7x8 element MMIC array at 26-30 GHz for radio astronomy applications (Netherlands Foundation for Research in Astronomy, 1999). 
7x8 ELEMENT MMIC ARRAY AT 26-30 GHZ FOR RADIO ASTRONOMY APPLICATIONS
V.B.Khaikin, E.K.Majorova, Yu.N.Parijskij
The Special Astrophysical Observatory of Russian Academy of Sciences Karachai-Cherkessia, N.Arkhyz, 357147, Russia E-mail: vkh@ratan.sao.ru
M.D.Parnes, R.G.Shifman, V.A.Dobrov, V.A.Volkov, V.D.Korolkov and S.D.Uman
"Svetlana", "Rezonance", "Ascor", 194156, Engels pr. 27, St.Petersburg, 194156, Russia.
Multi-element MMIC array architecture for RATAN-600 radio telescope is offered. The proposed solution can be used for other wide-angle reflector radio telescopes with offset illumination as well. The description and characteristics of MMIC array prototype are given. Antenna characteristics of RATAN-600 in multi-beam operational mode and some radio astronomical applications are presented.
1. Introduction
Focal receiver arrays seem to be an unavoidable solution for the existing and the next generation reflector radio telescopes where high sensitive (or high speed) mapping is the main goal. The significant progress in MMIC array technologies gives us a chance to fully realize an important RATAN-600 radio telescope advantage - the wide aberrationless focal zone. A multi-element feed array if placed along the focal plane may significantly increase RATAN-600 sensitivity and the field of view.
2.Multi-element “terraced” MMIC array architecture
The main difficulty of construction of multi-element feed arrays for a radio telescope consists in necessity of their maximum dense packing. So it is a problem to fully sample all the information in the focal plane and fully illuminate the reflector. The main technical problem in MM range is how to place a receiver near an antenna element of an active focal array. The traditional solution is the "module architecture" where a compact receiver is placed behind the waveguide or a dipole microstrip radiator. One of the practical examples of 91 element MMIC array uses module-honey-comb architecture. In SKA bow-tie array elements are printed on PCB's and vertically oriented[7], so one board includes 64 or more radiators and receivers lying in one plane. We propose multi-level "terraced" architecture with horizontally oriented patch radiators and receivers. This construction is the most suitable for a radio telescope with offset illumination. In fact, together with technological advantages it gives us the best beam efficiency in comparison with a flat array.
The «terraced» three-dimensional construction of 7x8 element MMIC focal array in MM band is shown in Fig.1 a,b.
a
b
c
Fig.1."Terraced" 7x8 element MMIC array architecture (a, b), MMIC amplifier LMA422 of Litton SSD(c).
3. MMIC array applications for a
radio telescope
The described array
technology can be used at RATAN-600 for different radio astronomy applications.
It can give us new possibilities to study CMBA at sub-degree scales with high
integrated sensitivity in a wide field of view [12]. The search of Synaev?Zeldovich
effect at RATAN-600 is among other possible applications. Using focal arrays we
can study quick-variable cosmic objects like pulsars or Sun as well.
Another exciting possible field of application for multi-element “terraced” MMIC arrays at radio telescopes is holographic antenna measurements. So 8x8 element MMIC array can significantly (in 64 times) decrease time necessary to restore surface error map on strong cosmic or beacon satellite source that gives us a chance to correct surface errors practically in quasi-real time. It may give a powerful impulse to the development of an active and adaptive optics technique at radio telescopes including wave front correction.
We believe that described front end technology may be used together with correlator for self-correction of wide-angle radio telescope with “off set” illumination. It was shown in [13] that to capture 80% of the power incedent on a reflector with r.m.s. surface accuracy l/8 and M=D/5-D/20 (D is diameter of an aperture, M is the number of error coherence patches across the aperture) a total number of focal array elements may exceed 20-2000 so an inexpensive array technology with a very big element number is needed. It may be shown that “terraced” array do not lead to the loss of phase information or fall of S/N ratio for this type tasks.
We believe the described “terraced” MMIC array architecture may be applied for RATAN-600 or other wide-angle reflector radio telescope with offset illumination at least up to 40 GHz. Construction shown in Fig 1 a may be used at a radio telescope with symmetrical illumination but with longer wavelengths. In some cases an off-axis illumination may be made artificially.