* Hensoldt aims to sell 20-30% of company - sources

* Valuation seen at 2.5-3 bln euros, incl debt - sources

* Deal breathes life into dormant IPO market

* Springer Nature expected to file for IPO late Sept - sources (Adds details on timing, IPO market)

FRANKFURT, Sept 8 (Reuters) - German defence supplier Hensoldt has filed to list its shares in Frankfurt later this month, as the private equity-owned company seeks to raise funds for growth and to strengthen its balance sheet.

The deal is expected to value the former Airbus unit, which buyout group KKR bought in 2016, at 2.5-3 billion euros ($3-3.5 billion), including debt, people close to the matter said.

New and existing shares worth 20-30% of the company are expected to be listed on the stock exchange, the people said, adding that the listing would likely take place before a spin-off of Siemens Energy, which is scheduled for Sept. 28.

Reuters earlier reported the impending Hensoldt listing, which is breathing life into a dormant IPO market, all but halted by market turbulence caused by the COVID-19 pandemic.

Like German publisher Springer Nature, Hensoldt had originally planned for a spring IPO, but shelved its plans as markets slid.

Germany's blue-chip index is now back at levels recorded in late 2019, potentially allowing for rich valuations in stock market listings.

Caravan maker Knaus Tabbert last week announced listing plans.

Springer Nature is expected to announce its 1 billion euro flotation -- valuing it at about 7 billion euros, including debt -- in the final week of September, people close to that transaction said.

SpringerNature declined to comment.

Elsewhere, e-commerce retailer The Hut Group and Mobile games applications provider Huuuge have also filed for stock market listings.

FROM BINOCULARS TO DRONES

Given COVID-19 related social distancing rules, KKR is using Hensoldt drones to show investors production sites at the defence supplier and at other portfolio companies, a person close to the matter said.

KKR bought Airbus's defence electronics business for 1.1 billion euros in 2016 and rebranded it Hensoldt, naming it after a 19th-century German maker of binoculars and telescopes.

The German government, which is one of the group's major customers, holds a "golden share" in the company.

Hensoldt makes military sensors, electronic warfare equipment, avionics and optronics, with 16% of revenues coming from non-defence markets.

This year, Hensoldt expects to post adjusted earnings before interest, tax, depreciation and amortization (EBITDA) of about 210 million euros on revenue of 1.15 billion.

Next year, Hensoldt expects revenue of 1.4-1.6 billion euros. Its 2020 and 2021 adjusted EBITDA margin is expected to slightly decline to around 18% from 19.3% seen last year due to ramp-up costs in early stages of major projects, before recovering to 2019 levels, finance chief Axel Salzmann said.

The company this year won contracts such as a 1.4 billion euro order to jointly develop and produce a new active electronically scanned array - a type of phased array antenna - for the German and Spanish Eurofighter fleet.

Hensoldt competes with groups such as Ultra Electronics and Mercury Systems, which trade at 10.9 and 18.7 times their expected core earnings.

The company, which employs roughly 5,500 staff, had 762 million euros in net debt as of end-2019.

Its high-tech cameras are used in products including Tornado fighter jets that fly surveillance missions over Syria and Iraq. It also supplies radar for Eurofighter jets and periscopes for submarines and Leopard and Puma tanks.

In addition, the company makes identification systems for combat jets, night vision devices, radar for civil air traffic control and systems for civil and military efforts to counter drones.

Bank of America, JP Morgan, Deutsche Bank and KKR Capital Markets are organising the flotation with the help of Citigroup, Commerzbank, UniCredit and Crédit Agricole. ($1 = 0.8463 euros) (Additional reporting by Alexander Hübner and Douglas Busvine; Editing by Ed Osmond and Emelia Sithole-Matarise)