A 490 GHz planar circuit balanced Nb-Al2O3-Nb quasiparticle mixer for radio astronomy: Application to quantitative local oscillator noise determination

Abstract

This article presents a heterodyne experiment which uses a 380-520 GHz planar circuit balanced Nb-Al 2 O 3 -Nb superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4-8 GHz instantaneous intermediate frequency (IF) bandwidth to quantitatively determine local oscillator (LO) noise. A balanced mixer is a unique tool to separate noise at the mixer's LO port from other noise sources. This is not possible in singleended mixers. The antisymmetric IV characteristic of a SIS mixer further helps to simplify the measurements. The double-sideband receiver sensitivity of the balanced mixer is 2-4 times the quantum noise limit hν/k B over the measured frequencies with a maximum LO noise rejection of 15 dB. This work presents independent measurements with three different LO sources that produce the reference frequency but also an amount of near-carrier noise power which is quantified in the experiment as a function of the LO and IF frequency in terms of an equivalent noise temperature T LO . Two types of LO sources are used: a synthesizer driven amplifier/multiplier chain and a Gunn oscillator driven multiplier chain. With the first type of LO we find different near-carrier noise contributions using two different power pre-amplifiers of the LO system. For one of the two power pre-amplifiers we measure T LO = 30 ± 4 K at the LO frequency 380 GHz and T LO = 38 ± 10 K at 420 GHz. At the frequency band center 465 GHz of the Gunn driven LO we measure a comparable value of T LO = 32 ± 6 K. For the second power pre-amplifier a significant higher T LO value of the synthesizer driven LO is found which is up to six times larger compared with the best values found for the Gunn driven LO. In a second experiment we use only one of two SIS mixers of the balanced mixer chip in order to verify the influence of near-carrier LO noise power on a single-ended heterodyne mixer measurement. We find an IF frequency dependence of near-carrier LO noise power. The frequency-resolved IF noise temperature slope is flat or slightly negative for the single-ended mixer. This is in contrast to the IF slope of the balanced mixer itself which is positive due to the expected IF roll-off of the mixer. This indicates a higher noise level closer to the LO's carrier frequency. Our findings imply that near-carrier LO noise has the largest impact on the sensitivity of a receiver system which uses mixers with a low IF band, for example superconducting hot-electron bolometer (HEB) mixers.

Experimental Study of a Planar-Integrated Dual-Polarization Balanced SIS Mixer

“…Noise rejection ratio is the principal figure of merit of a balanced mixer. It is conventionally measured with two individual hot/cold-load measurement procedures, in which the two mixers are applied with co-polar bias and anti-polar bias respectively [14], [15]. Different bias polarities correspond to constructive or destructive interference of the signals at the output port.…”

“…The thermal contribution, an additive noise, can be reduced by a cold attenuator, while the non-thermal noise, which is inherent and proportional to the LO power, cannot. The measurement was done in a procedure similar to the NRR measurement [14], [15]. In order to separate the contributions of the thermal noise and the non-thermal noise, the measurement is done with and without an additional 10 dB attenuator placed on the 4 K stage immediately before the mixer mount.…”

A W-Band Chebyshev Waveguide Bandpass Filter with Wide Stopband Performance

“…For instance, wireless communication around 100 GHz, which can offer the potential for massive data rates and broad bandwidth, has attracted considerable attention for beyond 5G and 6G communications [1,5]. The interest in modern mmWave and THz communication systems and spectrum detectors has enabled a great demand for abundant active and passive devices, such as oscillators [6], multipliers [7], mixers [8], on-chip amplifiers [9], antenna arrays [10] and filters [11]. Filters, as one of the key devices, can play an invaluable role in most systems, blocking unwanted or spurious waves [12].…”

“…Compared with the substrate-based transmission lines such as substrate-integrated waveguide (SIW) [14,15], microstrip line [16] and coplanar waveguide (CPW) [17], the air-filled rectangular waveguide can exhibit advantages of low insertion loss, high Q-factor, high power handling, and simple assembling. Thus, rectangular waveguides are preferred as the transmission lines to construct BPFs [18][19][20][21][22][23][24][25][26][27], active circuits [7][8][9] as well as systems [2] from the W-band to THz band. However, the physical dimensions suffer from high precision requirements due to short wavelength and small size of the W-band BPFs.…”

Low-noise integrated balanced SIS mixer for 787–950 GHz

“…An alternative solution to reduce the LO noise contribution is to use a balanced mixer configuration, which also has the advantage of reducing the necessary LO power by more than an order of magnitude. Various balanced SIS mixers have hitherto been studied for radio astronomy applications at millimeter and submillimeter wavelengths [6][7][8][9][10][11][12][13][14][15][16]. Our group also demonstrated a low-noise balanced SIS mixer for the 790-950 GHz band [17]; this balanced mixer consisted of several modular components such as two double sideband (DSB) SIS mixers, a radio-frequency (RF) 90°hybrid coupler, IF isolators, and an IF power combiner.…”