A novel printed crossed dipole with broad axial ratio (AR) bandwidth is proposed. The proposed dipole consists of two dipoles crossed through a 90°phase delay line, which produces one minimum AR point due to the sequentially rotated configuration and four parasitic loops, which generate one additional minimum AR point. By combining these two minimum AR points, the proposed dipole achieves a broadband circularly polarized (CP) performance. The proposed antenna has not only a broad 3 dB AR bandwidth of 28.6% (0.75 GHz, 2.25-3.0 GHz) with respect to the CP center frequency 2.625 GHz, but also a broad impedance bandwidth for a voltage standing wave ratio (VSWR) ≤2 of 38.2% (0.93 GHz, 1.97-2.9 GHz) centered at 2.435 GHz and a peak CP gain of 8.34 dBic. Its arrays of 1 t 2 and 2 t 2 arrangement yield 3 dB AR bandwidths of 50.7% (1.36 GHz, 2-3.36 GHz) with respect to the CP center frequency, 2.68 GHz, and 56.4% (1.53 GHz, 1.95-3.48 GHz) at the CP center frequency, 2.715 GHz, respectively. This paper deals with the designs and experimental results of the proposed crossed dipole with parasitic loop resonators and its arrays.

Broadband Circularly Polarized Crossed Dipole With Parasitic Loop Resonators and Its Arrays

In this paper, we propose an approach to realize substrate integrated waveguide (SIW)-based leaky-wave antennas (LWAs) supporting continuous beam scanning from backward to forward above the cutoff frequency. First, through phase delay analysis, it was found that SIWs with straight transverse slots support backward and forward radiation of the $-1$ -order mode with an open-stopband (OSB) in between. Subsequently, by introducing additional longitudinal slots as parallel components, the OSB can be suppressed, leading to continuous beam scanning at least from $-40^\circ$ through broadside to 35°. The proposed method only requires a planar structure and obtains less dispersive beam scanning compared with a composite right/left-handed (CRLH) LWA. Both simulations and measurements verify the intended beam scanning operation while verifying the underlying theory.

Leaky-Wave Antennas Based on Noncutoff Substrate Integrated Waveguide Supporting Beam Scanning From Backward to Forward

A novel fixed-frequency electronically-steerable one-dimensional (1-D) leaky-wave antenna is presented. The antenna is based on a parallel-plate waveguide loaded with a planar partially reflective surface and a tunable high impedance surface (HIS), which creates a 1-D Fabry-Perot leaky-waveguide. The tunable HIS consists of printed patches loaded with varactor diodes that allow the electronic tuning of the cavity resonance condition. Using a simple Transverse Equivalent Network, it is theoretically shown how the variation of the varactors' junction capacitance allows the scanning of the antenna pointing angle from broadside towards the endfire direction at a fixed frequency. Experimental results of an antenna prototype operating at 5.6 GHz are reported, demonstrating that the new reconfigurable leaky-wave antenna can provide electronic beam scanning in an angular range from 9 $^{\circ}$ to 30 $^{\circ}$

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Electronically Steerable 1-D Fabry-Perot Leaky-Wave Antenna Employing a Tunable High Impedance Surface

This communication demonstrates for the first time the capability to independently control the real and imaginary parts of the complex propagation constant in planar, printed circuit board compatible leaky-wave antennas. The structure is based on a half-mode microstrip line which is loaded with an additional row of periodic metallic posts, resulting in a substrate integrated waveguide SIW with one of its lateral electric walls replaced by a partially reflective wall. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty that the leaky-mode leakage rate can be controlled by virtue of a sparse row of metallic vias. For this topology it is demonstrated that it is possible to independently control the antenna pointing angle and main lobe beamwidth while achieving high radiation efficiencies, thus providing low-cost, low-profile, simply fed, and easily integrable leaky-wave solutions for high-gain frequency beam-scanning applications. Several prototypes operating at 15 GHz have been designed, simulated, manufactured and tested, to show the operation principle and design flexibility of this one dimensional leaky-wave antenna.

Planar Leaky-Wave Antenna With Flexible Control of the Complex Propagation Constant

A simple technique is presented for the complete suppression of the open stopband in periodic leaky-wave antennas using two similar but nonidentical elements per unit cell. With the technique, one needs only to optimize the distance between the two elements and the dimension of the second element, starting with a quarter of the period and the dimension of the first element. With the simple design procedure, the technique is practical and effective for the open-stopband suppression for various periodic leaky-wave antennas. Two periodic leaky-wave antennas with the technique are demonstrated. The first one is a new developed substrate-integrated waveguide antenna with two nonidentical transverse slots per unit cell. The antenna has a wide scanning range from the backward endfire to the forward direction and does not suffer from blind scanning points at endfires (if it is placed on an infinite ground plane). The antenna is theoretically investigated. The simulation and measured results are consistent with the theoretical results. The second one is a microstrip combline leaky-wave antenna, in which each unit cell contains two nonidentical open-ended stubs. The two examples validate that the technique proposed in this paper can completely eliminate the open stopband in periodic leaky-wave antennas.

