| 1. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
79 GHz multilayer series-fed patch antenna array with stacked micro-via loading
- 2022
-
Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 21:10, s. 1990-1994
-
Tidskriftsartikel (refereegranskat)abstract
- A wideband compact series-fed patch subarray is proposed for 79 GHz multiple-input multiple-output (MIMO) radar. The proposed subarray is, for the first time, loaded with stacked micro-vias (SMVs). Two sets of patches in the subarray are fed 180-degrees out-of-phase. A low-cost, high-resolution multilayer PCB technology, called “Any-Layer PCB”, is used to implement the SMVs, which cannot be done by standard HDI PCB technology. Moreover, the technology supports small SMVs on different layers, hence thick machine-drilled vias can be avoided. For comparison, a series-fed patch subarray with no SMV loading is designed. It is shown that SMV loading facilitates a larger overlap of the impedance and gain bandwidths, leading to a larger operating bandwidth. The measured 10 dB impedance and 3 dB gain bandwidths are 15% and 9.6%, respectively. The sidelobe suppression is above 12.9 dB, and the maximum array gain is 12.67 dBi at 79.1 GHz. This subarray is suitable for MIMO radar, as its width is around 1/2-wavelength and the SMVs around it mitigate the crosstalk between the transmitting and receiving arrays.
|
|
| 2. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Characteristic mode analysis of millimeter-wave series patch array
- 2022
-
Ingår i: 2022 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting. IEEE - Institute of Electrical and Electronics Engineers Inc.. - 9781665496582 ; , s. 225-226
-
Konferensbidrag (refereegranskat)abstract
- In this paper, characteristic mode analysis is used to gain insight into the operation of millimeter-wave series patch array. It is shown that the series patch array (broadside) mode has lower modal bandwidth and higher resonant frequency than the corresponding mode of a constituting patch element, whereas the other dominant orthogonal (broadside) mode is identical between the array and the single element. Moreover, it is found that unlike the use of shorting vias, non-shorted microvias along the array direction can help to decrease the resonant frequency of the series array mode. A parametric study is performed to show the effect of the length and position of the microvias on the series array mode.
|
|
| 3. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Characteristic mode analysis of planar dipole antennas
- 2019
-
Ingår i: 2019 13th European Conference on Antennas and Propagation (EuCAP). - 9788890701887 - 9781538681275
-
Konferensbidrag (refereegranskat)abstract
- Planar monopole antennas are popular due to their attractive properties, but their operating mechanisms are still not well understood. Based on image theory, planar monopoles can be analyzed using their dipole counterparts. Here, the bandwidth and radiation pattern of planar dipoles is studied in detail using characteristic mode analysis for different design parameters. The results show that insignificant modes can help to improve the bandwidth without contributing to the radiation property. Moreover, a tradeoff is observed between pattern stability and impedance bandwidth as the dipole width varies. Furthermore, it is found that an offset in the feed point leads to a degradation in both the modal and impedance bandwidths.
|
|
| 4. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Enhanced low band MIMO terminal antenna based on selective feeding of chassis modes
- 2020
-
Ingår i: 14th European Conference on Antennas and Propagation (EuCAP).
-
Konferensbidrag (refereegranskat)abstract
- Multiple-input multiple-out (MIMO) is a mature technology in modern wireless communications. However, it is challenging to implement multi-antennas for MIMO operation in compact mobile terminals, due to high mutual coupling and correlation among closely spaced antenna elements. Moreover, a conventional terminal chassis only offers one resonant mode below 1 GHz, complicating multi-antenna design. Recently, it has been shown that the chassis can be modified to facilitate a few resonant modes below 1 GHz. However, attempts to excite these modes selectively using a single coupling feed per antenna port result in limited bandwidth and isolation. In this work, we propose dual-feed antenna ports to improve selective feeding of the resonant modes of an existing two-port MIMO terminal antenna below 1 GHz. Simulation results reveal significantly enhanced bandwidths of 30% and 15% for the two ports, as well as high isolation of over 32 dB.
|
|
| 5. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Impact of capacitive coupling element design on antenna bandwidth
- 2018
-
Ingår i: European Conference on Antennas and Propagation (EuCAP), 2018.. ; :CP741
-
Konferensbidrag (refereegranskat)abstract
- A coupling element is typically used to excite one of more characteristic modes of a structure to form some desired radiation properties. In particular, non-resonant coupling elements (CEs) are attractive, since it is electrically small and can be more conveniently integrated into the structure, such as the chassis of a mobile terminal. In this case, the chassis is the primary radiator of the mobile terminal. However, there is still limited knowledge on how to design andoptimize coupling elements. In this paper, we examine how the dimensions of a single capacitive coupling element (CCE) influence the potential bandwidth of exciting the fundamental dipole mode of a rectangular terminal chassis. The parametric study shows that the CCE must not be too small electrically, for the sake of bandwidth. However, the bandwidth saturates when the size of the CCE is increased beyond a certain threshold. Therefore, this study provides some useful insights and guidelines for CCE design.
