Derivation of the system equation for null-balanced total-power radiometer system NCS1

Abstract

A system equation of a recently developed null-balanced, tulal-pcnver radknnclcr system h rigorously derived. Delivered noise ptpwer and temperature is related to available power (temperature) through an extcnskin uf (he mismatch factor to broadband systems. The available power ratio a,, the available gain G^ and the delivered power ratio (efficictjcy) jji are defined. Properties of idealized, but in principle realizable components such as an infinitely directive isolator and a lossless matched wavcguide-below-cutoff attenuator are used. A cascading technique is repeatedly applied to the fundamental noise equation. Mathematically modeling the experimental pmcedure of seijucntially attaching the two noise standards and the unknown source to the system input, we obtain the system of three equations that can be solved for the noise temperature of the unknown noise source. K^ ifMds: broadband; calibratioo; noise power, noise temperature; nullbajanccd; ^tem equation; total power radiometer section. Accepted: October 12, J993

Development of radiometer operating between 50 MHz and 26.5 GHz using gain-stabilized LNA

“…The noise power values obtained at the output of the radiometer as P a , P s , and P x when ambient, standard, and unknown noise sources are connected, respectively, are used to calculate the corresponding noise temperature of an unknown noise source by the well-known relationship P n = kT n B where n is a, s, or x. The actual noise temperature of an unknown noise source is calculated by [4]:…”

“…For traceability of noise temperature, the characterization of the noise sources is performed using radiometers like total power radiometers [3]. The noise temperature equation for the total power radiometer in [4] is valid in the case of stable radiometer gain during measurements. The low-noise amplifier (LNA) is the most important component that determines the radiometer gain stability, since it is the amplifier in which microwave noise is amplified and filtered as a first step in the radiometer [5,6].…”

A null-balanced total-power radiometer system NCS1

“…Following [ 3 ] and [ 4 ], the available noise temperature T x of the DUT can be calculated by comparing it to the available noise temperatures T s and T a of the two standards, according to where M s /M x is the mismatch correction at the input reference plane, and A a , A s and A x are the attenuator settings (in dB) needed for balance.…”

“…Each of the three sources is sequentially attached to the radiometer input port, and the noise power is adjusted by the attenuator so that the receiver balances in all three cases. Following [3] and [4], the available noise temperature Ti of the DUT can be calculated by comparing it to the available noise temperatures Tj and T, of the two standards, according to where M,/M, is the mismatch correction at the input reference plane, and ^j, A^, and A, are the attenuator settings (in dB) needed for balance.…”

“…3.3.1 The available noise temperature T, of the DUT is calculated from the system equation [3] where, as before, Ts and T^ are the available noise temperatures of the two standards, MJMi is the mismatch correction at the input reference plane, and At, Ai, and A^ are the attenuator settings needed for balance. Furthermore, T|SW./T|SW, is the input path asymmetry correction, a consequence of slightly different efficiencies of the two sides of the input switch.…”