Circularly polarized microstrip line antenna

A circularly polarized microstrip line antenna for receiving or transmitting a signal of a particular wavelength comprising:

• a dielectric substrate having a ground plate provided on one surface thereof and having a microstrip line formed on another surface thereof;
• wherein said microstrip line has an omega shaped fundamental portion composed of a loop portion and a pair of straight portions;
• and wherein said loop portion is a regular polygon having a length .lambda.g equal to said particular wavelength;
• and wherein said loop portion is symmetrical about an axis which is on one of said surfaces of said substrate and is at right angles to said straight portions of said microstrip line;
• and wherein an angle .alpha. is defined by one of said pair of straight portions and a side of the polygon connected to said straight portion, said angle .alpha. being obtained by the equation:
• ##EQU5## where .theta..sub.m is the direction of a main beam of said antenna and .eta. is an effective wavelength reduction rate thereof;
• and wherein a total length of said pair of straight portions d is obtained by the equation:
• d=.lambda.g/(1-.eta. cos .theta..sub.m).