In this article, a new Beamforming Network (BFN) realized in Broadside Coupled Stripline (BCS) is proposed to feed 1×4 and 2×2 arrays antenna at 28 GHZ-Band. The new BFN is composed only of couplers and phase shifters. It doesn't require any crossover compared to the conventional Butler Matrix (BM) which requires two crossovers. The tight coupling and low loss characteristics of the BCS allow a design of a compact and wideband BFN. The new BFN produces the phase differences of (±90°) and (±45°, ±135°) respectively in x- and y-directions. Its integration with a 1×4 linear array antenna reduces the array area by 70% with an improvement of the gain performance compared with the conventional array. The integration with a 2×2 array allows the realization of a full 2-D beam scanning. The proposed concept has been verified experimentally by measuring the fabricated prototypes of the BFN, the 1-D and 2-D patch arrays antennas. The measured 11.5 dBi and 11.3 dBi maximum gains are realized in θ0 = 14° and (θ0, φ0) = (45°,345°) directions respectively for the 1-D and 2-D patch arrays. The physical area of the fabricated BFN is only (0.37λ0×0.3λ0×0.08λ0), while the 1-D array and 2-D array antennas areas without feeding transmission lines are respectively (0.5λ0×2.15λ0×0.08λ0) and (0.9λ0×0.8λ0×0.08λ0).

We attempt to design and fabricate of a 4×4 Butler matrix for short-millimeter-wave frequencies by using the microfabrication process for a polytetrafluoroethylene (PTFE) substrate-integrated waveguide (SIW) by the synchrotron radiation (SR) direct etching of PTFE and the addition of a metal film by sputter deposition. First, the dimensions of the PTFE SIW using rectangular through-holes for G-band (140-220 GHz) operation are determined, and a cruciform 90 ° hybrid coupler and an intersection circuit are connected by the PTFE SIW to design the Butler matrix. Then, a trial fabrication is performed. Finally, the validity of the design result and the fabrication process is verified by measuring the radiation pattern.

A multibeam massive multiple input multiple output (MIMO) configuration employs beam selection with high power in the analog part and executes a blind algorithm such as the independent component analysis (ICA), which does not require channel state information in the digital part. Two-dimensional (2-D) multibeams are considered in actual power losses and beam steering errors regarding the multibeam patterns. However, the performance of these 2-D beams depends on the beam pattern of the multibeams, and they are not optimal multibeam patterns suitable for multibeam massive MIMO configurations. In this study, we clarify the performance difference due to the difference of the multibeam pattern and consider the multibeam pattern suitable for the system condition. Specifically, the optimal multibeam pattern was determined with the element spacing and beamwidth of the element directivity as parameters, and the effectiveness of the proposed method was verified via computer simulations.

The microfabrication technique based on SR (Synchrotron Radiation) direct etching process has recently been applied to construct PTFE microstructures. This paper attempts to fabricate an integrated PTFE-filled waveguide Butler matrix for short millimeter-wave by SR direct etching. First, a cruciform 3-dB directional coupler and an intersection circuit (0-dB coupler) are designed at 180 GHz. Then, a 4×4 Butler matrix with horn antennas is designed and fabricated. Finally, the measured radiation patterns of the Butler matrix are shown.

A 42×42-way one-body 2-D beam-switching Butler matrix with waveguide short-slot 2-plane couplers is designed and fabricated in the 22GHz band. The one-body configuration using the commutativity and the overlapping of units allows reducing the size and loss in comparison with a cascade of matrices beam-switching for the horizontal and the vertical planes. It is achieved by replacing 2×2-way 1-plane couplers in the conventional block configuration for a Butler matrix with 22×22-way 2-plane couplers. The measured bandwidth is approximately 2% restricted by the frequency characteristics of the 2-plane couplers. In the radiation from the aperture array antenna of the 42 output ports, the 3.9dB-down coverage of 3-D solid angle by the sixteen beams is around 1.72 steradian which is same as 27.4% of hemisphere at the design frequency for the aperture spacing of 0.73×0.73 wavelength.

