July 11, 2012 by admin Комментировать »

Kuzmin S. E., Radzikhovsky V. N.

State Research Center “Iceberg”, Kiev, Ukraine Phone: (044) 4783145, E-mail: iceberq@ukrpack.net

In 3 mm wavelengths band the small-sized radiometric sensor has been developed as a base element for design of multichannel receiving array. The heterodyne circuit with input mixer has been chosen for sensor design. The block diagram of the sensor (Fig. 1) includes the following: the mixer operating in a double-sideband (DSB) mode, intermediate frequency amplifier (IFA), square-law detector and low frequency amplifier (LFA). The conical horn is used at sensor’s input as a feed of the main antenna.

The circuit of the sensor does not contain local oscillator (LO), because all sensors in array must be driven from common LO.

The subharmonic type of a mixer is chosen in order to ease the problem of producing sufficient LO power and distributing this power to the sensors of an array. At LO frequency 45 GHz and intermediate frequencies 0.1 2.5 GHz the frequencies band of the input signals is 87.5 92.5 GHz.

The mixer circuit is shown in Fig. 2. The circuit uses beamlead antiparallel-pair Shottky diodes of UAA101G-3 type, (SPA "Saturn"). The diodes have capacitance C(0) = 30 fF and resistance Rs = 6 Ohm. A good match between the diodes in the pair is necessary to eliminate mixing on odd LO harmonics.

The first LPF after diodes has 50 GHz cut frequency, allowing LO power to feed the diodes and to reject the input signal. The distance between the filter and the diodes is chosen for the optimum matching of diodes with input signals circuit. LO leakage into the IF amplifier is suppressed with quarter-wave opencircuit stub to 45 GHz (second LPF), which is at the same time the matching LC network for IF signal. The microstrip circuit of the mixer was manufactured using 0,127 mm Duroid.

The mixer has SSB conversion loss of 7-10 dB and required LO power ~ 12 mW.

IFA after mixer contains three amplifying stages. As the first stage the broadband amplifier microcircuit of MGA-71543 type (Hewlett Packard) with noise factor 0.8 dB is used. The second and third stages are made using INA-03184 microcircuits with noise factor 2.6 dBB. The total gain factor of IFA is 55 dB in 0.1-

2.5 GHz frequency band.

The detector is realized on zero bias Shottky diode of HSMS-2850 type (Hewlett Packard). Output LFA is designed on base of OP27GS microcircuit. Temperature sensitivity of the sensor does not exceed 0.05 K/Hz1/2.

Appearance of the sensor is shown in Fig. 3. This construction is convenient for design of an array in form of two rows of receiver sensors, which are arranged in a focal plane of quasioptical antenna.

Thus, in 3 mm waves band the small-sized radiometric sensor for receiver array is developed. The sensor can find application for design of the passive imaging systems in a short-wave part of a millimeter waves band.

Источник: Материалы Международной Крымской конференции «СВЧ-техника и телекоммуникационные технологии», 2003г.

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