Microwave characteristics of the Schottky-barrier diode power sensor

A theory of the detection law of the Schottky-barrier diode (SBD) detector is developed. The detection law is a function of frequency, temperature, DC bias and diode parameters such as n (ideality factor) and Is (saturation current). The theory is in good agreement with the experimental results. In general, the detection law can only be solved numerically. At low power levels, however, the detection law can be expressed by a closed-form formula of which, for a fractional error, the dynamic range is 12 dB wider than the square-law range. In deriving the detection law, the expression for the I-V characteristic of an SBD, I = Is exp(ev/nKT[1 - exp(-ev/kT)],is adopted rather than the expression I = Is[exp(ev/nKT)-1] even though the latter is more often used in the literature. Evidence is given to show that the former more accurately describes our Rh-Si Schottky-barrier diode. The effect on the detection law of the second harmonic of the power source is calculated and measured. For a particular diode, 1% 2nd-harmonic power caused more than 10% error when the input power was greater than ¿¿ l0dBm. The effect of a third harmonic is calculated, and is shown to be less serious at low power levels.