This paper proposes an easy-to-design, theory-consistent compact feeding circuit, with a single input and four outputs, being comprised of two hybrid circuits that are capable of switching a beam in three directions. The circuits that determine the phase differences between the antennas are present on the same single layer, and thus there is no effect of vias and the design agrees well with the underlying theory. In addition, the vertically and horizontally symmetrical circuit pattern contributes to a substantial reduction in design time. The circuit is designed for use in the ISM band and its properties are evaluated using an RF circuit simulator. A prototype is fabricated and evaluated. The results of the simulation and measurement agree well with the theoretical values. The dimensions of the feeding circuit are 75 (H)55 (W)3.0 (T) mm.

The authors propose a single-layer hollow-waveguide 8-way Butler matrix. All components of the Butler matrix are in a single layer which contributes to low-cost fabrication. To reduce the length of the couplers, a step structure is installed in the coupled region. 50% length reduction is obtained in comparison with the conventional design using reflection-suppressing posts in the coupled region. The total size of the matrix is 17.1λg6.0λg. The full structure of the matrix is fabricated by hollow waveguides at 22 GHz band and the total measured loss is only 0.25 dB.

The authors realize a 50% length reduction of short-slot couplers in a post-wall dielectric substrate by two techniques. One is to introduce hollow rectangular holes near the side walls of the coupled region. The difference of phase constant between the TE10 and TE20 propagating modes increases and the required length to realize a desired dividing ratio is reduced. Another is to remove two reflection-suppressing posts in the coupled region. The length of the coupled region is determined to cancel the reflections at both ends of the coupled region. The total length of a 4-way Butler matrix can be reduced to 48% in comparison with the conventional one and the couplers still maintain good dividing characteristics; the dividing ratio of the hybrid is less than 0.1 dB and the isolations of the couplers are more than 20 dB.

The authors proposed a switching beam slot array antenna with a 4-way Butler matrix. All are integrated in one substrate with post-wall waveguide techniques. The planar Butler matrix is realized by using short slot directional couplers (cross coupler). Experiments in 26GHz band confirmed the key operation of this antenna; almost identical four beams are switched to cover the total of horizontal 90-degree sector with equal angular spacing.

Adaptive antenna is a promising to increase the spectral efficiency of mobile radio systems. We developed a compact, cost effective planar Butler Matrix as a beam forming network of a multi beam antenna. This circuit consists of a thin substrate that the conductor attaches to both sides, and two thick substrates that the ground conductor attaches to one side. In this circuit, coupling by crossover causes amplitude and phase error of the Butler Matrix. By narrowing the strip width of the crossover, crossover coupling can be suppressed 10 dB. The measurement results of the experimental 88 Butler Matrix were 0.75 dB amplitude deviation, 9.5 degree phase deviation and VSWR of less than 1.15 within the relative bandwidth of 10% at 900 MHz band.

This paper describes a radial open stub and its application to a simple design of a four-element planar Butler matrix. In the first stage of our work, we propose a 45-degree phase shifter composed of an eighth-wavelength delay line and a serial connection of a quarter-wavelength straight line and a quarter-wavelength straight open stub. Next, in order to improve relative-phase characteristics between output ports, we propose a 45-degree phase shifter configuration using a quarter-wavelength radial open stub instead of using a quarter-wavelength straight open stub. It is shown by simulation that relative-phase characteristics of the configuration using the radial open stub are better than that using the straight open stub at the high frequencies. Finally, an experimental UHF-band four-element planar Butler matrix is presented. Over the frequency range from 0.83 to 0.92 GHz, the experimental four-element planar Butler matrix exhibits power splits of -6.510.29 dB, return losses of greater than 13 dB, errors in the desired relative-phase difference between output ports of less than 2 degrees.

We propose a novel feeding circuit for a 30 GHz planar multibeam antenna applied to high-speed wireless communication systems. The feeding circuit is a bi-layer 8-port Butler matrix constructed with phase adjusted slot-coupled hybrids and branch-line hybrids. The new circuit configuration eliminates troublesome vias and line crossings, so it can be manufactured by traditional photolithograph. The feeding circuit is designed by using the spectral domain moment method considering bonding film effects. A prototype of a multibeam antenna which has seven pencil-beams with 10 beamwidths is manufactured and tested; the beam scan angle error is less than 3 at 30 GHz.