Wireless communication is one of the rapidly-growing fields of the communication industry. This continuous growth motivates the antenna community to design new radiating structures to meet the needs of the market. The 5G wireless communication has received a lot of attention from both academia and industry and significant efforts have been made to improve different aspects, such as data rate, latency, mobility, reliability and QoS. Antenna design has received renewed attention in the last decade due to its potential applications in 5G, IoT, mmWave, and massive MIMO. This paper proposes a novel design of broadband antenna for 5G mmWave and optical communication networks. It is a hybrid structure that works for both spectrums and contains an absorption dielectric material with an electrical large size. A hybrid transmission line theory ray-tracing technique is proposed efficient and rapid simulation and optimization of the proposed antenna design. The operating frequency and wavelength of the proposed antenna are 28 GHz in the mmWave band and 1550 nm for the optical spectrum. The spatial frequency is 30 lp/mm when the contrast transfer function is reduced to 0.7 for the optical signal. The effective focal length and aperture are 816.86 and 200 mm. The half-power beamwidth is
High speed and large capacity are the development needs of next-generation communications. Free space optical communication has a high transmission rate (Gbit/s), large capacity, and good confidentiality [
As early as 2004, the Advanced Research Projects Agency of the U.S. Department of Defense began to try to combine space optical communication and radio frequency communication into one network and launched the free-space optical and radio frequency combined link experimental project [
The authors in [
To this end, this paper proposes a transmission line G-ray tracing hybrid algorithm, using geometric optics method to trace millimeter-wave rays, and at the same time, the antenna medium area is equivalent to a transmission line, which not only guarantees the calculation rate but also analyzes the influence of the composite antenna medium parameters on the radiation characteristics. This article uses the proposed method. The algorithm obtained the optimal parameters of the FSO/MMW composite antenna and accurately calculated its millimeter-wave performance.
The Cassegrain structure can be applied to optical/radio frequency dual-mode guidance device to realize the common-aperture composite of two working band signals. The Cassegrain structure can make full use of its aperture to composite optical signals and millimeter-wave signals, and the optical axis and electrical axis of the composite signal coincide. Also, the optics and millimeter waves in the system share the same aperture, with simple structure, small size, low quality and low cost. Because the antennas are reciprocal in transmission and reception, the system can be used not only as a transmitting antenna but also as a receiving antenna. The following only discusses its design as a transmitting antenna, and this method is also suitable for composite receiving antenna design.
The working principle of the free-space optical signal/millimeter-wave signal common-aperture composite antenna is shown in
The design of hybrid mmWave/optical antennas is divided into two parts: optical system design and millimeter-wave antenna design. These two parts are related to each other and need to be considered comprehensively during design. Because the optical signal wavelength is shorter and the requirements for the composite structure are high, the optical structure is first designed, and the millimeter-wave antenna structure is optimized after the optical structure meets the requirements. Since the millimeter-wave signal and the optical signal share the front surface of the parabolic mirror and the dichroic mirror, their size and surface shape are temporarily fixed after the optical structure design is completed, and no adjustment is made in the millimeter-wave structure design unless the millimeter-wave indicator cannot satisfy, the optical structure is redesigned and adjusted. After the optical structure design is fixed, according to the millimeter-wave transmittance requirements of the dichroic mirror, the structural parameters of the dichroic mirror are determined based on the proposed hybrid transmission line and ray-tracing theory, to determine the structure of the composite antenna. The commercial software FEKO is used to analyze and calculate its millimeter-wave properties. If the millimeter-wave design requirements are not met, the optical structure is redesigned and adjusted until the optical indicators and millimeter-wave indicators meet the requirements.
