Petri Piironen

Measurement of the Odin telescope at 119 GHz with a hologram-type CATR

Development work of a 119 GHz compact antenna test range (CATR), based on a 2.4 m/spl times/2.0 m hologram and its application on the Odin telescope tests are described. The hologram element comprises seven parts, which are fabricated using silk-screen printing techniques. Comparison between the theoretical and the measured quiet-zone fields of the hologram CATR is made, which demonstrates the correctness of the analysis method and also the importance of high quality physical joints between the hologram parts. The CATR has been successfully used in the measurement of a 1.1-m offset reflector antenna onboard the Odin spacecraft. The measured and calculated antenna radiation patterns are in good agreement in the main beam region. The effects of the imperfections in the quiet-zone field and in the aperture field of the antenna on the measurement results are simulated.

Novel tunable waveguide backshort for millimeter and submillimeter wavelengths

A new tunable waveguide backshort with low loss and reliable performance has been designed. Based on a fixed short and dielectric phase shifter, it has a simple structure which is easy to design and fabricate. These properties make it a sound alternative for millimeter- and submillimeter-wave applications. A W-band (75-110 GHz) backshort has been designed and tested showing excellent performance with a return loss of less than 0.21 dB.

A 119 GHz planar schottky diode mixer for a space application

A planar single-ended GaAs Schottky diode mixer has been designed, built, and tested at 119 GHz. The mixer front end includes also a waveguide filter for image rejection, and a temperature compensated ring filter. Measurements at room temperature showed a conversion loss of 7 dB and a noise temperature of 900 K (SSB). At 100 K the measured noise temperature of the mixer was 500 K (SSB).

Optical distribution of microwave signals for Earth Observation satellites

Optical distribution of signals is playing a key role in ESA Earth Observation satellite SMOS (Soil Moisture and Ocean Salinity). This paper is describing a possible evolution of the optical harness in which the Local Oscillator, the calibration microwave signal and the clock reference are distributed in a single fiber thanks to Wavelength Division Multiplexing (WDM). Due to the high sensitivity of the on-board RF Front-ends, degradation effects induced by the optical link can severely affect the overall performance. Therefore, system level requirements like signal isolation or phase noise are to be taken into account. Preliminary test measurements have shown that isolation over 70dB can be obtained in the RF domain. This study is a first step towards the fully distribution of signals through optic fiber in SMOS-like missions.

Improved receiver architecture for future L-band radiometer missions

Microwave radiometer measurements are viable technique for measurement of soil moisture and ocean salinity. Therefore, there is a strong interest in new L-band remote sensing radiometers. For example, European Space Agencys SMOS (soil moisture and ocean salinity) satellite is currently under development. SMOS applies Noise Injection Radiometer subsystem for the measurement of the average brightness temperature of the scene. This paper proposes the use of reference channel control method for the future L-band radiometer missions, e.g., for potential SMOS follow-on mission. According to analysis, significant improvement in radiometric resolution (up to 40%) would be achieved compared to traditional antenna channel noise injection architecture. The proposed system is based on the use of an active cold load (ACL) as cold reference.

Cryogenic millimeter-wave ring filter for space application

A tunerless cryogenic millimeter-wave ring filter has been designed for a space application. Detuning of the center frequency caused by thermal deformations has been compensated by a novel mechanism based on the use of two materials with different temperature expansion coefficients. An improvement of 1:8 in the detuning of the center frequency, compared to an uncompensated ring filter, is reported. By applying the new design, external tuning aids can be avoided even in applications where a wide operational temperature range is of interest. Thus, the new ring filter is especially advantageous in space-borne millimeter-wave receivers.

Space Qualification of the Radioastron 22 GHz Receiver

The Radioastron space VLBI satellite, expected to be launched in 1995, will have on board four sensitive two-channel radiometers. Finland is responsible for the 22 GHz receiver. The most important properties of the receiver are sensitivity, phase stability and gain stability. To reach maximum sensitivity, a modern space qualified low noise HEMT amplifier has been designed. The measured receiver noise temperature is 140 K. For maximum phase and amplitude stabilities, temperature stabilisation and a high Q dielectric resonator oscillator design have been utilized. The measured phase stability is better than 3 o/h. The main aspects of the space qualification tests and the reliability analysis are described.

Characterisation of low-barrier Schottky diodes for millimeter wave mixer applications

This paper presents the characterization measurements and simulations performed with ACST InGaAs low-barrier Schottky diodes for millimeter wave mixing applications. While these low-barrier Schottky diodes have been successfully used for millimeter wave detector design, their performance when acting as mixers has not been tested yet. This paper shows the performance for this type of diodes in a fundamental mixing configuration with evaluation of conversion loss and noise temperature. A fundamental mixer test-jig is used as the measurement platform with low-loss E-H impedance tuners for RF and LO signal matching. In addition to the measurements, 3D HFSS and ADS circuit simulations are also performed and results are presented. Conversion loss of less than 5 dB is obtained for 0.1 mW LO power in mixer operation at 181-183 GHz.

Model of quasi-vertical planar anti-parallel Schottky diode

A model of Quasi-Vertical planar Anti-parallel Schottky Diode (QVPAPD) is developed by using electromagnetic (EM) analyses of the diode structure. The mounting structure of the diode is taken into account. The model is used in the design of a 220 GHz subharmonic mixer with the QVPAPD. A preliminary experimental result is given.

Tunerless millimeter wave ring filter for wide temperature range

Awaveguide ring filter design for the 119 GHz heterodyne receiver of the Odin satellite is reported. The relatively narrow band filter is designed to operate without external tuners although the ambient temperature can vary from 100 K to 300 K. The critical temperature related changes in the center frequency of 114.85 GHz are compensated by the mechanical design with use of suitable materials. A maximum frequency shift of 440 MHz was reduced to 80 MHz in the first prototype, with further improvements to be expected in later models.