What Problem Does a 698–4200 MHz Quad-Port Dual-Polarized Directional Antenna Actually Solve?

In recent years, when engineers working on base station antennas meet, the most common remark is: “The antenna space is running out.” In the 4G era, one pole carried three antennas. With 5G, 3.5 GHz needs one more, 4.8 GHz may need another, and operators require co-building and sharing. Tower companies charge by antenna count. More antennas mean higher wind load, tighter tower load, and—more troublesome—coupling between different bands degrades radiation patterns. Once the back lobe rises, adjacent-cell interference follows. Common aperture or multi-band integration is an unavoidable path in engineering.

Recently I looked closely at a product: Anhui Luxun’s LX-698-4200-QD, a quad-port dual-polarized directional antenna. Below, starting from the physical meaning behind the parameters, I will discuss the scenarios where this antenna is worth choosing and where caution is needed.

First, a Concrete Answer: What Scenarios Is This Antenna Suitable For?

If your deployment requirements meet any two of the following, this antenna deserves serious evaluation:

1. The same site must simultaneously carry 698–960 MHz 4G low-band coverage and 3.3–4.2 GHz 5G capacity layers, while antenna space or pole load is already near the limit.
2. You are deploying 4×4 MIMO and need four physical ports to provide sufficient polarization and spatial diversity, without adding another antenna just to reach the port count.
3. The deployment environment is dense urban or an industrial park, with clear requirements for PIM suppression and front-to-back ratio. Back-lobe leakage cannot be too high.
4. Installation locations are restricted—street light poles, building walls, tunnel entrances. The 450 mm height and 2 kg weight mean mechanical requirements for the mounting structure are much lower than for conventional panel antennas.

If you are mainly doing 700 MHz wide-area coverage or mmWave scenarios, this antenna has limited value. Its design positioning clearly falls in the Sub-6 GHz multi-band co-site range.

Core Parameter Table: Translating Numbers into Engineering Judgment

The electrical specifications on the product page are fairly complete. I have listed the key indicators below, with engineering judgment added after each row.

Mechanical aspects: dimensions 450×278×138 mm, weight 2 kg (excluding bracket), UPVC radome, IP55, operating temperature -40°C to +70°C. At 2 kg, it is light for a quad-port directional antenna. The weather resistance and UV resistance of a UPVC radome are better than ABS—a material detail worth attention for long-term outdoor deployment.

Physical Meaning of Several Key Concepts

Since this article is meant to explain this antenna clearly, several terms cannot be given only as definitions. We need to explain what they mean in actual engineering.

±45° dual polarization. Traditional GSM base stations use space diversity: two antennas separated horizontally by several meters, using the low spatial correlation of arriving signals for diversity reception. ±45° dual polarization integrates two orthogonally polarized antennas into the same radiating aperture. The +45° and -45° ports still receive signals with low correlation, but the spatial separation between two antennas is eliminated. One sector needs only one antenna. Polarization diversity gain is theoretically about 5 dB, but in practice it is usually 3–4 dB. It is more reliable than space diversity in high-tower scenarios, because the higher the tower, the harder it is to achieve sufficient spacing.

VSWR ≤ 1.5. VSWR measures the relationship between the reflected wave and the incident wave at the antenna input. VSWR = 1.5 corresponds to a return loss of about -14 dB, meaning about 4% of the incident power is reflected back. For a base station antenna, this value is “acceptable but not impressive.” Every point of VSWR degradation affects feeder loss and PA efficiency, especially in high bands, where feeder loss itself is already a non-negligible factor. If actual testing can consistently stay below 1.4 across the entire band, that would be a clear engineering advantage.

Third-order PIM ≤ -150 dBc. The root cause of passive intermodulation is the nonlinearity of metal contact in the RF path. When two high-power signals at different frequencies pass simultaneously through connectors, solder joints, or metal contact surfaces inside the antenna, the nonlinear effect generates new frequency components. If they fall within the receive band, they become interference. Under the test condition of 2×43 dBm (single carrier 20 W), -150 dBc means the absolute power of the intermodulation product is on the order of -107 dBm. In the 700–900 MHz band, base station receive sensitivity can reach -110 dBm or even lower, so -150 dBc is a meaningful threshold. If a product only specifies -140 dBc, then in co-sited multi-operator scenarios it may raise the noise floor and affect uplink throughput. This is a hard indicator for whether an antenna can be used in co-site scenarios.

