Development of microwave devices for millimeter and sub-millimeter receivers

Abstract

The Atacama Large Millimeter/Submillimeter Array (ALMA) is one of the largest astronomical facilities in the world. Each of the 66 antenn as accommo dates ten ob servational band s, covering from 35-950 GHz. To extend the op erative lifesp an of ALMA, a conti nuous upgrade program is in place. Among other ob jectives, this program pursues the increase of bandwidth of the instruments and the need to complement ALMA with another observatories supp orting multi-pixel arrays. This thesis work is placed within two pro jects that attemp t to reach those goals. The first is th e ALMA Band-2+3 upgrade prop osal, that attempts to merge Bands 2 and 3 in a single receiver. The second one is the development of instrumentation for the CCAT-p Telescope, to be placed next to the site of ALMA, at Cerro Chajnantor. A heterodyne receiver is composed by the feed antennas which captures the radiation concentrated by the main dishes. Depending on the structure of the receiver, an orthomode transducer (OMT) separates the polarization in two orthogonal components. Subsequently the signal is mixed with a local oscillator signal in order to down-convert the original signal. More specifically, this thesis presents the design, construction and characterization of a turnstile OMT for ALMA Band 2+3 receiver and the study and design of a LO power distribution scheme for the CCAT-p Heterodyne Array Instrument. The OMT should comply with the stringent ALMA requirements set for all passive devices. A design was conceived to solve construction issues of a previous version. The measurements show that the OMT does comply with most of them. However, a disagreement between the simulations and measurements prompted us to determine the effective conductivity of milled waveguides at 15, 77 and 290 K. In order to do so, we characterized waveguide meanders. These results improved the agreement and could used on future design efforts. The LO power distribution of CHAI requires to deliver the LO signal to an 4 × 4 array, which will serve as a basic block for larger arrays configurations. The 4 × 4 array will be assembled out of 4 rows of 1× 4 pixels. The distribution must cover the 800-820 GHz band, the imbalance between power delivered to each mixer must be lower than −3 dB and the whole distribution must fit within a footprint of 40 × 40 mm^2. We have presented two designs based on coplanar waveguides (CPW) and waveguide technology, a balanced scheme based on hybrids and an imbalanced scheme based on Wilkinson power dividers. The balanced scheme required waveguides of considerable length, generating standing waves that created a considerable imbalance in the power distribution. The second scheme is an unequal power distribution that has a theoretically better performance but requires 3:1, 2:1 and 1:1 Wilkinson dividers. The simulations of 3D model of a CPW 3:1 Wilkinson shows that the actual model does not achieve the expected performance. However, further optimization promises an improvement in performance. In both projects we have demonstrated that careful design makes possible to obtain devices whose performance surpass the current state of the art.