplifier chain at all input conditions by choosing an appropriate attenuation level. This set-up allowed us to measure gain and noise temperature of the mixer versus IF frequency.
Source publication
In this article we answer experimentally the question of how much spurious signal power level (relative to LO power) can be tolerated by an SIS mixer. Spurious signals that are inside and outside of the signal sideband have been considered. It is demonstrated that about −20 dBc of in-RF-band spurious level can be tolerated. For out-of-RF-band spuri...
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Citations
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical observatory that is being built on a 5000 m altitude plateau in Chile to perform heterodyne measurements in the frequency range of 30 to 950 GHz. These measurements will reveal the presence of characteristic molecules that tell us more about the evolution of the early universe and the formation of stars and planetary systems. Because of the limited atmospherical transmission of radiation at these frequencies, ALMA is divided into 10 frequency bands with a sufficiently high transmission. This thesis describes the research that has been done to develop superconductor - insulator - superconductor (SIS) tunneljunctions as detectors for Band 9 of ALMA (602 - 720 GHz). To realize these devices, a tuning circuit has been developed that optimizes the coupling of electromagnetic radiation from the antenna to the SIS junction. Further, a new method has been developed to create SIS junctions with aluminum nitride (AlN) as the insulating material. This method uses a remote plasma from an inductively coupled plasma source. Junctions that have been grown with this new method show a much better uniformity in transmissivity of the tunneling barrier at high critical current densities. Using the new method, SIS devices with AlN tunnel barriers have been developed that have a record low noise temperature over the full bandwidth of Band 9.
