A novel wideband waveguide antenna with excellent performance is proposed, which is composed of a coaxial-waveguide transition and an open-ended rectangular waveguide loaded with a pair of horizontal umbrella-shaped metallic brims. The brims perpendicular to two broad walls of the waveguide are constructed to modulate the antenna to radiate nearly identical E- and H-plane radiation patterns. A wideband impedance matching performance is achieved with a fractional bandwidth of 40% through the introduction of short-stepped ladders. The antenna has the advantages of simple structure, symmetric radiation pattern, low-cross polarization, moderate back lobe, and almost constant beamwidth.
The demand for the wideband, low-profile antennas with stable gain as well as symmetrical radiation patterns is on the rise with the fast growth of microwave and millimeter-wave wireless communication systems. Up to date, the pursuing of these high-performance antennas has attracted much attention and long-held interest. Microstrip patch antennas exhibiting the advantages of low profile, light weight, low cost, easy fabrication, and high integration with other devices have been widely adopted for electric systems. However, their impedance bandwidths are not sufficient, and also the gains are impossible to remain stable across a broad frequency range, which restricts considerably the practical applications. Although some impedance bandwidth enhancement techniques have been developed such as multilayer structure [
Dipole is a fundamental radiator and is often used as an equivalent source in the analysis of antenna. It is evident that unequal radiation patterns are achieved in the two principal planes for both an electric dipole and a magnetic dipole. This is because interchanged radiation patterns of figure-o and figure-8 are obtained between both dipoles. To implement equal E- and H-plane radiation patterns with low back radiation, Clavin and his coworkers presented the idea of complementary antennas [
In this paper, a simplified feed is introduced to excite the complementary antenna which is evolved from the open-ended rectangular waveguide antenna. Unlike the complicated corrugated conical horns [
Figure
The fabricated prototype and topology of the proposed antenna. (a) The photograph of the prototype antenna. (b) The cut-open view of the proposed antenna. (c) The cross-section along E-plane of the proposed antenna. The detailed dimensions (unit: mm) are
The rectangular waveguide antenna is simply excited by a coaxial probe with the diameter of 1.27 mm, which is accompanied by a dielectric and a coaxial-waveguide transition. The dielectric in the SMA connector covering the probe has a relative permittivity of
As an antenna, a conventional open-ended rectangular waveguide cannot be well matched to free space over the entire operating frequency band [
Simulated relative input impedance of conventional open-ended WR62 waveguide without ladders within entire Ku-band.
To corroborate the elucidation, Figure
Simulated and measured VSWRs of the proposed antenna versus the dimensions of the stepped ladders (a) as a function of
Surface current distributions of the proposed antenna in the case of different excitation phases. Aperture current distributions in the case of (a)
To investigate the operation mechanism of the proposed waveguide antenna, the surface current distributions of the antenna excited in the case of different phases
From the observation of the operation mechanism of the proposed antenna, we can conclude that the current distribution on the aperture is mainly determined by the geometrical shape of the aperture. Although the distribution of the inside surface current for the TE10 mode of rectangular waveguide is determined when its transverse size is given, we still can control the aperture current distribution by changing the shape of the aperture. In this case, it is particularly interesting to study the relation between the dimensions of metallic brims and radiation performance of the antenna. The study would afford us a useful guideline in the design of the waveguide antenna with equal E- and H-plane radiation patterns by exciting simultaneously the complementary antenna with appropriate amplitude and phase. Figure
Comparison of beamwidths in E- and H-planes as functions of
Note that the width of the brim is selected equal to that of the waveguide in the above analysis. For comprehensive study, extensive simulations have also been performed in the case when
Simulated and measured 3-dB beamwidths and gains of the proposed antenna.
Freq. |
3-dB beamwidth (deg.) | Gain (dBi) | ||||
---|---|---|---|---|---|---|
Simulation | Measurement | Simulation | Measurement | |||
E-plane/H-plane |
E-plane/H-plane |
E-plane/H-plane |
|
|
|
|
12 | 72/71.6 | 72.6/70.8 | 70.5/65.8 | 8.16 | 8.36 | 7.47 |
15 | 67/66.3 | 60.9/61.7 | 60.6/64.2 | 8.95 | 9.76 | 8.7 |
18 | 62.8/62.5 | 60.9/57.7 | 68.6/65.1 | 9.73 | 9.95 | 9.36 |
Study of variations in radiation patterns versus the changes of lengths of metallic brims at 12, 15, and 18 GHz, respectively. (a)-(b) E-plane and H-plane at 12 GHz, (c)-(d) E-plane and H-plane at 15 GHz, and (e)-(f) E-plane and H-plane at 18 GHz.
E-plane
H-plane
E-plane
H-plane
E-plane
H-plane
For numerical characterization, the proposed antenna is simulated using commercial software Ansoft HFSS. For verification, a prototype of the antenna is fabricated (see Figure
The antenna radiation patterns are measured through the far-field measurement system in an anechoic chamber. Figure
Simulated (a)–(c) and measured (d)–(f) radiation patterns of the proposed antenna at 12, 15, and 18 GHz, respectively.
12 GHz
15 GHz
18 GHz
12 GHz
15 GHz
18 GHz
A novel open-ended rectangular waveguide antenna has been proposed, which features wide bandwidth, low cross-polarization, moderate backward radiation, and uniform pattern bandwidth (almost identical E- and H-plane patterns) across the whole Ku-band. Furthermore, the proposed antenna exhibits a simple structure and is conceptually easy to design. Hence, it can be widely employed as an efficient feed for circular-aperture antennas to obtain the desired pencil-beam radiation patterns.
This work is supported in part by the National Science Foundation of China under Grants nos. 60990320, 60990324, 61138001, and 60921063, the National High Tech (863) Projects under Grants nos. 2011AA010202 and 2012AA030702, and the 111 Project under Grant no. 111-2-05. M. Q. Qi would like to thank the anonymous reviewers for their constructive comments.