| Title: |
Design and Performance of 30/40 GHz Diplexed Focal Plane for BICEP Array |
| Authors: |
Shiu, Corwin, Soliman, Ahmed, O'Brient, Roger, Steinbach, Bryan, Bock, James J., Frez, Clifford F., Jones, William C., Megerian, Krikor G., Moncelsi, Lorenzo, Schillaci, Alessandro, Turner, Anthony D., Weber, Alexis C., Zhang, Cheng, Zhang, Silvia |
| Source: |
The Astrophysical Journal Supplement Series, Vol 272, 2024 |
| Publication Year: |
2024 |
| Collection: |
Astrophysics |
| Subject Terms: |
Astrophysics - Instrumentation and Methods for Astrophysics |
| More Details: |
We demonstrate a wide-band diplexed focal plane suitable for observing low-frequency foregrounds that are important for cosmic microwave background polarimetry. The antenna elements are composed of slotted bowtie antennas with 60% bandwidth that can be partitioned into two bands. Each pixel is composed of two interleaved 12$\times$12 pairs of linearly polarized antenna elements forming a phased array, designed to synthesize a symmetric beam with no need for focusing optics. The signal from each antenna element is captured in-phase and uniformly weighted by a microstrip summing tree. The antenna signal is diplexed into two bands through the use of two complementary, six-pole Butterworth filters. This filter architecture ensures a contiguous impedance match at all frequencies, and thereby achieves minimal reflection loss between both bands. Subsequently, out-of-band rejection is increased with a bandpass filter and the signal is then deposited on a transition-edge sensor bolometer island. We demonstrate the performance of this focal plane with two distinct bands, 30 and 40 GHz, each with a bandwidth of $\sim$20 and 15 GHz, respectively. The unequal bandwidths between the two bands are caused by an unintentional shift in diplexer frequency from its design values. The end-to-end optical efficiency of these detectors are relatively modest, at 20-30%, with an efficiency loss due to an unknown impedance mismatch in the summing tree. Far-field beam maps show good optical characteristics with edge pixels having no more than $\sim$ 5% ellipticity and $\sim$10-15% peak-to-peak differences for A-B polarization pairs.
Comment: 17 pages, 13 figures. Accepted for publication in ApJS |
| Document Type: |
Working Paper |
| DOI: |
10.3847/1538-4365/ad34d8 |
| Access URL: |
http://arxiv.org/abs/2405.03767 |
| Accession Number: |
edsarx.2405.03767 |
| Database: |
arXiv |
