A low profile circularly polarized (CP) antenna with reconfigurable polarization is designed and presented, which can radiate omnidirectional patterns that can be switched between left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP). A pair of arc-shaped complementary dipoles is acted as reconfigurable elements by bridging four pin diodes at the dipole arced arms. A meander phase shift line is employed to connected the arc dipole arms and plate cavity to adjust the phase relationship of two sources. The proposed antenna exhibits the omnidirectional radiation pattern by combining six identical elements placed in a circular array configuration. 24 p-in diodes are exploited to six elements, by manipulating the dc bias voltage across the diodes, the polarization state of the antenna can be switched. The patterns of the antenna are similar to that of a dipole, but its size is only about Φ0.87 × 0.029λ 0 at 5.8 GHz. The overlapped bandwidth of measured 3-dB axial ratio (AR) and 10-dB return loss is 5.724-5.87 and 5.738-5.91 GHz for two polarization states, which are right on the target of ISM band. It can be well adapted to medical diagnosis systems.
A reconfigurable, planar, and end-fire circularly polarized (CP) antenna with wide beamwidth is presented, which exhibits the bidirectional radiation with the same sense by combining two pairs of identical CP elements placed in a back-to-back configuration. The design of the element includes a meandering phase delay line, which connects a printed electric dipole and a quarter-wavelength shorted microstrip patch. Then, eight p-in diodes are employed in the two dipoles arms to realize either left-handed CP (LHCP) or right-handed CP (RHCP) by manipulating the DC bias voltage across p-in. The prototype is designed to operate at a center frequency of 5.8 GHz with a size of 0.61 × 0.50 × 0.029 (λ 0 3), where λ 0 is the wavelength of the center frequency. Also, its end-fire beam is in parallel with its plane. Experimental results show that the overlapped bandwidth for 10-dB return loss and the 3-dB axial ratio (AR) of the bidirectional end-fire antenna is from 5.72 to 5.89 GHz for the two CP states. The half-power beamwidth (HPBW) in the horizontal and vertical plane are 95 /115 at the 5.8 GHz.
This article proposes a dual‐element antenna working in the 2.4/5‐GHz WLAN bands with high isolation. The antenna element is a coupled‐fed structure, which is formed by a driven monopole and a shorting branch. The decoupling structure disposed between the elements is a hybrid structure, which includes a protruded ground for the 2.4‐GHz WLAN band and a narrow slot etched on the ground plane for the 5‐GHz WLAN band. Moreover, to reduce the dimension of the protruded ground, two 8.2‐nH lumped inductors are embedded in the branches. The measured −10 dB reflection coefficient bandwidths are in the range of 2400‐2497 MHz and 5150‐5940 MHz. The measured transmission coefficient indicates that a good isolation higher than 20 dB over the two bands is obtained.
In this paper, a broadband circular polarized (CP) reflectarray using a linear polarized (LP) feed is proposed. First, a single-layer broadband dual-line polarized reflectarray unit is designed. This unit converts the LP incident waves into CP reflected waves by providing a phase difference of 90 in the orthogonal direction components of the incident waves. Based on the units proposed, a 109-element reflectarray was designed and fabricated. The measured results indicate that the reflectarray has a 1-dB gain bandwidth of 9.15 to 12.79 GHz, or equivalent to a bandwidth of 33.2%. Its 3-dB axial ratio (AR) bandwidth for CP operation is 37% (9.06-13.19 GHz). The reflectarray antenna has a peak gain of 23.53 dBi and its highest aperture efficiency is 64.1% achieved at 10 GHz.
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