A novel broadband matching and decoupling network (MDN) for symmetric two-element array of microstrip patch antennas is proposed. As a distributed multiple inductive-capacitive loading, this MDN employs two groups of parallel shorting posts (vias) on the nonradiating edges of the high-coupled patches with a very-low edge-to-edge distance. This MDN excites two controllable new modified resonant half-modes, TM1/2,1 and TM3/2,0, whose aggregation provides a well-matched broad bandwidth with broadside pattern. Furthermore, a reasonable offset between these two groups of vias helps obtaining a balance between the mutual capacitive and inductive couplings, and then a broadband high isolation across the overlapped bandwidth without using the conventional large isolating structures. A resonator-based equivalent-circuit model including different mutual and cross couplings is proposed and discussed to study the coupling mechanism between the modes and the antennas. Finally, the measurement proves a bandwidth of 9.8% (3.38–3.73 GHz) with an enhanced isolation of over 27 dB. A fair comparison with the state-of-the-art approaches is drawn, and greatly reduced spatial correlation (with envelop correlation coefficient (ECC) of less than 0.06) and over 72% total efficiency (with 25% increase) make the proposed design appropriate for fifth-generation (5G) multi-input–multi-output (MIMO), and the other sensitive bi-element systems.

Bandwidth and Isolation Improvement of Highly Coupled Printed Array Antenna Using Multiple Shorting Posts

In this paper, low-profile compact microstrip magnetic dipole antennas with large beamwidth and broad bandwidth are proposed for vehicular applications. At first, by introducing a strip on the bottom layer of microstrip magnetic dipole antenna, the electric current sources are introduced for the enhancement of beamwidth together with the magnetic current source. The operation principle of an equivalent complementary source model is then revealed to provide a physical insight. As seen, the half-power beamwidth (HPBW) can be controllable and effectively enlarged by the electric length of the planar magnetic dipole antenna. Next, by using a stub crossing on the strip, the impedance bandwidth is significantly improved comparing with the unloaded counterpart. After that, the antenna size is miniaturized by etching a pair of slots to extend the length of current path. Experimental results indicate that, under a very low profile of 0.016λ0 and 0.032λ0, the antenna prototypes can still achieve an impedance bandwidth of 14.5% and 20.8%, and a maximum HPBW of 99° (E-plane)/180° (H-plane) and 112° (E-plane)/159° (H-plane). It is also demonstrated that when the antenna size is reduced to 0.442λ0×0.284λ0, the impedance bandwidth up to 14.9% and the maximum HPBW of 93° (E-plane)/231° (H-plane) can be guaranteed with a low profile about 0.032λ0. Comparing with other design approaches, the proposed designs feature a very low profile structure, and superior beamwidth and bandwidth properties, as well as simple configuration and compact size.

Low-Profile Compact Microstrip Magnetic Dipole Antenna With Large Beamwidth and Broad Bandwidth for Vehicular Applications

This paper proposes a compact dual-polarized cross-dipole antenna with low-pass filtering radiation response. The antenna consists of two pairs of orthogonally placed cross-dipoles, a circular patch, a filtering balun and a folded ground plane. Shape of the dipoles and installation of the patch are designed collaboratively to realize wideband and high efficiency in a compact size. The balun, which also contributes a resonance, simultaneously realizes low-pass filtering response at wide stop-band and low loss in passband, with a simple structure. For demonstration, the proposed antenna is implemented. Size of the radiator is 0.28*0.28*0.29 λ3. The measured 15-dB return-loss bandwidth of the prototype is 32.7%, which covers the 4G bands (from 690 MHz to 960 MHz). In the passband, efficiencies beyond 90% and peak gains of 9.05 ± 0.55 dBi are measured. The half-power beamwidth at passband is maintained 65° ± 5°. At frequencies ranging from 1.7 GHz to 4.0 GHz, the prototype can provide beyond 13 dB gain suppression. The proposed antenna can be a good candidate to integrate with elements operating at higher frequencies to form an aperture-shared array for shore-to-ship communication.