|
|
| 6. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Large screen enabled tri-port MIMO handset antenna for low LTE bands
- 2021
-
Ingår i: IEEE Open Journal on Antennas and Propagation. - 2637-6431. ; 2, s. 911-920
-
Tidskriftsartikel (refereegranskat)abstract
- In recent years, the screen-to-body ratio of mobile handsets has been increasing. Today, the screen nearly fills up the entire front side. Conventionally, the screen is mainly seen as a metallic object that adversely affects antenna performance. In this paper, the large screen is used for the first time to facilitate an additional uncorrelated MIMO port in a tri-port design, for several LTE bands below 1 GHz. To this end, the screen and the terminal chassis are modeled as two metal plates and their characteristic modes are analyzed. Four modes are then tuned to resonance and selectively excited to yield three uncorrelated MIMO ports. Simulation and measurement results are in good agreement. The measured bandwidths are 23%, 17% and 21%. Within the operating band, the measured isolation is above 13 dB, envelope correlation coefficient below 0.16 and average total efficiency above 72%.
|
|
| 7. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Low-band MIMO antenna for smartphones with robust performance to user interaction
- 2021
-
Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 20:7, s. 1195-1199
-
Tidskriftsartikel (refereegranskat)abstract
- This letter proposes a two-port MIMO smartphone antenna for frequency bands below 1 GHz, which is robust to user effects. The design is achieved by first analyzing the characteristic modes of a chassis that includes the large screen. Two modes predicted to be less affected by the user than other commonly used modes are selected. The modal currents and near-fields of the two desired modes then guide the design: The monopole-like mode introduced by the screen is tuned to resonance using shorting pins and selectively excited using the center feed location. The non-resonant loop mode is selectively excited for the first time by four inductive feeds added along the longer sides of the chassis, with proper phase shifts provided by a feeding network. The proposed antenna features isolation of above 19 dB and envelope correlation coefficient of below 0.12 in the considered scenarios. The measured bandwidth is above 15% for both ports, and the average radiation efficiency is 2 dB and 4.57 dB higher for two user scenarios with respect to a reference design. Moreover, no adaptive matching is needed as the impedance matching is robust to the user hand/head.
|
|
| 8. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
Low-profile two-port MIMO terminal antenna for low LTE bands with wideband multimodal excitation
- 2020
-
Ingår i: IEEE Open Journal on Antennas and Propagation. - 2637-6431. ; 1, s. 368-378
-
Tidskriftsartikel (refereegranskat)abstract
- Multiple-input multiple-output (MIMO) is a key enabler for high data rates in mobile communications. However, it is challenging to design MIMO terminal antennas for LTE bands below 1 GHz, due to the conventional chassis offering only one resonant characteristic mode (CM). Recently, it was shown that minor structural changes can yield up to two additional resonant modes for designing two-port MIMO antennas. Nonetheless, the resulting bandwidth for the second port is relatively small. To simultaneously meet bandwidth and other practical requirements (including low profile and no off-ground clearance), a step-by-step approach for structural changes and feed design is applied in this work to exemplify the use of physical insights from CM analysis to achieve a competitive wideband two-port solution. The main novelty is that an entirely new mode is identified and appropriately tuned by structural modification for creating an additional resonance below 1 GHz. Moreover, two simple probe-feed ports are designed to jointly excite different subsets of four modes over frequency. In addition, far-field pattern orthogonality is guaranteed by the different phase shifts of the characteristic electric fields at the port locations. Furthermore, bulkier self-resonant antenna elements are avoided. To show design flexibility, a three-port version is also demonstrated.
|
|
| 9. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
On modal excitation using capacitive coupling elements and matching network
- 2019
-
Ingår i: 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting. - 9781728106922
-
Konferensbidrag (refereegranskat)abstract
- A resonant characteristic mode (CM) is useful for antenna design if it is properly excited and well matched to the source. In this paper, we consider the feed design for the excitation of the fundamental CM of a rectangular chassis. The tradeoff between the required number of capacitive coupling elements (CCE) and matching elements used for achieving a given antenna bandwidth is studied. The results reveal that in order to attain the modal bandwidth of the fundamental mode, the use of multiple CCEs with optimal placement and phase simplifies the required matching network.
|
|
| 10. |
- Aliakbari Abar, Hanieh, et al.
(författare)
-
On user effects of a low-profile MIMO terminal antenna with wideband multimodal excitation
- 2021
-
Ingår i: 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting : APS/URSI 2021 - Proceedings - APS/URSI 2021 - Proceedings. - 9781728146706 ; , s. 1245-1246
-
Konferensbidrag (refereegranskat)abstract
- When in use, a mobile terminal is often held in the hand by the user. However, conventionally terminal antennas are only evaluated in free space, disregarding the effects of user interaction. In this paper, the performance of a low-profile twoport multiple-input multiple-output (MIMO) antenna that offers wide symmetrical bandwidth and low correlation in free space is investigated in presence of a user hand. Full-wave simulation results show that the one-hand grip mainly causes an unbalanced absorption loss across the two ports and a degraded correlation performance, with the latter being due to pattern distortion.
|
|
