Planar, directive, X band antennas were constructed with wide microstrips printed on phainolic paper substrates. Every microstrip functions as a cavity with loses due to radiation from the slots formed between their wide edjes and the earth plane. A number of approximations, mentioned below, form the theory of their opperation. A way is given to cancel out the effect of the fringe capacitance of the microstrip edges on the tunning of the cavity, and a simple way to feed two radiating strips in tandem.