In this article, a modular designed intermodulation (IM) modulator based on coherent nonlinearity superposition is demonstrated. A coherent combination network for two nonlinear sources (diodes) is composed, excited by a set of two-tone carriers, and the IM products generated from two diodes are inherently coherent. The designed IM phase and magnitude are synthesized by using two IM signals with different magnitudes. The modulator is achieved by modular design, and the manufacture is simplified by using low IM laminate and normal FR-4 substrate to the section with different IM sensitive levels. The work proves a solution to generate an IM phase and magnitude tunable reference for IM measurement, which also proves that IM can be used to carry some information.

Compact Intermodulation Modulator for Phase Reference in Passive Intermodulation Measurements

Accurate measurement of Radio Frequency (RF) component’s passive intermodulation (PIM) and systematic evaluation of PIM’s effect on mobile communication require flexible PIM generator. This work presents a wide-band high dynamic-range PIM generator using a fabric-over-foam (also known as RF Interference Shielding Gasket) as superstrate of low-PIM microstrip line (MS-line). An air gap of 1 mm introduced between the foam and the MS-line to ensure long-term repeatability by avoiding the nonlinearity that can be generated by the metal-to-metal contact. To make the PIM generator adjustable, the foam moved transversely over the MS-line. The size of the gasket selected in such a way that it slightly changes the S-parameters of the MS-line. Due to the variation of the exposure area of the foam (which is an electromagnetic magnetic material) to the electromagnetic (EM) field generated by the MS-line; the PIM level of the MS-line changes with the foam’s location. The minimum PIM level of the proposed generator determined by the PIM level of the MS-line, which is no more than - 125 d B m @ 2 × 43 d B m . However, the maximum PIM level can be as high as - 48 d B m @ 2 × 43 d B m , achieved by placing a gasket piece on the top of the MS-line. The proposed generator verified from 700 M H z to 2.7 G H z and all of the measurement results show its feasibility. Moreover, presented PIM generator can be used a single-port or two-port calibration device.

Wide-band high dynamic range variable passive intermodulation generator using fabric-over-foam gasket

A broadband intermodulation (IM) tuner using reconfigurable nonlinearity to generate tunable IM magnitude and phase reference is proposed and demonstrated in this work. The IM-tuning mechanism is based on changing the physical positions of nonlinear source in the cavity transmission field line. In this design, the high-density electromagnetic (EM) field is optimized to be focused around the center of the transmission line; by regulating the position of nonlinear reactor (NR) in this EM field, the IM phase and magnitude can all be adjusted. By tolerance design principle, the port reflection of the transmission line can always keep stable although in different NR positions. The experiment proves the IM tuning can reach more than 65 dB in magnitude and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> in phase from 700 to 2700 MHz, while the minimal IM level is below −112 dBm at 2 dBm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times43$ </tex-math></inline-formula> dBm and the finest IM magnitude and phase resolution reach 0.1 dB and 1°, respectively. The tunable IM reference can serve for the IM measurement on passive devices and also work as an IM calibrator and mitigator for IM test and suppression in whole S band. 

Broadband Mechanical Intermodulation Tuner Using Reconfigurable Distributed Nonlinearity

This paper presents an approximate method that allows the calculation of the maximum measurable gain (MMG) in an anechoic chamber. This method is realized by using a low passive intermodulation (PIM) medium-gain directional antenna. By reducing the distance between the antenna and the wall of the chamber to reduce path loss, the purpose of replacing a high-gain antenna with a medium-gain antenna is achieved. The specific relationship between distance and equivalent gain is given in this paper. The measurement interval is determined by the 3 dB beamwidth of the measurement antenna to scan the whole chamber. A set of corresponding data for the residual PIM level and the MMG of the chamber can be obtained by the method of measurement outlined herein. The feasibility of this method was verified by measurements in two PIM measurement chambers.

A Method for Measuring the Maximum Measurable Gain of a Passive Intermodulation Chamber

An intermodulation (IM) generator based on substrate integrated waveguide (SIW) is demonstrated. This generator has maximal 80 dB dynamic range with a size that is smaller than 65 mm × 40 mm × 1.5 mm. A biased Schottky diode is mounted onto the slotted plane of SIW and it consists of a nonlinear dipole to radiate nonlinear signal to the carrier domain and serve as reference signal. A polarized slot helps focus the linear carrier wave onto the diode and construct a bias-controlled IM distortion. The experiment proves that this device can generate the IM3 reference ranges from -112 to -32 dBm at 2 × 43 dBm, while its minimum step can reach lesser than 0.5 dB. This proposed device can serve as tunable IM standards in PIM test and calibrate the commercial PIM tester.

Anfeng Huang

Papers

Coplanar Intermodulation Reference Generator using Substrate Integrated Waveguide with Integrated Artificial Nonlinear Dipole