Front-to-back ratio. The difference between the maximum side-lobe level within the rear ±30° range and the forward main-lobe level. Low band >15 dB is basic. Mid band >18 dB is acceptable. High band >20 dB is relatively comfortable in dense urban areas. If back-lobe control is poor and there is a neighboring base station behind the antenna, the probability of overshooting and handover anomalies rises significantly.

Three Real Trade-offs of This Antenna

Every product has trade-offs. Explaining them clearly is more useful than stacking specifications.

Trade-off 1: The wider the band, the harder it is to maintain consistency. 698 MHz to 4200 MHz covers a 6:1 bandwidth ratio. Keeping VSWR below 1.5 for all ports over such a wide range requires considerable optimization of the feed network and radiating element matching. Judging from the sub-band gain and beamwidth, the three sub-bands have clearly different design parameters. This indicates the manufacturer performed independent matching per band rather than taking the lazy approach of “one radiator for everything.” However, in actual deployment, the most important area to watch is performance in the transition region—for example, between 960 and 1710 MHz. The product page does not provide transition-region data. During field testing, it is advisable to focus on sweeping this section.

Trade-off 2: Electrical downtilt is fixed at 0°. This means the antenna can only adjust its coverage angle through mechanical downtilt during installation. For scenarios requiring precise coverage-edge control—such as street coverage between high-rise buildings—the precision and consistency of mechanical downtilt are not as good as remote electrical tilt. If your deployment requires frequent downtilt adjustment, or fine coverage coordination among multiple sectors, this point must be considered.

Trade-off 3: Four ports, but each port is limited to 50 W. The four-port configuration is suitable for 4×4 MIMO, but the 50 W per-port upper limit means it is better suited to medium-power base station RRUs, not high-power macro base station scenarios. If your RRU single-port output exceeds 40 W, you need to calculate the total power margin after combining.

FAQ

Can this antenna run 4G and 5G simultaneously?

Yes. The three sub-bands correspond to 4G 700/800/900 MHz, 1800/2100/2600 MHz, and 5G n77/n78 (3.3–4.2 GHz). The four ports are independent RF channels. Signals from different bands are fed through external combiners or directly by an RRU that supports multiple bands.

In a 4×4 MIMO scenario, how should the four ports be connected?

The four N-Female connectors are at the bottom. Usually, two diagonal ports correspond to the same polarization direction. 4×4 MIMO requires four independent RF channels, so the RRU or AAU must provide four transmit/receive ports. If the base station equipment has only two ports, this antenna can be used as 2×2 MIMO plus dual band, but it cannot realize the full capacity gain of 4×4.

Is the -150 dBc PIM specification sufficient in actual deployment?

For single-operator co-site scenarios, -150 dBc is sufficient. If multiple operators share the antenna space and each operator’s power is not low, it is recommended to perform an on-site PIM sweep after system integration to confirm that PIM under actual installation conditions—including jumpers, connectors, and grounding—has not degraded above -140 dBc.

How long can IP55 protection support outdoor deployment?

IP55 means dust protected—dust ingress is not completely prevented but does not affect operation—and protected against water spray. The UV aging resistance of a UPVC radome in hot and humid southern environments usually maintains effective protection for 5–8 years. What needs regular inspection is the waterproofing of the bottom connectors. If N-type connectors are not properly sealed, water ingress is a common cause of PIM degradation and VSWR rise.

Final Word

The positioning of this antenna is clear: within limited antenna space, use one 450 mm-high panel antenna to simultaneously solve low-band coverage and high-band capacity. Four ports support 4×4 MIMO, and the PIM and front-to-back ratio specifications allow it to be used in co-site scenarios. It is not a universal antenna, but within the 698–4200 MHz span, the completeness of its parameter table is qualified. During selection, the two things that most need attention are actual measured performance in the transition bands and actual PIM after installation. These two factors, more than paper specifications, determine whether it works well in your network.