Zhenxin Hu

Reconfigurable Leaky-Wave Antenna Based on Periodic Water Grating

A reconfigurable leaky-wave antenna using periodic water grating on the top of a grounded glass slab is presented in this letter. A probe-fed unidirectional surface-wave launcher is designed to feed the antenna. Two prototypes of the proposed antenna are fabricated and tested to demonstrate its radiation performance and tuning capability. Measured results of the first static antenna show that a maximum gain of 16 dB, a wide impedance bandwidth (|S11|<;-10 dB) from 4.1 to 6.6 GHz (46.7%), and a large beam-scanning range over the impedance band from the back-fire to nearly broadside direction are obtained. Measured results of the second dynamic antenna show that the beam-pointing angle can be tuned from -32° to 18 ° at 5.5 GHz, while the return loss maintains better than 10 dB.

Low-Profile Top-Hat Monopole Yagi Antenna for End-Fire Radiation

A top-hat monopole Yagi antenna is presented to produce an end-fire radiation beam. The antenna has an extremely low profile and wide operating bandwidth. It consists of a folded top-hat monopole as the driven element and four short-circuited top-hat monopoles as parasitic elements. A broad bandwidth can be achieved by adjusting the different resonances introduced by the driven and parasitic elements. A prototype operating at the UHF band (f0 = 550 MHz) is fabricated and tested. Measured results show that a fractional bandwidth (|S11| <; -10 dB) of 20.5% is obtained while the antenna height is only λ0/28 at the center frequency.

Low-Profile Log-Periodic Monopole Array

This paper presents a low-profile log-periodic monopole array antenna with end-fire radiation and vertical polarization. It consists of 15 monopole elements and a conductor-backed coplanar strip line as the feeding line. The monopoles are of the same height but loaded with top hats of different sizes to achieve the required resonant frequencies. A wideband transition from coaxial line to conductor-backed coplanar strip line is designed for the antenna feed. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 1.5 to 6.8 GHz (4.53:1) for VSWR <;2.3 and a gain better than 4.5 dBi over the same operating frequency band are obtained while the antenna has a very low profile of only 0.047 λL (λL is the free-space wavelength at the lowest operating frequency).

A low-profile frequency and polarization reconfigurable circularly polarized water antenna for satellite navigation

A low-profile circularly polarized (CP) antenna with frequency and polarization reconfigurability is presented in this paper, which is a rectangular water patch mounted on a large ground plane with a thin air gap, and etched with a slot on the broad side to achieve circular polarization. Two top-hat probes are used to feed the antenna at its corner, generating both LHCP and RHCP. By varying the height of the water patch, the 3-dB axial ratio (AR) band can be tuned, covering 0.85 GHz to 1.45 GHz (52%), with good impedance match (|S11| <; -10 dB) over all AR bands. The proposed antenna has a very low profile of only 0.06λ0 and high transparency, and should be useful for satellite navigation.

A Yagi monopole antenna made of pure water

A pure-water Yagi monopole operating at 1.62 GHz is presented in this paper, which comprises a probe-fed water monopole as the driven element and a water cylinder as the parasitic element. Both the driven and parasitic elements are isolated from the ground plane of infinite size using a thin layer of Teflon. By varying the diameter and radius of the parasitic element and the spacing between the two water cylinders, a unidirectional far field pattern can be obtained. Simulation results show that a maximum gain of 9.3 dB and a fractional bandwidth of 24.7% are achieved. The operating frequency can be tuned by changing the heights of the cylinders, covering a wide range from 1.22 GHz to 2.08 GHz.

Excitation of electromagnetic waves in a thin water layer using a coaxial probe

In this paper, two transitions between a coaxial line and a thin water layer are presented: one with symmetric structure and the other for a unidirectional wave propagation. In order to have a smooth transition and to achieve a wide bandwidth, an inverted glass cone is employed in the axially symmetric transition between a coaxial probe and a thin water layer. For the unidirectional design, a parabolic cavity made of a thin glass layer is added at one side of the water layer to reflect the electromagnetic waves to the desired direction. Simulation results show that omnidirectional and unidirectional propagation of electromagnetic waves can be successfully excited in the thin water layer through these two transitions respectively. The 10 dB bandwidths from 454 MHz to 914 MHz (67.3%) for the symmetric transition and from 463 MHz to 915 MHz (65.6%) for the unidirectional transition are obtained.

Low-Profile Helical Quasi-Yagi Antenna Array With Multibeams at the Endfire Direction

This letter presents a novel helical quasi-Yagi antenna array with low profile and multibeams at the endfire direction. First, a planar normal-mode helical quasi-Yagi antenna with top-hat loading for low profile is designed to achieve endfire radiation. It is mounted on a conducting plane, consisting of a top-loaded folded helix as the driven element and three top-loaded unfolded helices as parasitic elements. A broadband can be achieved by controlling the resonance difference between the driven and parasitic elements. Second, a microstrip beamforming network based on Butler matrix is designed to feed a 1 × 4 helical quasi-Yagi array. The proposed antenna array is fabricated and tested. Measured results show that three endfire beams at ϕ = 90°, (90 ± 47)° are obtained while the antenna has a very low profile of 0.054λ at its center frequency, showing that the antenna may be useful in many airborne applications such as unmanned aerial vehicles.

A low-profile top-loaded folded helical antenna

This paper presents a low-profile folded helical antenna with a top hat loading. It consists of two identical normal mode helices mounted on a large ground plane and a square conducting plate on the top of them to achieve a low profile. One helix is fed by a coaxial probe while the other one is connected to the ground, forming a folding structure for high resonant resistance. Parametric study is conducted to show the effect of the size of the top hat and the helix on the antennas resonance character. A prototype is fabricated and tested, measured results show that an impedance bandwidth of 8% is achieved with an antenna height of 0.08λ0 (λ0 is the free-space wavelength at its center operating frequency).

A pattern reconfigurable low-profile Yagi monopole antenna with 360° beam-scanning ability

A pattern reconfigurable Yagi monopole antenna with beam-scanning ability in the horizontal plane is presented in this paper. It employs a symmetrical folded top-hat monopole in the center as driven element and six top-hat monopoles around it in a circle as parasitic elements. Two PIN diodes are used to make each parasitic element connected to or isolated with the ground plane. Beam scanning in the horizontal plane over a 360° range can be achieved by using DC bias voltages switching these PIN diodes. A prototype operating at ƒ0 = 2.4 GHz is fabricated and measured. The experimental results show that a fractional bandwidth of 10.8% is obtained with an antenna height of only 0.048 λ0 (λ0 is the free-space wavelength at the center operating frequency).

A tapered long slot antenna of conical radiation beam based on substrate integrated waveguide

In this paper, a long slot antenna of conical radiation beam is presented, which is based on the substrate integrated waveguide (SIW). The antenna consists of a pair of tapered long slots etched out of both the top and bottom broad walls of a substrate integrated waveguide to produce the conical radiation beam. Experiment results of the fabricated antenna show that the realized beam-pointing angle is 55.2° and its maximum realized gain is 12 dB with a ripple of 3.5 dB in the E-plane at the operating frequency of 15 GHz. The 10 dB return loss bandwidth is 29.3%, from 13.6 GHz to 18 GHz.