Study On Wide Beamwidth Planar Endfire Circularly Polarized Antennas

It has been a long history since circularly polarized(CP)antennas are studied.CP antennas are widely used in electronic reconnaissance and jamming,polarization diversity of radar,satellite navigation,communication systems and Radio Frequency Identification(RFID)system due to their distinguished CP waves.For CP antennas,the 3dB axial ratio(AR)beamwidth is an important performance criterion.CP antennas with wide 3dB-AR beamwidth,i.e.,half spherical,or even broader beams large than 180°,are extremely desired to receive the wireless signals from a wide range of directions.In order to obtain a wide beamwidth,early researches commonly focus on some relatively non-planar complicated structures or turnstile array with feeding network consisted of power dividers and directional couplers.Most of the reported antennas exhibit broadside radiation patterns or endfire patterns perpendicular to the major plane.Therefore,it is a challenging task to design a planar,non-turnstile CP antenna with a wide 3dB-AR beamwidth and a main beam in parallel with its plane while maintaining a low profile.In this thesis,design approach of a symmetric V-shape open loop combined antenna is developed.The main content of this thesis is organized as follows:1.A novel planar CP antenna with an endfire wide beam in parallel with the antenna's plane is proposed in this thesis.At first,ways to obtain a directional beam are analyzed and then a fundamental CP antenna designing method is explored.Additionally,an original combined antenna configuration of planar magnetic dipole and V-shape open loop is deduced based on the equivalent sources model.Furthermore,the normalized far field and operating principle are analyzed.2.An axial ratio design formula with two design degrees of freedom is deduced and studied accordingly.The formula is numerically validated by employing Ansoft HFSS.Two prototype antennas are respectively designed at the 2.4 GHz and the 5.8GHz band.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,for the 2.4GHz band prototype,the reflection coefficient bandwidth lower than-10 dB is in 2.27-2.75 GHz.A 3dB-AR beamwidth is achieved in an extremely wide angular region over 220° within the principal elevational plane over a frequency range of 2.41-2.51 GHz.The average gain is 1.5dBic.In addition,its endfire beam is in parallel with its plane and it is also promisingly applied in RFID system and other communication systems.