The design of a diplexer, coupled to a planar bowtie antenna for two-band Cosmic Microwave Background detection is proposed, using both HFSS™ and ADS™ softwares. The two photometric bands are centered on 150 GHz and 220 GHz respectively. The diplexer is composed of two three-elements distributed filtering circuits, taking into account the complex impedance of the antenna and the impedance of the two resistive loading bolometers. The distributed elements are transmission lines Coplanar Strip Lines (CPS) and Broadside Coupled Lines (BCL). Their balanced geometry matches to the differential signal delivered by the bow-tie antenna, avoiding the addition of a balun circuit. The envisaged technology for strips and antenna is superconducting niobium at a few 100mK on Si substrate. The overall size of the antenna/diplexer structure is around 2 mm2, allowing to consider it as a pixel suitable for integration in a bolometer array.
The design of a diplexer, coupled to a planar bowtie antenna for two-band Cosmic Microwave Background detection is proposed, using both HFSS™ and ADS™ softwares. The two photometric bands are centered on 150 GHz and 220 GHz respectively. The diplexer is composed of two three-elements distributed filtering circuits, taking into account the complex impedance of the antenna and the impedance of the two resistive loading bolometers. The distributed elements are transmission lines Coplanar Strip Lines (CPS) and Broadside Coupled Lines (BCL). Their balanced geometry matches to the differential signal delivered by the bow-tie antenna, avoiding the addition of a balun circuit. The envisaged technology for strips and antenna is superconducting niobium at a few 100mK on Si substrate. The overall size of the antenna/diplexer structure is around 2 mm2, allowing to consider it as a pixel suitable for integration in a bolometer array.
We propose a pixel design, aimed to be included in an array, receiving and de- tecting simultaneously two bands of the Cosmic Microwave Background (CMB). It is composed of a bowtie antenna, feeding a diplexer structure to separate the signal towards two bolomet- ric detectors at 150 and 220GHz. The diplexer makes use of difierential transmission lines of Coplanar Striplines (CPS) and Broadside Coupled Lines (BCL) types, for flltering and separation purposes. The antenna and diplexer are planned to be fabricated in a superconductive niobium thin fllm deposited on a Silicon substrate, while NbSi bolometers will lie on a SiN membrane. The device has been simulated by means of ADS (Agilent), CST Microwave Studio and HFSS (Ansoft) softwares. Final dimensions that take into account the kinetic inductance of the super- conducting lines are proposed. Promising computation results are found, with signal separation up to 20dB.
Cosmic microwave background (CMB) studies require observations in several frequency bands simultaneously. For example, the detection of clusters of remote galaxies can be performed by comparing CMB photon fluxes at different frequencies, using the spectral deformation of the Planck law, due to the Sunyaev–Zeldovich effect. We propose a single pixel design to receive and detect simultaneously two frequency bands of the (CMB), centered at 150 and 220 GHz. It is composed of a bow-tie antenna, sensitive to the polarization of the incident radiation, feeding a diplexer structure to separate the signal towards two kinetic inductance resonators associated respectively with the 130–170 and 200–270 GHz frequency bands. The diplexer makes use of 150 nm thick niobium-based superconducting transmission lines of the coplanar strip-lines (CPS) type, for filtering and separation purposes, deposited on a 30 μm thick quartz substrate. A new coplanar matching structure, taking into account the kinetic inductance of the superconducting films, is proposed and achieves a nearly perfect match over more than 25% of each frequency band, along with a signal separation ratio above 30 dB at both center frequencies. The size of a single pixel is 0.9 mm × 1.2 mm.
This article presents a multichroic Kinetic Inductance Bolometer (KIB) polarimeter that utilizes coplanar waveguide (CPW) diplexers. The CPW diplexers function as filters, providing two passbands centered at 220 GHz and 280 GHz. The high-quality-factor resonant units deliver excellent transmission and isolation characteristics. Additionally, the quasi-lumped-element resonator design enables a significant reduction in size compared to conventional microstrip diplexers. The entire polarimeter—comprising orthomode transducer (OMT) probes, diplexers, KIBs, and CPW feed lines—is integrated on a single plane, allowing for one-layer superconducting thin-film fabrication with a simplified process. The compact size, superior frequency response, and streamlined fabrication process make the proposed pixel scheme suitable for integrated array development.
The opacity due to water vapor in the Earth's atmosphere obscures portions of the sub-THz spectrum (mm/sub-mm wavelengths) to ground based astronomical observation. For maximum sensitivity, instruments operating at these wavelengths must be designed to have spectral responses that match the available windows in the atmospheric transmission that occur in between the strong water absorption lines. Traditionally, the spectral response of mm/sub-mm instruments has been set using optical, metal-mesh bandpass filters [1]. An alternative method for defining the passbands, available when using superconducting detectors coupled with planar antennas, is to use on-chip, superconducting filters [2]. This paper presents the design and testing of superconducting, lumped element, on-chip bandpass filters (BPFs), placed inline with the microstrip connecting the antenna and the detector, covering the frequency range from 209-416 GHz. Four filters were designed with pass bands 209-274 GHz, 265-315 GHz, 335-361 GHz and 397-416 GHz corresponding to the atmospheric transmission windows. Fourier transform spectroscopy was used to verify that the spectral response of the BPFs is well predicted by the computer simulations. Two-color operation of the pixels was demonstrated by connecting two detectors to a single broadband antenna through two BPFs. Scalability of the design to multiple (four) colors is discussed.
We propose a novel antenna-coupled low Tc superconducting bolometer which makes use of the thermal boundary resistance and the trapping of quasiparticles at metal-superconducting interfaces. A thin strip of superconductor, whose temperature is regulated at the midpoint of its resistive transition, serves both as a resistive load to thermalize the infrared current from the antenna and as a thermometer to measure the resulting temperature rise. Calculations give a noise equivalent power (NEP)≊7×10−16 T5/2 WHz−1/2 and a time constant τ≊10−8 T−2 s for a 2×2 μm2 thermometer area at temperature T (K). Designs for efficient on-chip rf matching and filter networks with well-defined bandpasses are presented. These detectors can be used to make frequency-multiplexed array receivers for astronomical observations at near millimeter wavelengths.
Superconducting Josephson junctions have major advantages as detectors of millimeter wave radiation. Frequency of the radiation can be easily derived from the Shapiro steps of the current-voltage characteristics. However, system performance is highly sensitive to impedance mismatch between the antenna and the junction; therefore, optimization is essential. We analyzed and implemented an improved antenna structure, in which the junction is displaced from the antenna center and placed between the ends of two matching strips. Based on theoretical analysis and advanced electromagnetic simulations, we optimized strip dimensions, which affect both the detection magnitude and the frequency of the reflection coefficient dip. Accordingly, two Au bow-tie antennas with different matching strip widths were fabricated. Superconducting Yttrium Barium Copper Oxide (YBCO) thin films were deposited exactly at the bicrystal substrate misorientation points, forming Josephson junctions at the ends of two matching strips. We found a very high correlation between the simulations and the response to Radio Frequency (RF) radiation in the range of 145–165 GHz. Experimental results agree extremely well with the design, showing best performance of both antennas around the frequency for which impedance matching was derived.