A 400–500 GHz Balanced SIS Mixer with a Waveguide Quadrature Hybrid Coupler

Abstract

We have developed a 400-500 GHz low-noise balanced SIS (Superconductor Insulator Superconductor) mixer, which is based on a waveguide RF quadrature hybrid coupler. The RF quadrature hybrid was designed and fabricated as a broadband hybrid with good performance at 4 K. The fabricated RF quadrature hybrid was measured at room temperature with a submillimeter vector network analyzer to check amplitude and phase imbalance between two output ports. Then the balanced mixer was assembled with the RF hybrid, two DSB mixers, and a 180 • IF hybrid. Several important parameters such as noise temperature, LO power reduction, and IF spectra were measured. The LO power reduction is defined as how much LO power the balanced mixer saves compared with a typical single-ended mixer. The measured noise temperature of the balanced mixer was ∼ 55 K at the band center which corresponds to ∼ 3 times the quantum noise limit (hf/k) in DSB, and ∼ 120 K at the band edges. The noise performance over LO frequency was almost the same as that of the worse DSB mixer used in the balanced mixer. In addition the LO power required for the balanced mixer is ∼ 11 dB less than that of the single-ended mixers.

Time-Delay Multiplexing of Two Beams in a Terahertz Imaging Radar

“…The measured coupling is about 6-7 dB, which for a 3-dB coupler implies an insertion loss of around 3.5 dB. This loss is comparable with other quadrature hybrid implementations at these frequencies [10]. As with the twist, this additional loss is consistent with HFSS simulations of the waveguide wall roughness and conductivity, and it represents a significant drawback of using discrete waveguide blocks for duplexing.…”

Terahertz Heterodyne Array Receivers for Astronomy

“…In addition, any LO amplitude noise, which can be considerable (Section 4.3.1), is suppressed [54]. Integrating the hybrid coupler on-chip is very attractive for array applications as it results in a very small mixer footprint compared to the more conventional waveguide hybrid solution [55].…”

Development of a 385–500 GHz Sideband-Separating Balanced SIS Mixer

“…The developed balanced 2SB mixer consists of two quadrature hybrid type single balanced SIS mixers, because the quadrature hybrid type mixer is simple in its mechanical structure. The quadrature hybrid type SIS mixers with good performance at 385-500 GHz have been developed with waveguide technology and demonstrated as the sideband-separating SIS mixer [6], and the balanced SIS mixer [27].…”

“…4. The RF quadrature hybrid couplers were simulated, designed, and fabricated by almost the same way described in the previous paper [27]. It was found that the return loss, amplitude imbalance, and phase imbalance were < −20dB, < 1.5dB, and < 10deg respectively by the measurement with a submillimeter network analyzer [6].…”