The goal of a hybrid antenna design is to achieve a common-aperture synthesis of free-space light and millimeter-wave signals. At the same time, both optical signals and millimeter-wave signals have high gain and small divergence angles to ensure strong signal transmission capabilities and Long transmission distance. It can be seen from
The position of the millimeter-wave feed is denoted as
The front surface of the dielectric dichroic mirror can be expressed as
Tracing the ray
The interface normal slope
Therefore, the incident angle
According to the law of refraction, the refraction angle
From the refraction angle
Furthermore,
After the ray is refracted by the dichroic mirror, it exits from point
where
The slope of the interface normal at the point
For a parabolic mirror, the incident angle is equal to the reflection angle, so the slope
The expression of
Only tracing the light will ignore the loss of the lossy dielectric dichroic mirror to the millimeter-wave, so it is necessary to analyze the attenuation of the millimeter-wave signal by the dichroic mirror from the trace to the dichroic mirror. Since the radius of curvature and size of the dielectric dichroic mirror is relatively large relative to the working wavelength of the antenna, the dielectric dichroic mirror can be locally approximated as a flat plate structure [
where
In
where
Comparing
The equivalent characteristic impedance of vertically polarized and horizontally polarized waves is different, which can be expressed as
where
Solving the transmission line matrix equation, the transmission coefficient of the single-layer flat plate can be obtained as
From
The technical indicators of the composite antenna are shown in
Parameter/indicator | Value |
---|---|
mmWave frequency | 28 GHz |
Optical signal wavelength | 1550 nm |
Diameter of the primary mirror |
400 mm |
Diameter of the dielectric dichroic mirror |
40 mm |
Optical field angle |
|
Focal length of Cassegrain system |
816.86 mm |
Detector photosensitive surface size |
250 |
Loss of dielectric dichroic mirror to mmwave signal | |
Millimeter-wave gain |
It can be seen from
The design is performed using the reverse design method, calculate the structural parameters of the parabolic mirror and the dielectric dichroic mirror from the optical relationship, add an aspheric correction lens on this basis, and use the global optimization function in ZEMAX to design and optimize the optical system structure (
Parameter | Surface 1 | Surface 2 | Surface 3 |
---|---|---|---|
Thickness | −175 mm | 195 mm | 10 mm |
Radius | −400 mm | −50 mm | 51.12 mm |
Conic | −1 | −1 | −0.575 |
gLASS | Mirror | Mirror | N-BK7 |
According to the output parameters of ZEMAX, the diameter of the primary mirror of this structure is
The optimized design of the antenna millimeter-wave structure uses the sinc function to simulate the millimeter-wave feed pattern of a certain beam width
The dielectric dichroic mirror needs to be coated with a film system that highly reflects the optical signal. Quartz is selected as the dielectric dichroic mirror material, its relative permittivity
It can be seen from
Device | Parameter | Value |
---|---|---|
Parabolicsplitter | Diameter | 200 mm |
Hole diameter | 22 mm | |
Ratio of focal length to diameter | 1 | |
Beam splitter | Diameter | 40 mm |
Radius offront face | 100 mm | |
Thickness | 11 mm | |
Antenna | Mmwave frequency | 28 GHz |
Optical signal wavelength | 1550 nm | |
Aperture | 200 mm | |
Effective focal length | 816.86 mm | |
Dimension |
According to the structure of the above hybrid antenna, two-dimensional space tracking is performed in the Matlab simulator based on TLTG-RTM, and the power transmittance of the dielectric dichroic mirror in the
According to the composite antenna structure in
where
According to
The point spread function of the composite antenna is shown in
The intersection of the light and the image plane is used to calculate the enclosing energy circle of the optical system, and a circle is drawn from the center point with a certain radius, and the system is evaluated according to the ratio of the energy in the circle to the total energy. It can be seen from
Using the commercial software FEKO, the MLFMM algorithm is used to calculate the millimeter-wave far-field pattern of the composite antenna as shown in
Since the dichroic mirror is a lossy medium, the millimeter-wave transmission dichroic mirror will cause energy loss. Also, energy will leak from the middle hole of the parabolic mirror and diffract from the edge of the parabolic mirror. Let
where
where
This paper proposed a novel broadband hybrid antenna for 5G networks. The designed structure is aimed to work in both optical and mm-wave bands. Also, we proposed a hybrid transmission and ray-tracing technique for evaluation and analysis of the proposed antenna which not only has the advantages of high geometrical optics calculation efficiency but also can obtain more accurate calculation results. It is suitable for the fast and efficient optimization design of electrically large composite antennas containing lossy dielectrics. The composite antenna optimized and designed using this hybrid algorithm can realize the common-aperture composite of a free-space optical signal with a wavelength of 1500 nm and a millimeter-wave signal with a frequency of 28 GHz. The effective aperture of the composite antenna is 200 mm, the field of view angle is 0.3 mrad, and the modulation transfer function in each field of view is close to the diffraction limit. The loss of the dielectric dichroic mirror to the millimeter-wave is about 9%, the millimeter-wave gain can reach 32.97 dBi, and the half-power width is only
The author would like to thank the editor and reviewers for their timely review and recommendations.