A Simple Technique for Open-Stopband Suppression in Periodic Leaky-Wave Antennas Using Two Nonidentical Elements Per Unit Cell

A new substrate integrated waveguide (SIW) leaky-wave antenna is investigated for endfire-radiation with a narrow beam and sidelobe suppression. Maximum directivity conditions for endfire-radiation from line sources with different amplitude distributions are theoretically discussed as a design aid. Interestingly, for endfire beams it is seen that designs that have a lower sidelobe level can also have a higher directivity, contrary to what is normally encountered for broadside beams. An SIW leaky-wave antenna with tapered transverse slots on only the top and bottom planes is presented. Compared with a previous leaky-wave antenna having uniform transverse slots on the top plane, the presented leaky-wave antenna has a main beam that can radiate exactly at endfire and also has a lower sidelobe level. The design of the low sidelobe antenna is based on the leaky mode, which loses physical significance as the beam is scanned to the endfire direction. Nevertheless, the antenna retains a good beam shape and a low sidelobe level when it radiates at endfire. A prototype is made, and measured results are consistent with theoretical and simulated results.

Investigations of SIW Leaky-Wave Antenna for Endfire-Radiation With Narrow Beam and Sidelobe Suppression

A center-fed circular patch antenna with shorting vias and a coupled annular ring is proposed. With a low-profile configuration, the antenna provides a wide bandwidth by merging three resonant modes, including the TM02 mode of the circular patch, the TM01 mode generated by the shorting vias, and the TM02 mode of the coupled annular ring. The antenna operating in these modes would produce an omnidirectional pattern in the horizontal plane similar to that generated by a monopole antenna. A reduced structure is used to simplify the simulation in optimizing the bandwidth of the antenna. Measured results show that the antenna achieves a bandwidth of 27.4% for a profile of 0.029 wavelengths and has a gain of about 6 dBi.

Broadband Monopolar Microstrip Patch Antenna With Shorting Vias and Coupled Ring

A new leaky-wave antenna based on substrate integrated waveguide (SIW) with H-shaped slots is proposed and investigated. The SIW with H-shaped slots is analyzed as a rectangular waveguide with H-shaped slots. Using an aperture magnetic field integral equation (MFIE), it is found that the SIW with H-shaped slots supports a leaky waveguide mode, a surface-wave mode and a proper waveguide mode depending on frequency. The radiation property is also evaluated using the MFIE. The leaky-wave antenna based on the SIW with H-shaped slots has a narrow beam that scans from broadside to endfire with frequency. The antenna produces an elliptical polarization, including circular polarization. Measured results are consistent with the simulation from HFSS and the theoretical analysis from the MFIE.

Substrate Integrated Waveguide Leaky-Wave Antenna With H-Shaped Slots

The periodic half-width microstrip leaky wave antenna (MLWA) with a backward to forward scanning capability is presented in this paper. The proposed antenna consists of a series of half-width MLWA. The radiating periods place on the different sides of the transmission line. The radiating period works in cutoff region of the first higher order mode, the periodic construction radiates the slow wave out along the edge. The experimental results show the main lobe scans electronically and continuously from 149° to 28° in H-plane ( y-z plane) toward end fire (+ z direction) when the operating frequency increases from 4.2-.9 GHz.

The Periodic Half-Width Microstrip Leaky-Wave Antenna With a Backward to Forward Scanning Capability

A band-notched ultrawideband monopole antenna with a novel segmented radiating patch is presented. Band-notched characteristic in the 5.7-GHz WLAN band is obtained by segmenting a circular monopole patch into three parts. The measured results are in good agreement with the simulated ones. Moreover, the surface current and electric field distributions are analyzed and an equivalent parallel RLC circuit concept is applied to explain the band-notched function. On the basis of the equivalent parallel RLC circuit analysis, the notch frequency and bandwidth of the notched band can be widely adjusted by optimizing the key parameters.

Yuanxin Li

Papers

Investigations of SIW Leaky-Wave Antenna for Endfire-Radiation With Narrow Beam and Sidelobe Suppression

Broadband Monopolar Microstrip Patch Antenna With Shorting Vias and Coupled Ring

Substrate Integrated Waveguide Leaky-Wave Antenna With H-Shaped Slots

The Periodic Half-Width Microstrip Leaky-Wave Antenna With a Backward to Forward Scanning Capability

Band-Notched UWB Printed Monopole Antenna With a Novel Segmented Circular Patch