This paper presents the newly-developed microstrip leaky-wave antennas (MLWA) with periodical loading of shorting pins. Working mechanisms of periodical loading of shorting pins on the first two operating modes in the microstrip line (MSL), i.e., fundamental EHo-mode and first higher-order Efh-mode are explicated at first. Then advanced functionalities of MLWAs under the proposed pin-loaded EHo-and Eflr-mode are explicitly exhibited. Brand-new features such as flexible selection of strip width, arbitrary-determined cut-off frequency, intrinsic dual symmetric main beams, etc., demonstrate the unique advantages of our pin-loaded technique utilized into various developments of advanced MLWAs.