Single-feed circularly polarized microstrip ring antenna and arrays

An analysis is presented for a microstrip-feed proximity-coupled ring anten na and a four-element array. Interactions between the Embedded microstrip f eed and the radiating element(s) are rigorously included. Results demonstra te that circular polarization of both senses can be achieved with a ring an tenna with proper design of two inner stubs located at angles of +/-45 degr ees with respect to the feedline, Theory and experiment demonstrate an axia l ratio 3-dB bandwidth of 1% and the voltage standing wave ratio (VSWR) <2 bandwidth of 6.1%, The axial ratio bandwidth is typical for a microstrip an tenna with perturbations, while the VSWR bandwidth is larger than for the c ircular or rectangular patch with perturbations. A mutual coupling study be tween two elements shows that the axial ratio is less than 2 dB for interel ement spacing greater than 0.55<lambda>(eff), while the VSWR <2 for all spa cings considered. A comparison between theory and experiment is provided fo r a 2 x 2 element array. The benefits of sequentially rotating the antenna elements in an array environment are presented, The axial ratio and VSWR ba ndwidths are both increased to 6.1% and 18% for a four-element array. A sin gle-element antenna with two orthogonal feeds to provide both senses of pol arization is demonstrated. The ring antenna is small (D/<lambda>(0) = 0.325 ), the substrate thickness is thin (H/lambda (0) similar to 0.035), and the microstrip feed produces a completely planar antenna system, which is comp atible with microwave and millimeter integrated circuits (MICs), and monoli thic microwave integrated circuits (MMICs).