Tunable square waveguide polarizer with irises and posts

Polarization signal processing is widely used in modern information and telecommunication systems for various purposes. Signal polarization processing is carried out in polarization-adaptive antenna systems. The key element of such systems is transformation devices for polarization processing. They perform the transformation of the types of polarization and separate the different types. The most commonly applied systems are the ones using a single circular polarization or two orthogonal circular polarizations simultaneously.The absence of the need for an accurate angle orientation between the transmitting and receiving antennas to establish communication is one of the basic advantages of this type of polarization. When using antenna systems with linear polarization, signal losses appear due to inconsistency in the orientation of the polarization planes of the transmitting and receiving antennas. This feature of circular polarization is important for satellite and many other telecommunications systems. In such systems it is difficult to maintain a fixed orientation of one antenna relative to the other. In addition, circular polarization is used to communicate with satellites orbiting the direction of the radio link. Regardless of antenna orientation, when using circular polarization, the received signal level is constant. These advantages explain why circular polarized antennas are widely used in radio engineering systems for various purposes. The paper presents the results of the development of a polarization device based on a square waveguide with two posts and two diaphragms in the frequency range from 7,7 to 8,5 GHz. The article contains the results of calculations using the developed mathematical model of the device. In addition, the results of modeling the device using the finite element method are presented for comparison. A comparison was made of the polarization characteristics and the match of the developed polarizer. The created mathematical model makes it possible to effectively analyze the characteristics when changing design parameters. These parameters include the size of the wall of the square waveguide, the heights of the diaphragms and pins, the distance between them, the thickness of the diaphragms and pins. The developed polarizer is suggested for the application in satellite telecommunication and radar systems.

Polarization of hot Jupiter systems: a likely detection of stellar activity and a possible detection of planetary polarization

ABSTRACT We present high-precision linear polarization observations of four bright hot Jupiter systems (τ Boo, HD 179949, HD 189733, and 51 Peg) and use the data to search for polarized reflected light from the planets. The data for 51 Peg are consistent with a reflected light polarization signal at about the level expected with 2.8σ significance and a false alarm probability of 1.9 per cent. More data will be needed to confirm a detection of reflected light in this system. HD 189733 shows highly variable polarization that appears to be most likely the result of magnetic activity of the host star. This masks any polarization due to reflected light, but a polarization signal at the expected level of ∼20 ppm cannot be ruled out. τ Boo and HD 179949 show no evidence for polarization due to reflected light. The results are consistent with the idea that many hot Jupiters have low geometric albedos. Conclusive detection of polarized reflected light from hot Jupiters is likely to require further improvements in instrument sensitivity.

Spin characterization of systematics in CMB surveys – a comprehensive formalism

ABSTRACT The CMB B-mode polarization signal – both the primordial gravitational wave signature and the signal sourced by lensing – is subject to many contaminants from systematic effects. Of particular concern are systematics that result in mixing of signals of different ‘spin’, particularly leakage from the much larger spin-0 intensity signal to the spin-2 polarization signal. We present a general formalism, which can be applied to arbitrary focal plane setups, that characterizes signals in terms of their spin. We provide general expressions to describe how spin-coupled signals observed by the detectors manifest at map-level, in the harmonic domain, and in the power spectra, focusing on the polarization spectra – the signals of interest for upcoming CMB surveys. We demonstrate the presence of a previously unidentified cross-term between the systematic and the intrinsic sky signal in the power spectrum, which in some cases can be the dominant source of contamination. The formalism is not restricted to intensity to polarization leakage but provides a complete elucidation of all leakage including polarization mixing, and applies to both full and partial (masked) sky surveys, thus covering space-based, balloon-borne, and ground-based experiments. Using a pair-differenced setup, we demonstrate the formalism by using it to completely characterize the effects of differential gain and pointing systematics, incorporating both intensity leakage and polarization mixing. We validate our results with full time ordered data simulations. Finally, we show in an Appendix that an extension of simple binning map-making to include additional spin information is capable of removing spin-coupled systematics during the map-making process.

Inevitable imprints of patchy reionization on the cosmic microwave background anisotropy

ABSTRACT Reionization of the cosmic neutral hydrogen by the first stars in the Universe is an inhomogeneous process, which produces spatial fluctuations in free electron density. These fluctuations lead to observable signatures in cosmological probes like the cosmic microwave background (CMB). We explore the effect of the electron density fluctuations on CMB using photon-conserving seminumerical simulations of reionization named SCRIPT. We show that the amplitude of the kinematic Sunyaev–Zeldovich (kSZ) and the B-mode polarization signal depends on the patchiness in the spatial distribution of electrons along with the dependence on mid-point and extent of the reionization history. Motivated by this finding, we provide new scaling relations for the amplitude of kSZ and the B-mode polarization signal which can capture the effects arising from the mean optical depth, width of reionization, and spatial fluctuations in the electron density arising from patchy reionization. We show that the amplitude of the kSZ and the B-mode polarization signal exhibits different dependency on the width of reionization and the patchiness of reionization, and hence a joint study of these CMB probes will be able to break the degeneracy. By combining external data sets from 21-cm measurements, the degeneracy can be further lifted by directly exploring the sizes of the ionized regions.

Polarization measurements of the polluted white dwarf G29-38

ABSTRACT We have made high-precision polarimetric observations of the polluted white dwarf G29-38 with the HIgh Precision Polarimetric Instrument 2. The observations were made at two different observatories – using the 8.1-m Gemini North Telescope and the 3.9-m Anglo-Australian Telescope – and are consistent with each other. After allowing for a small amount of interstellar polarization, the intrinsic linear polarization of the system is found to be 275.3 ± 31.9 parts per million at a position angle of 90.8 ± 3.8° in the SDSS g′ band. We compare the observed polarization with the predictions of circumstellar disc models. The measured polarization is small in the context of the models we develop, which only allows us to place limits on disc inclination and Bond albedo for optically thin disc geometries. In this case, either the inclination is near-face-on or the albedo is small – likely in the range 0.05–0.15 – which is in line with other debris disc measurements. A preliminary search for the effects of G29-38’s pulsations in the polarization signal produced inconsistent results. This may be caused by beating effects, indicate a clumpy dust distribution, or be a consequence of measurement systematics.