Radiation from microstrip circuits: An introduction

Abstract

Microstrips are open structures, that tend to radiate as the frequency of the signal increases within the microwave range. Radiation becomes significant in the vicinity of discontinuities, particularly when parts of thestructure resonate. This situation is encountered in the design of filters, which often are arrays of radiating dipoles. When circuits are placed within metal enclosures, the radiated waves are reflected on the walls, and produce interference.The mechanism of radiation is linked to the excitation of three kinds of waves: radiated waves, leaky waves, and surface waves. The latter remain trapped within the dielectric substrate and propagate with little attenuation (i.e., optical fibers), producing spurious coupling and diffraction.An analysis technique originally developed for patch antennas provides a means to rigorously analyze the radiation from unenclosed microstrip circuits. It is based on a mixed potential integral equation formulation (MPIE), making use of Green's functions provided by Sommerfeld integrals, for which an exact evaluation technique was developed. The currents flowing on the circuits are expanded over a set of subsectional basis functions, and their intensities are determined by a method of moments. This approach provides both the circuit parameters (impedance or scattering matrices), and its radiation characteristics (antenna pattern). It allows one to determine the effect produced by a radiating element on another one, even when the two are not closely located with respect to one another.

Design and Validation of Microstrip Gap Waveguides and Their Transitions to Rectangular Waveguide, for Millimeter-Wave Applications

“…We can conclude that the wider the structure is, the more critical is the non-contact effect. Moreover, it is very probable 1 Operating bandwidth is defined as the frequency band where return loss is higher than 10 dB and dissipation loss is better than the specified level as "worst value" on this table. that the presence of discontinuities combined with the noncontact between pins and PCB at certain points is the main cause for the performance degradations. It would be possible to improve the measured results by employing foams that can fill the gap everywhere to ensure uniform contact.…”

“…for high frequency applications. However, they experience high conductive and dielectric losses, radiation leakage and presence of surface waves [1]. The losses become especially critical when designing microstrip feed networks [2].…”

Radiated emissions and immunity of microstrip transmission lines :

“…If we use the approximations in eqs ( 16) through ( 19) and retain only If we substitute eqs (20) and (21) into eq (13) , we can perform the 9 and 4> integrations analytically with the following result: The result in eq (23) agrees with the power radiated by a vertical half loop of area Lh carrying a constant current I_ over a perfectly conducting plane in free space [16].…”

“…The field radiated by an infinitesimal horizontal dipole Idx' can be written in terms of scalar and vector potentials [13] or an electric Hertz vector [8].…”

“…Generally the double integration in eq (13) needs to be performed numerically, but in the following section we perform the integration analytically for the low-frequency limit.…”