Compact Dual-Polarized Antenna with Low-Pass Response for Marine Communication

A linearly polarized low-profile complementary antenna with enhanced bandwidth and wide broadside beamwidth is proposed. To realize a wide half-power beamwidth (HPBW), an equivalent electric dipole is introduced by the strip on the bottom layer at first. As seen, it not only contributes to the beamwidth enlargement in yz -plane due to the superposition of complementary sources but also introduces a lower resonance. Then, in order to obtain a broad bandwidth, a stub is crossed on the strip to make the lower resonance move up, meanwhile merging with the higher one. After this, a tapered aperture structure is employed to reduce the input inductance for a further bandwidth enhancement. Finally, antenna prototype of center frequency 5 GHz is fabricated and tested. As experimentally demonstrated, a wide HPBW up to 180° and a broad bandwidth around 30% are achieved under a low-profile about 0.035λ0 as well as excellent gain flatness property, which outperforms most of the reported counterparts.

A Linearly Polarized Low-Profile Complementary Antenna With Enhanced Bandwidth and Wide Broadside Beamwidth

This article describes two high gain array antennas for 24 GHz FMCW automotive radar. The bandwidth of the antenna is improved by applying the slot-loaded technique. To further enhance the gain characteristics, series-fed and corporate-fed planar array antennas are developed, and their performance is studied. The measurement results show that the proposed array antennas have an excellent performance over the 24 GHz ISM band. The proposed array antennas are suitable for 24 GHz FMCW automotive radar applications. 

High gain array antenna for 24 GHz FMCW automotive radars

This article proposes gain-enhanced circular patch antenna and array with introduction of multiple shorting pins. The antenna consists of a circular patch and several shorting pins. Equivalent inductance is brought to the patch after introducing shorting pins. Thus, resonance of the patch shifts at higher frequency. Compared to a conventional circular patch without any pins, radiation area of the proposed patch is enlarged given the same resonance frequency, hence leads to gain enhancement. The number of pins introduced to a circular patch can be set freely due to its symmetrical feature. Moreover, surface current is restricted within a small area around the center of the patch after introducing multiple pins, leading to more concentrated radiation. An equivalent circuit model is built for the proposed antenna. Layout and number optimization rules for introducing shorting pins are formulated. With these rules, gain of a circular patch can be maximized for the applications under certain size restrictions. A prototype operating at 5.8 GHz is designed and fabricated. Furthermore, a 2*2 array based on the gain-enhanced circular patch elements is implemented. In the measurements, high gain, high efficiency, and narrowed half-power beamwidth of the patch antenna and the array are observed.

High-Gain Circular Patch Antenna and Array With Introduction of Multiple Shorting Pins

A half-power beamwidth (HPBW) extended patch antenna with harmonic suppression is proposed in this article. The antenna consists of one driven patch and two parasitic patches. The parasitic patches are placed parallel to the two adjacent edges of a driven patch. By introducing four sets of shorting pins near the outer edges of the patches, surface currents on the patches flow through the pins to the edges of the ground plane periodically, making those edges radiate as electrical dipole elements. Huygens’-like radiation with extended HPBW and low back-lobe level is formed by the interaction of dipole and patch-like radiation sources. On the other hand, the resonance at the second harmonic frequency is suppressed, and resonances at higher order modes are shifted away from the third harmonic frequency because of the joint effect of introducing shorting pins and coupling between patches. The mechanism of the antenna is analyzed. A verifying prototype is implemented. In the measurement, the antenna operates at 5.23 GHz. HPBWs of 135°/132° are found, while front-to-back ratios of 13.5/13.3 dB are achieved in the XoZ / YoZ -plane. Resonances at the second and third harmonic frequencies are successfully suppressed.

Jingwen Huang

Papers

High-Gain Circular Patch Antenna and Array With Introduction of Multiple Shorting Pins

A Compact Microstrip Antenna With Extended Half-Power Beamwidth and Harmonic Suppression