Understanding the coupling mechanism between SQUID (superconducting quantum interference device) loop and resonator in high‐frequency SQUIDs is essential for the application of these devices in sensitive magnetometers or controllable microwave devices. We have investigated, therefore, two kinds of planar microstrip tank circuit resonators: (1) S‐shaped &lgr;/2‐resonators with direct or indirect coupling to the SQUID loop with optional flux‐focussing pads and (2) conventional rf‐washer‐SQUID structures for which we have found resonant modes of the washer providing a coupling to the SQUID loop. A lumped element representation of SQUID loop and resonator is presented in order to describe the effective SQUID‐resonator coupling in case of direct or indirect coupling. According to this approach, the square of the effective coupling constantkin both cases is equal to the ratio of the magnetic energy stored in the SQUID loop to that stored in the resonator. For the indirect coupled S‐shaped &lgr;/2‐resonators,kcan be described in terms of a geometry‐defined mutual inductance. The predictions of the lumped element description are compared with simulations using a standard full‐wave analysis computer program in order to quantify the effect of the different layouts on microwave current distribution and onk. A method for the determination ofkby simulation is described, leading to useful design rules for the optimization of high‐frequency SQUIDs. The simulation results will also be compared with experimental data. ©1995 American Institute of Physics.