Study On High Performance Wideband Wide Beamwidth Planar Endfire Circularly Polarized Antennas

Endfire circularly polarized(CP)antennas have a wide usage in many wireless applications,such as the global navigation satellite system,the radio frequency identification(RFID)systems,and etc.For CP antennas,the 3dB axial ratio(AR)beamwidth is an important criterion.CP antennas with wide 3dB-AR beamwidth,(i.e.,half spherical,or even broader beams large than 180°),are extremely desired to receive wireless signals from a wide range of directions.It is a challenging task to design a planar,non-turnstile CP antenna with a wide 3dB-AR beamwidth and a high front-to-back ratio while maintaining a low profile.In this thesis,design approach to a semicircular magnetic dipole and a V-shape loop combined antenna is developed.The main content of this thesis is organized as follows:1.Design approach to a novel non-turnstile planar endfire circularly polarized(CP)antenna with broadened beamwidth and enhanced front-to-back ratio is presented.At first,an original combined antenna configuration of a semicircular magnetic dipole and a V-shape loop is deduced based on the equivalent sources model.Furthermore,the normalized far field and operating principle are analyzed.2.The basic parameters of the antenna are obtained by the above analysis method.Using the numerical simulation software,the antenna model with the best performance is optimized and then the antenna sample is made.3.The prototype antennas are fabricated and measured by Agilent's 8720 ET vector network analyzer and Satimo Starlab near field antenna measurement systems.The good agreement between the simulated and measured results convinces the correctness of the theoretical design approach.Especially,the measured impedance bandwidth for |S11| <-10 dB covers a frequency range from 2.25 to 2.50 GHz(10.5% in fraction),and the axial ratio(AR)bandwidth of less than 3dB is from 2.30 to 2.57 GHz(11.1% in fraction).The measured 3-dB AR beamwidths of the proposed antenna are equal to 180° and 115° in the elevational and azimuthal plane at 2.35 GHz.In addition,the measured in-band average front-to-back ratio reaches up to 13.7dB.