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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. [ABSTRACT FROM AUTHOR]

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‐i‐n 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 × 0.029λ0 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. [ABSTRACT FROM AUTHOR]

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‐i‐n 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‐i‐n. The prototype is designed to operate at a center frequency of 5.8 GHz with a size of 0.61 × 0.50 × 0.029 (λ03), where λ0 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. [ABSTRACT FROM AUTHOR]

A dual‐mode patch antenna with pattern diversity that is beam‐tilted in a specific direction is presented. By placing a rectangular metal cavity below the circular patch and simultaneously shorting one end of the patch, the antenna produces tilted beams for dual‐mode radiation patterns. One pattern is excited using a proximity‐fed L‐shaped probe that generates a beam with a tilt angle of 25° from the broadside direction. The second pattern is excited using a coplanar waveguide (CPW)‐based feeding network that generates two beams with a tilt angle of θmax = ±45° in the directions of ϕmax = 70° and − 70°. The tilt angle can be varied by adjusting the metal cavity's length. A prototype antenna for operation at 2.38 GHz was fabricated and measured. The results indicate that the overlapped bandwidth (|S11| < −10 dB) for the two patterns is 330 MHz (2.22‐2.55 GHz). The measured peak gains for the two patterns are 6.74‐6.94 dBi and 5.82‐6.74 dBi, respectively. The isolation between the two ports is 18 dB. [ABSTRACT FROM AUTHOR]